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SSH Secure Shell for Servers Version 3.2.9 Administrator`s Guide

1. The file server received an SSH_FXP_EXTENDED message from the client SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 94 Chapter 5 Log Messages Received bad SSH_FXP_INIT Received bad SSH_FXP_INIT The server received a bad SSH_FXP_INIT message Negotiated protocol version Negotiated version lt version number gt The server has negotiated to use the specified protocol version with the client Uploading file Uploading lt filename gt flags append trunc creat excl The server has received a write request for the specified file with the specified flags Downloading file Downloading lt filename gt The server has received a read request for the specified file Failed to open file Failed to open file lt filename gt Error lt errornumber gt The server failed to open the specified file Closed file Closed Received error when closing file lt filename gt handle lt handle gt The server closed the file possibly with an error happening during the close 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference Statting file Statting file lt filename gt The server is statting the specified file Lstatting file Lstatting file lt filename gt The server is Istatting the specified file Fstatting file Fstatting file lt filename gt The server i
2. Check that the VAR_ACE environment variable is set It has to be set before starting sshd2 and its value must be top ace data Start sshd2 See Section 4 3 Keyboard Interactive Authentication for more information on keyboard interactive authen tication Note SSH Communications Security does not provide technical support on how to configure RSA ACE Server Our support only covers SSH Secure Shell applications 4 3 Keyboard Interactive Authentication Keyboard Interactive is a generic authentication method that can be used to implement different types of authentication mechanisms 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 4 3 Keyboard Interactive Authentication 51 4 3 1 Overview What Is Keyboard Interactive Keyboard interactive is a relatively new authentication method designed in the Secure Shell Working Group of the Internet Engineering Task Force IETF The Working Group s abstract contains the following intro duction to the subject This document describes a general purpose authentication method for the SSH protocol suitable for interac tive authentications where the authentication data should be entered via a keyboard The major goal of this method is to allow the SSH client to support a whole class of authentication mechanism s without knowing the specifics of the actual authentication mechanism s What Can Be Done with It Basically any currently supported a
3. Host based authentication refused for user hostbased authentication rhosts refused client user lt loginname gt server user lt loginname gt client host lt hostname gt The host based authentication attempt has failed Client s host certificate is not valid in host based authentication Hostbased User lt loginname gt s client host certificate not valid The host certificate sent by the client during host based authentication could not be successfully validated 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 61 Client s host certificate does not contain host names in host based authentication Certificate does not contain any hostnames The host certificate sent by the client during host based authentication does not contain any host names Certificate does not contain the client host name in host based authentication Certificate does not contain client hostname lt hostname gt The host certificate sent by the client during host based authentication does not contain the client s host name Certificate could not be decoded in host based authentication Received certificate could not be decoded The host certificate sent by the client during host based authentication could not be decoded Public key could not be extracted from the received certificate in host based authentication Could not extract public key from received certificate Extracting the public k
4. Key Files The system public key pair DSS only consists of the following files e etc ssh2 hostkey e etc ssh2 hostkey pub Host keys that are recognized for all users on the local system should be placed in the etc ssh2 hostkeys directory User specific host keys should be placed in the ssh2 hostkeys directory If you are using host based authentication the system wide file for recognized host keys is etc ssh2 knownhosts User specific known host keys should be located in ssh2 knownhosts License File Commercial packages of SSH Secure Shell use the license file License_ssh2 dat Non commercial packages do not include this file To verify the type of the SSH Secure Shell package you are using display version information with the following command ssh2 V When you acquire a license for an evaluation version of the software the appropriate license file must be copied in the correct location The license file is typically stored in the etc ssh2 directory but a different location can be specified by setting the environment variable SSH_LICENSE FILE The license file specifies the type of the license and indicates that the software has been legally purchased The file should be safely stored 3 1 2 Generating the Host Key Host keys are generated during the installation of SSH Secure Shell You only need to regenerate them if you want to change your host key or if your host key was not generated
5. Multiple high security algorithms and strong authentication methods that prevent such security threats as identity spoofing Multiple ciphers for encryption including 3DES Blowfish and AES e Transparent and automatic tunneling of X11 connections and arbitrary TCP IP based applications such as e mail 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 2 3 Different Versions of the SSH Protocol 13 e Automatic and secure authentication of both ends of the connection Both the server and the client are authenticated to prevent identity spoofing Trojan horses and so on e Multiple channels that allow multiple terminal windows and file transfers through one secure and au thenticated connection 2 3 Different Versions of the SSH Protocol The current version of the SSH protocol is version 2 SSH2 More information on the protocol can be found in the IETF secsh Internet Drafts http www ietf org ID html Note SSH Communications Security considers the Secure Shell protocol version 1 SSH1 deprecated and does not recommend the use of it The SSH statement regarding the vulnerability of SSH1 protocol is avail able at http www ssh com company newsroom article 210 Several different versions of the Secure Shell client and server exist Please note that the different versions may use different implementations of the ssh protocol and therefore you may not be able to connect to an ssh1 server using ssh2 clien
6. There must be at least one auth one account and one session module in the configuration file Oth erwise the connection will be refused Also modules which require PAM_TTY will not work because TTY allocation is done in SSH Secure Shell after the authentication PAM Examples The following are examples of different PAM configurations 1 The etc pam d sshd2 file on Red Hat Linux auth required lib security pam_pwdb so shadow nullok auth required lib security pam_nologin so account required lib security pam_pwdb so password required lib security pam_cracklib so password required lib security pam_pwdb so shadow nullok use_authtok session required lib security pam_pwdb so 2 The etc pam conf entry on Solaris sshd2 auth required usr lib security pam_unix so debug sshd2 account required usr lib security pam_unix so debug sshd2 password required usr lib security pam_unix so debug sshd2 session required usr lib security pam_unix so debug See Section 4 3 Keyboard Interactive Authentication for more information on keyboard interactive authen tication Note SSH Communications Security does not provide technical support on how to configure PAM Our support only covers SSH Secure Shell applications and source code 4 2 7 SecurID If SecurID is to be used the Keyboard Interactive authentication method must be enabled on the client Please familiarize yourself with the RSA ACE Server documentation before reading fu
7. for more information Note for example the product FAQ pages e Bug Reports http www ssh com support contact bug report shell mpl e Feature Requests http www ssh com support contact feature request shell mpl Note The above two links are for submissions only you will not receive a response to emails sent using these forms 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 15 Chapter 3 Configuring SSH Secure Shell This chapter gives instructions on configuring SSH Secure Shell 3 1 Basic Configuration This section covers some basic configuration options that are commonly modified 3 1 1 Default Locations of Secure Shell Files The system wide configuration files are the most important They are located in the directory etc ssh2 User and system binaries are stored in usr local bin and usr local sbin respectively In usr local sbin you will find ssha2 All other binaries are stored in usr local bin System Wide Configuration Files The system wide configuration files for the client and server respectively consist of the following files e etc ssh2 ssh2_config e etc ssh2 sshd2_config Example files sshd2_config example and ssh2_config example can be found in the same direc tory Users can have their own configuration files These are stored in ssh2 SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 16 Chapter 3 Configuring SSH Secure Shell
8. D file Derive the public key from the private key file B number The number base for displaying key information default 10 V Print version string and exit r file Stir in data from file to the random pool x file Convert private key from X 509 format to ssh2 format k file Convert a PKCS 12 file to an ssh2 format certificate and private key 7 file Extract certificates from a PKCS 2003 SSH Communications Security Corp 7 fil SSH Secure Shell Admin Guide A 2 ssh certenrol12 109 F file Dump the fingerprint of a given public key The finger print is given in the Bubble Babble format which makes the fingerprint look like a string of real words making it easier to pronounce A 2 ssh certenrol1l2 ssh certenrol112 allows users to enroll certificates It will connect to a CA certification authority and use the CMPv2 protocol for enrolling a certificate The user may supply an existing private key when creating the certification request or allow a new key to be generated SYNOPSIS ssh certenroll2 V S SOCKS server P proxy url g t rsaldsal l key size o base name p cmp ref num cmp key a ca access url s subject nam ca cert file private key OPTIONS V Print version string and exit S SOCKS server The SOCKS server URL to be used when connecting to the certification authority P proxy url The HTTP pro
9. IdPgpKeyFingerprint lt fingerprint of OpenPGP key in PgpSecretKeyFile gt IdPgpKeyld lt id of the OpenPGP key in PgpSecretKeyFile gt 4 Copy your public key ring pbubring gpg to the ssh2 directory on Remote scp2 pubring gpg user remote_host ssh2 5 Create an authorization file in your ssh2 directory on Remote Add the following lines to the authorization file PgpPublicKeyFile lt filename of the user s public key ring gt PgpKeyName lt name of the OpenPGP key gt PgpKeyFingerprint lt fingerprint the OpenPGP key gt PgpKeylId lt id of the OpenPGP key gt 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 4 2 User Authentication 39 6 Now you should be able to login to Remote from Local using Secure Shell Try to login Local gt ssh Remote Passphrase for pgp key user comment lt user Local gt After you have entered the passphrase of your PGP key a Secure Shell connection will be established Optional Additional Configuration Settings The following configuration steps are optional e It is possible to use different settings depending on which key is used in public key authentication Your authorization file could for example contain the following Key master pub Key maid pub Options allow from trusted org Key butler pub Options deny from X evilcrackersl org deny from phoney org no pty When someone now logins using the master key the connection is not l
10. 3 Also define the LDAP server s in the ssh2_config file LDAPServers ldap serverl domainl port1 ldap server2 domain2 port2 4 If necessary define also the SOCKS server in the ssh2_conf ig file SocksServer socks socks_server port network netmask network netmask The SOCKS server must be defined if CA services OCSP CRLs are located behind a firewall 4 2 User Authentication Different methods can be used to authenticate users in SSH Secure Shell These authentication methods can be combined or used separately depending on the level of functionality and security you want User authentication methods used by the client by default are in the following order public key keyboard interactive and password authentication if available Public key and certificate authentication are combined into the public key authentication method The server allows public key and password authentication by default Different authentication methods are discussed in more detail in the following sections 4 2 1 Password Authentication With passwords it is also possible to use keyboard interactive authentication See Section 4 3 Keyboard Interactive Authentication for more information The password authentication method is the easiest to implement as it is set up by default Password authenti cation uses the etc passwdor etc shadow file on a UNIX system depending on how the passwords are set up To enable password authentication
11. Destroying session channel lt channel number gt The server is destroying the session channel with the specified id number Session channel extension request received Received a session channel extension request of type lt extension type gt for channel number lt channel number gt Received a session channel extension request of the specified type for the channel with specified id number Setting environment variable denied User tried to set environment variable lt environment variable gt to lt variable value gt in lt filename gt but was denied by policy Setting the environment variable denied by server policy Opening log for internal SFTP server Opening log for internal sftp server The server opened the log for the internal SFTP server SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 78 Chapter 5 Log Messages Chrooting user User lt login name gt will be chrooted to directory lt directory name gt The server is chrooting the user into a directory Changed to run on user privileges Now running on lt login name gt s privileges The server has dropped root privileges and is now running on user s privileges Setting environment variable denied by public key options User tried to set environment variable lt environment variable gt to lt variable value gt in public key options but was denied by policy Setting the enviro
12. Password change required after password change User lt login name gt password must be changed after password change strange For some reason the system requires the user to change their password even after a mandatory password change Password change failed Password change for user lt login name gt failed reason lt error message gt Password change failed The server does not allow root logins root login denied for user lt login name gt The server s configuration doesn t allow root logins or doesn t allow root logins with a password The server does not allow logins with empty passwords attempt to login as lt login name gt with empty password denied The server s configuration does not allow logins with empty passwords The server does not allow logins with passwords longer than 256 characters attempt to login as lt login name gt with password longer than 256 characters denied The server does not allow logins with passwords longer than 256 characters 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 71 Kerberos password accepted Kerberos password accepted for user lt login name gt lt kerberos name gt The server accepted the Kerberos password for the user Password accepted User lt login name gt s local password accepted The server accepted the user s local password Password not accepted Wro
13. Should be assigned to the pointer to the context allocated SshkKbdlat8obMethodCB gt Type typedef void SshKbdIntSubMethodCB sizet num_resp char resps Boolean cancel void context Description A function of this type is passed to the conversation function It is called after the responses are received from the client Arguments num_resp The size of the resps array resps The responses received from the client cancel If this value is TRUE the submethod should abort the authentication and get ready to be destroyed with the free function context The allocated context SshK bd IntSubMethod Conv Type typedef void SshKbdIntSubMethodConv SshKbdIntResult code const char instruction size t num_reqs char reqs Boolean echo SshKbdIntSubMethodCB method_cb void method ctx void context 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 4 3 Keyboard Interactive Authentication 55 Description The submethod calls this function when it has the requests Arguments code Indicates the state of the authentication If the submethod authentication is a success this should be SSH KBDINT_SUBMETHOD_RESULT_SUCCESS if failed SSH_KBDINT_SUBMETHOD_RESULT_FAILED and if the authentication is not complete SSH_KBDINT_SUBMETHOD_RESULT_NONE_YET instruction This field should contain a short description
14. any yet The client sent a response packet prematurely Client sent invalid packet auths pam client sent invalid packet as a response to our conversation message The client sent an invalid packet 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 69 Client sent continuation packet when expecting start packet Client sent continuation packet when expecting start packet for PAM auth The client sent continuation packet when the server was expecting a start packet Extra data in SSH_MSG_USERAUTH_REQUEST packet from client Extra data at end of SSH_MSG_USERAUTH_REQUEST packet for PAM authentication Extraneous data was included in the SSH_MSG_USERAUTH_REQUEST packet received from client Pipe creation failed in PAM authentication ssh_server_auth_pam pipe creation failed The forking and pipe creation to the subprocess failed in PAM user authentication Error happened during the PAM transaction PAM transaction resulted in error There was an error during the PAM transaction 5 1 9 User Authentication Password User not allowed to log in after password change User lt login name gt not allowed to log in after password change strange For some reason the system disallows login for the user after a mandatory password change SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 70 Chapter 5 Log Messages
15. lt maximum connections gt now open lt open connections gt The server has refused a connection because it would have otherwise exceeded the limit of simultaneously open connections Denied connection because of tcp_wrappers Denied connection from lt connection originator gt by tcp wrappers The server has refused a connection because it was denied by tcp_wrappers SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 88 Chapter 5 Log Messages Forking for new connection failed Forking a server for a new connection failed The server tried to fork to handle a new connection but the forking failed Server warning WARNING lt message gt A warning was received from the server Fatal server error FATAL ERROR lt message gt The server has encountered a fatal error condition SIGHUP handler received an invalid signal Invalid signal received by SIGHUP handler Server s SIGHUP handler received an illegal signal License file error License file error lt message gt The server encountered an error when checking the license file Server restarting restarting The server is restarting 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference Server starting in inetd mode Starting daemon in inetd mode The server is starting in inetd mode Server created a listener Listener created on lt address gt lt port gt
16. make sure that the AllowedAuthentications field of the etc ssh2 sshd2_config and etc ssh2 ssh2_config configuration files contain the param eter password AllowedAuthentications password Other authentication methods can be listed in the configuration files as well SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 36 Chapter 4 Authentication 4 2 2 Public Key Authentication Per user configuration information and encryption keys are by default stored in the ssh2 subdirectory of each user s home directory In the following instructions Remote is the SSH Secure Shell server machine into which you are trying to connect and Local is the machine running an SSH Secure Shell client Keys Generated with ssh keygen2 In order to set up user public key authentication do a manual setup according to the following instructions The following terms will be used in this example Remote is the SSH Secure Shell server into which you are trying to connect RemoteUser is the user name on the server into which you would like to login Local is the machine running a SSH Secure Shell client LocalUser is the user name on the client machine that should be allowed to login to Remote as RemoteUser 1 To make sure that public key authentication is enabled the Al lowedAuthentications field in both the etc ssh2 sshd2_config file on Remote and in the etc ssh2 ssh2_config file on Local should contain the word publickey All
17. Forwarding 3 5 4 Agent Forwarding 4 Authentication 4 1 Server Authentication 00 4 1 1 Public Key Authentication 4 1 2 Certificate Authentication 4 2 User Authentication 4 2 1 Password Authentication 4 2 2 Public Key Authentication 4 2 3 Host Based Authentication 4 2 4 Certificate Authentication 4 2 5 Kerberos Authentication 4 2 6 Pluggable Authentication Module PAM AT secur Ds neues aes ee Be phew ee 6 es 4 3 Keyboard Interactive Authentication AL OVENIEW oe Re ha OS a ee Oe a R 4 3 2 Configuring the Server and Client 2003 SSH Communications Security Corp CONTENTS SSH Secure Shell Admin Guide CONTENTS 5 4 3 3 Adding New Authentication Methods o a 52 5 Log Messages 57 5 1 Log Message Reference pc ooo oaan 2 ee 57 5 1 1 User Authentication Common 0 0 00 eee eee eee 57 5 1 2 User Authentication Host Based o e e 59 5 1 3 User Authentication Keyboard Interactive PAM 0 63 5 1 4 User Authentication Keyboard Interactive Password 65 5 1 5 User Authentication Keyboard Interactive o o 66 5 1 6 User Authentication Kerberos TGT ooo 66 5 1 7 User Authentication Kerbe
18. HTTP connections that would otherwise be insecure see Figure 3 1 Encrypted SSH2 tunnel 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 3 5 Forwarding 27 Internet TCP traffic IL session Client Sshdserver Figure 3 1 Encrypted SSH2 tunnel The client server applications using the tunnel will carry out their own authentication procedures if any the same way they would without the encrypted tunnel The protocol application might only be able to connect to a fixed port number e g IMAP 143 Otherwise any available port can be chosen for port forwarding Privileged ports below 1024 can be forwarded only with root privileges There are two kinds of port forwarding local and remote forwarding They are also called outgoing and incoming tunnels respectively Local port forwarding forwards traffic coming to a local port to a specified remote port For example if you issue the command ssh2 L 1234 localhost 23 username host all traffic coming to port 1234 on the client will be forwarded to port 23 on the server host Note that localhost will be resolved by the sshdserver after the connection is established In this case Localhost therefore refers to the server host itself Remote port forwarding does the opposite it forwards traffic coming to a remote port to a specified local port For example if you issue the command ssh2 R 1234 localhost 23 username host all traffic which
19. Pki 44 PkiDisableCRLs 44 platforms 13 Pluggable Authentication Module PAM 48 51 63 policy system 57 POP3 tunneling 26 port 22 101 103 port forwarding 26 port forwarding log messages 80 port forwarding dynamic 29 private key 105 process identifier PID 102 protocol version 12 13 25 public key 31 public key ring 38 public key authentication 31 36 43 public key authentication log messages 72 Public Key Cryptography Standards PKCS 113 publickey 38 rc local 100 101 rep 11 12 RedHat 100 reference log messages 57 remote forwarding 27 RequireReverseMapping 59 resetting server daemon 102 restricting user login 20 reverse mapping 59 revoked certificate 33 rexec 12 RFC 1950 19 RFC 1951 19 RFC 2315 112 RFC 2459 112 RFC 2460 113 RFC 2510bis 112 RFC 2559 112 RFC 2560 112 RFC 2585 112 rhosts 21 59 60 rlogin 11 12 103 root login 20 SSH Secure Shell Admin Guide INDEX RSA 49 111 RSA ACE A gent 49 RSA ACE Server 49 RSA key pair 32 RSA SecurID 49 rsh 11 103 scp 104 scp1 104 scp2 19 104 Secsh Working Group 12 secure copy 104 secure file transfer 104 Secure Shell 11 Secure Shell version 1 protocol SSH1 13 Secure Shell version 2 protocol SSH2 12 13 SecurID 49 51 SecurID authentication log messages 75 security policy Xserver 30 security risks 11 SerialAndIssuer 45 server authentication 31 33 serv
20. Run the server and the client with the d3 option This is a good way to see if a host key file is missing or if something is misconfigured Using Certificates It is possible to use a certificate instead of the traditional public key pair to authenticate the Local host To use certificates perform the following tasks 1 Enable host based authentication in ssh2_config on Local and in sshd2_config on Remote by using the Al lowedAuthent ications keyword 2 Define Local s server certificate in sshd2_config on Local HostKeyFile lt private key gt HostCertificateFile lt server certificate gt The certificate must contain a dns extension which contains the fully qualified domain name of Local 3 Set the DefaultDomain value in ssh2_config on Local 4 Set the HostCA and LdapServers values in sshd2_config on Remote HostCA lt trusted ca certificate gt LdapServers ldap server domain port 5 Make sure that the shosts file on Remote contains the following localhostname yourdomain com LocalUser More information is available in the ssh certificates man pages and in Sections 4 1 2 Server and 4 2 4 User 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 4 2 User Authentication 43 Optional Additional Configuration Settings To make the host based authentication more secure you may want to consider the following optional config uration settings e Setting the AllowSHosts and DenySHosts ke
21. be extracted from a PKCS 7 package by specifying the 7 flag with ssh keygen2 2 Certificate authentication is a part of the publickey authentication method Make sure that you have enabled it in the sshd2_conf ig file AllowedAuthentications publickey 3 Specify the CA certificate and the mapping file s in the sshd2_config file Pki lt ca cert path gt MapFile lt map file path gt You can disable the use of CRLs by adding the PkiDisableCRLs keyword below the Pki keyword PkiDisableCRLs yes Note CRL usage should only be disabled for testing purposes Otherwise it is highly recommended to always use CRLs You can define several CA certificates by using several Pk i keywords Pki lt ca cert pathl gt apFile lt map file pathl gt Pki lt ca cert path2 gt apFile lt map file pathl gt apFile lt map file path2 gt Note that multiple MapFile keywords are permitted per Pki keyword Also if no mapping file is defined all connections are denied even if user certificates can be verified using the defined CA certificate Server will accept only certificates issued by defined CA s 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 4 2 User Authentication 45 4 Also define the LDAP server s in the sshd2_conf ig file LDAPServers ldap serverl domainl port1 ldap server2 domain2 port2 5 If necessary define also the SOCKS server in the sshd2_config file SocksServer socks socks_
22. client has requested SSH1 agent forwarding but the server configuration forbids it SSH1 Agent forwarding requested Agent forwarding requested creating a listener The client has requested agent forwarding and the server is creating a listener for it SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 80 Chapter 5 Log Messages Forwarding an SSH1 agent connection Opening an agent forwarding channel The server has received an agent connection in the agent forwarding listener and is opening an agent for warding channel to the client Closing an SSH1 agent connection Closing an agent forwarding channel The agent forwarding channel from the server to the client has been closed 5 1 17 Port Forwarding Direct TCP port forwarding request denied Direct TCP IP forwarding request lt host gt lt port gt denied for user in configuration A direct TCP port forwarding request has been denied because of system policy Direct TCP port forwarding forbidden Direct TCP IP forwarding request denied in configuration A direct TCP port forwarding request was denied because the system policy forbids TCP port forwarding Connection received to forwarded port Connection to forwarded port lt forwarded port gt from lt host gt lt port gt The forwarded port received a connection 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 81 Remote port forwarding
23. connect received Remote fwd connect from lt connection originator gt to local port lt port gt A remote port forwarding request was received Remote listener creation failed Creating remote listener for lt address gt lt port gt failed A remote listener creation failed Port set up for remote forwarding Port lt port gt set up for remote forwarding A port was successfully set up for remote forwarding Received a remote forwarding request Remote TCP IP forwarding request received from host lt host gt by authenticated user lt login name gt Received a remote forwarding request Forwarding a privileged port Privileged user lt login name gt forwarding a privileged port Forwarding a privileged port under 1024 for a privileged user Remote TCP port forwarding forbidden Remote TCP IP forwarding request denied in configuration A remote TCP port forwarding request was denied because the system policy forbids TCP port forwarding SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 82 Chapter 5 Log Messages Remote TCP port forwarding request denied Remote TCP 1P forwarding lt host gt lt port gt request denied for user in configuration A remote TCP port forwarding request has been denied because of system policy Connection to direct forwarding received direct fwd connect from lt connection originator gt to local port lt port gt Received a
24. inetd but started on its own When the daemon is listening for a socket it waits until a client initiates a socket connection Once con nected the daemon forks a child process which in turn initiates key exchange with the client The child process handles the actual connection with the client including authentication supported cipher negotiation encrypted data transfer and termination of the connection After the connection has been terminated the child process terminates as well The parent process continues listening for other connections until explicitly stopped Login Process When a user successfully logs in sshd2 performs the following operations 1 Changes to run with normal user privileges 2 Sets up a basic environment 3 Reads etc environment if it exists 4 Changes to the user s home directory 5 Runs the user s shell or specified command SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 102 Chapter 6 Using SSH Secure Shell 6 1 4 Resetting and Stopping the Server Daemon When the Secure Shell daemon is started its process identifier PID is stored in var run sshd2 22 pid or if the directory var run does not exist in etc ssh2 sshd2_22 pid This makes it easy to kill the appropriate daemon kill cat var run sshd2_22 pid or send signals to it kill SIGNAL cat var run sshd2_22 pid The Secure Shell daemon handles signals like inetd you can send it a SIGHUP signal t
25. login name gt uid lt uid number gt coming from lt host gt authenticated A general message stating that the user has successfully authenticated herself User authenticated root login ROOT LOGIN User lt login name gt uid lt uid number gt coming from lt host gt authenticated General message stating that a superuser has successfully authenticated herself User authentication failed Authentication failed for user lt login name gt coming from lt host gt An user tried to log in but failed the user authentication 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 87 User logged out Logout for user lt login name gt The specified user has now logged out or has been logged out Login grace time exceeded LoginGraceTim xceeded The LoginGraceTime value was exceeded This means that the client did not succeed in logging in during time limit defined by the configuration option LoginGraceTime Connection received connection from lt host gt listen port lt listen port gt The server has received a connection from a host Connection received in interface connection from lt host gt listen iface lt address gt lt port gt The server has received a connection from a host to a port on specific interface Refusing connection too many open connections Refusing connection from lt host gt Too many open connections max
26. or products emphasis See SSH Sentinel User Manual 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 11 Chapter 2 Introduction to SSH Secure Shell SSH Secure Shell is a program that allows secure network services over an insecure network such as the Internet The Secure Shell concept originated on UNIX as a replacement for the insecure Berkeley services that is the rsh rcp and rlogin commands SSH Secure Shell replaces other insecure terminal applications such as Telnet and FTP It allows you to securely login to remote host computers to execute commands safely in a remote computer to securely copy remote files to forward X11 sessions on UNIX and to provide secure encrypted and authenticated communications between two non trusted hosts Also arbitrary TCP IP ports can be forwarded over the secure channel enabling secure connection for example to an email service SSH Secure Shell with its array of unmatched security features is an essential tool in today s network envi ronment It is a powerful guardian against the numerous security hazards that nowadays threaten network communications This chapter gives an overview of some of the security risks facing the Internet user and introduces the SSH2 protocol to combat these risks 2 1 Network Security Risks The open architecture of the Internet Protocol IP makes it a highly efficient cost effective and flexible communications protocol for lo
27. that they are connecting to the correct sshd2 daemon Inform your users to notify you if the fingerprints do not match or if they receive a message about a host key change and do not receive a corresponding message from you notifying them of the change This procedure can help ensure that you do not become a victim of a man in the middle attack as your users will notify you if the host key fingerprints do not match You will also be aware if the users encounter host key change messages when you have not regenerated your host key pair It is also possible to send the public host key to the users via an unalterable method The users can save the key to the ssh2 hostkeys directory as key_22_machinename pub In this case manual fingerprint check is not needed 3 1 3 Ciphers and MACs The algorithm s used for symmetric session encryption can be chosen in the sshd2_config and ssh2_config files Ciphers twofish blowfish SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 18 Chapter 3 Configuring SSH Secure Shell The system will attempt to use the different encryption ciphers in the sequence specified on the line Currently supported cipher names are the following des 3des blowfish twofish cast arcfour aes Of these ciphers Blowfish and Twofish are especially suitable for file transfers Special values for this option are the following Any allows all the cipher values including none
28. the ssh1 client The ssh2 command line options are documented in detail on the ssh2 1 manual page SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 104 Chapter 6 Using SSH Secure Shell 6 2 2 Client Configuration File and Command Line Options Ssh2 reads configuration data from etc ssh2 ssh2_ config and from SHOME ssh2 ssh2_config or the file specified with the F option on the command line The last obtained value will prevail The file contains keyword value pairs one per line Lines starting with the number sign as well as empty lines are interpreted as comments For detailed information about the options available in the configuration file and on the command line please refer to the ssh2_config 5 and ssh2 5 manual pages 6 3 Using Secure Copy scp2 Scp2 is a program for copying files securely over the network It uses ssh2 for data transfer and uses the same authentication and provides the same security as ssh2 Scp2 uses a sft p2 over ssh2 for data exchange between the client and server This is not to be confused with FTP The basic syntax for scp2 is like this scp user source directory file user destination directory file Note As shown in the example above in the normal case you do not have to type scp2 The installation process creates a symbolic link scp that points to the actual scp2 executable If ssh1 was installed before ssh2 was you will need to type scp1 to run the ssh1 c
29. too many connections lt message gt Disconnected because the internal connection limit was exceeded Disconnect User authentication failed User authentication failed lt message gt Disconnected because the user authentication failed This message should only occur when the other end is of version 2 0 13 or older Disconnect Authentication cancelled by user authentication cancelled by user lt message gt Disconnected because the authentication was cancelled by the user Disconnect No more authentication methods no more authentication methods on local remote lt message gt Disconnected because of running out of authentication methods This generally means that the client failed in all the authentication methods available on the server Disconnect Illegal user name illegal user name lt message gt Disconnected because the user name was illegal SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 86 Chapter 5 Log Messages Disconnect Unknown reason Unknown reason code lt reason code gt for disconnect msg lt message gt Disconnected reason code unknown Idle timeout exceeded Idle timeout exceeded The idle timeout limit was exceeded Remote protocol version string received Remote protocol version lt version string gt The server has received the remote protocol version string from the client User authenticated User lt
30. using it are supported 3 Only Kerberos5 is supported 4 SecurID tokens 5 RSA ACE Server or RSA ACE Agent software 6 Only PAM on Linux and on Solaris 2 6 or later is supported 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide Index rhosts 21 43 59 60 shosts 21 40 43 59 ssh2 15 36 63 etc passwd 35 etc shadow 35 etc ssh2 15 32 Ssubst 45 3DES 112 3des 18 account 49 account id 45 ACE Agent 49 ACE Server 49 active mode 28 adding authentication methods 52 AES 111 aes 18 agent 105 agent forwarding 30 agent forwarding log messages 76 agent forwarding SSH1 log messages 79 allow list 58 allow list group 58 allow list host 59 AllowedAuthentications 35 36 38 42 AllowGroups 22 AllowHosts 21 AllowSHosts 43 AllowUsers 21 AnyCipher 18 AnyMac 19 AnyStdCipher 18 AnyStdMac 19 Arcfour 112 arcfour 18 auditing 57 auth 49 authentication 31 authentication agent 105 authentication log messages 57 115 authentication log messages authentication log messages authentication log messages authentication log messages host based 59 Kerberos 67 Kerberos TGT 66 Keyboard Interactive 66 authentication log messages PAM 63 authentication log messages Keyboard Interactive Keyboard Interactive password 65 authentication log messages password 69 authentication log messages public key 72 authen
31. 0 Passphrase Again Private key saved to home user ssh2 id_rsa_2048_a Public key saved to home user ssh2 id_rsa_2048_a pub 3 Create an identification file in your ssh2 directory on Local Local gt cd ssh2 Local gt echo IdKey id_dsa_2048_a gt identification You now have an identification file which consists of one line that denotes the file containing your identification your private key For special applications you can create multiple identifications by executing ssh keygen2 again This is however not usually needed 4 Copy your public key id_dsa_2048_a pub to your ssh2 directory on Remote 5 Create an authorization file in your ssh2 directory on Remote Add the following line to the authorization file Key id_dsa_2048_a pub This directs the SSH Secure Shell server to use id_dsa_2048_a pub as a valid public key when authorizing your login If you want to login to Remote from other hosts create a key pair on the hosts steps 1 and 2 and repeat steps 3 4 and 5 on Remote Remember to specify a different file name for each key pair 6 Now you should be able to login to Remote from Local using SSH Secure Shell Try to login Local gt ssh Remote Passphrase for key home user ssh2 id_dsa_1024_a with comment 2048 bit dsa created by user Local Wed Mar 22 2002 00 13 43 0200 After you have entered the passphrase of your private key a Secure Shell connection will be established
32. 3 SSH Communications Security Corp 8 CONTENTS 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide Chapter 1 About This Document This document SSH Secure Shell for Servers Administrator s Guide contains instructions on the basic ad ministrative tasks of SSH Secure Shell The document is intended for the system administrators responsible for the configuration of SSH Secure Shell software To use the information presented in this document you should be familiar with UNIX system administration The document contains the following information introduction to SSH Secure Shell configuration options authentication options keyboard interactive authentication options using SSH Secure Shell appendix list of supported standards and authentication methods Installation instructions for SSH Secure Shell software can be found in SSH Secure Shell for Servers Quick Start Guide included in the CD ROM package and available on the SSH Web site http www ssh com support For more information see the manual pages included in the distribution 1 1 Available Manual Pages The following manual pages are included in the distribution e ssh2 secure shell client remote login program SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 10 Chapter 1 About This Document e scp2 secure copy client e sftp2 secure ftp client e ss e ss e ss e ss h add2 adds identities
33. AnyStd allows only standard ciphers and none none forbids any use of encryption AnyCipher allows any available cipher apart from the non encrypting cipher mode none AnyStdCipher the same as AnyCipher but includes only those ciphers mentioned in JETF SecSH draft excluding none This is the default value The MAC Message Authentication Code algorithm s used for data integrity verification can be chosen in the sshd2_config and ssh2_conf ig files MACs hmac shal hmac md5 The system will attempt to use the different MAC algorithms in the sequence they are specified on the line Supported MAC names are the following hmac shal hmac shal 96 hmac md5 hmac md5 96 hmac ripemd160 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 3 1 Basic Configuration 19 e hmac ripemdl60 96 Special values for this option are the following e Any allows all the MAC values including none e AnyStd allows only standard MACs and none e none forbids any use of MACs e AnyMac allows any available MAC apart from none e AnyStdMac the same as AnyMac but includes only those MACs mentioned in JETF SecSH draft excluding none This is the default value Both cipher and MAC can also be defined using command line arguments with ssh2 and scp2 scp2 c twofish m hmac md5 foobar user remote tmp Note Algorithm names are case sensitive 3 1 4 Compression SSH Secure Shell uses GNU ZLIB LZ77 for
34. H2 for SSH1 Compatibility 25 3 3 1 Troubleshooting TCP Wrappers If configuring TCP wrappers causes problems please check the following 1 Make sure that you are not experiencing any network connectivity problems 2 Make sure that SSH Secure Shell server is running kill 0 cat var run sshd2_22 pid or kill 0 cat etc ssh2 sshd2_22 pid If you receive the message No such process restart the sshd2 daemon 3 Check your etc hosts allowand etc hosts deny files e Ensure that the client s IP address or host name is correct e If you are using a host name you must supply the fully qualified domain name 4 If you changed something in the sshd2_config file you need to HUP the sshd2 daemon 5 Run tcpdchk and tcpdmatch These programs are used to analyze and report problems with your TCP Wrappers setup Please see the man pages for more information on these commands 3 4 Configuring SSH2 for SSH1 Compatibility Note SSH Communications Security considers the Secure Shell version 1 protocol deprecated and does not recommend the use of it For more information see http www ssh com company newsroom article 210 The SSH1 and SSH2 protocols are not compatible with each other This inconvenience is necessary since the SSH2 protocol includes remarkable security and performance enhancements that would not have been possible if protocol level compatibility with SSH1 had been retained However the current implementatio
35. INIT Received SSH_FXP_INIT The file server received the SSH_FXP_INIT message from the client Could not decode request id Couldn t decode request id Destroying file server A protocol error happened and the file server is being terminated Received SSH_FXP_OPEN Received SSH_FXP_OPEN The file server received an SSH_FXP_OPEN message from the client 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 91 Received SSH_FXP_CLOSE Received SSH_FXP_CLOSE The file server received an SSH_FXP_CLOSE message from the client Received SSH_FXP_READ E Received SSH_FXP_READ The file server received an SSH_FXP_READ message from the client Received SSH_FXP_WRITE Received SSH_FXP_WRITE The file server received an SSH_FXP_WRITE message from the client Received SSH_FXP_STAT Received SSH_FXP_STAT The file server received an SSH_FXP_STAT message from the client Received SSH_FXP_LSTAT Received SSH_FXP_LSTAT The file server received an SSH_FXP_LSTAT message from the client Received SSH_FXP_FSTAT Received SSH_FXP_FSTAT The file server received an SSH_FXP_FSTAT message from the client SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 92 Chapter 5 Log Messages Received SSH_FXP_SETSTAT Received SSH_FXP_SETSTAT The file server received an SSH_FXP_SETSTAT message from the client Received SSH_FXP_FSETSTAT R
36. REALPATH 93 SSH_FXP_REMOVE 92 SSH_FXP_RENAME 93 SSH_FXP_RMDIR 93 SSH_FXP_SETSTAT 92 SSH_FXP_STAT 91 SSH_FXP_SYMLINK 93 SSH_FXP WRITE 91 SSH_LICENSE_FILE 16 SSH_MSG_USERAUTH_REQUEST 69 SSH_PAM_OP_SUCCESS 64 SSH_PAM_OP_SUCCESS_WITH_PAYLOAD 64 SSH_REGEX_SYNTAX_EGREP 20 45 SSH_REGEX_SYNTAX_ZSH_F ILEGLOB 21 sshd 99 sshd2 15 25 32 48 99 101 102 2003 SSH Communications Security Corp 120 sshd2_22 pid 102 sshd2_config 15 17 18 20 23 25 32 34 36 38 40 42 45 47 102 sshd2_subconfig 23 SshKbdInt SubMet hodCB 54 SshKbdIntSubMethodConv 54 sshregex 20 standards 111 starting client 103 starting server daemon 99 100 stopping server daemon 102 StrictHostKeyChecking 32 StrictModes 60 subconfigurations 22 Subject 45 SubjectRegex 45 subsystem 102 support 14 supported cipher negotiation 101 supported platforms 13 supported standards 111 SuSE 100 Symbian OS 14 symmetric encryption 17 system configuration 15 system policy 57 System V 100 taking over a communication 12 TCP traffic tunneling 26 TCP wrappers 23 TCP IP 11 tcp_wrappers 82 87 tcpd 24 tcpdchk 25 tcpdmatch 25 technical support 14 Telnet 11 12 termination of connection 101 TGT ticket granting ticket 47 third party products 14 tic
37. SH Secure Shell Admin Guide 5 1 Log Message Reference Removing directory Removing directory lt filename gt The server is removing the specified directory Failed to remove directory Failed to remove dir lt filename gt Error lt errornumber gt The server failed to remove the requested directory Resolving path Resolving path to lt filename gt The server is resolving the path to the specified file Renaming file Renaming file lt filename gt to lt new filename gt The server is renaming the specified file Failed to rename file Failed to rename lt filename gt Error lt errornumber gt The server failed to rename the specified file Reading link Reading link lt linkname gt The server is reading the specified link SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 97 98 Readlink failed Chapter 5 Log Messages Readlink failed for lt linkname gt Error lt errornumber gt The readlink operation failed in the server Creating link Creating link lt linkname gt with value The server is creating the specified link Creating link failed Failed to create symlink lt linkname gt Creating the specified link failed in the server Got EXTENDED request got The server received an extended request from the client EXT END ED request lt request number
38. SSH Secure Shell for Servers Version 3 2 9 Administrator s Guide September 2003 1996 2003 SSH Communications Security Corp No part of this publication may be reproduced published stored in an electronic database or transmitted in any form or by any means elec tronic mechanical recording or otherwise for any purpose without the prior written permission of SSH Communications Security Corp This software is protected by international copyright laws All rights re served ssh B is a registered trademark of SSH Communications Security Corp in the United States and in certain other jurisdictions SSH2 the SSH logo SSH IPSEC Express SSH Certifier SSH Sentinel SSH NAT Traversal and Making the Internet Secure are trademarks of SSH Communications Security Corp and may be registered in certain ju risdictions All other names and marks are property of their respective owners THERE IS NO WARRANTY OF ANY KIND FOR THE AC CURACY OR USEFULNESS OF THIS INFORMATION EXCEPT AS REQUIRED BY APPLICABLE LAW OR EXPRESSLY AGREED IN WRITING SSH Communications Security Corp Fredrikinkatu 42 FIN 00100 Helsinki FINLAND SSH Communications Security Inc 1076 East Meadow Circle Palo Alto CA 94303 USA SSH Communications Security K K House Hamamatsu cho Bldg SF 2 7 1 Hamamatsu cho Minato ku Tokyo 105 0013 JAPAN http www ssh com e mail ssh sales ssh com sales http www ssh com support Tel 358 20 5007030 Fin
39. SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 38 Chapter 4 Authentication Keys Generated with ssh keygenl Beginning with version 3 0 SSH Secure Shell enables the usage of keys generated with ssh keygenl However the keys must be converted from the ssh1 format to ssh2 format ssh keygen2 1 lt keyname gt pub Successfully converted public key to lt keyname gt pub_ssh2 ssh keygen2 1 lt keyname gt Passphrase Successfully converted private key to lt keyname gt _ssh2 PGP Keys SSH Secure Shell only supports the OpenPGP standard and the PGP programs conforming to it GnuPG is used in the following instructions If you use PGP the only difference is that the file extension is pgp instead of GnuPGP s gpg 1 To make sure that user public key authentication is enabled the Al lowedAuthentications field both in the etc ssh2 sshd2 _config file on Remote and the etc ssh2 ssh2_config file on Local should contain the word publickey AllowedAuthentications publickey Other authentication methods can be listed in the configuration file as well 2 Copy your private key ring secring gpg to the ssh2 directory on Local 3 Create an identification file in your ssh2 directory on Local if you do not already have one Add the following lines to the identification file PgpSecretKeyFile lt filename of the user s private key ring gt IdPgpKeyName lt name of the OpenPGP key in PgpSecretKeyFile gt
40. TF SecSH draft 18 19 incoming tunnel 27 inetd 89 101 INIT 90 init 53 Internet Engineering Task Force IETF 12 Internet Protocol IP 11 SSH Secure Shell Admin Guide 117 Internet Protocol version 6 IPv6 113 IP Internet Protocol 11 IP spoofing 12 IPv6 Internet Protocol version 6 113 Kerberos 47 Kerberos authentication log messages 67 Kerberos TGT authentication log messages 66 key exchange 31 33 101 key fingerprint 31 key format converting 34 46 key format ssh2 34 46 key format X 509 34 46 key generation 16 key host log messages 83 key PGP 38 key PKCS 12 46 key private 105 key ssh1 format 38 Keyboard Interactive authentication 49 50 keyboard interactive authentication 35 48 Keyboard Interactive PAM authentication log mes sages 63 Keyboard Interactive password authentication log mes sages 65 Keyboard Interactive user authentication log messages 66 knownhosts 16 LDAP Lightweight Directory Access Protocol 33 43 112 LDAP server 35 44 LdapServers 42 legal issues 13 libwrap a 24 license file 16 license commercial 14 license non commercial 14 license_ssh2 dat 16 Lightweight Directory Access Protocol LDAP 33 43 112 Linux 13 list allow 58 list allow host 59 list deny 58 list deny host 59 list group allow 58 list group deny 58 listening 101 local forwarding 27 2003 SSH Communication
41. The server has successfully created a listener Server created an UDP listener UDP Listener created on lt address gt lt port gt The server has successfully created an UDP listener Setsid failed setsid lt error message gt A call to set sid failed in the server Server running Daemon is running 89 The server process has successfully performed all initialization operations and is now listening for connec tions 5 1 22 SFTP File closed File s closed written lt bytes written gt lt bytes read gt SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 90 Chapter 5 Log Messages A file has been closed This is the only log message of a completed transfer of a file Typically the whole file 1s read or written but this is not the only possibility This log message will report the sum of all reads and the sum of all writes since the opening of the file Note even the same client can open a file multiple times which will result in multiple closes each with possibly different number of read and written bytes Bad message received Received bad message lt message number gt The protocol code received a bad message from the client Got wrong message before receiving INIT Got message type d before receiving INIT This is a protocol error destroying the file server A protocol error occurred and the file server is being terminated Received SSH_FXP_
42. ation can also be defined in the ssh2_config file see below Server Side Configuration To configure the server side functionality perform the following tasks 1 Enroll a certificate for the server This can be done with the supplied ssh certenroll2 command line utility Note that the DNS Address parameter needs to correspond to the fully qualified domain name of the server Example Enrollment using ssh certenrol12 ssh certenroll2 g p id key e s C FI O SSH CN testserver dns testserver trusted org a http test ca trusted org 8080 pkix 0o etc ssh2 hostcert_rsa etc ssh2 test ca certificate crt Generated 1024 bit private key saved to file etc ssh2 hostcert_rsa prv SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 34 Chapter 4 Authentication Remember to also define the SOCKS server S or the HTTP proxy P if required For more information on the ssh certenro112 syntax see Appendix A 2 ssh certenroll2 2 The server s private host key must be in the ssh2 format To convert X 509 keys to ssh2 format use the x flag with ssh keygen2 ssh keygen2 x lt keyname gt Private key imported from X 509 format Successfully saved private key to lt keyname gt _ssh2 PKCS 12 keys can be converted to ssh2 format by using the k flag with ssh keygen2 Note As the server s private key must have an empty passphrase just press enter when you are prompted for the new
43. cal and global communications It has been widely adopted not only on the global Internet but also in the internal networks of large corporations The IP protocol suite including TCP IP was designed to provide reliable and scalable communications over real world networks It has served this goal well However it was designed twenty years ago in a world where the Internet consisted of a few hundred closely controlled hosts The situation has changed The Internet now connects dozens of millions of computers controlled by millions of individuals and organizations The core network itself is administered by thousands of competing operators and the network spans the whole globe connected by fibers leased lines dial up modems and mobile phones SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 12 Chapter 2 Introduction to SSH Secure Shell The phenomenal growth of the Internet has peaked the interest of businesses military organizations govern ments and criminals Suddenly the network is changing the way business is done It is changing the nature of trade and distribution networks and the way individual people communicate with each other The upsurge of business scientific and political communications on the Internet has also brought out the usual negative elements Criminals are looking for ways of getting a cut of the emerging business In dustrial espionage has moved online Intelligence agencies are showing a gr
44. comes to port 1234 on the server host will be forwarded to port 23 on the client localhost It is important to realize that if you have three hosts client sshdserver and appserver and you forward the traffic coming to the client s port x to the appserver s port y only the connection between the client and sshdserver will be secured See Figure 3 2 Forwarding to a third host The command you use would be something like the following ssh2 L x appserver y username sshdserver SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 28 Chapter 3 Configuring SSH Secure Shell session Internet Insecure TCP traffic connection E Encrypted ssh2 tunnel o Terminal Client Sshdserver Appserver Figure 3 2 Forwarding to a third host Forwarding FTP With SSH Secure Shell version 3 0 and above it is possible to easily forward FTP connections by using a command with the following syntax ssh2 L ftp x ftpdserver y username sshdserver FTP forwarding is an extension to the generic port forwarding mechanism The FTP control channel can be secured by using generic port forwarding but since the FTP protocol requires creating separate TCP connections for the files to be transferred all the files would be transferred unencrypted when using generic port forwarding as these separate TCP connections would not be forwarded automatically To protect also the transferred files use FTP forwarding instead It wor
45. compression The zlib compression is described in RFC 1950 and in RFC 1951 By default compression is disabled Compression can be enabled in the ssh2_conf ig file Compression yes Alternatively compression can be enabled on the command line ssh2 C username remot The client can request a compression level with a number after C from C1 to C9 In this case the compression level is between the levels requested by the client and offered by the server For example if the server offers level 6 the default and the client asks for level 1 level 2 is used Compression is worth using if your connection is slow for example a modem connection The efficiency of the compression depends on the type of the file and varies widely It is close to 0 for already compressed files like zip and often 50 or even more for text files SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 20 Chapter 3 Configuring SSH Secure Shell 3 1 5 Configuring Root Logins If you want to permit someone to login directly to the root login account via ssh you can define three methods of control in the sshd2_config file PermitRootLogin no This will disable all root logins To enable root logins with any authentication method use the following setting PermitRootLogin yes You can limit the authentication methods by using the following setting PermitRootLogin nopwd This allows root logins only when an authentication met
46. connection to forwarded port 5 1 18 X11 Forwarding X11 connection refused by tcp_wrappers Fwd X11 connection from lt connection originator gt refused by tcp_wrappers The X11 connection was refused by tcp_wrappers X11 connection received X11 connection from lt ip address gt lt port gt lt host gt An X11 connection was received 5 1 19 Common Code Disconnection happened Local Remote host disconnected lt reason message gt The connection was disconnected by the local or the remote end for the reason given 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 83 5 1 20 Host Key I O PIN request received PIN requested PIN label lt pin label gt at keypath lt keypath gt ignoring A PIN request was received when reading host keys and since the user is not available at this point the request is ignored 5 1 21 General Server Log Messages Disconnect Host not allowed to connect Disallowed connect from denied host lt message gt The server has disconnected the client because the client is not allowed to connect Disconnect Protocol error Protocol error in local remote lt message gt Disconnecting because of a protocol error in local or remote end Disconnect Key exchange failed Key exchange failed in local remote lt message gt Disconnecting because key exchange failed in local or remote end Disconn
47. during the installation To generate the host key perform the following tasks 1 Login as root 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 3 1 Basic Configuration 17 2 Kill the sshd2 daemon listening to port 22 kill cat var run sshd2_22 pid If the directory var run does not exist sshd2_22 pidis in directory etc ssh2 3 Generate the host key with the following command ssh keygen2 P etc ssh2 hostkey Note This will generate a DSA 2048 bit host key pair without a passphrase For more information on the key generation options see the ssh keygen2 man page 4 Restart sshd2 usr local sbin sshd2 Note Administrators that have other users connecting to their sshd2 daemon should notify the users of the host key change If you do not the users will receive a warning the next time they connect because the host key the users have saved on their disk for your server does not match the host key now being provided by your sshd2 daemon The users may not know how to respond to this error You can run the following to generate a fingerprint for your new public host key which you can provide to your users via some unalterable method such as digitally signed email ssh keygen2 F hostkey pub When the users connect and receive the error message about the host key having changed they can compare the fingerprint of the new key with the fingerprint you have provided in your email and ensure
48. e keys for authentication With the Ssh add2 command you can add identities to the authentication agent When you use the authentication agent 1t will automatically be used for public key authentication This way you only have to type the passphrase of your private key once to the agent Authentication data does not have to be stored on any other machine than the local machine and authentication passphrases or private keys never go over the network Start ssh agent 2 with the command eval ssh agent2 or with the command exec ssh agent SSHELL After that you can add identities like this ssh add2 id_dsa_1024_ a Adding identity id_dsa_1024_a Need passphrase for id_dsa_1024 a 1024 bit dsa user localhost Tue Aug 01 2000 19 41 42 Enter passphrase When you connect to a remote host and use public key authentication you will get straight in If you want the connection to the agent to be forwarded over ssh remote logins you should have this line in your etc ssh2 sshd2_config file AllowAgentForwarding yes The ssh agent2 and ssh add2 command line options are documented in detail on the ssh agent2 1 and ssh add2 1 manual pages SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 106 Chapter 6 Using SSH Secure Shell 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 107 Appendix A Tool Syntax The basic syntax of ssh keygen2 and ssh certenrol12 is explained h
49. e necessary information to the SOCKS server which is actually the Secure Shell client mimicking a SOCKS server The client will use this information in creating port forwarding to the Secure Shell server and relying the traffic back and forth securely as with user specified port forwarding For more information please see the ssh2 1 man pages 3 5 3 X11 Forwarding To enable X11 forwarding SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 30 Chapter 3 Configuring SSH Secure Shell 1 Make sure that the SSH Secure Shell software was compiled with X forwarding support The binary packages contain runtime X detection in SSH Secure Shell version 3 2 and above However if X security extensions are wanted it is necessary to compile from source When compiling make sure not to run configure with any X disabling options 2 Ensure that xauth is in the path of the user running configure Also make sure that you have the following line in your etc ssh2 sshd2_config file AllowX11Forwarding yes X11 forwarding also needs to be enabled in the client by setting the following line in the ssh2_config file ForwardX11 yes 3 Log into the remote system and type xclock This starts a X clock program that can be used for testing the forwarding connection If the X clock window is displayed properly you have X11 forwarding working Note Do not set the DISPLAY variable on the client You will most likely disable encr
50. e server will obtain additional information about the user does the user exist what is the user s UID and what groups does the user belong to With this information the server can read the user specific configuration files specified by UserSpecifiConfig in the main sshd2 configuration file The syntax is the following UserSpecificConfig pattern subconfig file You can use patterns of the form user group host where user is matched with the user name and UID group is matched with the user s primary and sec ondary groups both group name and GID and host is matched as described under Al lowHosts see the sshd2_subconfig man page For example the following would match any user in group sftp connecting from company com Ssftpecompanycom See the sshd2_subconf ig man pages for more information 3 3 Configuring SSH Secure Shell for TCP Wrappers Support To enable usage of TCP Wrappers with SSH Secure Shell perform the following operations 1 If SSH Secure Shell was previously installed from binaries you may want to uninstall it before contin uing 2 Compile the source code configure with libwrap make SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 24 Chapter 3 Configuring SSH Secure Shell Then become root and run make install Note If configure does not find 1ibwrap a do the following e Locate libwrap a e Run configure again make distclean configure with libwra
51. e using Kerberos credentials forwardable TGT ticket granting ticket and passing TGT to remote host for single sign on It is also possible to use Kerberos password authentication Please note that SSH Secure Shell only supports Kerberos5 To enable Kerberos support perform the following tasks 1 Compile the source configur with kerberos5 make make install 2 Make sure that you have the following line in your etc ssh2 sshd2_config file AllowedAuthentications kerberos 1ftssh com kerberos tgt 1fssh com Other authentication methods can be listed in the configuration file as well 3 Also make sure that you have the following line in your etc ssh2 ssh2_config file for SSH Secure Shell versions 2 3 and 2 4 SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 48 Chapter 4 Authentication AllowedAuthentications kerberos 1fssh com kerberos tgt 1fssh com If you are using SSH Secure Shell version 3 0 or later make sure that you use the new versions of kerberos authentication methods AllowedAuthentications kerberos 2fssh com kerberos tgt 2fssh com Note SSH Communications Security does not provide technical support on how to configure Kerberos Our support only covers SSH Secure Shell applications and source code 4 2 6 Pluggable Authentication Module PAM We recommend the use of keyboard interactive authentication with PAM When PAM is used SSH Secure Shell transfers the control of authentica
52. eceived SSH_FXP_FSETSTAT The file server received an SSH_FXP_FSETSTAT message from the client Received SSH_FXP_OPENDIR Received SSH_FXP_OPENDIR The file server received an SSH_FXP_OPENDIR message from the client Received SSH_FXP_READDIR Received SSH_FXP_READDIR The file server received an SSH_FXP_READDIR message from the client Received SSH_FXP_REMOVE Received SSH_FXP_REMOVE The file server received an SSH_FXP_REMOVE message from the client Received SSH_FXP_MKDIR Received SSH_FXP_MKDIR The file server received an SSH_FXP_MKDIR message from the client 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 93 Received SSH_FXP_RMDIR Received SSH _FXP_RMDIR The file server received an SSH_FXP_RMDIR message from the client Received SSH_FXP_REALPATH Received SSH_FXP_REALPATH The file server received an SSH_FXP_REALPATH message from the client Received SSH_FXP_RENAME Received SSH_FXP_RENAME The file server received an SSH_FXP_RENAME message from the client Received SSH_FXP_READLINK Received SSH_FXP_READLINK The file server received an SSH_FXP_READLINK message from the client Received SSH_FXP_SYMLINK Received SSH_FXP_SYMLINK The file server received an SSH_FXP_SYMLINK message from the client Received SSH_FXP_EXTENDED Received SSH_FXP_EXTENDED
53. ect Illegal code RESERVED this is an illegal code in local remote lt message gt Disconnecting with illegal code as reason SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 84 Chapter 5 Log Messages Disconnect MAC failed MAC failed in local remote disconnecting lt message gt Disconnecting because MAC failed in local or remote end Disconnect Compression error compression error in local remote disconnecting lt message gt Disconnecting because of a compression error Disconnect Service not available service not available lt message gt Disconnecting because a requested service was not available Disconnect Protocol version not supported protocol version not supported in local remote lt message gt Disconnecting because the protocol version was not supported Disconnect Host key not verified host key not verifiable in local remote lt message gt Disconnecting because the host key could not be verified Disconnect Connection was lost connection lost lt message gt Disconnecting because the connection was lost 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 85 Disconnect Disconnected by application disconnected by application in local remote lt message gt Disconnected by application Disconnect Too many connections
54. ection the local copy of the server s public key will be used in server authentication If you want to avoid the risk associated with the first connection you can copy the server public key in advance tothe etc ssh2 hostkeys directory on the client computer and set the StrictHostKeyChecking keyword in the ssh2_config file to yes After this ssh2 will refuse to connect if the server s public key is not in the etc ssh2 hostkeys directory The key pair used for server authentication is defined on the server in the sshd2_config file with the following parameters HostkeyFile lt private hostkey gt PublicHostKeyFile lt public hostkey gt During the installation process one DSA key pair with the file names hostkey and hostkey pub is generated and stored in the etc ssh2 directory By default this key pair is used for server authentication Beginning with SSH Secure Shell version 3 0 each server daemon can have multiple host keys The daemon supports one DSA and one RSA key pair You could have for example the following set of parameters in your sshd2_config file RSA key HostkeyFile hostkey_rsa PublicHostKeyFile hostkey_rsa pub DSA key HostkeyFile hostkey_dsa PublicHostKeyFile hostkey_dsa pub Both keys are stored in memory when the sshd2 process is started which means that either one of them can be used to authenticate the server 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 4 1 Serve
55. ed from X 509 format Successfully saved private key to lt keyname gt _ssh2 Also PKCS 12 keys can be converted to ssh2 format This is done by specifying the k flag with ssh keygen2 ssh keygen2 k lt keyname gt Password needed for PFX integrity check Integrity check ok Got shrouded key New passphrase for private key Again Successfully saved private key to lt keyname gt _ssh2 Safe decrypted succesfully Got certificate Certificate written to file lt keyname gt _ssh2 crt 3 Make sure that public key authentication is enabled in the ssh2_config file AllowedAuthentications publickey 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 4 2 User Authentication 47 4 Specify the private key of your software certificate in the ssh2 identification file CertKey lt private key path gt The certificate itself will be read from private key path crt PKCS 11 Tokens To configure the system for PKCS 11 tokens for example smart cards perform the following tasks 1 Enable public key authentication in the ssh2_conf ig file AllowedAuthentications publickey 2 Also define the external key provider and the initial string EkProvider lt provider name gt EkInitString lt init string gt The above mentioned options can be also defined using the E and I flags with ssh2 respectively 4 2 5 Kerberos Authentication When Kerberos support is enabled it is possible to authenticat
56. ell daemon This means that sshd will be started in runlevels 3 4 and 5 its starting priority is 34 and its killing priority is 70 You can choose the runlevels and priorities as you want as long as sshd is started after the network is up After adding the links manually or giving the command chkconfig add sshd2 you should have the links etc rc d rc d similar to lrwxrwxrwx 1 root root 14 Aug 16 10 07 S34sshd gt init d sshd lrwxrwxrwx 1 root root 14 Aug 16 10 07 K70sshd gt init d sshd 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 6 1 Using the Secure Shell Server Daemon sshd2 101 Starting from etc rc local On BSD based operating systems you have to add a similar line to the following to the rc local file in the etc directory echo Starting sshd2 usr local sbin sshd2 After this the Secure Shell daemon will start automatically at boot time 6 1 3 Operation of the Server Daemon When ssha2 is started it begins to listen on a port for a socket The default port is port 22 now a well known port for Secure Shell This can be changed to suit any custom environments e g if you want to run sshd2 from a non privileged account however make sure that no other process is using the port you are planning to use The Secure Shell daemon can also be started from the Internet daemon inetd For the purpose of this text it is assumed that sshd2 is not invoked through
57. er certificate 33 server daemon 25 99 server daemon operation 101 server daemon resetting 102 server daemon starting 99 100 server daemon stopping 102 server deny list 58 server log messages 83 server side configuration 33 44 server SFTP log messages 75 session 49 session channel related log messages 77 setsid 89 sftp 103 105 SFTP log messages 89 SFTP server log messages 75 sftp2 104 SHA 1 111 shadow password 99 shosts 21 40 59 shosts equiv 43 59 SIGHUP 88 102 SIGKILL 102 smart card 46 47 SMTP tunneling 26 socket connection 101 SOCKS server 29 35 45 46 software certificate 46 SSH Secure Shell Admin Guide 119 software version 13 spoofing 12 ssh 103 SSH Secure Shell 11 ssh add2 105 ssh agent2 105 ssh certenrol12 33 46 109 ssh keygen1l 38 ssh keygen2 17 34 36 37 44 46 107 ssh1 103 SSH1 agent forwarding log messages 79 SSH1 compatibility 25 sshl key format 38 SSH1 protocol 13 25 ssh2 19 63 103 ssh2 key format 34 46 SSH2 protocol 12 13 25 ssh2 server daemon 25 ssh2 1 29 ssh2 _config 15 17 20 32 36 38 40 42 46 47 104 ssh_channel_request env 79 SSH_FXP_CLOSE 91 SSH_FXP_EXTENDED 93 SSH_FXP_FSETSTAT 92 SSH_FXP_FSTAT 91 SSH_FXP_INIT 90 94 SSH_FXP_LSTAT 91 SSH_FXP_MKDIR 92 SSH_FXP_OPEN 90 SSH_FXP_OPENDIR 92 SSH_FXP_READ 91 SSH_FXP_READDIR 92 SSH_FXP_READLINK 93 SSH_FXP_
58. ere For more information see the relevant man pages A 1l ssh keygen2 ssh keygen2 is a tool that generates and manages authentication keys for ssh2 Each user wishing to use ssh2 with public key authentication can run this tool to create authentication keys Additionally the system administrator may use this to generate host keys for the server Please note that PKI and PKCS 11 support is only available in commercial distributions of SSH Secure Shell for Servers SYNOPSIS ssh keygen2 b bits t dsalrsa c comment_string e file p passphrase P h q 1 file i file D file B number V r file x file k file 7 file F file keyl key2 OPTIONS b bits Length of the key in bits for example 1024 bits t dsa rsa Choose the type of the key Valid options are dsa and rsa SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 108 c comment_string Specify the key s comment string e file Appendix A Tool Syntax Edit the specified key Makes ssh keygen2 interactive You can change the key s passphrase or comment p passphrase Specify the passphrase used P Specify that the key will be saved with an empty passphrase h Print a short summary of ssh keygen2 commands q Hide the progress indicator 1 file Convert key from sshl format to ssh2 format i file Load and display information on file
59. ey from the received certificate failed during host based authentication Cryptographic operation failed in host based authentication Hostbased Crypto operation failed for public key for user lt loginname gt Changing the hashing scheme in the public key failed in host based authentication Verifying the signature failed in host based authentication Hostbased authentication failed for lt loginname gt Verifying the signature failed in host based authentication SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 62 Chapter 5 Log Messages Host based authentication successful Hostbased authentication for user lt loginname gt accepted Authentication using the host based authentication method succeeded for the user Root logins not permitted in host based authentication Root logins are not permitted The server has been configured not to allow root logins Could not decode packet in host based authentication Error decoding hostbased packet Decoding the host based authentication protocol packet failed The host name given by the client does not match the one given by the client in host based authentica tion Client gave us a hostname lt hostname gt which doesn t match the one we got from DNS lt hostname gt sending failure The server has been configured to use strict host name checking and the host name gotten using reverse DNS lookup does not match the one in the host based a
60. for the authentication agent h agent 2 authentication agent h certenrol12 certificate enrollment client included only in the commercial distribution h certificates describes the configuration files and options needed when using certificates with ssh2 software included only in the commercial distribution ess ess ess ess ess ess hos ess e ss e ss h dummy she11 ultimately restricted shell h externalkeys general documentation about using external keys with ssh2 software h keygen2 authentication key pair generation h probe2 seeks ssh servers from the local network h2_config format of configuration file for ssh2 hd check conf check what your configuration allows or denies based on incoming user and or t name hd2 secure shell daemon hd2_config format of configuration file for sshd2 hd2_subconfig advanced configuration of sshd2 e ss scp hregex describes the regular expressions or globbing patterns used in filename globbing with 2 and sftp2 and in the configuration files ssh2_config and sshd2_config Please refer to the above mentioned man pages for command syntax descriptions and usage instructions 1 2 Documentation Conventions The following special conventions are used in this document Convention Usage Example Bold Menus GUI elements strong emphasis Click Apply or OK Monospace Filenames commands directories URLs etc Refer to readme txt Italics Reference to other documents
61. gt 2003 SSH Communications Security Corp lt target gt Error lt errornumber gt SSH Secure Shell Admin Guide 99 Chapter 6 Using SSH Secure Shell This chapter provides information on how to use the SSH Secure Shell software suite after it has been suc cessfully installed and set up 6 1 Using the Secure Shell Server Daemon sshd2 The server daemon program for Secure Shell is called sshd2 Ssha2 is normally started at boot time from etc rc local or its equivalent It forks a new daemon for each incoming connection The forked daemons handle key exchange encryption authentication command execution and data exchange The Secure Shell daemon is normally run as root If it is not run as root only the user the daemon is running as will be authorized to log in and password authentication may not work if the system uses shadow passwords An alternative host key pair must also be used 6 1 1 Manually Starting the Secure Shell Server Daemon To manually start the Secure Shell daemon type the command usr local sbin sshd2 Note If the installation was successfully completed sshd is a symbolic link to ssha2 If you also have ssh1 installed the ssh2 installation process modifies the existing link If ssh1 compatibility is desired sshd2 can be configured to execute sshd1 when the client only supports ssh1 However it is recommended to use sshd2 because sshd may start an OpenSSH server The sshd2 daemo
62. hod other than password is used It is also possible to create a separate subconfiguration file for root See Section 3 2 Subconfigurations for more information 3 1 6 Restricting User Logins By default SSH Secure Shell does not impose any login restrictions in addition to those provided by the operating system However you can restrict connections based on host user name or group The restrictions are defined in the sshd2_config file using the following syntax keyword pattern Note All the patterns used in the examples below are in accordance with SSH_REGEX_SYNTAX_EGREP which is the default regex syntax in SSH Secure Shell version 3 0 and above However the regex syntax can be chosen by using the metaconfig block in the beginning of ssh2_config and sshd2_config SSH CONFIGURATION FILE FORMAT VERSION 1 1 REGEX SYNTAX egrep end of metaconfig Possible values of REGEX SYNTAX are ssh egrep zsh_fileglob and traditional For more information please see the sshregex man pages 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 3 1 Basic Configuration 21 Previous versions of SSH Secure Shell always use SSH_REGEX_SYNTAX_ZSH_FILEGLOB Available keywords are the following e AllowHosts DenyHosts Login is allowed denied from hosts whose name matches one of the specified patterns Example 1 Listing complete hostname
63. host name of Local some tabs or spaces and LocalUser s user name Contents of shosts localhostname yourdomain com LocalUser Be sure to chown and chmod the shosts file The shosts file must be owned by RemoteUser and should have mode 0400 Check the files etc ssh2 sshd2_config on Remote and etc ssh2 ssh2_config on Lo cal Make sure that the AllowedAuthentications field contains the word hostbased For example it may read AllowedAuthentications hostbased password It does not matter what other authentication methods are allowed Just make sure that the hostbased keyword is first in the list Also check that IgnoreRhosts is set to no inthe etc ssh2 sshd2_config file on Remote IgnoreRhosts no If you had to modify the sshd2_config file you will have to send a HUP signal to sshd2 to make the change take effect 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 4 2 User Authentication 41 kill HUP cat var run sshd2_22 pid or kill HUP cat etc ssh2 sshd2_22 pid 7 Now you should be all set On Local log in as LocalUser and give the command ssh RemoteUser Remote uptime You should now get the results of upt ime run on Remote The first time you run ssh to that particular server you will have to answer yes when asked if you want to connect to the server This is because the local ssh does not yet have the remote server s public key For maximum security it i
64. ide 4 3 Keyboard Interactive Authentication 53 will create a method context for the submethod and start the authentication using the specified conversation function You need to define three functions init free and a callback for the conversation function int Type typedef void init void method_context SshAuthKbdIntSubMethods methods SshKbdIntSubMethodConv conv void conv_context Description The initialization function Arguments method_context Should be assigned to the pointer to the context allocated Assigning something to met hod_context is mandatory This simplifies the main method s bookkeeping on what submethods have actually been initialized This context is passed to the free function methods Should be stored by the submethod It contains for example the SshServer structure and an SshUser structure that can be used in the authentication process by the submethod conv The conversation function called by the submethod when it has the requests The prototype is described below conv_context Should be given to the conv function free S Type typedef void free void method context Description free is called by the main method during uninitialization The submethod should free all state including method_context at this stage SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 54 Chapter 4 Authentication Arguments method_context
65. ific and user specific files in etc ssh2 subconfig 3 2 1 Host Specific Subconfiguration The Host SpecifiConfig variable specifies host specific subconfiguration files for sshd2 The syntax is the following HostSpecificConfig pattern subconfig file pattern will be used to match the client host as specified under AllowHosts see the sshd2_subconfig man page The file subconfig file will then be read and configuration data amended accordingly 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 3 3 Configuring SSH Secure Shell for TCP Wrappers Support 23 The file is read before any actual protocol transactions begin and you can specify most of the options allowed in the main configuration file You can specify more than one subconfiguration file in which case the patterns are matched and the files read in the order specified Later defined values of configuration options will either override or amend the previous value depending on which option it is The effect of redefining an option is described in the documentation for that option For example setting Ciphers in the subconfiguration file will override the old value but setting Al lowUsers will amend the value For more information please see the sshd2_subconfig and sshd2_config man pages 3 2 2 User Specific Subconfiguration User specific subconfiguration files are read when the client has stated the user name it is trying to log in with At this point th
66. imited in any way by the authorization file However if the maid key is used only connections from certain hosts will be allowed And if the but ler key is used connections are denied from certain hosts and additionally the allocation of tty is prevented Note The options keyword is available only in SSH Secure Shell version 3 0 and later In the previous versions the only key specific keyword is command More information on opt ions and command keywords is available in the ssh2 man pages e The per user configuration directory can be changed by setting the UserConfigDirectory key word in the sshd2_config file and on the client settings 4 2 3 Host Based Authentication The following terms will be used in this example Remote is the SSH Secure Shell server to which you are trying to connect RemoteUser is the user name on the server into which you would like to login Local is the machine running a SSH Secure Shell client LocalUser is the user name on the client machine that should be allowed to login to Remote as RemoteUser 1 First install SSH Secure Shell on the Local and Remote machines Do not forget to generate a host key If your installation took care of this automatically or if you already have a copy of your etc ssh2 hostkey and etc ssh2 hostkey pub you can skip the host key generation Otherwise give the following command SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 40 Chapter 4 Authe
67. in is allowed or not Finally if connection is allowed the server makes sure that the user has a valid private key by using a challenge Compared to traditional public key authentication this method is more secure because the system checks that the user certificate was issued by a trusted CA In addition certificate authentication is more convenient because no local database of user public keys is required on the server SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 44 Chapter 4 Authentication It is also easy to deny a user s access the system by revoking his or her certificate The status of a certifi cate can be checked either by using the Online Certificate Status Protocol OCSP or Certificate Revocation Lists CRLs which can be published either to a Lightweight Directory Access Protocol LDAP or HTTP repository OCSP is used if the certificate contains a valid authority info access extension Correspondingly CRLs are used if the certificate contains a valid CRL distribution point extension If LDAP is used as the CRL publishing method the LDAP repository location can be also defined in the sshd2_config file see below Server Side Configuration To configure the server perform the following tasks 1 Acquire the CA certificate and copy it to the server machine You can either copy the X 509 certifi cate s as such or you can copy a PKCS 7 package including the CA certificate s Certificates can
68. ing 29 X11 forwarding log messages 82 SSH Secure Shell Admin Guide INDEX 121 X11 SECURITY extension 30 xauth 30 Xserver security policy 30 zlib compression 19 zsh_fileglob 20 SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp
69. is will generate a private key called mykey prv and a certificate called mykey 0 crt 2 Enroll a certificate using a supplied private key and provide an email extension ssh certenroll2 o mykey p 12345 ab a http www ca auth domain 8080 pkix s c ca o acme cn Rami Romi email rami acme ca ca certificate crt my_pri vate_key prv This will generate and enroll a certificate called mykey 0 crt 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 111 Appendix B Technical Specifications B 1 Supported Cryptographic Algorithms and Standards This section lists the supported cryptographic algorithms and standards supported by SSH Secure Shell B 1 1 Public Key Algorithms The following public key algorithms are the supported e RSA 768 1024 2048 or 3072 bit key e DSA 768 1024 2048 or 3072 bit key B 1 2 Data Integrity Algorithms The following data integrity algorithms are supported e SHA 1 20 byte key RFC 2104 e MDS 16 byte key RFC 2104 B 1 3 Symmetric Session Encryption Algorithms For symmetric session encryption the following algorithms are supported e AES 128 192 or 256 bit key SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 112 Appendix B Technical Specifications e Blowfish 128 bit key e Twofish 128 192 or 256 bit key e CAST 128 128 bit key e Arcfour 128 bit key e 3DES 168 bit key e DES B 1 4 Cer
70. ket granting ticket TGT 47 traditional 20 transfer 101 trusted CA 43 TTY allocation 49 tunnel incoming 27 tunnel outgoing 27 tunneling 26 tunneling log messages 80 2003 SSH Communications Security Corp INDEX tunneling agent 30 tunneling FTP 28 tunneling X11 29 tunneling X11 log messages 82 Twofish 112 twofish 18 UNIX 13 usage 99 user authentication 35 user authentication log messages 57 user authentication log messages host based 59 user authentication log messages Kerberos 67 user authentication log messages Kerberos TGT 66 user authentication log messages Keyboard Interactive 66 user authentication log messages Keyboard Interactive PAM 63 user authentication log messages Keyboard Interactive password 65 user authentication log messages password 69 user authentication log messages public key 72 user authentication log messages SecurID 75 user certificate 43 user login restricting 20 UserConfigDirectory 39 UserSpecificConfig 23 using authentication agent 105 using secure copy 104 using secure file transfer 104 using server daemon 99 using the client 103 VAR_ACE 50 version number 13 VMS 14 vulnerability of SSH1 protocol 13 well known port 101 Windows 2000 13 Windows 98 14 Windows Me 14 Windows NT 13 Windows XP 13 X 509 certificate 44 X 509 key format 34 46 X11 11 X11 connection 26 X11 forward
71. key sent by the client and the one stored in the known host keys directory differ in host based authentication Invalid client host key in host based authentication Importing client pubkey failed There was an error when decoding the host key sent by the client during host based authentication 5 1 3 User Authentication Keyboard Interactive PAM Pipe creation failed in Keyboard Interactive PAM authentication kbd int pam pipe creation failed SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 64 Chapter 5 An error occurred when trying to fork and create a pipe Error happened during PAM transaction PAM transaction resulted in error There was an error during PAM transaction Malformed packet received from PAM subprocess kbd int pam PAM subprocess sent a malformed packet packet type lt packet type gt The PAM subprocess sent a malformed packet of the specified type Wrong packet received from PAM subprocess kbd int pam PAM subprocess returned packet Log Messages SSH_PAM_OP_SUCCESS_WITH_PAYLOAD expecting SSH_PAM_OP_SUCCESS The PAM subprocess sent a packet of wrong type Error returned by PAM subprocess kbd int pam PAM subprocess returned packet lt packet type gt err_num lt errornumber gt err_msg lt error message The PAM subprocess returned an error Invalid packet type returned by PAM subprocess kbd int pam PAM subprocess returned invalid packet t
72. ks similarly to generic port forwarding except that the FTP forwarding code monitors the forwarded FTP control channel and dynamically creates new port forwardings for the data channels as they are requested To see exactly how this is done two different cases need to be examined the active mode and the passive mode of the FTP protocol FTP in passive mode In passive mode the FTP client sends the command PASV to the server which reacts by opening a listener port for the data channel and sending the IP address and port number of the listener as a reply to the client The reply is of the form 227 Entering Passive Mode 10 1 60 99 6 12 When the Secure Shell client notices the reply to the PASV command it will create a local port forwarding to the destination mentioned in the reply After this the client will rewrite the IP address and port in the reply to point to the listener of the newly created local port forwarding which exists always in a local host address 127 0 0 1 and pass the reply to the FTP client The FTP client will open a data channel based on the reply effectively tunneling the data through the SSH connection to the listener the FTP server has opened The net effect is that the data channel is secure all the way except from the Secure Shell server to the FTP server if they are on different machines This sequence of events happens automatically for every data channel Since the port forwarding is opened to a local h
73. land 1 650 2512700 USA 81 3 34596830 Japan Fax 358 20 5007031 Finland 1 650 2512701 USA 81 3 34596825 Japan 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide CONTENTS Contents 1 About This Document 1 1 Available Manual PageS 1 2 Documentation Conventions 2 Introduction to SSH Secure Shell 2 1 Network Security Risks 2 2 Protocol Features 2 3 Different Versions of the SSH Protocol 2 4 Legal Issues with Encryption 2 5 Supported Platforms 2 6 Support cen risa oi li ta 3 Configuring SSH Secure Shell 3 1 Basic Configuration 3 1 1 Default Locations of Secure Shell Files 3 1 2 Generating the Host Key 3 1 3 Ciphers and MACS 3 1 4 Compression 3 1 5 Configuring Root Logins 3 1 6 Restricting User Logins SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 3 2 Subconfigurations 3 2 1 Host Specific Subconfiguration 3 2 2 User Specific Subconfiguration 3 3 Configuring SSH Secure Shell for TCP Wrappers Support 3 3 1 Troubleshooting TCP Wrappers 3 4 Configuring SSH2 for SSH1 Compatibility 33 FOLWardIn Gy ta a a Le ow es Weve hed ee ps 3 5 1 Port Forwarding 3 5 2 Dynamic Port Forwarding 3 5 3 X11
74. lic key from the received certificate the server could not get the public key informa tion from the public key Key length too small in certificate Use of certificate for user lt login name gt is not allowed because public key is too small pk size lt key size gt min size lt minimum size gt The server has rejected the authentication using the certificate sent by the client because the public key in the certificate is too short Key length too large in certificate Use of certificate for user lt login name gt is not allowed because public key is too large pk size lt key size gt max size lt maximum size gt 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 73 The server has rejected the authentication using the certificate sent by the client because the public key in the certificate is too long Signature check failed Signature verify failed for certificate from user lt login name gt The signature verify failed for the user in certificate authentication Certificate authentication accepted Certificate authentication for user lt login name gt accepted The server has accepted the certificate authentication for the user Certificate authentication rejected Certificate authentication for user lt login name gt rejected The server has rejected the certificate authentication for the user Public key options prohibit using the key U
75. lient Scp2 can be used to copy files in either direction that is from the local system to the remote system or vice versa Local paths can be specified without the user system prefix Relative paths can also be used they are interpreted relative to the user s home directory The scp2 command line options are documented in detail on the scp2 1 manual page 6 4 Using Secure File Transfer sft p2 Sftp2 is an FTP like client that works in a similar fashion to scp2 Just like scp2 sftp2 runs with normal user privileges and uses ssh2 for transport Even though it functions like ftp sft p2 does not use the FTP daemon or the FTP client for its connections The sft p2 client can be used to connect to any host that is running the Secure Shell server daemon ssha2 The basic syntax for sft p2 is like this sftp2 options user host 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 6 5 Using Authentication Agent ssh agent2 ssh add2 105 Note As shown in the example above in the normal case you do not have to type s tp2 The installation process creates a symbolic link sftp that points to the actual s ftp2 executable sftp was not included in sshl Actual usage of sft p2 is similar to the traditional ftp program The sftp2 command line options and commands are documented in detail on the sftp2 1 manual page 6 5 Using Authentication Agent ssh agent2 ssh add2 Ssh agent2 is a program to hold privat
76. mmand root login permitted for forced command The server has been configured to not allow root logins but will allow forced commands as root Public key authentication accepted Public key authentication for user lt login name gt accepted The server has accepted the public key authentication for the user 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 75 Bad packet when verifying key got bad packet when verifying user lt login name gt s publickey The server received an invalid packet when trying to verify the user s public key Public key is authorized Public key lt filename gt authorized for user lt login name gt verifying signature The server has determined that the public key supplied by the client is authorized for a login and will now verify the signature supplied by the client 5 1 11 User Authentication SecurID The server does not allow root logins root login denied for user lt login name gt The server s configuration does not allow root logins 5 1 12 Certificate specific code Certificate verification failed Certificate verification failed search state lt search state gt Verifying a certificate failed in user or host authentication lt search state gt contains the search status bits that give information about what went wrong 5 1 13 SFTP Server Starting SFTP subsystem Starting SFTP subsystem for
77. mmunications Security FTP site ftp ftp ssh com pub ssh As of this publication of this document the latest version is ssh 1 2 33 SSH1 compatibility fallback requires version 1 2 26 or later 2 Install ssh2 3 If you previously had ssh1 installed please make sure that the old sshd is no longer run at boot Only sshd2 should be run If you have the ssh version of sshd running you should kill the master daemon You can find its process id in var run sshd pid or if the directory var run does not exist in etc ssh2 sshd2_22 pid 4 Make sure that usr local sbin sshdz2 is run automatically at boot On most systems you should add the command to start it to etc rce local or under etc rc d e When you run sshd2 the ssh daemon should not be running When using ssh2 with sshl compatibility you should only run ssha2 It will then automatically start the sshl daemon as needed 5 If you do not want to reboot you should now manually run usr local sbin ssha2 or etc rc d init d sshd2 start 3 5 Forwarding The SSH2 connection protocol provides channels that can be used for a wide range of purposes All of these channels are multiplexed into a single encrypted tunnel and can be used for forwarding tunneling arbitrary TCP IP ports and X11 connections 3 5 1 Port Forwarding Port forwarding or tunneling is a way to forward otherwise insecure TCP traffic through SSH Secure Shell You can secure for example POP3 SMTP and
78. n 19 configuration 15 configuration file locations 15 configuration file client 104 configuration file daemon 102 configuration client side 34 46 configuration root logins 20 configuration server side 33 44 configuration SSH1 compatibility 25 configuration TCP wrappers 23 converting key format 34 46 CRL certificate revocation list 33 34 43 CRL distribution point 33 44 CRL disabling 34 44 cryptographic algorithms 111 customer support 14 daemon 25 99 daemon command line options 102 daemon configuration file 102 daemon operation 101 daemon resetting 102 daemon starting 99 100 daemon stopping 102 data transfer 101 DefaultDomain 42 deny list 58 deny list group 58 deny list host 59 DenyGroups 22 2003 SSH Communications Security Corp INDEX DenyHosts 21 DenySHosts 43 DenyUsers 21 deprecation of SSH1 protocol 13 DES 112 des 18 Diffie Hellman key exchange 31 33 disabling CRL 34 44 DNS Address 33 DNS entry 43 documentation conventions 10 draft ietf pkix rfc25 10bis 03 112 DSA 111 DSA key pair 32 dynamic port forwarding 29 eavesdropping 12 egrep 20 Email 45 EmailRegex 45 encrypted data transfer 101 encryption 13 encryption algorithm 17 encryption legal issues 13 environment 101 environment variable 16 evaluation 14 evaluation version 16 export regulations 13 EXTENDED 98 failed authentica
79. n can be configured using command line options or a configuration file Command line options override values specified in the configuration file SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 100 Chapter 6 Using SSH Secure Shell 6 1 2 Automatically Starting the Server Daemon at Boot Time If you have installed from RPM packages on RedHat or on SuSE sshd2 is already starting at boot time The same is true if you have installed from depot on HP UX In the following sections two different methods for starting the Secure Shell Daemon at boot time are intro duced If neither of these methods work on your system consult your operating system documentation on how to start services at boot time Starting from etc rc d rc local In order to start sshd2 automatically at boot time on System V based operating systems the startup script sshd2 should be located in the etc rc d init d directory and there should be symbolic links to sshd2 startup seript in etc rc d rc d where is the runlevel You can either add these links manually or use chkconfig Note chkconfig is only available on RedHat distributions With SuSE add the symbolic links manually If you want to use chkconfig check that the first lines in sshd2 are similar to the following bin sh Author Sami Lehtinen lt sjl ssh com gt sshd2 This shell script takes care of starting and stopping sshd2 chkconfig 345 34 70 description Secure Sh
80. ng password given for user lt login name gt The password supplied by the client was invalid Password authentication accepted Password authentication for user lt login name gt accepted The client passed the password authentication but the server still needs to check whether the password needs to be changed Badly formatted password change request Badly formatted password change reques denying already successful authentication The server received a badly formatted password change request and the authentication will be noted as failed Changing user s password Changing lt login name gt s password The server is now trying to change the user s password SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 72 Chapter 5 Log Messages Password change needed for the user User lt login name gt forced to change password The server has determined that the user s password must be changed 5 1 10 User Authentication Public Key Certificate not authorized for login Authorization check for user lt login name gt s certificate rejected reason lt error message gt The server s authorization check for the certificate produced a negative result meaning that public key au thentication with this certificate is denied Error in public key decoded from certificate Couldn t get info from certificate public key used by user lt login name gt After extracting the pub
81. nment variable denied by public key options Starting internal SFTP server Starting internal sftp server for user lt login name gt sshd2 PID lt pid number gt The internal SFTP server is starting Stopping internal SFTP server Stopping internal sftp server for user lt login name gt sshd2 PID lt pid number gt The internal SFTP server is stopping 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 79 Bad data received in environment variable setting Bad data on ssh_channel_request_env Decoding an environtment variable setting request failed in the ssh_channel_request env function Invalid values received in environment variable setting Invalid values on request to set environment variable name lt variable name gt value lt variable value gt The environment variable setting request contained invalid values Environment variable setting forbidden by policy Client tried to set environment variable lt variable name gt to lt variable value gt but it is forbidden by policy The environment variable setting failed because of server policy Terminal access denied Terminal access is denied for user lt login name gt The server configuration doesn t allow a terminal for the user 5 1 16 SSH1 Agent Forwarding SSH1 agent forwarding request has been denied SSH1 agent forwarding request denied in configuration The
82. ns of ssh2 and ssh1 software are designed so that both can be run on the same computer This makes the transition from the old but well established SSH1 protocol to the more secure and more flexible SSH2 protocol much easier The ssh2 server daemon includes a fallback function that automatically invokes the sshl server when required Furthermore the SSH Secure Shell client now contains internal ssh1 emulation allowing it to communicate with ssh1 servers without using an external sshl program With the Ssh1Compat ibi1lit y option sshd is executed when the client supports only SSH 1 x protocols The argument must be yes or no The default is no which means that you have to manually set ssh2 to use ssh1 even if ssh is installed SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 26 Chapter 3 Configuring SSH Secure Shell SshdlPath Specifies the path to the sshd1 executable to be executed in SSH1 compatibility mode The arguments for sshd2 are passed on to sshd1 SshdlConfigFile specifies the alternate configuration file for sshd1 when sshd2 runs in compatibility mode It is only used if sshd2 is executed with the command line option otherwise the default sshd1 configuration file is used See the sshd2_config man page for more information To set up both ssh and ssh2 servers on the same Unix system you should do the following 1 Install the latest available version of ssh1 available on the SSH Co
83. nt that remote users run on their computers is additionally available also for Microsoft Windows 98 Me and the Symbian operating systems A list of the officially supported platforms for SSH Secure Shell products is available at http www ssh com products Independent third parties have also ported Secure Shell to other platforms such as OS 2 and VMS These independent software products are intended to be compatible with the Secure Shell standard However SSH Communications Security can only provide support for software developed by SSH Communications Security 2 6 Support Commercial users are entitled to technical support from SSH Communications Security for ninety 90 days from the date of purchase of the software If you have purchased a maintenance agreement review your agreement for specific terms Commercial users and those evaluating the software prior to purchase can contact the SSH Secure Shell tech nical support by filling out a support request form at http www ssh com support contact e Commercial support requests http www ssh com support contact support request shell mpl Non commercial licensees are welcome to submit bug reports and feature requests but are not entitled to tech nical support from SSH Communications Security Please note that SSH Communications Security makes every effort to make available information on issues that impact non commercial licensees See the SSH Web site http www ssh com support
84. ntication ssh keygen2 P etc ssh2 hostkey Note Beginning with SSH Secure Shell version 3 0 you can also use RSA keys Copy the Local machine s etc ssh2 hostkey pub file over to the Remote machine and name 1t like this etc ssh2 knownhosts hostname domain ssh dss pub Replace hostname domain with the long host name of the Local machine the fully qualified domain name You will run into problems if the system does not recognize the host name as hostname domain somewhere com but recognizes it only as hostname You can find this out while running sshd2 in verbose mode when trying to establish connections The Remote machine now has the Local machine s public key so the Remote machine can verify the Local machine s identity based on a public key signature By contrast rsh only uses the IP address for host authentication Note If you use RSA keys the name of Local s etc ssh2 hostkey pub file which is copied over to the Remote needs to be etc ssh2 knownhosts hostname domain ssh rsa pub To make sure that SSH Secure Shell finds your complete domain name not just the host name edit the following line in the etc ssh2 ssh2_config file on Local DefaultDomain yourdomain com Note The keyword mentioned in this and the following steps will only be effective in the global ssh2_config file On Remote create a file in the home directory of RemoteUser named shosts The contents of this file should be the long
85. ntication Kerberos Login denied for user Kerberos authentication as lt login name gt denied for lt kerberos name gt The server received a negative result from Kerberos authentication module for logging in as the specified user Login accepted for user Kerberos authentication as user 100s accepted for 100s The server received a positive result from Kerberos authentication module for logging in as the specified user 5 1 8 User Authentication PAM Malformed packet from PAM subprocess auths pam PAM subprocess sent a malformed packet packet type d The server received a malformed packet from the PAM subprocess SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 68 Chapter 5 Log Messages Wrong packet received from PAM subprocess auths pam PAM subprocess returned packet SSH_PAM_OP_SUCCESS_WITH_PAYLOAD expecting SSH _PAM_OP_SUCCESS 1 The PAM subprocess sent a packet of wrong type Error returned by PAM subprocess kbd int pam PAM subprocess returned packet lt packet type gt err_num lt errornumber gt err_msg lt error message The PAM subprocess returned an error Invalid packet type returned by PAM subprocess auths pam PAM subprocess returned packet Sd which is invalid The packet type returned by the PAM subprocess was invalid Client sent response packet prematurely auths pam client sent response packet and we weren t expecting
86. o make it reread its configuration file The daemon can be stopped by sending the SIGKILL signal All sshd processes can be terminated if needed This should be done only when root is logged in locally as the server process for the root user who is remotely logged in will also be terminated Another option is to start anew sshd2 daemon on a different port before terminating sshd processes sshd2 p 1234 Only the sshd processes e g usr local sbin ssha will be terminated killall sshd 6 1 5 Daemon Configuration File and Command Line Options Sshd2 reads configuration data from etc ssh2 sshd2_config or the file specified with the f flag on the command line The file contains keyword value pairs one per line Lines starting with the number sign as well as empty lines are interpreted as comments Subconfiguration files can also be specified in the main configuration file See Section 3 2 Subconfigurations for more information For detailed information about the options available in the configuration file and on the command line please refer to the sshd2_config 5 and to the sshd2 8 manual pages 6 1 6 Subsystems Subsystems can be defined in the sshd2_config file using the following syntax 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 6 2 Using the Secure Shell Client ssh2 103 subsystem lt name gt argument The argument is the command which will be executed when the subsystem is reques
87. of what the user should do num_reqs Indicates the size of reqs and echo arrays If the code is not SSH_KBDINT_SUBMETHOD_RESULT_NONE_YET this should be 0 and reqs and echo should be NULL reqs The requests sent to the client echo Tells the client whether the user s response to the corresponding request should be echoed method_cb The main method will call this when it has obtained the responses from the client method_ctx This is given to met hod_cb by the main method context The allocated context Please see auths kbd int submethods c for an example of using a password submethod This submethod is implemented in auths kbd int passwd ch Please follow the style of those files when creating new submethods Complete documentation for the API is located in apps ssh auths kbd int submethods h SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 56 Chapter 4 Authentication 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 57 Chapter 5 Log Messages The log messages generated by SSH Secure Shell for Servers are listed in the following sections based on their subject matter 5 1 Log Message Reference 5 1 1 User Authentication Common Authentication failed lt methodname gt authentication failed Login to account lt loginname gt not allowed or account non existent The system administrator has denied logging in for the
88. ost address the FTP client must be run on the same machine as the Secure Shell client if passive mode is used FTP in active mode In active mode the FTP client creates a listener on a local port for a data channel from the FTP server to the FTP client and requests the channell by sending the IP address and the port number to the FTP server in a 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 3 5 Forwarding 29 command of the following form PORT 10 1 60 99 6 12 The Secure Shell client intercepts this command and creates a remote port forwarding from the Secure Shell server s localhost address to the address and port specified in the PORT command After creating the port forwarding the Secure Shell client rewrites the address and port in the PORT command to point to the newly opened remote forwarding on the Secure Shell server and sends it to the FTP server Now the FTP server will open a data channel to the address and port in the PORT command effectively forwarding the data through the SSH connection The Secure Shell client passes the incoming data to the original listener created by the FTP client The net effect is that the data channel is secure the whole way except from the Secure Shell client to the FTP client This sequence of events happens automatically for every data channel Since the port forwarding is made to a local host address on the Secure Shell client machine the FTP client must be run in
89. owedAuthentications publickey Other authentication methods can be listed in the configuration file as well 2 Create a key pair by executing ssh keygen2 on Local Local gt ssh keygen2 Generating 2048 bit dsa key pair 1 000 000 0 Key generated 2048 bit dsa user Local Wed Mar 22 2002 00 13 43 0200 Passphrase Again Private key saved to home user ssh2 id_dsa_2048_a Public key saved to home user ssh2 id_dsa_2048_a pub Ssh keygen2 will now ask for a passphrase for the new key Enter a sufficiently long 20 characters or so sequence of any characters spaces are OK Ssh keygen2 creates a ssh2 directory in your home directory if it is not already present and stores your new authentication key pair in two separate files One of the keys is your private key which must never be made available to anyone but yourself The private key can only be used together with the passphrase 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 4 2 User Authentication 37 In the example above the private key file is id_dsa_2048_a The other file id_dsa_2048_a pub 1s your public key which can be distributed to other computers Note Beginning with version 3 0 SSH Secure Shell includes support for RSA keys They can be generated by specifying the t flag with ssh keygen2 Local gt ssh keygen2 t rsa Generating 2048 bit rsa key pair 2 000 0000 000 Key generated 2048 bit rsa user Local Wed May 02 2002 14 15 41 030
90. owing interest towards net worked communications and they often exchange information with domestic commercial interest and politi cal groups Crackers exchanging information and source code make attacks that ten years ago were thought to be within the reach of only the most powerful intelligence agencies It has turned out that the IP protocol while very tolerant of random errors is vulnerable to a number of malicious attacks The most common types of attacks include e Eavesdropping a transmission for example looking for passwords credit card numbers or business secrets e Hijacking or taking over a communication in such a way that the attacker can inspect and modify any data being transmitted between the communicating parties e IP spoofing or faking network addresses in order to fool access control mechanisms based on them or to redirect connections to a fake server The SSH2 protocol is designed to protect network communications against security hazards like these 2 2 Protocol Features The SSH Secure Shell products from SSH Communications Security use the Secure Shell version 2 SSH2 protocol The SSH2 protocol is being standardized in the Secsh Working Group of the Internet Engineering Task Force IETF The SSH2 protocol contains the following features e Secure terminal sessions utilizing secure encryption e Full secure replacement for FTP and Telnet as well as the UNIX r series of commands rlogin rcp rexec
91. p path_to_libwrap a Note It is only necessary to specify the path to 1ilbwrap a if the library and the include files are located in a non standard directory i e if the library has been compiled to a local directory or has been installed to somewhere else than the default location 3 Create or edit the etc hosts allowand etc hosts deny files When a user tries to connect to the SSH Secure Shell server the TCP wrapper daemon t cpd reads the etc hosts allow file for a rule that matches the client s hostname or IP If etc hosts allow does not contain a rule allowing access tcpd reads etc hosts deny for a rule that would deny access If neither of the files contains an accept or deny rule access is granted by default The syntax for the etc hosts allowand etc hosts deny files is as follows daemon client_hostname_or_IP The typical setup is to deny access to everyone listed in the etc hosts deny file This example shows both ssh and ssh2 sshdl ALL sshd2 ALL sshdfwd X11 ALL or simply ALL ALL And then allow access only to trusted clients in the etc hosts allow sshdl trusted_client_IP_or _hostname sshd2 ssh com foo bar fi sshdfwd X11 ssh com foo bar fi Based on the etc hosts allow file above users coming from any host in the ssh com domain or from the host foo barfi are allowed to access 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 3 4 Configuring SS
92. p allow list exists and user s group didn t match Authentication failed because the user s group is not on the server s group allow list Authentication not allowed from a host lt methodname gt authentication failed Connection from lt hostname gt denied Authentication as user lt loginname gt was attempted The server has determined that the user is not allowed to login from the current host 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 59 Authentication not allowed unable to reverse map hostname Login not allowed because host s IP address lt ip address gt could not be mapped to a host name and reverse mapping is required The server could not map the connecting host s IP address to a host name and the configuration option RequireReverseMappingis on Authentication not allowed host is on the deny list Login not allowed because the connecting host lt hostname gt is on the server s deny list The connecting host is on the server s deny list so the authentication is not allowed Authentication not allowed host is not on the allow list Login not allowed because the connecting host lt hostname gt is not on the server s allow list The connecting host is not on the server s allow list so the authentication is not allowed 5 1 2 User Authentication Host Based Using host based authentication denied for a host U
93. passphrase ssh keygen2 k lt keyname gt Password needed for PFX integrity check Integrity check ok Got shrouded key New passphrase for private key Again Successfully saved private key to lt keyname gt _ssh2 Safe decrypted succesfully Got certificate Certificate written to file lt keyname gt _ssh2 crt 3 Define the private key and the server certificate in the sshd2_config file HostkeyFile lt private key gt HostCertificateFile lt server certificate gt Client Side Configuration To configure the client side functionality perform the following tasks 1 Copy the CA certificate s to the client machine You can either copy the X 509 certificate s as such or you can copy a PKCS 7 package including the CA certificate s Certificates can be extracted from a PKCS 7 package by specifying the 7 flag with ssh keygen2 2 Define the CA certificate s to be used in host authentication in the ssh2_config file HostCA lt ca certificate gt Only one CA certificate can be defined per a Host CA keyword The client will only accept certificates issued by the defined CA You can disable the use of CRLs by using the Host CANoCr1s keyword instead of Host CA 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 4 2 User Authentication 35 HostCANoCrls lt ca certificate gt Note CRL usage should only be disabled for testing purposes Otherwise it is highly recommended to always use CRLs
94. r Authentication 33 4 1 2 Certificate Authentication Certificate support is included in the commercial version of SSH Secure Shell Server authentication is performed using the Diffie Hellman key exchange This is what happens when certificates are used The server sends its certificate which includes its public key to the client As the server certificate is signed with the private key of a certification authority CA the client can verify the validity of the server certificate by using the CA certificate The client checks that the certificate contains the fully qualified domain name of the server The client verifies that the server has a valid private key by using a challenge When certificates are used a man in the middle attack is no longer a threat during key exchange because the system checks that the server certificate has been issued by a trusted CA During authentication the system checks that the certificate has not been revoked This can be done either by using the Online Certificate Status Protocol OCSP or a Certificate Revocation List CRL which can be published either to a Lightweight Directory Access Protocol LDAP or HTTP repository OCSP is automatically used if the certificate contains a valid authority info access extension Cor respondingly CRLs are automatically used if the certificate contains a valid CRL distribution point extension If LDAP is used as the CRL publishing method the LDAP repository loc
95. r to the one in Figure 4 1 Windows client s first connection to a remote host At this point you should verify the validity of the fingerprint for example by contacting the administrator of the remote host computer preferably by telephone and asking her to verify that the key s fingerprint is correct If the fingerprint is not verified it is possible that the server you are connecting to is not the intended one this is known as a man in the middle attack After verifying the fingerprint it is safe to continue connecting The server s public key will then be stored on the client machine The location depends on the client implemantation on UNIX it is the ssh2 hostkeys directory SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 32 Chapter 4 Authentication Host Identification Eg A You are connecting to the host isolaukku for the first time The host has provided you its identification a host public key A EN ay The fingerprint of the host public key is xoriv zevyv palov humeh sywyc homag vesyk hubet vukad fugag vexox You can save the host key to the local database by clicking Yes You can continue without saving the host key by clicking No You can also cancel the connection by clicking Cancel Do you want to save the new host key to the local database i No Cancel Help Figure 4 1 Windows client s first connection to a remote host After the first conn
96. rent map file definitions testuser email testuser ssh com testuser subject C FI 0O SSH CN Secure Shell Tester testuser serialandissuer 1234 C FI O SSH CN Secure Shell Tester Ssubst subjectregex C FI O SSH CN a z S subst emailregex a z ssh com The last line permits logging with any email address with only letters in the user name See man sshregex for more information on the regular expression syntax SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 46 Chapter 4 Authentication Client Side Configuration Configure the client side according to the certificate storage method used a software or a PKCS 11 token for example a smart card Software Certificates To configure the system for software certificates perform the following tasks 1 Enroll a certificate for yourself Example Enrollment using ssh certenroll2 ssh certenroll2 g p id key e s C FI O SSH CN user email user trusted org a http test ca trusted org 8080 pkix o home user ssh2 user_rsa etc ssh2 test ca certificate crt Generated 1024 bit private key saved to file home user ssh2 user_rsa prv Remember to define also the SOCKS server with the S flag or an HTTP proxy with the P flag 1f necessary 2 The private key must be in the ssh2 format To convert X 509 keys to ssh2 format specify the x flag with ssh keygen2 ssh keygen2 x lt keyname gt Private key import
97. ros o e e o 67 5 1 8 User Authentication PAM e 67 5 1 9 User Authentication Password e o 69 5 1 10 User Authentication Public Key o o e 72 5 1 11 User Authentication SecurID o e e 75 5 1 12 Certificate specificcode i pri y maradona 2 2 a E a ee 75 SETI SBTP Servers ls 3 42 ge A ee te pee ech Ae watt ad la ta 75 5 1 14 Agent Forwarding 76 5 1 15 Session Chammels o e ee ee ee 77 5 1 16 SSHl Agent Forwarding 0 0 000000 00000 79 DML Port Forwarding a ob oe A Tigh yk a ee a bi ft 80 5 1 18 XII Forwarding pc sote dese pe RE EE EAR Ree le eS 82 3 1 19 Common Code 8 oa eA e haw eS 82 51 20 Host Key O Sy a5 ve ye he ee RRP Oe Beate A we ee PPR OME e 83 5 1 21 General Server Log Messages 2 0000000000 0004 83 9 1 22 SREP ie A SM ee Sn ew OB ot Mae ee eee 89 SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 6 CONTENTS 6 Using SSH Secure Shell 99 6 1 Using the Secure Shell Server Daemon sshd2 o o e eee 99 6 1 1 Manually Starting the Secure Shell Server Daemon 99 6 1 2 Automatically Starting the Server Daemon at Boot Time 100 6 1 3 Operation of the Server Daemon 00 000 101 6 1 4 Resetting and Stopping the Server Daemon o 102 6 1 5 Daemon Configura
98. rther In the instructions below the top directory refers to the RSA ACE Server top level directory 1 In order to enable SecurID support you need to compile the source code on a computer where RSA ACE Server master or slave or RSA ACE A gent software is already installed configured and running SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 50 Chapter 4 Authentication configur with serversecurid PATH make make install Replace PATH with the absolute PATH to the directory containing the sdiclient a file For RSA ACE Server 4 0 the file is usually located in the top ace examples directory for 5 0 in the top ace inc directory Note If you do not want to make the compilation as root make sure that all the above mentioned files are readable by the user you are compiling as When using the Keyboard Interactive SecurID submethod make sure that you have the following lines in the etc ssh2 sshd2_config file AllowedAuthentications keyboard interactive AuthKbdInt Optional securid And the following line in the etc ssh2 ssh2_config file AllowedAuthentications keyboard interactive In case you are not using Keyboard Interactive make sure that you have the following line both in your etc ssh2 sshd2_config file and in your etc ssh2 ssh2_config file AllowedAuthentications securid 1 ssh com Check that the user s shell is not top ace prog sdshell Start RSA ACE Server
99. s AllowHosts localhost foobar com friendly org This allows connections only from specified hosts Example 2 Using patterns with hostnames AllowHosts Dresa Narn This pattern matches for example house foobar com house com but not housel com Note that you have to input the string when you want to specify a literal dot Example 3 Using patterns with IP addresses AllowHosts digit 1 3 3 digit 1 3 This pattern matches any IP address xxx xxx xxx xxx However some host s hostname could also match this pattern Example 4 Using 4 AllowHosts MOZA 3 When i is used in the beginning of a pattern only the host IP addresses are used The above pattern matches for example 192 0 0 3 e AllowSHosts DenySHosts The shosts rhosts etc shosts equivand etc hosts equiv entries are honored only for hosts whose name matches one of the specified patterns It is recommended to use these keywords with host based authentication e AllowUsers DenyUsers Login is allowed denied as users whose name matches one of the specified patterns Example 1 Using complete user names DenyUsers devil evil org warezdude 1337 This denies login as devil when the connection is coming from evil org It also denies login from all addresses as warezdude and as user whose UID is 1337 Example 2 Using patterns with user names SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 22 Chapter 3 Config
100. s Security Corp 118 location of files 15 log message reference 57 logging 57 login process 101 login restricting 20 login root 20 LoginGraceTime 87 MAC Message Authentication Code 18 maintenance 14 man pages 9 man in the middle attack 31 33 manual pages 9 manually starting server daemon 99 MapFile 44 MDS 111 Message Authentication Code MAC 18 message reference log 57 Microsoft Windows 13 multiple host keys 32 NAT Network Address Translation 43 negotiation 101 Network Address Translation NAT 43 network security risks 11 non commercial user 14 OCSP Online Certificate Status Protocol 33 43 112 Online Certificate Status Protocol OCSP 33 43 112 OpenPGP standard 38 operating system 13 operation of server daemon 101 options 39 OS 2 14 outgoing tunnel 27 PAM Pluggable Authentication Module 48 51 63 PAM authentication log messages Keyboard Interactive 63 pam conf 49 PAM_TTY 49 passive mode 28 passphrase 36 password authentication 35 51 password authentication log messages 69 password authentication log messages Keyboard Interactive 65 password shadow 99 PermitRoot Login 20 permitting root logins 20 PGP keys 38 2003 SSH Communications Security Corp INDEX PID process identifier 102 PKCS 11 token 46 47 PKCS 11 v2 10 112 PKCS 12 key 46 PKCS 12 v1 0 112 PKCS 7 112 PKCS 7 package 34 44
101. s fstatting the specified file Setstatting file Setstat file lt filename gt size uidgid perms acmodtime The server is setstatting the attributes of the specified file Fsetstatting file Fsetstat file lt filename gt size uidgid perms acmodtime The server is fsetstatting the attributes of the specified file Opening directory Opening directory lt filename gt The server is opening the specified directory SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 95 96 Chapter 5 Log Messages Failed to open directory Failed to open dir lt filename gt Error lt errornumber gt The server failed to open the specified directory Readdir on directory Readdir on directory lt filename gt handle lt handle gt The server performed a readdir operation on the specified directory Removing file Removing file lt filename gt The server is removing the specified file Failed to remove file Failed to remove file lt filename gt Error lt errornumber gt The server failed to remove the specified file Creating directory Creating directory lt filename gt The server is creating the requested directory Failed to create directory Failed to make dir lt filename gt Error lt errornumber gt The server failed to create the requested directory 2003 SSH Communications Security Corp S
102. s highly recommended to verify the fingerprint of the remote host s public key as described in Section 4 1 1 Public Key Authentication to avoid man in the middle attacks This will only be necessary when connecting for the first time Troubleshooting Host Based Authentication If you have problems with host based authentication check the following e Did you name the local host key file appropriately on Remote It should be either etc ssh2 knownhosts HOSTNAME ssh dss pub or etc ssh2 knownhosts HOSTNAME ssh rsa pub where HOSTNAME has to be the long host name fully qualified domain name e Did you copy the host key properly e Check that the key on Remote is actually the same as host key pub on Local On Local ssh keygen2 F etc ssh2 hostkey pub On Remote ssh keygen2 F etc ssh2 knownhosts hostname domain ssh dss pub or ssh keygen2 F etc ssh2 knownhosts hostname domain ssh rsa pub The key fingerprints should match SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 42 Chapter 4 Authentication e Check your spelling in the shosts file e Make sure the shosts file is owned by Remote User and check that its permissions are 0400 ls la shosts P 2 1 RemoteUser users 178 May 28 15 05 home RemoteUser shosts e Make sure that RemoteUser s home directory on Remote is owned by RemoteUser and is not writable by anyone byt RemoteUser e
103. se of lt filename gt denied for lt hostname gt Use of host based authentication is denied for the host in server configuration Configuration files missing for host based authentication hostbased authentication rhosts refused for lt loginname gt no shosts or rhosts files and no system wide files ie etc shosts equiv The required files for host based authentication are missing SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 60 Chapter 5 Log Messages Home directory missing in host based authentication hostbased authentication rhosts refused for lt loginname gt no home directory lt directory gt The user s home directory does not exist Home directory ownership or permissions invalid in host based authentication hostbased authentication rhosts refused for lt loginname gt bad ownership or modes for home directory If the StrictModes option for the server is switched on then this message means that the user s home directory is not owned by either the user or the root or that its permission bits are not correct rhosts file ownership or permissions invalid in host based authentication hostbased authentication rhosts refused for lt loginname gt bad modes for lt file gt If the St rictModes option for the server is switched on then this message means that the user s rhosts file is not owned either by the user or by the root or that its permission bits are not correct
104. se of public key lt key name gt is not allowed in public key options for the host the user lt login name gt is logging in from Using the public key for the user and host has been denied based on the public key options set on the server for the key Error in public key Couldn t get info from public key lt key name gt used by user lt login name gt The server could not get the public key information from the public key SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 74 Chapter 5 Log Messages Key length too small Use of public key lt key name gt by user lt login name gt is not allowed because public key is too small pk size lt key size gt min size lt minimum size gt The server has rejected the authentication using the public key sent by the client because the key is too short Key length too large Use of public key lt key name gt by user lt login name gt is not allowed because public key is too large pk size lt key size gt max size lt maximum size gt The server has rejected the authentication using the public key sent by the client because the key is too long Crypto operation failed for RSA key Crypto operation failed for RSA key of user lt login name gt A cryptographic operation failed for a key Root logins not permitted root logins are not permitted The server has been configured to not allow root logins Root login permitted for forced co
105. server port network netmask network netmask The SOCKS server must be defined if CA services OCSP and CRLs are located behind a firewall 6 Next you need to create the map file It specifies which certificates authorize logging into which accounts The format of the file is the following lt account id gt lt keyword gt lt argument gt The keyword can be either Email Subject SerialAndIssuer EmailRegex or SubjectRegex The arguments depend on the keyword e Email The argument is the email address which must be present in the certificate e Subject The argument is the required subject name in LDAP DN distinguished name string format e SerialAndIssuer The argument is the required serial number and issuer name in LDAP DN string format separated by spaces or tabs e EmailRegex The argument is the regular expression which must match an email ad dress in the certificate If account id contains the string subst it is substituted with the first parenthesized part of the regular expression The patterns are matched using SSH REGEX_SYNTAX_EGREP e SubjectRegex The argument is the regular expression which must match a subject name in the certificate If account id contains the string Ssubst it is substituted with the first parenthesized part of the regular expression The patterns are matched using SSH REGEX_SYNTAX_EGREP Examples The following are examples of diffe
106. ssword must be changed 5 1 5 User Authentication Keyboard Interactive Client sent fewer responses than server sent requests auth kbd int client sent us fewer responses than we sent requests sent lt sent requests gt recv lt received responses gt Protocol error the client sent fewer responses that the server sent requests Login denied faking transaction auth kbd int User lt login name gt login denied faking real transaction The user is not allowed to login but the rest of the transaction proceeds normally except that all results are marked as failures 5 1 6 User Authentication Kerberos TGT Login denied for user Kerberos TGT authentication as lt login name gt denied for lt kerberos name gt The server received a negative result from Kerberos authentication module for logging in as the specified user Kerberos V5 ticket granting ticket rejected for user Kerberos V5 TGT rejected for user lt login name gt lt error message gt 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 67 The server received a result from the Kerberos authentication module the user s ticket granting ticket has been rejected The Kerberos TGT authentication succeeded Kerberos TGT authentication as user lt login name gt accepted for lt kerberos name gt The user s login has been accepted by the Kerberos authentication 5 1 7 User Authe
107. t software or vice versa However the SSH Secure Shell server software includes support for fallback functionality 1f SSH Secure Shell version 1 x is already installed SSH Secure Shell for Windows Servers does not include this func tionality Furthermore the SSH Secure Shell client now contains internal ssh1 emulation allowing it to communicate with ssh1 servers without using an external sshl program For optimal results however upgrade all servers and clients to the latest available version of SSH Secure Shell Please note that the version number of the SSH Secure Shell software product does not reflect the version number of the secure shell protocol but the version of the software 2 4 Legal Issues with Encryption The encryption software included in SSH Communications Security products is developed in Europe and therefore these products are not subject to US export regulations SSH Secure Shell software can be used in any country that allows encryption including the United States of America 2 5 Supported Platforms The SSH Secure Shell Server software the software component that allows remote users to connect to your computer is available for most UNIX and Linux platforms and for Microsoft Windows NT4 Service Pack 5 SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 14 Chapter 2 Introduction to SSH Secure Shell required Windows 2000 and Windows XP The associated client software the compone
108. ted ssh2 s lt name gt user remot The argument can be a list of commands separated with semicolon or it can for example refer to a script One example of a subsystem is sftp subsystem sftp usr local bin sftp server The sftp subsystem also has an internal alternative This should be used for example when the user is chrooted and does not have access to the sftp server binary subsystem sftp internal sftp server 6 2 Using the Secure Shell Client ssh2 The basic Secure Shell client program is called ssh2 Ssh2 can be used either to initiate an interactive session resembling r1ogin or to execute a command in a way similar to the rsh command The Secure Shell client connects to the server on port 22 which is a well known port for Secure Shell 6 2 1 Starting the Secure Shell Client Ssh2 has a very simple syntax ssh options hostname command The most common usage is to establish an interactive session to a remote host This can be done simply by typing ssh hostname domain A real world example could be ssh root somehost ssh com As with rsh and rlogin the user ID to be used can also be specified with the 1 option for example ssh l root somehost ssh com Note As shown in the above example in the normal case you do not have to type ssh2 The installation process creates a symbolic link ssh that points to the actual ssh2 executable If ssh1 was installed before ssh2 you will need to type ssh1 to run
109. ted for password Server Configuration Keyboard interactive is not enabled by default on the server Make sure that you have the following line in the etc ssh2 sshd2_config file AllowedAuthentications keyboard interactive The submethods and policy for keyboard interactive are configured as follows SSH CONFIGURATION FILE FORMAT VERSION 1 1 REGEX SYNTAX egrep Aut Aut Aut Aut KbdInt Reqgquired securid KdbInt Optional pam password KbdInt NumOptional 1 KbdInt FailureTimeout 2 This allows for maximum configurability without being too hard to implement See the sshd2_config man pages for more information on the keywords The default for required submethods is 0 although if no required submethods are specified the client must always pass at least one optional submethod 4 3 3 Adding New Authentication Methods This sections covers advanced implementation of keyboard interactive Please note that SSH Communications Security does not provide technical support on how to implement your own keyboard interactive submethod Also consider carefully the security implications when implementing a submethod of your own New submethods are added to the submethods array in apps ssh auths kbd int submethods c You need to create an initialization and uninitialization function for the submethod The initialization function 2003 SSH Communications Security Corp SSH Secure Shell Admin Gu
110. the same host as the Secure Shell client if passive mode is used Where end to end encryption of FTP data channels is desired the FTP server and Secure Shell server need to reside on the same host and the FTP client and the Secure Shell client will likewise need to reside on the same host If this is the case both active or passive mode can be used Note Consider using sftp2 or scp2 instead of FTP forwarding to secure file transfers It will require less configuration than FTP forwarding since the SSH Secure Shell server already has sftp server2 as a subsystem and sftp2 and scp2 clients are included in the distribution Managing remote user restrictions on the server machine will be easier since you do not have to do it also for FTP 3 5 2 Dynamic Port Forwarding Dynamic port forwarding is a transparent mechanism available for applications which support the SOCKS4 or SOCKSS client protocol Instead of configuring port forwarding from specific ports on the local host to specific ports on the remote server you can specify a SOCKS server which cab be used by the user s applications Each application is configured in the regular way except that it is configured to use a SOCKS server on a local host port The Secure Shell client application opens a port in the local host and mimics a SOCKS4 and SOCKSS server for any SOCKS client application When the applications are connecting to services such as IMAP4 POP3 SMTP HTTP and FTP they provide th
111. tication Methods 113 B 1 7 Other Supported Standards Other supported standards are e RFC 2460 Internet Protocol Version 6 IPv6 Specification S Deering Cisco R Hinden Nokia December 1998 B 1 8 Additional Information Additional information on RFCs and Internet Drafts is available at the IETF Web site http www ietf org At the RSA Web site you can find additional information on the Public Key Cryptography Standards PKCS http www rsasecurity com rsalabs pkcs B 2 Authentication Methods The following table shows the available authentication methods and limitations on their use Available Suitable for Requires Requires from scripting additional additional binaries software hardware Password xX User public key ssh2 keys x x ssh1 keys X PGP keys x x x Certificates software x x PKCS 11 tokens x x Host based x X Kerberos5 client x3 server x3 RSA securID client xX x4 server x PAM client xX server x SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 114 Appendix B Technical Specifications If Available from binaries is not checked the authentication method in question can be enabled by compiling from source See Chapter 4 Authentication for instructions Explanation 1 Use ssh agent2 or NULL passphrase Note that in the latter case it is extremely important that no one else can access your private key 2 Only the OpenPGP standard and programs
112. tication log messages SecurID 75 authentication methods 31 113 authentication authentication authentication authentication authentication adding new methods 52 certificate 33 43 failed 57 59 host based 16 39 Kerberos 47 authentication Keyboard Interactive 49 50 keyboard interactive 35 48 PAM 48 51 password 35 51 public key 31 36 43 SecurlD 49 51 server 31 33 authentication authentication authentication authentication authentication authentication authentication user 35 authority info access 33 44 authorization 37 39 automatically starting server daemon 100 basic configuration 15 Berkeley services 11 Blowfish 112 blowfish 18 BSD 101 CA certification authority 33 CA certificate 44 cast 18 CAST 128 112 certificate 33 42 43 certificate authentication 33 43 certificate revocation list CRL 33 34 43 116 certificate specific log messages 75 certificate revoked 33 certificate software 46 certification authority CA 33 channel 26 channel session log messages 77 chkconfig 100 cipher negotiation 101 ciphers 17 client command line options 104 client configuration file 104 client program 103 client side configuration 34 46 client starting 103 command 39 command line options client 104 command line options daemon 102 commercial user 14 common code log messages 82 compatibility SSH1 25 compressio
113. tificate Standards The supported certificate standards and drafts are e RFC 2315 PKCS 7 Cryptographic Message Syntax Version 1 5 B Kaliski March 1998 e RFC 2459 Internet X 509 Public Key Infrastructure Certificate and CRL Profile R Housley W Ford W Polk and D Solo January 1999 e PKCS 12 v1 0 Personal Information Exchange Syntax RSA Laboratories June 1999 e draft ietf pkix rfc2510bis 03 txt RFC 2510bis Internet X 509 Public Key Infrastructure Certificate Management Protocols C Adams and S Farrel February 2001 B 1 5 Certificate and CRL Publishing Solutions For certificate and CRL publishing the following solutions are supported e RFC 2585 Internet X 509 Public Key Infrastructure Operational Protocols FTP and HTTP R Hous ley SPYRUS P Hoffman IMC May 1999 e RFC 2559 Internet X 509 Public Key Infrastructure Operational Protocols LDAPv2 S Boeyen T Howes and P Richard April 1999 e RFC 2560 X 509 Internet Public Key Infrastructure Online Certificate Status Protocol OCSP M Myers VeriSign R Ankney CertCo A Malpani ValiCert S Galperin My CFO C Adams Entrust Technologies June 1999 B 1 6 Cryptographic Token Standards Supported smart card and cryptographic token related supported standards are e PKCS 11 v2 10 Cryptographic Token Interface Standard RSA Laboratories December 1999 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide B 2 Authen
114. tion 57 59 faking network addresses 12 fallback functionality 13 file locations 15 File Transfer Protocol FTP 11 12 104 112 fingerprint 31 firewall 35 forwarding 26 forwarding agent 30 forwarding agent log messages 76 79 forwarding FTP 28 forwarding local 27 forwarding port log messages 80 forwarding remote 27 forwarding X11 29 forwarding X11 log messages 82 free 53 FTP File Transfer Protocol 11 12 104 112 FTP forwarding 28 SSH Secure Shell Admin Guide INDEX general server log messages 83 generating host key 16 GNU ZLIB LZ77 19 GnuPGP 38 group allow list 58 group deny list 58 hijacking 12 hmac md5 18 hmac mad5 96 18 hmac ripemd160 18 hmac ripemd160 96 19 hmac shal 18 hmac shal 96 18 host allow list 59 host deny list 59 host key 31 host key generation 16 host key I O log messages 83 host key multiple 32 host based authentication 16 39 host based user authentication log messages 59 hostbased 40 HostCA 34 42 HostCANoCr1ls 34 hostkey 16 32 hostkey pub 16 32 hostkeys 16 hosts allow 24 hosts deny 24 hosts equiv 43 HostSpecificConfig 22 HP UX 100 HTTP HyperText Transfer Protocol 112 HTTP proxy 46 HTTP repository 33 43 HTTP tunneling 26 HUP 25 40 HyperText Transfer Protocol HTTP 112 identification 37 38 47 IETF Internet Engineering Task Force 12 IETF secsh Internet Drafts 13 IE
115. tion File and Command Line Options 102 6 1 6 gt SUBSYSteMS 6 100 Ae eR le ee A EES Pee ee A E A 102 6 2 Using the Secure Shell Client ssh2 2 0 e 103 6 2 1 Starting the Secure Shell Client o a 103 6 2 2 Client Configuration File and Command Line Options 104 6 3 Using Secure Copy s p2 2 weg fe eek Ro See Boe oe So dR Sas 104 6 4 Using Secure File Transfer sftp2 2 0 ee 104 6 5 Using Authentication Agent ssh agent2 ssh add2 o oo 105 A Tool Syntax 107 AT Ssh keygen u e a A A Pate ee aw pt N 107 AL SSHACET EER TOU de gud oversee pie ee Pe pew Pes Aa ected eee eet ee eee E 109 B Technical Specifications 111 B 1 Supported Cryptographic Algorithms and Standards 111 B 1 1 Public Key Algorithms 2 2 2 0 2 0 e 111 B 1 2 Data Integrity Algorithms 0 ee eee eee ee 111 B 1 3 Symmetric Session Encryption Algorithms o o 111 B 14 Certificate Standards ojos eso rea Bag aa Se ded oe Soak 112 B 1 5 Certificate and CRL Publishing Solutions o 112 B 1 6 Cryptographic Token Standards e 112 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide CONTENTS 7 B 1 7 Other Supported Standards ee 113 B 1 8 Additional Information 113 B 2 Authentication Methods 0 0000 e 113 SSH Secure Shell Admin Guide 200
116. tion to the PAM library which will then load the modules specified in the PAM configuration file Finally the PAM library tells SSH Secure Shell whether or not the authentication was successful SSH Secure Shell is not aware of the details of the actual authentication method employed by PAM Only the final result is of interest To enable PAM support perform the following tasks 1 Compile the source configure make make install By default the PAM service name is sshd2 If you want to change it you can add the configure flag with daemon pam service name name 2 When using keyboard interactive PAM submethod make sure that you have the following lines in the etc ssh2 sshd2_config file AllowedAuthentications keyboard interactive AuthKbdInt Optional pam And the following line in the etc ssh2 ssh2_config file AllowedAuthentications keyboard interactive In case you are not using keyboard interactive make sure that you have the following line in both your etc ssh2 sshd2_config file and etc ssh2 ssh2_config file AllowedAuthentications pam 1 ssh com 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 4 2 User Authentication 49 The PAM configuration settings are located either in etc pam conf or in etc pam d ssha2 The modules are usually either in the 1ib securit y directory or in the usr lib security directory Currently SSH Secure Shell supports PAM on Linux and on Solaris 2 6 or later
117. uring SSH Secure Shell AllowUsers sj s digit s jllamza This pattern matches for example sjj sjjj sl s123 and samza but not s x or slj Example 3 Using i AllowUsers sj31 i192 3 This would allow login as user sj from only those hosts whose IP address matches the specified pattern AllowGroups DenyGroups Login is allowed denied when one of the groups the user belongs to matches one of the specified patterns Example 1 AllowGroups root staff users For more information on keywords please see the sshd2_config man pages 3 2 Subconfigurations You can also specify configuration options in so called subconfiguration files which have the same basic format as the main configuration file The process forked to handle the user s connection reads these files They are read at run time so if they are modified it is not necessary to restart the server process If parsing of the subconfiguration files fails the connection is terminated for host specific configuration or access denied for user specific configuration by the server The subconfiguration files are divided into two categories host specific and user specific Subconfiguration files are very flexible and because of that dangerous if the logic of the files is not carefully planned Note Host specific subconfiguration files are always read before the user specific subconfigura tion files See the example file sshd2_config example and the host spec
118. user lt login name gt parent sshd2 PID lt pid number gt SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 76 Chapter 5 Log Messages The SFTP server is starting Stopping SFTP subsystem Stopping SFTP subsystem for user lt login name gt parent sshd2 PID lt pid number gt The SFTP server is stopping 5 1 14 Agent Forwarding Agent forwarding requested Agent forwarding requested creating a listener The client has requested agent forwarding and the server is creating a listener for it Agent forwarding request has been denied Agent forwarding request denied in configuration The client has requested agent forwarding but the server configuration forbids it Forwarding an agent connection Opening an agent forwarding channel The server has received an agent connection in the agent forwarding listener and is opening an agent for warding channel to the client Closing an agent connection Closing an agent forwarding channel The agent forwarding channel from the server to the client has been closed 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 77 5 1 15 Session Channels Session channel open request received Received a channel open request type lt channel type gt channel id lt channel number gt Received a session channel open request of the specified type with specified channel id Closing session channel
119. user or the user is trying to log in using a non existent account Authentication failed user does not exist User lt login name gt does not exist Authentication failed because the specified user account does not exist Authentication failed system policy doesn t allow user s login User lt login name gt s login is not allowed due to system policy SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 58 Chapter 5 Log Messages Authentication failed because the system policy does not allow the user to log in The account may be locked or expired for example Authentication failed username is on deny list User lt login name gt is denied login because username matched with deny list Authentication failed because the specified user name is included in the server s deny list Authentication failed username not on allow list User lt login name gt is denied login because allow list exists and username was not matched Authentication failed because the specified user name is not included in the server s allow list Authentication failed user s group is on deny list User lt login name gt is denied login because user s group is on group deny list Authentication failed because the user s group is included in the server s group deny list Authentication failed user s group is not on group allow list User lt login name gt is denied login because grou
120. uthentication method that requires only the user s input can be performed with Keyboard Interactive Currently the following methods are supported e password e SecurID e PAM but see Section 4 3 1 What Cannot Be Done With It What Cannot Be Done with It If passing of some binary information is required as in public key authentication keyboard interactive cannot be used PAM has support for binary messages and client side agents and those cannot be supported with keyboard interactive However currently there are no implementations that take advantage of the binary messages in PAM and the specification may not be cast in stone yet 4 3 2 Configuring the Server and Client Client Configuration To enable keyboard interactive authentication make sure that you have the following line in the etc ssh2 ssh2_config file AllowedAuthentications keyboard interactive SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 52 Chapter 4 Authentication Keyboard interactive 1s enabled by default on the client Note The client cannot request any specific keyboard interactive submethod if the server allows several optional submethods The order in which the submethods are offered depends on the server configuration However if the server allows for example two optional submethods SecurID and password the user can skip SecurID by pressing enter when SecurID is offered by the server The user will then be promp
121. uthentication packet The host name given by client does not match the one given by the client in host based authentication ignored Client gave us a hostname lt hostname gt which doesn t match the one we got from DNS lt hostname gt trusting that client is valid if signature verification succeeds The host name gotten using reverse DNS lookup does not match the one in the host based authentication packet but the server does not require a match 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 63 Invalid packet received in host based authentication Invalid packet extra data at end The received packet in host based authentication contains extra data and will be discarded as invalid Client is using a public key algorithm not supported by server in host based authentication Client s public key algorithms are not supported by us client sent lt algorithmname gt The public key sent by the client in host based authentication uses a public key algorithm not supported by the server User s ssh2 directory is missing in host based authentication Couldn t find or create user lt loginname gt s ssh2 directory The user s ssh2 directory could not be found or created in host based authentication Received host key and stored host key differ in host based authentication The public key stored in s and the one given by the client wer different The host
122. xy server URL to be used when connect ing to the certification authority zg Generate a new private key t rsaldsa Type of key to be generated Valid types are rsa or dsa Rsa is the default 1 key size The size of the key to be generated in bits 1024 is the default 0o base Specify the base prefix of the generated files The private key if generated will be lt base gt prv SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 110 Appendix A Tool Syntax and the certificate will be lt base gt num crt p cmp ref num cmp key Specify the CMP enrollment referenc number and key the pre shared secret Enable extensions in the subject name If for example ip dns or email extensions are used the e flag must be present a S u EXAMPLE ca access url The full URL to the certification authority subject dn name Specify the subject name for the certificate For xample c ca o acme ou development cn Rami Romi would specify the common user name Rami Romi in the organizational unit Development in the orga nization Acme in ca Canada number Optionally gives the key usage bits 1 Enroll a certificate and generate a DSA private key ssh certenroll2 g t dsa o mykey p 12345 abcd S socks fw myfirm com 1080 a http www ca auth domain 8080 pkix s c fi o acme cn Rami Romi ca certificate crt Th
123. ype lt packet type gt The packet type returned by the PAM subprocess was invalid 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 5 1 Log Message Reference 65 5 1 4 User Authentication Keyboard Interactive Password Login with empty password denied for user kbd int passwd login with empty password denied for user lt login name gt The server policy forbids login with empty password Login with overtly long password denied kbd int passwd user lt login name gt tried to login with too long password 256 The server does not allow logins with passwords longer than 256 characters Kerberos password accepted kbd int passwd kerberos password accepted for user lt login name gt lt kerberos name gt The server accepted the user s Kerberos password in Keyboard Interactive password authentication Password accepted kbd int passwd user lt login name gt s local password accepted The server accepted the user s local password This message is only generated on Windows platforms Password not accepted kbd int passwd wrong password given for user lt login name gt The password supplied by the client was invalid SSH Secure Shell Admin Guide 2003 SSH Communications Security Corp 66 Chapter 5 Log Messages Password must be changed kbd int passwd user lt login name gt forced to change password The server has determined that the user s pa
124. yption X connections forwarded through Secure Shell use a special local display setting In SSH Secure Shell 3 2 and above if X11 SECURITY extension is compiled in the X11 client applications are treated as untrusted by default the effects of this depend on your Xserver s security policy For more information please see the ssh2_config man pages 3 5 4 Agent Forwarding For information about agent forwarding see Section 6 5 Using Authentication Agent 2003 SSH Communications Security Corp SSH Secure Shell Admin Guide 31 Chapter 4 Authentication SSH Secure Shell provides mutual authentication the client authenticates the server and the server authenti cates the client Both parties are assured of the identity of the other party 4 1 Server Authentication The remote host can authenticate itself using either traditional public key authentication or certificate authen tication At the beginning of the connection the server sends its public host key to the client for validation If certificate authentication is used the public key is included in the certificate the server sends to the client 4 1 1 Public Key Authentication Server authentication is done during Diffie Hellman key exchange through a single public key operation When public key authentication is used to authenticate the server the first connection is very important During the first connection the SSH Secure Shell client will display a message simila
125. ywords in the sshd2_config file you can filter the shosts rhosts etc hosts equivand etc shosts equiv entries e If you want to allow only global configuration files etc hosts equiv and etc shosts equiv make sure that you have the following entry in your sshd2_config file IgnoreRhosts yes After this modification the shosts and rhosts files will not be used in host based authentication e To force an exact match between the host name that the client sends to the server and the client s DNS entry make sure that you have the following definition in your sshd2_config file HostbasedAuthForceClientHostnameDNSMatch yes Please note that with the above mentioned definition host based authentication through NAT will not work Note This keyword is available in SSH Secure Shell version 3 0 and later 4 2 4 Certificate Authentication The commercial version of SSH Secure Shell includes support for certificate authentication Also certificate authentication is performed via the public key authentication method Instead of the client sending just a public key it sends a certificate containing a public key In brief certificate authentication works in the following way The client sends the user certificate which inludes the user s public key to the server The server uses the CA certificate to check that the user s certificate is valid The server uses the user certificate to check from its mapping file s whether log

SSH Secure Shell for Servers Version 3.2.9 Administrator`s Guide

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