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A Secure and Distributed Architectural Model for File Sharing

1. Convert filelength into the best possible value Mb Kb or bytes strFinal modClient getFileSize FileSize with rs AddNew Fields Item Filename strName Fields Item Filesize strFinal Update End With End If End If strName Dir Loop David Brown BSc Hons Computing 2002 40 The send process begins with the transmission of the protocol code SHARED START to the server which informs the server that a shared file list is about to be sent Each entry from the ADO record set is then sent to the server with a control code added to the end that acts as a record delimiter which is discussed earlier in this chapter After the last entry has been sent the server is informed of this with the transmission the protocol code SHARED END The send process is performed using the following code frmMain ServerConn SendData SHARED START amp vbCr use the recordset to send the files first check there are files in it If rs RecordCount gt 0 Then rs MoveFirst Do While rs EOF False frmMain ServerConn SendData rs Fields Item Filename amp vbCr frmMain ServerConn SendData rs Fields Item Filesize amp vbCr rs MoveNext Loop End If now that all files are sent inform the server frmMain ServerConn SendData SHARED_END amp vbCr 4 3 3 Submit File Search While logged on to the server a user is free to submit file search queries either by the name of the file or by the username of the
2. No Send List of Shared Files Client Connected Authenticate Submit File Receive File Details Search From Client Send File to Client Submit File Receive File Search From Client Send File to Client Authenticated No Disconnect from Server David Brown BSc Hons Computing 2002 8 Appendix 2 Server Design 68 David Brown BSc Hons Computing 2002 9 Appendix 3 RSA Encryption Module RSA Encryption module Modified from the original sourcecode created by W G Griffiths Available from PlanetSourceCode Fast 64bit RSA Encryption Algorithm zip http www planetsourcecode com vb scripts ShowCode asp txtCodeId 6749 amp 1ngWId 1 First declare the public variables Public primeNumA As Double Public primeNumB As Double Public valueN As Double Public EncryptionKey As Double Public DecryptionKey As Double Public PHI As Double Public Sub CreateKeys Const AB UPPER As Integer 9999 set upper limit of random number Const AB LOWER As Integer 3170 set lower limit of random number Const KEY LOWER_LIMIT As Long 10000000 initialise the variables primeNumA 0 primeNumB 0 valueN 0 EncryptionKey 0 DecryptionKey 0 PHI 0 Randomize Ensure that the keys are a 64bit minimum Do Until DecryptionKey gt KEY LOWER LIMIT Ensure that A and B are prime numbers Do Until IsPrime primeNumA And IsPrime primeNumB primeNumA Int AB_ UPPER AB LOWER 1
3. Figure 27 Client Test Results Graph David Brown BSc Hons Computing 2002 59 5 5 4 Encryption Speed Tests The purpose of the encryption speed tests was simply to discover the length if time it would take to encrypt a file of a given size The testing process began with a one Megabyte file which was scaled up to a ten Megabyte file this would give an indication if the time taken to encrypt a file was directly related to the size of the file and therefore it would possible to project the encryption time for any file size Five computers of differing specifications were used during this test in order to gain a varied number of results Each file size was encrypted five times and an average time was calculated from the five results Table 3 shows the average encryption time for each computer specification which are combined in the chart featured in Figure 28 The results of these tests showed that there was a linear increase in the encryption time of a file relating directly to 1ts size This would make it possible to project the encryption time of any file based on its size File Size P41 7 P4 1 4 P3 500 P3 800 P3 1000 1Mb 0 45 0 58 1 68 0 99 0 77 2Mb 0 92 1 16 3 36 1 87 1 57 3Mb 1 40 1 75 4 99 2 75 2 37 4Mb 1 86 2 34 6 83 3 74 3 15 5Mb 2 28 2 93 8 63 4 67 3 96 6Mb 2 74 3 51 10 48 5 57 4 73 7Mb 3 20 4 14 12 07 6 46 5 50 8Mb 3 76 4 75 13 84 7 49 6 32 9Mb 4 14 5 27 15 36 8 44 7 12 10Mb 4 69 5 88 17 20 9 50 7 89 Tabl
4. The results of these tests showed that the encryption employed in the system is not as strong as previously thought as it would only take 12 hours to decrypt a code using eight average specification computers If it were the government or the military attempting to break the code they would be able to do it in minutes as they would have access to unlimited computing resources Processors Year 0 Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 1 98304 49152 24576 12288 6144 3072 1536 2 49152 24576 12288 6144 3072 1536 768 3 24576 12288 6144 3072 1536 768 384 4 12288 6144 3072 1536 768 384 192 5 6144 3072 1536 768 384 192 96 6 3072 1536 768 384 192 96 48 7 1536 768 384 192 96 48 24 8 768 384 192 96 48 24 12 Table 5 Decryption Times 5 6 Conclusions The testing process was performed throughout this project from the initial unit testing stage through to the final system requirements testing stage Because of this the process of catching and repairing bugs was a relatively simple task to perform The performance tests proved that the system was scalable and robust as the system functioned normally with a large number of clients performing concurrent operations The strength of the encryption proved to be a point of concern as it would not take a great deal of computing resources to break an encrypted message using the system David Brown BSc Hons Computing 2002 62 6 Co
5. amp searchParam amp AND SharedFiles Username lt gt amp userName amp Else searchSQL SELECT Filename Filesize ConnectedUsers Username IPAddress FROM SharedFiles ConnectedUsers Where ConnectedUsers Username SharedFiles Username AND SharedFiles Username searchParam amp AND SharedFiles Username lt gt amp userName amp End If Let the client know search results are on their way tcpServer Index SendData FILE START vbCr Now conduct searches using the parameters supplied by the client First on the local server If LocalDb State 1 Then Perform search rsl Open searchSQL LocalDb adOpenStatic adLockReadOnly rs1 Close If rsl EOF False Then Send the results to the client rsl MoveFirst Do While rs1l EOF False Send the results tcpServer Index SendData rsl filename amp vbCr tcpServer Index SendData rsl filesize amp vbCr tcpServer Index SendData rsl Username vbCr tcpServer Index SendData rsl IPAddress vbCr rs1l1 MoveNext Loop rs1 Close End If End If Now on Server 1 Local Db connection If ServerlDb State 1 Then Perform search rs2 Open searchSQL ServerlDb adOpenStatic adLockReadOnly If rs2 EOF False Then Send the results to the client rs2 MoveFirst Do While rs2 EOF False Send the results tcpServer Index SendData rs2 filename amp vbCr tcpServer Index SendData rs2 filesize amp vbCr
6. 3 4 8 User Interface Design The design of the User Interface UI began after the client and server operations of the system were identified as these operations describe how a user would interact with the client application and how an administrator would interact with the server application Instead of sketching out possible client and server application UI s on paper non functional prototypes were developed using the Rapid Application Development RAD capabilities of Visual Basic This made the creation of the required amount of forms for each application simplistic with each form given a number of relevant controls such as list boxes command buttons etc The RAD capabilities also allowed the layout of the controls on each form to be easily arranged so the controls are laid out in a visually pleasing manner It was very important to consider the potential user for each application in order to determine the level of complexity The client application could conceivably be used by someone with very little computing experience so the UI must be straightforward and give the user access to the client functions easily The server application however would be used by a system administrator who would have a great deal of experience with configuring systems and would require detailed information on the performance of the server and access to complex configuration options Creating non functional prototypes of the client and server applicat
7. tt LocalDb adOpenStatic adLockPessimistic If rs2 EOF False Then rs2 MoveFirst Do While Not rs2 EOF rs2 Delete rs2 MoveNext Loop End If rs2 Close The user will send filenames and filesizes ending with SHARED END First get the new length of the recieved string minus protocol code stringLen Len recString For count2 1 To stringLen get the character David Brown BSc Hons Computing 2002 53 workString Mid recString count2 1 Check to see if this is a returncode signifies end of string If workString vbCr Then Check if this string is the protocol code that indicates end of list If searchString SHARED_END Then tcpServer Index SendData SHARED ACK amp vbCr Exit Sub End I retCount retCount 1 The retcount variable is used to count the number of strings recieved as there are two strings filename and filesize If retCount 1 Then recFile searchString searchString workString Else recSize searchString Write the username filename and filesize to the table rs2 Open insert into SharedFiles values amp userName amp amp recFile N ET amp recSize amp ER A LocalDb adOpenStatic adLockOptimistic searchString workString retCount 0 End If End If append this to the session key variable searchString searchString amp workString Next count2 45 Conclusions This chapter has covered the implementation of the system wh
8. 1 Client connects to a server and sends the message EXIST_USER 2 Client sends username encrypted password and current IP address 3 Server looks up the username from the database and retrieves the password and public modulus keys associated with that username The received password is decrypted and compared against the password from the global database 4 Server sends either LOGON_ACK or LOGON_NAK depending on the result of the comparison of the received password against the global database password If LOGON_ACK were sent to the client they would then start to send their list of shared files to the server using the Shared File List Protocol If LOGON_NAK were sent the server would then send a message to the client identifying the reason for the rejection There are two possible messages LOGON_PASSWD invalid password or LOGON_USER Invalid username David Brown BSc Hons Computing 2002 29 Shared File List Protocol This protocol is used when an existing user has just logged onto a server or if they are already connected and they wish to update their list of shared files This process is illustrated in Figure 13 Local Db Client Figure 13 Shared File List Protocol 1 Client sends the message SHARED START to the server 2 Client sends the filename and the file size repeated until all the files in the shared directory are processed 3 Client sends SHARED END to indicate the end of the file list 4 Se
9. e Security As resources can be freely shared over a network and there is no form of authentication thus it is not possible to refine security privileges e Scalability As there are limitations on the viewpoint that nodes have over the network Gnutella suffers in this area as it does not scale well as the network traffic increases exponentially with the number of connected clients This report will focus on design issues for both security and scalability Network bandwidth will be discussed but it is not an aim of this report to analyse this factor The report splits into seven main sections these are e Introduction This chapter and outlines the basic aims of the project and its context e Theory This chapter outlines the theory related to the technical background of the project such as Window s sockets the principles of encryption file sharing architecture and so on e Requirements Analysis This chapter defines the high level abstraction of the system and it basic functionality and the main system properties e Design This chapter outlines the full design process to match the requirements analysis e Implementation This chapter outlines the main highlights for the coding These identify the key elements of the overall system such as registering a user and encrypting a file e Testing This analyses the key functional tests for the system such as encryption speed encryption strength database comparisons and
10. most of which are based on the Gnutella protocol The problem with all current file sharing technologies is that none of them can guarantee the security of the shared file This report describes the design development and evaluation of a file sharing system that proposes a novel solution to the shared file security problem The system will allow users to share files in a secure manner and comprises of client and server applications The client allows users to connect to a server and shares their files amongst all other system users The client also gives users the ability to search for files shared by the other system users and when a file is found it could be transferred from the other user securely as the file would be encrypted The server allows valid users to connect records their shared file list and enables connected users to search this list The server authenticates connected users by performing a test that only a valid user can respond to in the correct manner The report outlines research in the area of networking including technological backgrounds such as distributed file system architectures cryptographic techniques and network programming methods The novel feature of the system is the method used to address the security problem inherent to all current file sharing technologies The system developed uses cryptographic techniques to implement a framework in which to model system security including authentication of system users
11. Oram 2001 also provided information on the popularity of Napster before it was closed of course where the directory servers kept track of thousands of clients holding millions of files which amounted to over several terabytes of data Napster gave Internet users a new and exciting way of sharing files previously users would have to upload their files onto a central web server in order for them to become accessible to everyone An overview of Napster s architecture is defined in the research papers written by Kant et al 2002 and Ratnasamy et al 2001 From the papers it was discovered that Napster dispensed with the task of uploading leaving the files on the client s PCs simply brokering file requests from one PC to another so only the file addressability information would have to be stored on the central Napster servers not the file itself 1 2 2 Gnutella Aberer and Hauswirth 2001 state that Gnutella was the first fully decentralised peer to peer system running on the Internet Rather than using a central server that clients use to find files each client runs an application that connects directly to other clients File search requests are then passed from client to client until one acknowledges that it has the requested file A connected client in the Gnutella network is both a client and an ad hoc server as they both get and or send files A horizon in Gnutella defines the boundary up to which a client can see other
12. pp 94 7 CMP Media Inc USA Dumas A 1995 Programming WinSock Indianapolis Prentice Hall Forte D Peer to peer file sharing is here to stay Network Security Feb 2001 pp 9 10 Elsevier UK Gerwig K V Business The 8 Layer Computing power to the people Networker vol 5 no 1 March 2002 pp 13 16 New York USA Gnutella development page 2002 Protocol specification URL http www gnutelladev com protocol gnutella protocol html 11 June 2002 Gnutella home page 2002 URL http welcome to gnutella 11 June 2002 Griffths W 2000 Fast 64bit RSA encryption algorithm URL http www planetsourcecode com vb scripts ShowCode asp txtCodeld 67498 IngWId 1 27 August 2002 Kant K Iyer R amp Tewari V A framework for classifying peer to peer technologies Proceedings CCGRID 2002 2nd IEEE ACM International Symposium on Cluster Computing and the Grid IEEE Comput Soc 2002 pp 368 75 Piscataway NJ USA Krishna Ramanathan M Kalogeraki V amp Pruyne J Finding good peers in peer to peer networks Proceedings 16th International Parallel and Distributed Processing Symposium IEEE Comput Soc 2002 pp 232 9 Los Alamitos CA USA Lai K 2002 Binary encryption class URL http www planetsourcecode com vb scripts showcode asp txtCodeld 36457 amp IngWId 1 3 September 2002 Lv Q Cao P Cohen E Li K amp Shenker S Search and replication in unstructured peer to peer networks Proceedings
13. tcpServer Index SendData rs2 Username amp vbCr tcpServer Index SendData rs2 IPAddress amp vbCr rs2 MoveNext Loop rs2 Close End If End If Finally inform the client that there is no more search results tcpServer Index SendData FILE END amp vbCr 4 4 6 Client Password Key Change The change password process begins when the protocol code PASSWD_CHNG is received from a connected client which is followed by the username encrypted old password and encrypted new password The server then obtains the public modulus keys for the client from the global database decrypts the received old password and validates it against the password stored in the database If the decrypted password matches the password from the David Brown BSc Hons Computing 2002 51 database the new password is written to the database The following code illustrates this process Now we have the data use the db connection and validate the OLD password against the one in the Global database SystemUsers table Set rsl New ADODB Recordset Set rs2 New ADODB Recordset rsl Open SELECT Password Pubkey Modkey FROM SystemUsers Where Username amp userName amp GlobalDb adOpenDynamic adLockPessimistic pubKey rsl1 Pubkey modKey rsl Modkey Decrypt the password using the pub and mod keys decOldPasswd RSAvl dec encOldPasswd pubKey modKey If decOldPasswd rsl Password Then password valid
14. the socket API is the de facto standard 2 5 1 Windows Sockets WinSock WinSock provides connection oriented reliable two way communication or unreliable connectionless communication between applications on two computers WinSock is the Microsoft implementation of the Berkeley Sockets Application Programming Interface API with the addition of Windows specific extensions to support the message driven nature of the Windows operating system and is implemented as a dynamic link library DLL Examples of Windows applications that are implemented using WinSock include Internet Explorer Telnet and FTP 2 5 2 Sockets A socket is the logical endpoint between two communicating hosts on a network Two sockets form a bi directional communications path between applications on two different host computers A socket is comprised of an IP address and a port number Some port numbers are reserved for well known services such as port 21 for FTP and others are for use by applications Sockets can be configured to provide either a connection oriented reliable service or a connectionless unreliable service Davis 1995 describes the function of the reliable service which is based on TCP and requires that a connection is established between the two processes before data can be sent or received The data is in a stream of bytes which has no record delimiters in the data stream so if a process sends a 200 byte packet of data the recipient process may re
15. David Brown BSc Hons Computing 2002 24 2 3 Multiple Server This model consists of three servers and when a client successfully connects to either of them their session details and files they are sharing are recorded in the server database This information is then replicated to the other two servers so each server maintains a global list of connected clients and shared files This gives a client connected to Server one the ability to search and commence download of a file hosted by a client connected to Server 2 or Server 3 Unfortunately this model suffers from a problem that may lead to database inconsistencies This would occur if one of the servers were to become unavailable as the databases in the functional servers would indicate that clients are still connected to the unavailable server and that their files are still available Multiple Server with Controlling Server This model consists of four servers with one used exclusively for administering replication between the three remaining servers This solves the database inconsistency problem in the multiple server model as functional servers are updated immediately when the controlling server detects that a server is unavailable In this model when a client connects to any server their session details and files shared are recorded in the local server database which is replicated to the controlling server and finally replicated to the remaining two servers Unfortuna
16. Decrypt the new password first decNewPasswd RSAvl dec encNewPasswd pubKey modKey Update the password rs2 Open Update SystemUsers set Password amp decNewPasswd amp Where Username amp userName amp GlobalDb adOpenDynamic adLockPessimistic Send the protocol command code to the client tcpServer Index SendData PASSWD_ACK amp vbCr Else password invalid tcpServer Index SendData PASSWD_NAK amp vbCr tcpServer Index SendData LOGON_PASSWD vbCr End If The change public modulus keys process begins when the protocol code KEY CHNG is received from a connected client followed by the username encrypted password and the new public modulus keys The server then obtains the old public modulus keys for the client decrypts the received old password and validates it against the password stored in the database If the decrypted password matches the password from the database the keys are then validated to test if they are already in use If they are not the new public modulus keys are written to the database If the keys are in use the client is informed with the relevant protocol code The following code illustrates this process Now we have the data use the db connection and validate the Password against the one in the Global database SystemUsers table Set rsl New ADODB Recordset Set rs2 New ADODB Recordset Set rs3 New ADODB Recordset rsl Open SELECT Password Pubkey Mod
17. Privacy PGP Both secret key and public key cryptosystems are used in secure distributed systems but both have disadvantages In secret key both the sender and receiver must posses the same key to encrypt and decrypt the data Unfortunately the key would have to be passed from sender to recipient through a secret channel but there is no guarantee the channel is actually secure The main disadvantage of public key cryptosystems is the encryption algorithms require 100 to 1 000 times more processing power than their secret key counterparts do This disadvantage is highlighted by Singh 2001 To overcome this Zimmermann 1995 outlined a new technique named PGP which simplified the public key encryption process and significantly reduced processing times It operates by using a random session key which encipher the plaintext file conventionally It thus combines the RSA public key cryptosystem with the speed of conventional encryption This session key is enciphered by the recipient s public key and sent along with the enciphered text to the recipient The recipient then uses their private key to decrypt the session key and uses the recovered session key to decipher the ciphertext message 2 4 Network Protocols An important factor in both peer to peer and client server architecture is the protocol used for the nodes to talk to each other Typically this is achieved using a layered approach At the lowest level communication over a net
18. Set rs2 New ADODB Recordset rs2 Open insert into ConnectedUsers values amp Index amp amp userName amp amp localIP amp LocalDb adOpenStatic adLockReadOnly Send the protocol command code to the client tcpServer Index SendData LOGON_ACK vbCr Else password invalid tcpServer Index SendData LOGON_NAK vbCr rs1 Close End If David Brown BSc Hons Computing 2002 48 4 4 3 Connect to Server There are two methods to connect to another server creating a connection or listening for a connection If the server creates a connection 1t can be done manually or set to connect automatically If the automatic connection is chosen the server will attempt to establish a socket connection to the other servers every five seconds Using either method if a connection is established an ODBC connection is established to the remote server s local database which is used for client file searches This is achieved using the following code check that the server is connected If Serverl State sckConnected Then Call modFunction serverlConnStatus timerServlUptime Enabled True Now open the database connection to this server servConn connectionString amp txtServlDb Text Open Server 1 s local database using the connection string With ServerlDb connectionString servConn ConnectionTimeout 10 Open End With 4 4 4 Challenge Client Session The client session challenge
19. a white box approach which meant that the tests were developed using knowledge of the internal design The tests that were performed included e Logic and algorithms Must be unambiguous and have a clear resolution e Interfaces Data supplied from a calling module matches what the module receives and vice versa e Execution paths All independent paths through the module are ran through e Error trapping and handling Any routine in the module that may cause a failure due to an error is identified The amount of bugs caught by these four tests varied for each module although the greatest number discovered concerned the error trapping tests 5 3 Integration testing The purpose of integration testing is to locate bugs when integrating the individual components of each application consisting of modules and forms Although each individual module and form is unit tested there is still a need to perform integration tests as 1t may be possible that one module could affect other modules even though that module was successfully unit tested Integration testing begins with the testing of a small amount of combined modules and progresses to the testing of the complete application The bugs introduced by integration can be difficult to locate as the bug could theoretically exist in any of the combined components For this reason the integration process of the system was performed in small sections so any new bugs found could easily
20. be traced to the newly introduced component David Brown BSc Hons Computing 2002 55 5 3 1 User Interface Testing The User Interface UI was tested during the integration testing phase as the entire UI for both applications had been developed earlier during the design phase in the form of two non functional prototypes Each prototype contained all the forms menus and controls required for each application The main test performed on each UI was a functionality test to ensure that every control performed its relevant task and that error messages were displayed when required The other tests performed were cosmetic in ensuring that the UI followed Microsoft Windows standards and that there was no spelling mistakes 5 4 Requirements Testing The objective of requirements testing is to ensure that the software performs its functions as specified in the original system requirements and design documentation The documentation is reviewed and all the objectives stated in these documents are verified against the software to determine if they have been implemented in the software successfully Testing of the applications involves the creation of functional test cases which are developed from the perspective of the end user rather than from system requirements documentation as errors in the documentation would not be found Creating test cases from the perspective of a user allows the detection of documentation errors and allows the ove
21. client Horizons are defined to reduce the network communications to within a range of clients When a client connects to the network there can be any number of other clients connected at the same time but the client can only see clients within a given domain The horizon is defined using the Time to live TTL field in an IP datagram which defines the approximate distance that a packet can travel before it is discarded Oram 2001 states that the Gnutella horizon is set to seven decrements which effectively sets the maximum number of clients in a horizon to 10 000 MA terabyte is 1 024 GB s which is 1 099 511 627 776 Bytes David Brown BSc Hons Computing 2002 9 As Gnutella uses a horizon each connected client sees a limited distance that radiates out from the client As each client is situated differently in the network every client will therefore see a different network When clients connect and disconnect over time the network viewpoint changes and the connected clients see different clients as the network changes around them Lv et al 2002 view the Gnutella architecture as the most attractive method for sharing files as there is no requirement for centralised storage and no need to control the topology of the network in relation to where the files are located The main issues involved in peer to peer communications are e Bandwidth usage As the network traffic is likely to increase as the network size increases
22. data in a DBMS is accessed 2 Database Drivers Translates the API calls into ODBC function calls so the exact DBMS used can respond ODBC provides complete interoperability as 1t allows an application to access any SQL database using common code A developer using ODBC can build a client server application without having to specify what DBMS will be used as it can simply be linked up at a later stage ODBC has database drivers for over fifty of the most popular DBMS s including Microsoft Access MySQL and SQL Server David Brown BSc Hons Computing 2002 19 2 6 3 Database Access Technologies Currently there are three Microsoft database access technologies that may be used through applications Data Access Objects DAO Remote Data Objects RDO and ActiveX Data Objects ADO DAO was the first technology to provide an object oriented interface that allowed developers to connect directly to database tables using ODBC although it was not able to utilise the entire functionality of ODBC RDO provides the same style of object oriented interface to ODBC as DAO but practically all functionality of ODBC can be utilised Unfortunately RDO cannot access databases created with Microsoft Access ADO is the successor to DAO and RDO and provides the same interface to ODBC although the object model in ADO contains more methods and properties ADO is the only database access technology with a future as it is slowly replacing DAO and RD
23. each test the client logged on ten times with a delay of five seconds per logon to obtain an average time Each test was repeated twice in order to acquire an average for the entire test Table 1 shows the average times to write the user details for both databases which are combined in the chart featured in Figure 26 The results of these tests illustrated the fact that MySQL is vastly superior to Access XP The largest variance of the results between the two databases was when ten clients were logging on simultaneously as the MySQL time was 468 faster than the time of Access XP Number of clients Access XP time us MySQL time us 1 0 33 0 00 2 0 17 0 00 3 0 11 0 00 4 0 17 0 00 5 0 27 0 13 6 2 01 0 72 7 2 48 1 10 8 2 58 1 05 9 2 78 0 71 10 3 00 0 64 Table 1 Access XP and MySQL Test Results 3 5 K a N a Average Time Microseconds 0 5 0 r 2 g 1 r r r r r 1 2 3 4 5 6 7 8 9 10 Number of Users Access Time E mySQL Time Figure 26 Access XP and MySQL Times Graph David Brown BSc Hons Computing 2002 58 5 5 3 Client Speed Tests The purpose of the client speed testing is to discover the amount of time it takes for three client functions to be performed The functions are logging onto the server updating the shared file list and performing a file search Using the same technique as the database tests these tests began with one clien
24. is placed on the desktop When SDFS Client is launched for the first time SDFS Client will detect this and prompt for user details by presenting the window below Register User Details Connection Status 4 User Name Password Re Enter Password Shared File Directory G University Documents Year 4 Project Browse Public Key 10903463 Private Key 16100603 Modulus 57886601 Regenerate Keys Submit In this window the following details must be entered Username Password Shared File Directory Set by default to the installation directory and Public Private Modulus Keys A set is generated automatically 12 2 Running the Client After the settings have been entered the SDFS Client will launch and you will be presented with the following screen SDFS Client File View Help Connection Status Connect Filename Filesize David Brown BSc Hons Computing 2002 78 This screen displays the status of the server connection and gives the user access to the control buttons to connect disconnect with the SDFS Server There are four tabs on the SDFS Client window Shared Files File Search File Transfers and Settings which are all disabled when disconnected from the SDFS Server 12 3 Shared Files This section displays information on the files currently shared which are located in the shared file directory specified when registering user details At the bottom right of th
25. keyVal The file is then encrypted with the session key using modified code supplied from Lai 2002 which is attached in Appendix 4 Once the file has been successfully encrypted the session key is encrypted using the public and modulus keys of the requesting client using the enc method of the RSA module which is attached in Appendix 3 The target client then sends the protocol code TRANSFER ACK followed by the encrypted session key The target client begins the process of sending the encrypted file by setting the size of the data packet This packet is filled with data from the encrypted file and sent to the requesting client which is repeated until the entire file has been sent After the file has been successfully sent the encrypted file is deleted David Brown BSc Hons Computing 2002 42 During the send process a count is kept on the amount of bytes sent which is used to update the upload list on the client application form The send process is performed using the following code Set the packetsize to send packetsize 256 Used to make the sent file the same size as the original file lastdata False Temp Loop until End Of File Do Until EOF OpenedFileNbr If the last packet of data has been sent exit the loop If lastdata True Then Exit Do End If Adjust the packetsize for the last packet so too much data isn t sent If FileLength Loc OpenedFileNbr lt packetsize Then packetsi
26. of the 2002 ACM SIGMETRICS international conference on Measurement and modeling of computer systems ACM Press 2002 pp 258 9 New York USA David Brown BSc Hons Computing 2002 66 Mackenzie L 1998 Communications and Networks London McGraw Hill Microsoft Corporation 2002 WinSock development guide URL http msdn microsoft com library default asp url library en us winsock winsock high performance windows sockets applications 2 asp 13 July 2002 MySQL home page 2002 Replication capabilities of MySQL URL http www mysql com doc R e Replication html 28 July 2002 Napster home page 2002 URL http opennap sourceforge net 11 June 2002 Oram A 2001 Peer to Peer Harnessing the Benefits of Disruptive Technologies California O Reilly Portmann M Sookavatana P Ardon S amp Seneviratne A The cost of peer discovery and searching in the Gnutella peer to peer file sharing protocol Proceedings Ninth IEEE International Conference on Networks IEEE Comput Soc 2002 pp 263 8 Los Alamitos CA USA Rakitin S 1997 Software Verification and Validation Boston Artech House Ratnasamy S Francis P Handley M Karp R amp Shenker S A scalable content addressable network ACM Computer Communication Review vol 31 no 4 Oct 2001 pp 161 72 USA Ripeanu M Peer to peer architecture case study Gnutella network Proceedings First International Conference on Peer to Peer Computing IEEE Comp
27. or every system user would have to have the same key In either case the security of the key is not guaranteed In public key cryptography each user has two related keys a public key and a private key The private key is only known by owner of the key and is used to decrypt messages encrypted by the corresponding public key which is available to anyone This cryptographic technique is not suitable for the system either as public key encryption algorithms are up to 1000 times slower than secret key encryption algorithms The remaining cryptographic technique Pretty Good Privacy PGP combines both private and public key cryptography by using a random session key to encrypt the file conventionally and then encrypting the session key with the recipient s public key This cryptographic technique will be used in the system as 1t meets the security aspects set in the system requirements Additionally the use of PGP allows the server to detect invalid users as authentication can be achieved with public key cryptography The server can test the validity of a connected user at any time by enciphering a small plaintext message using their public key The ciphertext is then sent to the user where they will use their private key to recover the plaintext and send it back to the server for validation If the received value does not match the original value then the user is disconnected from the server 3 4 4 Client Design This section identifi
28. project The waterfall model will be selected over the other models as it suits the needs of this project as the requirements of the project are well understood and the software product is not required until the later stages Requirements Definition System and Software Design Implementation and unit testing Integration and system testing Operation and maintenance Figure 9 Waterfall Model 3 3 System Requirements Many existing technologies allow clients to share files amongst themselves The main improvement this system offers over the other available technologies is that the files will be shared securely The security aspects will involve encryption of the file before it is sent and subsequent decryption by the recipient of the file This means only the intended recipient will be able to read the contents of the file so 1f the data transmission were intercepted by a third party it would be undecipherable Another security measure of the system should allow it to detect invalid users Therefore if a hacker were able to break into a communication stream the system would be able to validate the authenticity of the user and then take appropriate action David Brown BSc Hons Computing 2002 23 The system must also provide users with a file search facility or they would be unable to share them This facility should allow users to search for files via a file name or the name of the
29. rr rar sr er nn 19 De CONCLUSIONS ciu cda dere 19 3 REQUIREMENTS ANALYSIS amp DESIGN oocccccconocnoonconocconnnccnocononccnnnccnooccnnnccoocoonnccnoccconeconnos 20 3 1 INTRODUCTION os ero evansevite ersehen 20 3 2 SOFTWARE ENGINEERING METHODS onii neee cnin eai e ie eia i i 20 3 2 1 Spiral DEvVelODMCNM smeseserrrrrerrsrerrrrerererrsrererrrrerrsr er ere raser sr sr ere KARE nn er KRA Re RK SRK rer r er er en on 20 3 2 2 Evolutionary Development eneeseseessessensessensesnensensennensneneenee nennen nennen 21 3 2 3 2 Woaterfall M del N 2 2u 2 0 20 a er ge en tt 22 3 3 SYSTEM REQUIREMENT S ocena nareset aranean iane rae aan aaan ia oain 22 3 4 DESIEN EEEE R E E A T 23 3 4 1 File System Architecture eseeesensensessensessensennenennnenennensneneenee nennen rss nenn 23 3423 System Model een Zu En A it hd A eher ee ee 23 3 43 IS TEMAS CCUNM A A i euere A e rede 25 344 CMCNE Desin iis NS zu nn i A A duce Si t 25 3 49 SEV DESIEn a a A A A A AS ee A E EE E 26 3 4 6 System Protocols Design cesesesesensensensenseenenseenennennnenenee arras 27 3 47 Database Desig un ei Spin een mein 32 3 4 8 User Interface Designern erien ee ERE a A ENE AAAA E 33 349 Technology Choices a e esate 33 3 5 CONCLUSIONS NN 34 4 IMPLEMENTATION sisciccsescccciss sacveccvscescasecasssetwccoseete cossecke scada soasevseccsseees cossesdecveusets ESEESE oriai 35 4 1 INTRODUCTION adi eras Sen dea 35 4 2 WINSOCK PROGRAMMING sonoro o
30. same start time for all clients in the test specify if the test is to be repeated and finally set the actual test that is to be performed When the start time is reached all the clients participating in a test would perform the required actions A screenshot of this application is shown in Figure 25 SDFS Client Automation Test Program Grab window Time From Atomic Clock Current Local Time 90 00 57 Current Window Test Parameters Start Time 00 00 00 l Repeat Test Number of Times Logon Logoff with SDFS Server Update Shared File List C Submit File Search Note If you select to repeat a test there willbe a delay of five seconds between each execution Exit Figure 25 Automated Test Program 5 5 2 Database Tests The purpose of the database testing is to discover the amount of time it takes for the details of a user to be written to the database when they first logon The tests began David Brown BSc Hons Computing 2002 57 with one client and were scaled to ten clients logging onto the server simultaneously This gave an indication of how scalable the system is as it would be entirely possible that there could be a far greater number of users attempting to connect simultaneously at any given time Even though Microsoft Access XP was not selected as the system database 1t was tested along with MySQL mainly out of curiosity in order to discover which of the two databases were faster In
31. to test the system the number of David Brown BSc Hons Computing 2002 64 clients should be scaled up to 10 000 as this will give a definite indication on how scalable the system is It would not be practical to use 10 000 computers to test the system as these resources are simply not available and it is not feasible to obtain these resources specifically for testing A more viable solution would involve simulating the required number of clients using a smaller number of computers The ideal set of performance tests would stress the system to its breaking point to reveal the maximum possible number of concurrent users Upon discovering the maximum number a constraint could be placed on the server application which would limit the total amount of concurrent users per server and therefore ensure that the system could never be overloaded and would always provide a service 6 2 5 Network Traffic Tests The purpose of network traffic testing would be to discover the volume of traffic occurring on the network from clients The tests could also provide information on the maximum number of simultaneous file transfers that a client is capable of handling These tests would involve recording the transfer time of a file with a determined file size between increasing numbers of clients Using the same testing method proposed by the further system performance tests the tests could begin with two clients and be scaled up to 10 000 clients
32. user which will return the entire list of files shared by that user 3 4 Design The original thinking behind this system was it could be deployed in a commercial environment where a group of users who require the need to share files amongst themselves in a secure manner could subscribe to the service and guarantee their authenticity Therefore 1f it were to be deployed in a business environment only authorised users would be able to gain access share files with each other File sharing can already be achieved with a standard network operating system as access permissions can be set to directories giving access only to authorised users However this is not the safest or most efficient method of sharing files as passwords can be obtained and transmitting files over a wide area using a network can be slow 3 4 1 File System Architecture The research conducted into distributed file system architectures outlined that the Client Server and Gnutella architectures are completely unsuitable for this type of application as both architectures do not meet the system requirements In the Client Server architecture files would have to be placed on the central server by the clients in order to be shared This does not meet the system requirements as only the client should host the file and should only release it when they want to If the file was to reside on a server it could be viewed by any user with enough access rights In the Gnutella a
33. user hosting the files This process comprises of two stages sending the search query and receiving the search results The send query process begins with the transmission of the protocol code FILE SEARCH to the server followed by a file name or username depending on the search type submitted by the user The process of receiving the results from a file search begins with the client receiving the protocol code FILE START to indicate the start of the search results The received string is then stripped down into its component parts and a count is maintained on the number of strings gathered as four are required per search result As soon as four string values are obtained the result is written into an ADO record set to store the search results When the protocol code FILE END is processed the entries in the ADO record set are then used to populate the list on the client application form This process is performed using the following code check to see if this is a returncode signifies end of string If workstring vbCr Then retCount retCount 1 check if this is the end of the list FILE END If searchString FILE END Then update the search file listview box Call populateFileSearch Exit Sub End If retcount used to count the strings received as there are four for each result Select Case retCount Case 1 filename recFile searchString searchString workstring David Brown BSc Hons Com
34. were based on the peer to peer model Waters 2001 then showed that the use of this model in file sharing applications is increasing rapidly which is mainly due to the general availability of the Internet Many David Brown BSc Hons Computing 2002 8 researchers believe that peer to peer applications have a great potential one such researcher is Doherty 2002 who states peer to peer shows great promise for file sharing and collaboration Peer to peer uses a different approach from Napster to sharing files Gerwig 2002 and Vrana 2001 define this approach as a decentralised network where client computers communicate with each other directly without the help of centralised servers So rather than using a central server to store file and client information each client uses an application that connects directly to other clients According to Gerwig 2002 out of the available peer to peer technologies the most popular is Gnutella 1 2 1 Napster Oram 2001 and Kant Iyler and Tewair 2002 describe the architecture of Napster as a mixture of centralisation and decentralisation consisting of centralised directory servers that built and maintained a file list adding and removing entries as individual clients connected and disconnected Yang and Garcia Molina 2001 brand Napster as a hybrid peer to peer system with their research concentrating on the issues and trade offs in the design of a scalable peer to peer system
35. will maintain consistency throughout the system as a user may register with one server and attempt to logon to another server at a later stage If this were to happen without replication the other server would have no record of this user and deny them access The global database will contain one table called SystemUsers which has the following fields Username Password PublicKey and ModulusKey e The local database will store details of the users currently logged on to the server and the list of files they are sharing When a user logs in their socket number username and IP address are written to this database This is followed by the names and sizes of any files they are sharing Instead of this information being replicated to the other server s databases the servers in the system connect to each other s local databases via an ODBC connection to submit file search queries which removes a large replication overhead from the system The local database will have two tables ConnectedUsers and SharedFiles The ConnectedUsers has the following fields SocketNumber Username and IPAddress The SharedFiles table has the following fields Username Filename and Filesize The database tables and their replication associations are illustrated in Figure 19 David Brown BSc Hons Computing 2002 33 Local Db SharedFiles SystemUsers ConnectedUsers SharedFiles SharedFiles Figure 19 Database Tables and Replication
36. 2 1 Figure 3 Gnutella Architecture David Brown BSc Hons Computing 2002 12 Unfortunately Gnutella has problems in terms of scalability and ineffective use of bandwidth Both of which are common problems with peer to peer architectures Krishna et al 2002 and Ripeanu 2002 propose that the problems are caused by the way the Gnutella peer to peer networks are formed Krishna et al 2002 propose a solution to improve the overall performance of the Gnutella network by creating small clusters of peers with similar file sharing interests These clusters further distribute the system and should generally reduce network traffic as fewer broadcasts are likely to be required for the smaller clusters 2 3 Security Techniques Peer to peer communications obviously have weaknesses in authentication as there is no intermediate server which can authenticate the client to the other client In order for us to under the problems that may be causes and their solution we must analyse key areas of security especially in data encryption which is the best way to secure both the data and any transactions Tanenbaum 1996 states that whenever a computer system is a potential target for a malicious or mischievous attack security measures must be incorporated into these systems to prevent such actions This is especially relevant for systems that contain classified confidential or financial information where integrity and secrecy
37. 2 3 3 Network Determines how network addresses are specified and the routing of data through interconnected networks A typical example of this layer is IP Internet Protocol 4 Transport Specifies reliable transport details and the support of multiple streams from a single computer A typical example of this layer is TCP Transport Control Protocol 5 Session Specifies the establishment maintenance and closing of a communication A typical example of this layer is HTTP Hypertext Transfer Protocol 6 Presentation Specifies how the data is represented as systems may use different data representation standards A typical example of this layer is HTML Hypertext Markup Language 7 Application Provides network services to an application and specifies how the application uses the network A typical example of this layer is a WWW Browser When a protocol is designed using the OSI model the protocol software is divided into distinct modules which correspond directly to a layer Layering also determines how the modules interact as each module communicates with the layer directly above or below so outgoing data will pass down through the layers and incoming data will pass up through the layers The most widely known and used protocols are those relating to the Internet and TCP and IP Out of these protocols the most relevant to this project is the File Transfer Protocol FTP 2 4 2 File Transfer Protocol FTP is one of th
38. 4 Client Figure 2 Napster Architecture 2 2 3 Gnutella Architecture Kant et al 2002 provide information on the Gnutella architecture which is based on a fully distributed approach where clients connect to each other directly through a software interface that forms a high level network This architecture is illustrated in Figure 3 When a client connects to the Gnutella network all the sharable files are made public to all other clients through a set of local folders that the client specifies as shared The Gnutella client software which is freely available from the Gnutella home page 2002 is essentially a file serving system and search engine in one Portmann et al 2001 provide function information on the underlying Gnutella protocol They outline that the discovery of peers and searching for files are the main elements of this protocol and are both implemented by sending messages to all connected clients within the network horizon When a connected client submits a search to the Gnutella Network the search parameters are flooded throughout the network horizon which returns any search matches The file download takes place between the requesting client and the client who hosts the file Technical information on this transfer was obtained from the Gnutella development WWW page 2001 which revealed that the transfer is based on an HTTP like connection 4 0 1 Search 2 Location 6 Peer 3 Request D 4 Response
39. A Secure and Distributed Architectural Model for File Sharing Secure Distributed File Sharing DAVID JOHN BROWN Submitted in partial fulfilment of the requirements of Napier University for the degree of Bachelor of Science with Honours in Computing School of Computing December 2002 David Brown BSc Hons Computing 2002 2 Authorship Declaration I David Brown confirm that this dissertation and the work presented in it are my own achievement 1 Where I have consulted the published work of others this is always clearly attributed 2 Where I have quoted from the work of others the source is always given With the exception of such quotations this dissertation is entirely my own work 3 I have acknowledged all main sources of help 4 If my research follows on from previous work or is part of a larger collaborative research project I have made clear exactly what was done by others and what I have contributed myself 5 I have read and understand the penalties associated with plagiarism Signed Date Matriculation Number 98004492 David Brown BSc Hons Computing 2002 3 Abstract There has been a huge growth in the use of file sharing software over the last year making file sharing one of the top uses of the Internet Napster was the first technology that empowered users with the ability to share files amongst themselves The demise of Napster led to the development of numerous file sharing technologies
40. Abs TempDByte Else ByteFinal TempDByte End If ByteOut i TempByte If i Mod 500 0 Then David Brown BSc Hons Computing 2002 73 DoEvents End If Next i SaveBinaryArray Destination ByteOut End Sub Public Sub DecryptFile Source As String Destination As String Password As String Dim ByteIn As Byte ByteOut As Byte ByteIn ReadBinaryArray Source ReDim ByteOut LBound ByteIn To UBound ByteIn As Byte Dim i As Long j As Long Dim PL As Integer PL Len Password Dim ChrBNow As Integer Dim PosNow As Integer Dim TempDByte As Integer ByteFinal As Integer For i LBound ByteIn To UBound Byteln PosNow i Mod PL ChrBNow AscB Mid Password PosNow 1 1 Xor 17 TempDByte ByteIn i ChrBNow If TempDByte lt 0 Then ByteFinal 256 Abs TempDByte Else ByteFinal TempDByte End If ByteOut i ByteFinal If i Mod 500 0 Then DoEvents End If Next i SaveBinaryArray Destination ByteOut End Sub David Brown BSc Hons Computing 2002 74 11 Appendix 5 SDFS Server User Manual 11 1 Installation Getting Started Double click the setup exe to install SDFS Server and follow the prompts When the installation process is finished an icon for SDFS Server is placed on the desktop When SDFS Server is launched for the first time SDFS Server will detect this and prompt for system settings to be entered by presenting the window below SDFS Ser
41. Again it would not be practical to use 10 000 computers to test the system so another method to perform the same test would be to use 500 computers with each client simultaneously transmitting an increasing number of files This would not only test the network traffic but also the number of simultaneous file transfers that a client could handle Upon discovering the maximum number of transfers a constraint could be placed on the client application which would limit the total amount of transfers so the client could never be overloaded Before these tests are performed it is obvious that the performance of the network will decrease as the number of client file transfers increases The network traffic tests would be far more productive if they were conducted using several variations of the file transfer protocol as this could lead to the discovery of the most efficient protocol David Brown BSc Hons Computing 2002 65 References Aberer K amp Hauswirth M Peer to Peer information systems concepts and models state of the art and future systems Proceedings 8th European software engineering conference ACM Press 2001 pp326 7 New York USA Aoki K Ichikawa T Kanda M Matsui M Moriai S Nakajima J amp Tokita T Camellia a 128 bit block cipher suitable for multiple platforms design and analysis Selected Areas in Cryptography 7th Annual International Workshop SAC 2000 Proceedings Lecture Notes in Compute
42. Main Client Form David Brown BSc Hons Computing 2002 38 When the user clicks the connect button on the main form the client application randomly selects a server which is achieved using the following code serverFile FreeFile Open stName amp Server dat For Input As serverFile now read in the values and store them in a dynamic array as it may be possible that the service is expanded to include more than three servers in the future Do Until EOF 1 Line Input serverFile stLine preserve the contents in the array ReDim Preserve dynArray count dynArray count stLine count count 1 Loop close the file Close serverFile get a random number from the number of server IP addresses read from file randVal Int Rnd count use that value to get the IP address out of the array and set the Winsock control RemoteHost variable frmMain ServerConn RemoteHost dynArray randVal frmMain ServerConn RemotePort 1001 After a server has been selected the client then attempts to connect to it If there is no response from the server after 20 seconds the connection attempt is abandoned and the user is informed If the server responds within this time the connection status control in the client window is updated and the client application continues to the next task This process is achieved with the following code attempt to connect to the server frmMain ServerConn Connect set the status of
43. O Tulloch 1996 states that using ADO means that an application will be completely interoperable with other database technologies through an ODBC driver A developer using ADO and ODBC can write an application that can connect to a range of different data sources using the same programming This means that the application will be completely interoperable with other database technologies as long as an ODBC driver exists for that data source 2 7 Conclusions This chapter has covered the key areas involved in the design and creation of a distributed file sharing application that will utilise cryptographic techniques to enforce security It covered important system design areas such as current distributed system architectures available cryptographic techniques and communication protocols especially in relation to the application level It also discussed areas that will be considered during the implementation phase of the application such as network programming techniques and available database technologies including methods to access these databases through applications David Brown BSc Hons Computing 2002 20 3 Requirements Analysis amp Design 3 1 Introduction The planning and design stage of any software project can be a difficult process This chapter highlights the actual specification of the proposed application what are its goals how it will function to achieve these goals and what improvements the application could brin
44. Prime True f IngNumber Mod IngCount 0 Then IsPrime False Exit Function End If IngCount 3 For x If lngNumber Mod x IsPrime False Exit Function End If Next End Function IngCount To lngSqr Step 2 0 Then Public Function Mult ByVal x As Double Double ByVal p As Double ByVal On Error GoTo errorl y 1 Do While p gt 0 70 2 m As Double As David Brown BSc Hons Computing 2002 Do While p 2 Int p 2 x nMod x x m p p 2 Loop y nMod x y m pre pie a Loop Mult y Exit Function errorl y 0 End Function Private Function nMod x As Double y As Double As Double On Error Resume Next Dim z z x Int x y y nMod z End Function Public Function enc tip As String eE As Double eN As Double As String On Error Resume Next Dim encSt As String encSt e2st If tip Then Exit Function For i 1 To Len tip encSt encSt amp Mult CLng Asc Mid tip i 1 eE eN amp Next i enc encSt End Function Public Function dec tip As String dD As Double dN As Double As String On Error Resume Next Dim decSt As String decSt For z 1 To Len tip ptr InStr z tip tok Val Mid tip z ptr decSt decSt Chr Mult tok dD dN z ptr Next z dec decSt End Function le David Brown BSc Hons Computing 2002 ie 10 Appendix 4 Binary Encryption Module Binary Encryption module Modified f
45. Rnd AB LOWER primeNumB Int AB_ UPPER AB LOWER 1 Rnd AB LOWER Loop valueN primeNumA primeNumB PHI primeNumA 1 primeNumB 1 EncryptionKey GCD PHI DecryptionKey Euler EncryptionKey PHI Loop End Sub Private Function Euler E3 As Double PHI3 As Double As Double On Error Resume Next Dim ul u2 u3 vik v2 v3 af Dim tlf t2 t3 z uu vv inverse ul u2 0 u3 PHI3 vl 0 v2 1 v3 E3 Do Until v3 0 q Int u3 v3 tl ul q vl t2 UE a a t3 u3 q v3 ul vl u2 v2 u3 v3 vl tl v2 t2 v3 t3 z 1 69 David Brown BSc Hons Computing 2002 Loop uu ul vv u2 If vv lt 0 Then inverse vv PHI3 Else inverse vv End If Euler inverse End Function Private Function GCD nPHI As Double As Double On Error Resume Next Dim nE y Const N_UP 99999999 set upper limit of random number for E Const N_LW 10000000 set lower limit of random number for E Randomize nE Int N UP N_LW 1 Rnd N_LW top x nPHI Mod nE y x Mod nE If y lt gt 0 And IsPrime nE Then GCD nE Exit Function Else nE nE 1 End If GoTo top End Function Private Function IsPrime lngNumber As Double As Boolean On Error Resume Next Dim IngCount Dim IngSqr Dim x ingSqr Int Sqr IngNumber Get the int square root f IngNumber lt 2 Then IsPrime False Exit Function End If IngCount 2 s
46. a connection to the server and allows the client to issue commands to the server This WinSock control supports multiple connections e Serverl amp Server2 Each control creates a connection to a remote server for the purpose of creating and maintaining an ODBC connection to the remote server s database The connection oriented nature of sockets allows the local server to detect if the remote server becomes inactive and to close the ODBC connection These WinSock controls allow only one connection 4 3 Client Implementation Figure 20 illustrates a high level view of the client application with each important section individually numbered This number corresponds directly to a sub section in this chapter where the functionality and corresponding code is explained in detail Logon to server 4 2 1 Send shared file list 4 2 2 Submit file Send file Receive file Authenticate Change keys Change search to client from client details password Shared File 4 2 3 4 2 4 4 2 5 4 2 6 4 2 7 Dir 428 Figure 20 Client Application High Level View 4 3 1 Logon to Server There are two functions within this area registering new user details and existing user logon When the client application is started a splash screen is displayed that secretly reads an entry from the Windows registry This is shown in the following code userName GetSetting SFDS Client Startup Username check is the username value has an entry If u
47. actions together and sending as one large transaction It also important to consider application behaviour when developing networked applications as some behaviours will work well on a local machine but can cause performance problems if run over a network One such behaviour to avoid is a chatty application which involves the application sending a large number of small transactions over the network This is not an efficient method as there is a large network overhead for each transaction in the same way as establishing a connection 2 6 Database Technologies A database is essentially a repository of data which allows information to be stored and retrieved quickly Databases come in two main types David Brown BSc Hons Computing 2002 18 e Relational Database Management System RDBMS This is where data is logically grouped into tables with each table consisting of columns and rows Begg et al 1998 state that RDBMS s are the dominant database technologies in use today with estimated sales between 8 10 billion per year and growing at a rate of 25 per year e Object Oriented Database Management System OODBMS This is where data is stored in the form of objects where each object has its own properties According to Begg et al 1998 OODBMS s only have a 3 share in the database market 2 6 1 Common Databases It is entirely possible to use either of these two types of database although relational
48. ain disadvantages e The produced software systems are often structured poorly This is a result of the continual changes to the software whose structure is often corrupted e The software development process is not visible As the software is developed quickly documentation for each version is not produced and the target users receive no deliverables to measure the development process Initial Specification Outline Development Intermediate Description 2 Figure 8 Evolutionary Development Model Final David Brown BSc Hons Computing 2002 22 3 2 3 Waterfall Model The Waterfall model consists of five stages that map onto specific development activities that flow from one to another when an activity is completed and is shown in Figure 9 The model can evolve if additional requirements are discovered at a later stage in the project which may involve repeating earlier stages For example during the implementation stage problems may be discovered which will require a change to the design of the software The main advantage of this model is it reflects normal engineering practice and therefore is commonly used and understood However this model suffers from two main disadvantages e It should only be used when the requirements of the project are well understood as 1t does not readily accommodate requirements changes e The software product will not usually be available for use until almost the final stages of the
49. and the files that they share The report defines the strength of the encryption and makes recommendations for enhancements A major objective of the system is to provide a model that can be easily scaled with a number of clients The tests performed show that the response time of the system remains fairly linear to the number of concurrent clients Additional tests have also shown that MySQL is vastly superior to Access XP especially with 10 clients logging on simultaneously In this case MySQL is almost five times faster than Access XP The report concludes with recommendations for future work such as an addition to the client application requirements improvements to the encryption speed and strength further performance tests and a test to investigate network traffic generated by clients David Brown BSc Hons Computing 2002 4 Table of Contents 1 INTRODUCTION 2365 22554060 230058 NN 7 1 1 SCOPE AND AIMS OF THE PROJECT eront e i e E ELN Eaa EAE S ELENE STENE E Tesk 7 1 2 BACKGROUND nasse BSR a 7 1221 Napster eene seele reinem eure rer E ters 1 2 2 GIL CLG se sc Sos cies ae ices Sec wis RNA 8 2 THEORY grd d vsssessevs vediossssessrsesessonssuesnssessessssssrdsnderisnsdsdesrnsdsssssndessssnnsdsnnsnssorsssersivessssvsnesnersssessden 10 2 1 INTRODUCTION a a RITA a 10 2 2 DISTRIBUTED FILE SYSTEM ARCHITECTURES ccssccecsscecesssececesseececsueeecessaeeecssaaeeeeneeeeenses 10 2 2 1 Client Server ArchiteCture cccccccc
50. arty to intercept the code key established between sender and receiver Even if someone did attempt to intercept the code key both legitimate communication parties would be warned about the eavesdropper Unfortunately Quantum cryptography requires the use of specialised equipment and therefore is not available outside laboratory conditions Additionally Quantum cryptography cannot currently be engineered to operate over extended distances However if these problems were to be resolved a completely secure method of communicating would be available to everyone Because Quantum cryptography will be unavailable for many years stronger encryption can be provided by another encryption algorithm The Camellia algorithm highlighted earlier in this chapter as a possible solution to increase encryption speed also offers a stronger encryption solution Camellia supports a key size of up to 256 bits giving a total number of 1 15 x 10 key combinations which is far greater than the four billion combinations from the 32 bit key currently used in the system 6 2 4 Further System Performance Tests Even though performance tests were carried out on the system they did not produce the desired results because it was not possible to scale the tests up to the point where the system could no longer function adequately As scalability is a major objective of the system additional performance tests should be performed Instead of using 10 concurrent clients
51. blic private keys at any time After selecting a new password the client application encrypts it along with the old password The protocol code PASSWD_CHNG is sent to the server followed by the username and the old new passwords This is achieved using the following code encrypt the old password with the users private key encryptOldPasswd RSAvl enc txtPasswd Text txtPrivate Text txtModulus Text encrypt the new password with the users private key encryptNewPasswd RSAvl enc txtPasswd Text txtPrivate Text txtModulus Text inform the server that a password change is being sent achieved by sending the code PASSWD_CHNG If ServerConn State lt gt sckConnected Then Connection failed ServerConn Close Else ServerConn SendData PASSWD_CHNG amp vbCr ServerConn SendData txtUser Text vbCr contents of username text box ServerConn SendData encryptOldPasswd amp vbCr encrypted old password ServerConn SendData encryptNewPasswd amp vbCr encrypted new password End If A new public private key set can be automatically generated 1f required by the user After a new key set is generated the client application encrypts the user s password and informs the server that a key change is being sent by sending the protocol code KEY CHNG followed by the username password and new public modulus keys This is achieved using the following code encrypt the password with the users OLD private key encryptPasswd RSA
52. by SPECWeb96 Server Client socket socket Create the Socket Create the socket bind Give the socket a name listen Listen for connections connect Connect to the server accept Create a new socket while original socket continues to wait for connections send recv Send and Receive Data send recv Send and Receive Data closesocket Close the connection closesocket Close the connection Figure 6 WinSock Client Server However many applications are developed so they do not take advantage of the performance capabilities of WinSock as they unintentionally implement techniques that hinder performance The most common mistake resulting in reduced application performance involves the TCP IP protocol mainly the overhead required for establishing and terminating a connection For example if an application uses the TCP IP protocol on an Ethernet network it must send four 60 byte packets to establish a connection and the same amount to terminate the connection An application that regularly establishes and terminates connections incurs this overhead on each occurrence Another common programming mistake involves the communication stream between the applications The most efficient way is to use a small number of large transactions rather than a large number of small transactions as large transactions are more efficiently streamed This may involve grouping smaller trans
53. cPasswd RSAvl dec encPasswd pubKey modKey If username amp pub pri keys not in the Db add Set rs3 New ADODB Recordset rs3 Open insert into systemusers values amp userName amp amp decPasswd En amp pubKey amp amp modKey GlobalDb adOpenStatic adLockReadOnly Now notify the client tcpServer Index SendData NEW USER ACK amp vbCr If the client is logging on the protocol code EXIST USER is received followed by the username encrypted password and the local IP address of the client The server then obtains the public modulus keys for the client decrypts the received password and validates it against the password stored in the database The client is then granted or denied access based on the result of the password validation The following code illustrates this process Now we have the data use the db connection and validate the password against the one in the Global database SystemUsers table Set rsl New ADODB Recordset rsl Open SELECT Password Pubkey Modkey FROM SystemUsers Where Username amp userName amp GlobalDb adOpenStatic adLockReadOnly pubKey rsl Pubkey modKey rs1l Modkey Decrypt the password using the pub and mod keys decPasswd RSAvl dec encPasswd pubKey modKey If decPasswd rs1 Password Then password valid This user is now validated so write their socket number username and IP address to the connectedUsers table
54. cal Server that listens for a connection to the remote Server Now both servers can invoke a connection to each other as both have the capability to listen and connect The following diagram illustrates the process David Brown BSc Hons Computing 2002 75 eL Serverl gt Server LocelPort 1040 RemotePoxt 1060 Server3 LocalPort 1050 RemotePoxt 1080 el Server2 H Server3 Serverl LocalPort 1060 RemotePoxt 1040 Serverl LocalPoxt 1080 RemotePoxt 1050 __ serve Gastro 1070 RemnotePot 1090 Server LocelPort 1090 RemptePoxt 1070 ODBC Settings Before entering any information in this section ODBC data sources must be created first On Windows NT 2000 amp XP it is located in Control Panel Administrative tools and on Windows 98 amp ME it is located in the Control Panel When these data sources are created the Data Source Names DSNs are entered for each server in this section Server Password This section requires the password for the SDFS Server This password will enable the administrator to change the Server settings at a later stage Without this password these settings cannot be changed which prevents unauthorised tampering Running the Server After the settings have been entered the SDFS Server will launch and the following screen will be displayed SDFS Server Start Server ie Client Connections if Serve
55. cccccccccsscssssscesececsessssssesecessssssssesececsesssassesecsesesssssasecens 10 LID Napster Archilecl re a n Finale en en N nee ac 10 2 2 3 Gnutella Architecture cccccccccccccccscsscccccccessessscesccecesssssssssccccessessssssesccsesesssssescesesessssseesess 11 2 3 SECURITY TECHNIQUES isses EA Te EEE EEEE A AE ES 12 2 31 E E 1 210482 2 ANEN A A ETE a E 12 23 20 DECKEL Eye en etek en nen dee a e ite e cd eu eh 13 23 3 Publie key reais bi Mite nn en A ne Mensen here nu ne 13 2 3 4 Pretty Good Privacy PGP eseensensensessensensensensennenee nennen nn nenn 13 2 4 NETWORK PROTOCOL Si 3 120 ans ben ren caceria etica 13 2 4 1 Protocol Layered Model suneesessensessensesnensennnnennneneenesnensennnne nenne nenn 14 2 4 2 File Transfer Protool ose iiser eiieeii een erie eai an sonen 15 2 5 NETWORK PROGRAMMING soriire inii oeoa E AR 16 2 5 1 Windows Sockets WihSOCK ssosrvtererersrrsrarerrrreresrsrererrrrer ere ar ere rare ere aren er RAA nennen nenn 16 IN A A bac ches mentees SES Eee re 16 2 5 3 Microsoft WinSock Guidelines smseosmrmrsrsrrrrrrerrrrsrererrrrerrsrsrererrrrerr sr cercana 16 2 6 DATABASE TECHNOLOGIES aerei rnoet ii reese r E Eea EER ETEEN EENE NEEE EE EE E EEEE E Ee 17 2 6 1 COMMON DI dE ee E essen E A ST 18 2 6 2 Open Database Connectivity ODBOCJsomsesersssrsrrsrrarrrrrarerrererrrsrerrsr eran rer rr rerna nr sr rre 18 2 6 3 Database Access Technologies ssmsssrrrssrrrsrerrrrrrrrarerrrsrerrarrrr renen narr
56. ceive the data as a single 200 byte packet or four packets of 50 bytes If an application were to depend on records of a fixed size being sent the application must be written to provide application level headers in the data stream as the packet size will not be preserved on the receiving end Dumas 1995 points out that the reliable service is suited to client server architectures Typically the server will create a socket give the socket a name and wait for clients to connect to the socket The client creates a socket and connects to the server s named socket When the server detects the connection it creates a new socket and uses the new socket to communicate with the client The server s named socket continues to listen for connections from other clients This process is illustrated in Figure 6 2 5 3 Microsoft WinSock Guidelines WinSock was developed by Microsoft to enable Windows applications to take full advantage of the available network bandwidth allowing them to achieve outstanding performance reliability and throughput This is illustrated by the following facts which were obtained from the Microsoft sockets development page 2002 e Over 200 000 simultaneous TCP connections can be serviced by Windows David Brown BSc Hons Computing 2002 17 e A data transmission record of over 750 Mbps was set by Windows Windows serviced over 25 000 requests per second running Internet Information Server in a test performed
57. d detect this using their socket connections The servers would then close their ODBC connections to the unavailable server and only submit file searches to their local databases and the remote databases of the remaining connected servers 3 4 6 System Protocols Design Now that the client and server operations of the system have been identified the application level protocols can now be designed Using the client and server operations the following system protocols have been identified Register User Protocol This protocol is used when a new user is attempting to register their details with a server This process is illustrated in Figure 11 David Brown BSc Hons Computing 2002 28 Figure 11 Register User Protocol 1 Client connects to a server and sends the message NEW_USER 2 Client sends username encrypted password and public modulus keys 3 Server decrypts the password and validates the keys username 4 Server sends either NEW_USER_ACK or NEW_USER_NAK depending on the result of the validation of the details If NEW_USER_NAK were sent the server would then send a message to the client identifying the reason for the rejection There are two possible messages USER_EXIST username in use or PUB_EXIST public key in use Logon Protocol This protocol is used when an existing user is attempting to logon to a server This process is illustrated in Figure 12 Global Db Client Figure 12 Logon Protocol
58. d the file is built up from the received packets The following code illustrates this process put the session key in the global array for later retrieval sessionKey Index strSess Get the filename off the download listview Find the entry in the listview by using the function in modClient itemNumber modClient getDownloadListItem Index Set the filename to this strFileName lvwDownload ListItems itemNumber SubItems 1 Get the path of the SDFS Client App strPath modServer getProgramLocation Open the file for writing and give it an identifier DownloadingFile Index FreeFile Open strPath amp Temp amp strFileName For Binary Access Write As DownloadingFile Index Trim the session key off the the received string strData Right strData stringLen count Get the new length of the string and store it in the byte array stringLen Len strData Reset the array value as this may have been used by a previous connection downloadBytes Index 0 downloadBytes Index downloadBytes Index stringLen Write the remaining part of the received string to this file Put DownloadingFile Index strData When the file transmission is complete the socket connection between the remote and local clients is closed The old socket number is used to obtain the file entry from the David Brown BSc Hons Computing 2002 44 download list and the size of the downloaded file is compared against
59. databases are favoured due to their speed stability and maturity The three most commonly used relational databases in use today are as follows e Microsoft Access Is a RDBMS that can be run on any Windows platform but does not have any of the advanced capabilities of the other two database systems The performance of Access is poor compared to the other database system but is commonly accepted in industry due to its ability to integrate with other Microsoft technologies and its simplicity to set up e Microsoft SQL Server Is a RDBMS that runs only on the Server versions of Windows and is used for high volume transaction processing environments It consists of a server that runs the database software that processes requests submitted by the database client software e MySQL Is a RDBMS that can be run on any Windows platform which has the advantage of being an open source product so its advanced capabilities and performance can be used without incurring any costs 2 6 2 Open Database Connectivity ODBC Tulloch 1996 describes the function of Microsoft ODBC which provides an interface that allows Windows applications to access databases over a network through an appropriate ODBC driver ODBC provides applications with an API allowing them to be completely independent of the host DBMS that manages the data There are two main components used in ODBC 1 API Function calls that can be called from the application which define how the
60. e 1t increases the overall flexibility as new protocols can be created and used as required The most important factor in protocol design is the layered model which describes how the communication process can divide into subsections called layers A protocol suite is designed by specifying a protocol that corresponds to each layer Comer 1997 provides information on the most commonly used layered model which is the Open Systems Interconnection OSI developed by the International Standards Organization ISO and is illustrated in Figure 5 The OSI model provides a straightforward explanation of the associations between the hardware and protocol components of the network In the OSI model the lowest layer corresponds to the physical hardware and the following layers correspond to the software Stallings 2000 describes the purpose of each of the layers which are as follows Application Application Presentation Presentation Session Session Transport Transport Network Network Data Link Data Link Physical Figure 5 The OSI Layered Model David Brown BSc Hons Computing 2002 15 1 Physical Corresponds to the network hardware such as the characteristics of the voltage of transmitted signals or the intensity of the light pulses 2 Data Link Specifies how transmitted data is received in a reliable way and involves adding extra bits for error detection and so on A typical example of this layer is Ethernet IEEE 80
61. e 3 Encryption Speed Test Results Time to Encrypt Seconds 1 2 3 4 5 6 7 8 9 10 File Size Mb m P3 500 Mhz P3 1Ghz P4 1 4 Ghz x P4 1 7Ghz e P3 800 Mhz Figure 28 Graph of Encryption Speed Tests David Brown BSc Hons Computing 2002 60 5 5 5 Encryption Strength Tests Any encryption code is theoretically breakable the measurement of how strong the encryption code is the amount of time it would take to break the code by an unauthorised user In normal circumstances the user attempting to break the code would obtain the encryption algorithm by analysing the ciphertext They would then try every possible permutation of the code key until a match is found To find a match they would decrypt a portion of the ciphertext with each key permutation and look for any commonly occurring English words in the decrypted text such as the to and so on According to Buchanan 2000 the main factor in the security of an encryption code is its length as this length determines the maximum number of possible code permutations The research of Bahie Eldin Omar 1998 outlined that the strength of an encryption code can be evaluated by a complexity measure which involves the randomness of the code via the maximum amount of possible combinations from the code A single 1 bit code can only have a maximum combination of two keys a 2 bit code has a maxim
62. e a client server model where a client actively connects to a server which then provides it with a given resource This resource could be access to files print services and so on A client to client or peer to peer model provides an enhancement to this in that it allows clients to actively seek other clients without using a server as an intermediate device There are though many issues involved in this especially related to the amount of network traffic generated by peer to peer communications and security This project will try and analyse a model for peer to peer communications for file sharing and look at models for enhancing the security of such as system Distributed peer to peer file sharing is one of the fastest growing and controversial applications of the Internet In its most basic form file sharing can occur between two computers connected via the Internet or another form of network connection Napster was one of the first applications to use peer to peer communications and Oram 2001 stated that The first application that gave the Internet community the ability to share files freely was Napster which consisted of a centralised directory server that stored shared file and addressability information of connected clients After Napster a large number of file sharing applications became widely available Forte 2001 observed that there was a rapid appearance of these new applications and stated that the majority of them
63. e an invalid username or password If they are granted access the list of files the user is sharing is sent to the server and made available to all system users When the user logs out the server deletes the shared file entries for that user from the database e Account Maintenance When logged on a user will have the ability to change their password or their public private key combination In both cases the user will submit the new details to the server for validation The server will then inform the user if the change was successful or not e File Searching Transferring Updating When logged on a user can submit search queries by filename or username to the server which will return any matches The user can select any of these files and commence file transfer by establishing a connection to the user who hosts the file The file is encrypted by the user hosting the file using a randomly generated session key which is encrypted itself using the public key of the requesting user Finally both the encrypted file and the encrypted session key are then sent At any time a connected user can update their list of files they are sharing which happens automatically when the user first logs on to the server If the user is already logged on the server deletes the shared file entries for that user from the database and writes the new entries submitted by the user 3 4 5 Server Design This section identifies the operations and functionality of th
64. e oldest Internet protocols and is used to transfer files between two computers on a TCP IP network FTP is based on the client server architecture where an FTP client is an application running on a computer that connects to a remote computer running an FTP server application When the connection between the client and server is established the client can then choose to send or receive files Tulloch 1996 provides information on FTP which uses the Transmission Control Protocol TCP to establish a connection oriented session before initialising the data transfer TCP is used as it ensures reliable network communication guaranteeing that data will be delivered intact to the destination The FTP server listens on TCP port number 21 for connection attempts from an FTP client this port is also used as for the communication control port allowing the client to send FTP commands to the server and to send the response from the server David Brown BSc Hons Computing 2002 16 2 5 Network Programming Applications that communicate over a network use an interface to interact with the communication protocols which is typically known as an Application Programming Interface API The API defines the operations that the application can call and the number of arguments that the operation requires For example the API would contain an operation used to establish a connection to a remote computer Tulloch 1996 states that out of the available APIs
65. e server application illustrating how the server application interacts with the client and the other servers The server design is illustrated in Appendix 2 and has the following parts e Registering Client Information When a new user connects to the server they will supply their username encrypted password and public modulus keys To ensure the username and public modulus keys are unique the server checks them against the existing entries in the database and notifies the client if they have been registered successfully or not If the registration was successful the new user details are written to the database and immediately replicated to the other server databases e Validating Clients When an existing client connects they supply their username encrypted password and their current IP address The server looks up the username from the database and retrieves the password and public key associated with that username The received password is decrypted compared against the password from the database and the user is informed of the result If the logon attempt was successful the username and current IP address of the user is written to the server database so the other system users can connect directly via the IP address e Recording Shared Files When a user logs on to a server they automatically send the server a list of files they are sharing The server writes this file list into the database making the files available to all other sys
66. em beyond 10 clients This issue is addressed in section 6 2 4 of this chapter Tests performed have shown that MySQL is vastly superior to Access XP especially with 10 clients were logging on simultaneously In this case it was shown that MySQL is nearly five times faster than Access XP This is likely as MySQL is focused on multiple WWW based transactions whereas Access XP is based on single user systems A weakness in current file sharing technologies especially in relation to peer to peer systems is the lack of security and authentication In the system cryptographic techniques have been used to implement this A key factor is obviously the strength of the encryption used The results of these tests show that the encryption employed in the system is not particularly strong as it would only take 12 hours to decrypt a code using eight average specification computers 6 2 Suggestions for Future Work After requirements and performance testing was carried out on the final system three points were raised that would require additional work if the system was ever to become available for public use These points involve an addition to the requirements of the client application improvements to the encryption speed and strength further performance tests and a new test that would investigate traffic generated on the network by clients David Brown BSc Hons Computing 2002 63 6 2 1 Client Application Modification Even though the f
67. er sends the Filename File size Username and User IP Address repeated until all results from the search are sent 6 Server sends FILE_END to indicate the end of the file search results David Brown BSc Hons Computing 2002 31 nt Clie n t 5 Figure 16 File Search Protocol File Transfer Protocol This protocol is used when a client wishes to download a file from another client This process is illustrated in Figure 17 Requesting Client Target Client Figure 17 File Transfer Protocol 1 Requesting client sends the message FILE_TRANSFER to the target client 2 Requesting clients sends the filename public modulus keys and username 3 Requesting client can then receive one of two responses TRANSFER_ACK Filename exists or TRANSFER_NAK Filename does not exist If the target client sends TRANSFER ACK it generates a random session key encrypts the file with it and encrypts the session key with the requesting client s public key 4 Target client sends TRANSFER_START to indicate the start of the transfer followed by the encrypted session key and the encrypted file Client Validity Challenge Protocol This protocol is used when the server wishes to test the validity of a connected client This process is illustrated in Figure 18 Client Figure 18 Change Keys Protocol 1 Server randomly selects a connected client from the local database and reads their current socket co
68. es the operations and functionality of the client application illustrating how the client application interacts with the user and the server application The Client design is illustrated in Appendix 1 e Register User Details When the client application is run for the first time it will check ifthe user has previously registered possibly using the windows registry If no previous user details have been detected the application will prompt the user to register their details username password public key and modulus key Once the details are entered the application randomly selects one of the servers connects and informs the server that a new user is registering their details It then sends the user details to the server The Server then validates these details and informs the user if they have been accepted or rejected if they are rejected the server informs the user of the reason for rejection The user may be rejected if the username or the public modulus keys are already in use in either case the user can choose a new username or regenerate the public private key combination e Logging In Out When a registered user attempts to login the client application selects one of the servers at random and connects The server authenticates their details either granting or denying them system access If they are denied access David Brown BSc Hons Computing 2002 26 the server informs the user of the reason for rejection which may b
69. esssnsssssserasssssonsssossesessess 67 8 APPENDIX 2 SERVER DESIGN usansonsssssnssossnssnnsonsnnsnnsnnsnnsonssnssonsnnsonsnnsnnsnnsnensonsnnsonsnnssnnn 68 9 APPENDIX 3 RSA ENCRYPTION MODULE ssoocoo0o0occcococss0scsccscsrssrsorsrsresrorerrsrsrerrsrerersrsrt 69 10 APPENDIX 4 BINARY ENCRYPTION MODULE uususssnssssnsnessssossnnsonsnnssnsonsnnssnsnnssensnn 72 11 APPENDIX 5 SDFS SERVER USER MANUAL cussnssossnssonsonsnnsnnennssossnnsonsnssnnsonsnnssnsonssnnnnn 74 12 APPENDIX 6 SDFS CLIENT USER MANUAL ussussossnssonsonssnsonssnssnssnnsonsnnsnnsonsnnnsnssnssensnn 77 13 APPENDIX 7 PROJECT GANTT CHART z sussnrsossnnsonsonssnsonssnssnssnnsonsnssnnsonsnnssnsnnssensnn 80 David Brown BSc Hons Computing 2002 Figures Figure Description Figure 1 Client Server Architecture Figure 2 Napster Architecture Figure 3 Gnutella Architecture Figure 4 Encryption Decryption process Figure 5 The OSI Layered Model Figure 6 WinSock Client Server Figure 7 Spiral Model Figure 8 Evolutionary Development Model Figure 9 Waterfall Model Figure 10 Multiple Server System Model Figure 11 Register User Protocol Figure 12 Logon Protocol Figure 13 Shared File List Protocol Figure 14 Change Password Protocol Figure 15 Change Keys Protocol Figure 16 File Search Protocol Figure 17 File Transfer Protocol Figure 18 Change Keys Protocol Figure 19 Database Tables and Replication Figure 20 Client Application High Level View Fi
70. ex rsl SocketNumber strUserName rs1 Username Else rsl Close Exit Sub End If rsl Close Open the global databse and retrieve this client s public and modulus keys Set rs2 New ADODB Recordset rs2 Open SELECT FROM SystemUsers Where Username amp strUserName amp GlobalDb adOpenStatic adLockReadOnly dblPubKey rs2 Pubkey dblModKey rs2 Modkey rs2 Close The randval variable is used to generate a random session key set it to the maximum value that a long integer can hold Then generate a random number from this value randVal 2147483647 challValue Rnd randVal Convert this value into a string and encrypt it strRandNum Str challValue encryptChall RSAvl enc strRandNum dblPubKey dblModKey Send the encrypted value to the selected client if client is still connected If tcpServer connIndex State sckConnected Then tcpServer connIndex SendData SESS CHALL amp vbCr tcpServer connIndex SendData encryptChall amp vbCr End If When the client replies to the challenge the value they send back is compared against the original random value that is stored in the global variable and if they do not match the server sends the protocol code SESS_NAK to disconnect the client 4 4 5 Perform File Search The file search process is instigated by a connected client who transmits the protocol code FILE SEARCH followed by the search type and the search paramete
71. g the protocol code NEW USER is received followed by the username encrypted password and public modulus keys The server then validates the username and keys by checking if they are already in use If they are in use the relevant protocol code is sent to the server to inform the client that they will need to change their details If not in use the client information is written to the global database and the client is informed The following code illustrates this process Use the db connection and validate this info David Brown BSc Hons Computing 2002 47 Set rsl New ADODB Recordset rsl Open select username from systemusers where username amp userName GlobalDb adOpenStatic adLockReadOnly If rsl EOF False Then there is a record match in the table username in use Inform the connected client tcpServer Index SendData NEW_USER_NAK vbCr tcpServer Index SendData USER_EXIST amp vbCr rs1l Close Exit Sub End If Check if the pub mod key combo is in use Set rs2 New ADODB Recordset rs2 Open SELECT modkey FROM systemusers Where pubkey amp pubKey amp min GlobalDb adOpenStatic adLockReadOnly If rs2 EOF False Then there is a record match in the table keys in use Inform the connected client tcpServer Index SendData NEW_USER_NAK vbCr tcpServer Index SendData PUB_EXIST vbCr rs2 Close Exit Sub End If Now decrypt the password using the pub amp mod keys de
72. g to current existing file sharing technologies This chapter also highlights the available software process models According to Sommerville 2001 A software process is a set of activities and associated results that lead to the production of a software product Each of the software process models illustrates a different approach to developing a software product Each model will be reviewed and the most appropriate method will be used to plan and develop the project 3 2 Software Engineering Methods In any serious software project a software process model is used This allows the management of all aspects involved in the production of the software from the first stage of specifying the proposed system through to final stage of maintaining the system when it is complete and in use Three of most commonly used software process models illustrated by Sommerville 2001 will be evaluated with the most appropriate model selected for this project The three models are Spiral development Evolutionary development and Waterfall Although these are different process models each has common stages l Specification Defines the functionality and operation of the software set by customers and potential users 2 Design and Implementation The software is developed so it functions as defined in the initial specification 3 Evaluation The finished software is evaluated so it meets the functionality and operation defined in the specificat
73. gure 21 Register User Details Form Figure 22 Main Client Form Figure 23 File Search Results Figure 24 Server Application High Level View Figure 25 Automated Test Program Figure 26 Graph of Access XP and MySQL Times Figure 27 Graph of Client Test Results Figure 28 Graph of Encryption Speed Tests Tables Table Table 1 Table 2 Table 3 Table 4 Table 5 Description Access XP and MySQL Test Results Client Test Results Encryption Speed Test Results Key Permutations Decryption Times Acknowledgements I would like to thank Dr William Buchanan for his help and guidance throughout the project I would also like to thank my fianc e Claire for her patience and support David Brown BSc Hons Computing 2002 7 1 Introduction 1 1 Scope and aims of the project The main aim of this project was to create a system that allows files to be distributed over a wide area and to be shared in a secure manner The system should allow clients to search for other clients that have required files and provide them with a mechanism to share those files securely It involves research in the following subjects e Distributed File System Architectures e Security Techniques e File Transfer Protocols e Network Programming Methods e Database Technologies This research will be applied in the creation of a final working system which will be tested and evaluated 1 2 Background Most applications on the Internet currently us
74. he relevant procedure is executed using the variable holding the received string This process is shown in the following code example Read incoming data into the str variable strip the server command off it and strip the other pieces of data off the string ServerConn GetData recString get the length of the received string stringLen Len recString For count To stringLen get the character workstring Mid recString count 1 check to see if this is a returncode signifies end of string If workstring vbCr Then The server has a protocol command code so strip the code off the received string and execute the relevant procedure recString Right recString stringLen count Select Case serverCommand Case NEW USER ACK new user registration accepted Case NEW USER NAK new user registration rejected End Select End If append this to the server command variable serverCommand serverCommand amp workstring Next Count David Brown BSc Hons Computing 2002 36 In addition to the ServerConn WinSock control the client application has two more WinSock controls e ClientSend Creates a connection to a remote client to send a file This WinSock control supports multiple connections e ClientRecieve Creates a connection to a remote client to receive a file This WinSock control supports multiple connections The server application has three WinSock controls in total e TcpServer Creates
75. ich began with a solution to the problem of transmitting data via a socket connection Detailing the implementation of the system was achieved by adopting a high level view of the client and server applications This allowed the implementation of each important section of the application to be fully explained and illustrated with a code example David Brown BSc Hons Computing 2002 54 5 Testing and Analysis 5 1 Introduction It is important to consider the levels and methods of software testing from the initial stage of unit testing through to the final stage of validation testing Rakitin 1997 provided a great deal of information on these levels which form a hierarchy The base of the hierarchy is unit testing which is intended to locate bugs in the logic and algorithms in the individual modules Following unit testing is integration testing the objective of which is to find bugs in the interfaces between modules The final stage is validation testing which determines if the software actually meets all the requirements set at the beginning of the software development phase These testing levels are explained further in this chapter 5 2 Unit Testing The purpose of unit testing is to locate bugs in separate modules and is generally integrated with the coding of the module During unit testing the separate modules in both applications were tested separately as they were being developed The tests that were performed adopted
76. inal client application met the original requirements specification there is a need for an additional feature to the application Currently any files shared by a client are available to every other client connected to the system Even though only authorised clients may use the system a client may not wish to share their files amongst the entire population but only to a select few For these reasons the client application should be modified to include a feature that will enable a list of authorised clients to be created so only clients on this list will be able to download files from the client 6 2 2 Encryption Speed The Research of Aoki et al 2000 outlined a new encryption algorithm called Camellia which has an encryption speed that is far superior to the current algorithm employed in the system On a Pentium III 500 MHz an encryption rate of more than 276 Mbits per second was recorded using Camellia During performance testing a computer with the same specification was used to obtain the encryption rate of the current encryption algorithm The test resulted in an encryption rate of just under five Mbits per second 6 2 3 Encryption Strength Brassard et al 2000 and Singh 2000 provided information on Quantum cryptography which is completely different from any other type of encryption in that it is completely unbreakable Quantum cryptography is based on Quantum theory meaning that it is completely impossible for a third p
77. ion 4 Evolution The software must be able to evolve to meet changes in technology and user requirements 3 2 1 Spiral Development The spiral model is shown in Figure 7 and represents the software development process as a spiral instead of a sequence of activities The spiral starts at the centre with each loop representing a phase of the development In each phase of the spiral objectives are identified followed by risk analysis development and evaluation The main advantage of the spiral model is there are no fixed phases such as specification or design which allows the software to be adapted according to additional requirements David Brown BSc Hons Computing 2002 21 Risk ES Analysis Prototyping Requirements and Development and o Development planning Verification Review iL J Figure 7 Spiral Model 3 2 2 Evolutionary Development This model involves creating an initial version of the software and then allowing the target user to change the specification advancing the software through multiple versions until the final version is developed In this model the specification development and validation stages are conducted concurrently This model is illustrated in Figure 8 The advantage of this model is that the software can be produced in incremental stages with each stage having a revised specification from the target user However this model suffers from two m
78. ions allowed experimentation with each UI in order to find the right balance of simplicity with functionality for each application Additionally the creation of prototypes decreased the overall implementation time for each application as the functionality of the controls on each form were added during the development phase of the project 3 4 9 Technology Choices The technologies used to develop a software project may have a negative impact on the progress of the project so must be selected carefully The main decisions on the technologies used during this project relate to the design and implementation stages There were two possible candidates for the programming language to develop the applications which were Visual Basic VB and Java VB is considered the best application for Rapid Application Development RAD while Java is platform independent and has a large number of networking libraries available VB6 was used David Brown BSc Hons Computing 2002 34 instead of VB NET as VB NET is radically different as it fully supports objects and multithreading but no longer supports WinSock as a means for communicating over a network These issues combined with the availability of the language meant that VB NET would not be a viable option for this project InstallShield for Windows is an independent package that was used to create the installation program for both Client and Server applications It allows entries to be made to the Wi
79. is of paramount importance Whenever information is transmitted across a network it is vulnerable to tampering and eavesdropping Coulouris ef al 2001 state that cryptography is used to maintain the integrity and secrecy of information when it is exposed to such attacks 2 3 1 Cryptography Singh 2001 provides a definition of cryptography which is derived from the Greek word kryptos meaning hidden and its aim is to hide the meaning of a message Encryption typically uses a standard well published algorithm and varies the electronic cryptographic key A cryptographic key is a mathematical parameter used in an encryption algorithm so the encryption process cannot be reversed without the key As much as possible the encryption algorithm should be robust so that it does not have any weaknesses that can be exploited The process of encryption involves transforming plaintext into ciphertext with the reversal of this process called decryption Figure 4 illustrates that both the encryption and decryption is controlled by the cryptographic key There are two main types of encryption algorithm in use today The first uses a secret encryption key and the second uses public private key pairs Cryptographic Cryptographic OA O y iphert ext y i Figure 4 Encryption Decryption process David Brown BSc Hons Computing 2002 13 2 3 2 Secret key In secret key cryptosystems a single key is used for both encryption and decry
80. is purpose Figure 1 illustrates this model which is based on a central server that is responsible for providing a remote file service to clients On receipt of a valid client request the server executes the appropriate operation and sends a reply back to the client This type of interaction is known as request response or interrogation Server 1 Request IE 2 Response E 1 S s a h Client Client Client Figure 1 Client Server Architecture 2 2 2 Napster Architecture The Napster web page 2002 provided information on the Napster architecture which is based on a central directory server that contains addressability information on the connected clients and information on the files they are sharing This architecture is illustrated in Figure 2 The central server offers connected clients the facility to search David Brown BSc Hons Computing 2002 11 for a required file and assists in the identification of the most suitable location from which to download that file Kant et al 2002 stated that the centralisation of the directory server allows file searches to be performed relatively fast with the IP address of clients that host the required file passed to the requesting client The file download can then take place between the requesting client and the client who hosts the file via TCP IP Directory Server 1 Search a 2 Locations 3 Request 4 Response y 2 Client O Client
81. is section the current number of shared files is shown There are three control buttons in this section e Change Directory Allows the user to change their shared file directory to another directory e Update List If the user was to add some files to their shared file directory to submit these changes to the SDFS Server to make them visible to other system users they need to click this button e Delete File Simply deletes the selected file and automatically updates the shared file list on the SDFS Server 12 4 File Search This section displays the results of file searches which are performed by the name of the file or the name of the user holding the files All results from a search are displayed in the list by file name file size and the username of the user who is holding the file To download a file the user can either click on the filename in the list and click Download File or double click the filename in the list 12 5 File Transfers This section shows the progress of file uploads and downloads Each entry has a unique identifier file name file size username and upload download status The status of an upload can be e ENCRYPTING SDFS Client is encrypting the requested file This is then followed by a send progress indication as the amount of data sent is constantly updated and displayed e COMPLETED SDFS Client has successfully sent the file If an error occurs during the upload process such as
82. is triggered by a timer that is running on the main server form that has a 60 second delay The server first checks if there are any clients connected as there would be no point continuing if there are no clients to validate If there are connected clients the server picks one randomly from the local database and obtains their current socket number and username which is used to obtain the public modulus keys from the global database The server then generates a random number and stores it in a global variable This random number is then encrypted using the public modulus keys and the server then sends the protocol code SESS_CHALL followed by the encrypted number This is achieved using the following code Check how many users are connected if none there is no point continuing If lblConnClient Caption 0 Then Exit Sub End If Now randomly select a connected client from the local database Set rsl New ADODB Recordset rsl Open SELECT FROM ConnectedUsers LocalDb adOpenStatic adLockReadOnly Get a count of the records in the recordset clientRec rsl RecordCount Ensure that the number zero is never generated Do While clientRand 0 Get a random number from the recordset clientRand Int Rnd clientRec 1 Loop rsl MoveFirst rsl MovePrevious rsl Move clientRand connIndex rsl SocketNumber strUserName rs1 Username David Brown BSc Hons Computing 2002 49 If rsl EOF False Then connInd
83. key FROM SystemUsers Where Username amp userName amp GlobalDb adOpenForwardOnly adLockOptimistic pubKey rsl Pubkey modKey rsl1 Modkey Decrypt the password using the pub and mod keys decPasswd RSAvl dec encPasswd pubKey modKey If decPasswd rsl Password Then password valid This user is now validated so check if their keys are already in use rs2 Open SELECT Pubkey FROM SystemUsers Where Pubkey amp newPubKey amp GlobalDb adOpenStatic adLockReadOnly Check if this recordset contains any records If rs2 EOF False Then Send the protocol command code to indicate that the keys are in use tcpServer Index SendData KEY _NAK amp vbCr tcpServer Index SendData PUB EXIST vbCr rs1 Close rs2 Close David Brown BSc Hons Computing 2002 52 Update the fields with the new values rs3 Open Update SystemUsers set pubkey newPubKey amp modkey amp newModKey amp Where Username amp userName amp GlobalDb adOpenDynamic adLockPessimistic Send the protocol command code to the client to indicate a successful key change tcpServer Index SendData KEY ACK amp vbCr Else password invalid Send the protocol command code to the client tcpServer Index SendData PASSWD_NAK amp vbCr tcpServer Index SendData LOGON_PASSWD vbCr rs1l Close Exit Sub End If 4 4 7 Update Client Shared File List This process begins when
84. l View 4 4 1 Initialise Server When the server is started it first creates connections to its local and global databases and erases any entries from the two tables in the local database The server then begins to listen for any client connections 4 4 2 Accept Client Connection When a client connects to the server a new socket connection is created In order to reuse the socket numbers a global array is used which is searched for the first zero value indicating a free number The socket is created using the position in the array and as this number is now in use the array value is set to one Finally the global variable used to keep a count of the number of users connected is incremented and updated on the main server form The following code illustrates this process In order to reuse connections the clientConn array is used If the value in the array is 0 it s position is used to create a winsock object If the value in the array is 1 it is in use so try another one For i 1 To 2000000 If clientConn i 0 Then Found an empty value Load tcpServer i tcpServer i Accept requestID clientConn i 1 Exit For Found one so break from the loop End If Next i Get a count of all active client connections connCount connCount 1 Update the client connection label lblConnClient Caption connCount Once the connection is created the client will attempt to either register or logon Ifthe client is registerin
85. nclusions 6 1 Evaluation of Achievement The aim of creating a fully functioning system that allows files to be distributed over a wide area and to be shared in a secure manner was completed successfully All the features specified in the Requirements Analysis amp Design chapter of this report were implemented in the final system The client application gives users the ability to connect to a server and allows them to send that server a list of their shared files therefore making their files available to all other system users Users are free to query the server for any files they may require and when a file is found 1t can be downloaded from the other user securely as the file is encrypted before transmission The server application allows users to connect and either logon or register Once connected the server records the shared file list of each user and allows connected users to query the list of files on the local server and any other active servers in the system The server has the ability to authenticate connected users by performing a validation test to which only a valid user can answer correctly A major objective of the system was to make it scaleable It can be seen from Figure 27 that the relationship between the number of clients and the response time is almost linear This shows that the system is scaleable within the test parameters Unfortunately due to time and resource constraints it was not possible to test the syst
86. ndows registry regarding the installation directory of the application and allows required application DLLs to be registered in the Windows system directory As the server application is designed for use with an additional two servers aDBMS with replication capabilities was required Replication in Microsoft Access XP is limited as it requires the use of an additional application called Replication Manager that can only replicate tables after a time interval with the lowest interval being fifteen minutes Information on the replication capabilities of MySQL was obtained from the MySQL web page 2002 which justified the selection of MySQL as transaction based replication is fully supported There were three possible technologies for database access DAO RDO and ADO which are both Microsoft technologies Since ADO is the successor to DAO and RDO the other two technologies it is the only one that has a future Another benefit of using ADO is the application will be completely interoperable with other database technologies through an ODBC driver via SQL statements 3 5 Conclusions This chapter has covered the main decisions that were made during the analysis and design phase of the project These decisions such as using the waterfall software process model using the multiple server architecture and using PGP for system security had a fundamental effect on the implementation of the system which is covered in the next chapter David Br
87. nnection number and public modulus key values David Brown BSc Hons Computing 2002 32 2 Server generates a random value encrypts it using the public modulus keys and sends the message SESS_CHALL to the client followed by the encrypted value 3 Client then decrypts the value and sends the message CHALL_REPLY followed by the decrypted value 4 Server compares the received decrypted value with the original value and sends either SESS_ACK or SESS_NAK depending on the result of the comparison If the server sends SESS_NAK the client is disconnected from the server 3 4 7 Database Design There were two candidates for the database management system relational or object oriented The relational database was selected for use as they are fast stable and widely available Additionally the data that will be stored in the database is not complex MySQL was chosen for the database management system the justification of this decision can be found in the Technology Choices section later in this chapter From the identification of the server operations it is clear that each server in the system would require two databases a local database and a global database e The global database will store the details of all registered system users such as username password and public modulus keys When a user registers at a server their details are written to this database and immediately replicated to the other server s global database This
88. ns than the 20 bit key Therefore the length of time it takes to break a 20 bit key can then be multiplied by 4096 to obtain the time to break a 32 bit key David Brown BSc Hons Computing 2002 61 On a Pentium 4 1 7 GHz processor it takes 24 minutes to break a 20 bit key Therefore it would take 98 304 minutes 24 x 4096 to break a 32 bit key on this machine which is 1638 hours 68 days Using information from Buchanan 2000 computer processing power increases on a regular basis If a computer with an average specification were to take 68 days to break this code it would be safe to assume that the processing power would be at least doubled in one year therefore it would only take 34 days to break the code in the next year Not only is the increase in processing power a factor in reducing the time it takes to break the code but also the use of more than one processor working in parallel Each processor could then be allocated a number of keys to check against the encrypted message Each processor would then work independently on their key allocation Table 5 illustrates the time it would take to decrypt the code in minutes using parallel processors and an increase in computing power The table shows that with eight processors it would take only six years before the code is decrypted within 12 minutes Even without an increase in processing power 1t would take eight processors 768 minutes just over 12 hours to decrypt the code
89. option is enabled the user can view this log file The server records the date and time clients perform certain functions including connecting updating shared files changing password and changing public private keys 11 3 Server Connections This tab contains two sections one for each of the other SDFS Servers in the system Both these sections contain the same controls which have the following functions e The IP address remote port and local port of the remote server connection can be changed but this can only be done when the connection is idle and the server password is supplied e Information about the remote server connection can be saved to a log file information on connection attempts lost connections etc e If the remote server connection is listening connected or attempting to connect this is shown in the remote server connection status 11 4 ODBC Data Sources This tab shows the status on the ODBC connections to the two local database tables and the two database tables in the remote servers The user has the ability to change the DSN of these ODBC data sources but only when the SDFS server is inactive and a valid server password is entered David Brown BSc Hons Computing 2002 17 12 Appendix 6 SDFS Client User Manual 12 1 Installation Getting Started Double click the setup exe to install SDFS Client and follow the prompts When the installation process has finished an icon for SDFS Client
90. own BSc Hons Computing 2002 35 4 Implementation 4 1 Introduction This chapter highlights the implementation of the system corresponding to the design specification outlined in the previous chapter concentrating on the client and server applications A high level view of these applications is adopted which illustrates the integration of the system protocols This chapter also highlights a solution to the problem when sending data using a socket connection 4 2 WinSock Programming In the theory chapter of this report Davis 1995 highlighted that when data is sent using sockets it is sent in a stream of bytes which has no record delimiters in the data stream This meant that 1f an application were to depend on records of a fixed size being sent the application must be written to provide application level headers in the data stream as the packet size will not be preserved on the receiving end The main WinSock connection in the client application ServerConn is used to create a connection to the server and allows the client to issue commands to the server In order to understand responses from the server each received string is stripped down into its component parts This is performed by obtaining the length of the received string removing one character from the string at a time and storing each character in a variable until a control code is found When one is found any remaining characters in the string are stored and t
91. ption The encryption key cannot be revealed to anyone other than the sender and recipient Buchanan 2000 states the two most popular secret key techniques that are in use today are DES Data Encryption Standard and IDEA International Data Encryption Algorithm 2 3 3 Public key In public key cryptosystems each user has two related keys a public key and a private key The private key is only known by the user and is used to decrypt messages encrypted by that user s public key which is freely available to anyone Public and private keys are symmetrical so code encrypted by one key can be decrypted by the other This means that knowing the public key does not allow a user to deduce the corresponding private key Singh 2001 outlines that anyone can encrypt a message with a user s public key and the only person that can decrypt it is the intended recipient as no one else has access to the required private key Buchanan 2000 describes how authentication can be performed with public key cryptosystems This is achieved by encrypting a message with the sender s private key effectively creating a digital signature of the message which the recipient can check by using the sender s public key to decrypt it This proves that the sender was the true originator of the message and it has not been altered by a third party The most popular public key technique is RSA named after its creators Rivest Shamir and Adleman 2 3 4 Pretty Good
92. puting 2002 41 Case 2 filesize recSize searchString searchString workstring Case 3 Username recUser searchString searchString workstring Case 4 User ip address recIP searchString searchString workstring Add this received search into the recordset with rs2 AddNew Fields Item Filename recFile Fields Item Filesize recSize Fields Item Username recUser ce ecIP Fields Item Update End With IP 4 3 4 Send File to Client This process begins with the requesting client sending a connection request to the target client s ClientSend WinSock control When this is detected the target client creates a new instance of the socket and accepts the connection from the remote client The remote client then sends the protocol code FILE TRANSFER the name of the required file their public modulus keys and username The target client then checks if the requested file exists in the shared file directory If not the protocol code TRANSFER NAR is sent to inform the requesting client that the file no longer exists If the file does exist the target client then generates a random 32 bit key using the following code Dim keyVal As String Dim randVal As Integer Dim i As Integer Loop 32 times and generate a random 0 or 1 For i 1 To 32 randVal Rnd 1 Add the random number to the key string keyVal keyVal amp randVal Next i getEncryptionKey
93. r The server obtains the username of the requesting client so to omit any files shared by this client in the search The server then constructs the SQL statement based on the search type specified by the client by either file name or username The server informs the client that the file search results are about to be sent and then conducts the file search first on its own local database and the local databases of any other connected servers When all the results from the file search have been sent the server sends the protocol code FILE END to the client The following code shows an example of this process The index of the tcpServer winsock is used to find this client Set rsl New ADODB Recordset rsl Open SELECT Username FROM ConnectedUsers Where SocketNumber amp Index amp LocalDb adOpenStatic adLockReadOnly if the recordset contains no records a major failure has occured If rsl EOF True Then Send the protocol command code to disconnect this client tcpServer Index SendData SESS NAK vbCr rsl Close Exit Sub End If Store the username of this client David Brown BSc Hons Computing 2002 50 userName rsl Username rsl Close Constuct the SQL statement according to the search type If searchType FILE NAME Then searchSQL SELECT Filename Filesize ConnectedUsers Username IPAddress FROM SharedFiles ConnectedUsers Where ConnectedUsers Username SharedFiles Username AND Filename like
94. r Science Vol 2012 Springer Verlag 2001 pp 39 56 Berlin Germany Bahie Eldin M A amp Omar A A Complexity measure of encryption keys used for securing computer networks Proceedings 14th Annual Computer Security Applications Conference Cat No 98EX217 IEEE Comput Soc 1998 pp 250 5 Los Alamitos CA USA Begg C Connolly T amp Strachan A 1998 Database Systems A Practical Approach to Design Implementation and Management California Addison Wesley Brassard G Lutkenhaus N Tal Mor amp Sanders B C Security aspects of practical quantum cryptography Conference Digest 2000 International Quantum Electronics Conference Cat No 00TH8504 IEEE 2000 pp 1 Piscataway NJ USA Buchanan W 2000 Distributed Systems and Networks London McGraw Hill Comer D E 1997 Computer Networks and Internets New Jersey Prentice Hall Cornelisse M 2000 Atomic clock URL http www planetsourcecode com vb scripts showcode asp txtCodeld 1 1905 amp IngWId 1 01 October 2002 Coulouris G Dollimore J amp Kindberg T 2001 Distributed Systems Concepts and Design San Francisco Addison Wesley Daniel J 2000 Accurate Visual Basic 6 0 timer URL http www planetsourcecode com vb scripts showcode asp txtCodeld 13557 amp IngWId 1 01 October 2002 Davis R 1995 Windows NT Network Programming New Jersey Prentice Hall Doherty S P2P taps the enterprise Network Computing vol 13 no 6 18 March 2002
95. rConnections il Client Information Current Number of Connected Clients 0 Total Number of New Clients 0 Total Number of Existing Clients 0 Client Session Challenge Information Number of Clients Challenged 0 Number of Clients Validated 0 Number of Clients Invalidated 0 Exit Server There are three tabs on the SDFS Server window Client Connections Server Connections and ODBC Data Sources David Brown BSc Hons Computing 2002 76 11 2 Client Connections On this tab there are four sections Client Information Client Session Challenge Information Connection Status and Client Options Client Information This section provides information on the number of clients currently connected to the server and the number of new and existing clients there have been since the server was started which is shown by the uptime counter in the connection status section Client Session Challenge Information Every 60 seconds the server will randomly choose a connected client and challenge their session authenticity by generating a value and encrypting it with the selected client s public key This section provides information on these challenges such as the number performed and results of each challenge Connection Status This section simply displays the status of the server and how long the Server has been active Client Options This section allows the server to write client data to a log file and if this
96. rall quality of the software to be measured by how well the software meets the user requirements 5 5 Performance Testing After unit integration and requirements tests were performed on the system and the bugs found by these processes repaired the system was then subjected to a number of performance tests Several researchers have outlined tests for performance testing with peer to peer protocols such as Scarlata Levine amp Shields 2001 who compared the performance of peer to peer protocols against the client server type protocol They found that transfer times were doubled due to an increase in traffic between peers This will not be an issue in this system as the only traffic occurring between peers other than three protocol codes is actual file data The objectives of the performance tests are to indicate the scalability robustness and security of the system through detailed analysis of the test results In total there were four tests devised for the system e Database Tests e Client Speed Tests e Encryption Speed Tests e Encryption Strength Tests In order to measure the performance of the database and the client versions of the client and server applications were developed specifically for testing These versions David Brown BSc Hons Computing 2002 56 included code modified from Daniel 2000 that enabled the application to time certain events using a microsecond timer measuring them by millionths of a
97. rchitecture there is no central server to store user information as clients connect directly to one another This does not meet the system requirements either as there would be no method to validate the authenticity of a client The remaining Napster architecture will be used for the system model This architecture meets the requirements of the system as the central server can store user information to validate client authenticity In addition files are shared between the clients as the central server offers connected clients the facility to search for a file and provides the address of the client hosting that file 3 4 2 System Model The Napster architecture was used as a basis for system design out of which three system model candidates were developed 1 Single Server This model consists of one server and when a client successfully connects their session details and files they are sharing are recorded in the database When connected the client is free to interrogate the server for any required files with the connection details of clients that hold those files returned Unfortunately this model suffers from a serious problem as there is a central point of failure for the system So if the central server was to become unavailable so would the entire system This could be the result of a hacker launching a denial of service attack This bombards the server with requests that slows it down to the point where no one can gain access
98. rom the original sourcecode created by Kenny Lai Available from PlanetSourceCode Extremely102235752002 zip http www planet source code com vb scripts showcode asp txtCodeId 36457 amp lngWId 1 Private Sub SaveBinaryArray ByVal Filename As String WriteData As Byte Dim t As Integer t FreeFile Open Filename For Binary Access Write As t Put t WriteData Close t End Sub Function ReadBinaryArray ByVal Source As String Dim bytBuf As Byte Dim intN As Long Dim t As Integer Dim n As Long t FreeFile Open Source For Binary Access Read As t ReDim bytBuf 1 To LOF t As Byte Get t bytBuf ReadBinaryArray bytBuf Close t End Function Public Sub EncryptFile Source As String Destination As String Password As String Dim ByteIn As Byte ByteOut As Byte ByteIn ReadBinaryArray Source ReDim ByteOut LBound ByteIn To UBound ByteIn As Byte Dim i As Long j As Long Dim PL As Integer PL Len Password Dim ChrBNow As Integer Dim PosNow As Integer Dim TempByte As Integer Decrypt Dim TempDByte As Integer ByteFinal As Integer For i LBound ByteIn To UBound Byteln If disconnected from the server stop encrypting If frmMain ServerConn State 0 Then Exit Sub End If PosNow i Mod PL ChrBNow AscB Mid Password PosNow 1 1 Xor 17 TempByte ByteIn i ChrBNow Mod 256 TempDByte TempByte ChrBNow If TempDByte lt 0 Then ByteFinal 256
99. rses 54 5 1 INTRODUCTION a A ta 54 5 2 UNT TESTING iia 54 5 3 INTEGRATION TESTING Frere eoir eseo an raroa eE E E E EE ra gr NAN dr ss 54 5 3 1 User Interface Testings snieni i n 55 5 4 REQUIREMENTS TESTING oreore an EENE E E EEEE REEE E E 55 5 5 PERFORMANCE TESTING sessessccssssscsseesersnessesscsenscnonenssacsonecsonsnauscnsseseosensesensstsesnesenseneneenonens 55 5 5 1 Automation Test Application cneeseneensensensesnensenseeneenensneneesnensennnenensennnene nennen 56 59 2 Database Test ta cfs eid A A to is 56 39 3 Client Speed Lei ita id 38 39 4 ENCKYPUON Speed Tests iii liar tte nd s 59 39 9 Bneryption Strength Tests aaa ari 60 5 6 CONELUSIONS sts ana asien altea 61 6 CONCLUSION S TE E ETT E EET linie 62 6 1 EVALUATION OF ACHIEVEMENT 30 me eE E E EE E EEEE A ER RAEE 62 6 2 SUGGESTIONS FOR FUTURE WORK penna a o EARR REE E E E RE 62 6 2 1 Client Application Modification useensessensessersensesnensensnenenesnensennnse sense nennen 63 6 2 2 ENneryphon Ped ERE A RA E a EA ee 63 0 2 3 Eneryplion Strength RE E E A EEA OE a 63 6 2 4 Further System Performance 1CStlS semersrerrarsrarerrereresrsrererrererrsrererrrrererr sr er ere raser nennen 63 6 2 33 Network Traffic Tes ic 64 REFERENCES osd vovsissssvssssdssvsssnsuessssssessssesssoeseossesssnssesessderosesedssnsessedesvsssesdeneddssessesesssersesessessssessssssened 65 7 APPENDIX 1 CLIENT DESIGN b svssdes vovssssssssessesesbesssvosssvsnsosiesssnesvsnor
100. rver attempts to write the shared file list to the local database 5 Server sends either SHARED ACK or SHARED_NAK depending if the shared file list was successfully written to the database or not Change Password Protocol This protocol is used when an existing user is connected to a server and they request to change their password This process is illustrated in Figure 14 Figure 14 Change Password Protocol 1 Client sends the message PASSWD_CHNG to the server 2 Client sends username encrypted old password and encrypted new password 3 Server looks up the username from the database and retrieves old password public and modulus keys associated with that username from the global database 4 The received old password is decrypted and compared against the password from the database Server sends either PASSWD_ACK or PASSWD_NAK depending on the result of the comparison of the received old password against the global database password If PASSWD_ACK were sent to the client their new password would then be written to the global database 5 If PASSWD_NAK is sent there is only one David Brown BSc Hons Computing 2002 30 possible reason for the rejection so the server sends LOGON_PASSWD to inform the client that the incorrect password was supplied Change Keys Protocol This protocol is used when an existing user is connected to a server and they request to change their public modulus keys This process is illu
101. second The server application was given a timer to assess the length of time for the details of a connected client to be written to the local database The client application was given three timers to assess the time to logon to the server the time to update list of shared files and the time taken to receive the results from a file search Additionally the database tests required a number of clients to simultaneously logon to the server and the and client speed tests required that a number of clients were to simultaneously login update their shared files and submit a file search In order to achieve this an automated test application was developed which is discussed in the next section 5 5 1 Automation Test Application This application used code modified from Cornelisse 2000 to access an atomic clock web page so the clock used to time the tests running on each computer would be synchronised The automation application was able to access the client application controls by using the Application Programming Interface API of Windows which enables an application to locate controls situated on a window This is achieved by obtaining the handle of the parent window then accessing the relevant control as they are all children of the parent window and stored in a collection of controls The user coordinating the testing would obtain the handle of the client application window by using the Grab Window feature They would then specify the
102. serName Then David Brown BSc Hons Computing 2002 37 strCont MsgBox SDFS Client has detected that you are not registered do you want to register now vbInformation vbYesNo If strCont End Else vbNo Then frmRegister Show End If Else Unload frmRegister frmMain Show End If If the required entry is not found then it is clear that the user is unregistered so the form shown in Figure 21 is displayed to prompt the user to enter their details Register User Details Connection Status Password Re Enter Password Shared File Directory c Program Files SDFS Client Shared Browse Public Key 30149033 Private Key 25813337 Modulus 33260147 Regenerate Keys Submit Figure 21 Register User Details Form This form sets the shared file directory to the installation directory of the client application and generates a public private key set which the user can regenerate if required These keys are generated using the CreateKeys procedure of the RSA module which is modified from the code supplied by Griffths 2000 and attached in Appendix 3 Once successfully registered with the server the form shown in Figure 22 is presented to the user This same form is displayed if the entry is found in the Windows registry when the client application is started SDFS Client File View Help E Connection Status Filename Filesize Figure 22
103. so on e Conclusions This defines whether the main aims have been met and how they have been met It also discusses future work David Brown BSc Hons Computing 2002 10 2 Theory 2 1 Introduction Before the design of a secure file sharing application begins there are five main areas to be considered 1 Distributed File System Architectures It is important to consider the available system structures to discover which is the most suitable 2 Security Cryptography is a technique used to maintain consistency and secrecy of data which has many different methods that deserve consideration 3 File Transfer Protocols The application requires the transfer of data between two devices so the format of the data transfer must be researched 4 Network Programming As the application will communicate over a network available network programming techniques must be considered along with techniques for improving performance 5 Database Technologies The application will require storage to a database so the available database technologies must be researched to discover the most suitable Technologies for communicating with a database are also considered 2 2 Distributed File System Architectures 2 2 1 Client Server Architecture A distributed file system allows a file structure to be stored over one or more file servers Kantet et al 2002 revealed that the client server architecture is the most widely used for th
104. ssions In a process invisible process to the clients the server randomly selects a connected user from the database and obtains their current socket number and public modulus keys The server then generates a random value encrypts it with the public modulus keys of the selected client and sends the encrypted value to the client The client will decrypt the value using their private key and send the decrypted value back to the server for comparison If the decrypted value received from the client does not match the original the user is disconnected from the system e Other Server Connections When a server is started the administrator can attempt to connect to the other servers manually or allow the server to attempt to connect automatically If the automatic connection is chosen the server will attempt to establish a socket connection to the other servers every five seconds When a socket is not attempting to connect to a server it will listen for a connection This way if all servers in the system are set connect automatically they will all do so within a relatively small amount of time When a socket connection is established from one server to another an ODBC connection is also created Now every file search submitted by clients connected to either of these servers is queried first in the local database of the server followed by the other server s remote database If a server were to become unavailable the servers connected to it woul
105. stra ii nieta rica iaa 35 4 3 CEIENT IMBEEMENT ATION 4232 BE 2 e A e Er a E e eer a AAT 36 LIA Logon to SEVE on Asa a a e E a E e e a aeia i ANNA rese en 36 LIZ Sendas hared Fle Aast oi unse es e a ones E a aaa 39 LI gt 2SUDMIE Ale Carchi a vs ar a oe e a a a chee 40 4 34 ASCNG Fie e e e ages Me css nih een e e r a eek 41 David Brown BSc Hons Computing 2002 5 43 3 Receive Fue from Client rererere aaas e e e i tees 43 43 0 Authenticate D tails acatar a a aeiee 44 4 3 7 Change Password Public key uneseensessensessensensensensneneeneesnensennnnennnen nn nennen 45 4 3 8 Change Shared File Directory s s mmersrrsrsrsrrrrrrerrsrsrererrererrsrererrrrsrerrsr er ere Reese ere rean r rr rna 45 4 4 DER VER IMPLEMENTATION essen E E TE EANA R REN OSA ENERE STESA ARESE 45 44l IMiti lise Server ali at a a a Gali heen 46 4 4 2 Accept Client Connections inuna eee eai ikose 46 44 3 CONNCCELO DOUE o E AIER EE E E A AE 48 4 4 4 Challenge Client Session ceeeeseseessensessensesnensensnnensnnneneennensennnsensen nennen 48 443 Berform PileSearch acacia onen Bass 49 4 4 6 Client Password Key Change cnneeeeeeensensensensensensensee nennen 50 4 4 7 Update Client Shared File LiStisssmsvoserrsrrsrsrsrerrsrsrererrererrsrerererrsrerrsr sr ere rer rss nennen 52 4 5 CONCLUSIONS il E 53 5 TESTING AND ANALYSIS u 0 csccsssscsssscssscesecosscesescsssnessssnsesesssesessssenessssseesesscesessssenessesse
106. strated in Figure 15 Figure 15 Change Keys Protocol 1 Client sends the message KEY CHNG to the server 2 Client sends username encrypted password and new public modulus keys 3 Server looks up the username from the global database and retrieves the password and the old public modulus keys 4 The received password is decrypted using the old key values and compared against the password from the global database Server sends either KEY_ACK or KEY_NAK depending on the result of the comparison of the received password against the global database password If KEY_ACK were sent to the client their new public modulus keys would then be written to the global database 5 If KEY _NAK were sent the server would then send a message to the client identifying the reason for the rejection There are two possible messages LOGON_PASSWD invalid password or PUB_EXIST public key already in use File Search Protocol This protocol is used when an existing user is connected to a server and they submit a file search to the server This process is illustrated in Figure 16 1 Client sends the message FILE_SEARCH to the server 2 Depending on the search type chosen the client sends either FILE_NAME followed by the filename or USER_NAME followed by the username 3 Server searches its local database and the local databases of the other servers 4 Server sends FILE_START to indicate the file search results are being sent 5 Serv
107. t and scaled up to ten clients all performing the same tests simultaneously Again this gave an indication of how scalable the system would be in a working environment as it would be possible that the final system would have a large amount of users performing various actions at the same time In each test the client performed each test ten times with a delay of five seconds per logon to obtain an average time Each test was repeated twice in order to acquire an average for the entire test Table 2 shows the average times to write the user details for both databases which are combined in the chart featured in Figure 27 The results of these tests illustrated the fact that the system proved to be scalable and robust as the system continued to function within acceptable parameters even with 10 connected clients concurrently performing operations Number Of Clients Average Logon Time Average File Update Time Average File Search Time us us us 1 53 33 30 00 10 00 2 51 67 30 00 20 00 3 54 44 30 00 20 00 4 55 83 35 00 25 83 5 56 67 38 00 28 00 6 57 78 41 72 33 39 7 54 76 44 33 37 14 8 54 58 46 29 42 13 9 57 04 50 04 45 59 10 62 67 53 37 50 20 Table 2 Client Test Results 70 00 60 00 50 00 40 00 Average Time Microseconds 30 00 u 20 00 ra 10 00 0 00 r T r r r r r T r 1 2 3 4 5 6 f 8 9 10 Number of Clients 4 Logon Time E File Update Time 4 File Search Time
108. tely the multiple server model suffers from the same problem as the single server as there is a central point of failure for the system although if the controlling server was to become unavailable the three remaining servers would be able to provide a partial service to their locally connected clients Out of these three possible system models the model that will be used to implement the system is the Multiple Server model which is illustrated in Figure 10 The reason behind this decision is there is no central point of failure for the system which the other two models suffer from The database inconsistency problem that this model suffers from can be resolved using WinSock programming as each server will maintain a socket connection to the other two servers and will immediately be able to detect if a server disconnects due to the connection oriented nature of sockets Figure 10 Multiple Server System Model David Brown BSc Hons Computing 2002 25 3 4 3 System Security The Theory chapter of this report outlined the three main cryptographic techniques used for the encryption of files This section discusses the suitability of these three techniques in context of the system In secret key cryptography the sender and receiver must have the same key to encrypt and decrypt the file This cryptographic technique is not suitable for the system as the key would have to be sent from sender to recipient with every file transfer
109. tem users While connected a user can update their shared file list with the server any time e Searching for Files When a connected user submits a file search to the server it first queries its own local database for any files matching the search criteria If there are any active connections to the other servers the search query is then sent David Brown BSc Hons Computing 2002 27 to their databases via the ODBC connection Finally any results from the file search are sent to the user e Updating Client Passwords When a connected user requests to change their password they send their username encrypted old password and encrypted new password The server looks up the username from the database and retrieves the password and public modulus keys associated with that username The received old password is decrypted compared against the password from the database and if they match the database is updated with the new password e Updating Client Keys When a connected user requests to change their keys they send their username encrypted password and new public modulus keys The received password is decrypted using the old key values from the database and compared against the password from the database If they match the server checks the database for the new public modulus key combination in order to determine if they are currently in use If they are not in use the new keys are written to the database e Challenging Client Se
110. the connection Call connectionStatus startTime Timer Do While frmMain ServerConn State lt gt 7 And Timer startTime lt 20 DoEvents Loop if the Timer exceeds 20 Seconds the program times out If Timer startTime gt 20 Then GoTo Timeout Else connection established set connection status so user sees a result Call connectionStatus End If Exit Sub Timeout notify user connection has timed out Call MsgBox Connection timed out vbExclamation SDFS Client As soon as the client successfully connects to the server the client sends the user details to the server This process begins with the encryption of the user password using the enc method of the RSA module which is attached in appendix 3 The client then obtains its current IP address and sends this information along with the username to the server This is achieved with the following code David Brown BSc Hons Computing 2002 39 encryptPasswd RSAvl enc txtPasswd Text txtPrivate Text txtModulus Text get the IP address ipAddressVal ServerConn LocalIP inform server existing user is logging in by sending EXIST_USER If ServerConn State lt gt sckConnected Then Connection failed Call cmdDisconnect_Click Else frmMain ServerConn SendData EXIST USER amp vbCr send details to the server username password and current IP address frmMain ServerConn SendData txtUser Text vbCr username frmMain ServerConn SendData encr
111. the last packet has been sent Close OpenedFileNbr David Brown BSc Hons Computing 2002 43 4 3 5 Receive File from Client In order to request a file download the user must first select a file from the list of file search results which is illustrated in Figure 23 When the user clicks the download button an entry is made in the download list and the client then waits for a response from the remote client SDFS Client File View Help Connection Status Disconnect begged on gt Shared Files File Search FileTransfers Settings DavidBrown Filename Username Filename Filesize Username Submit Search Imagel jpg 31 Kb DavidBrown Image2 jpg 69 Kb DavidBrown Download File Robbie Wi 3 95 Mb illiams Rock DJ mp3 DavidBrown DayidBrown ip ics Handbags And Gladrags mp3 DavidBrown Talking Heads Burning Down The House mp3 DavidBrown Terrahawks rm DavidBrown The Cranberries Linger mp3 DavidBrown Wackyraces rm DavidBrown 9 Files found Figure 23 File Search Results The remote client will immediately respond with the protocol code TRANSFER NAR if the file is not available If the file is available the remote client will begin to encrypt the file and as soon as the file is encrypted the remote client sends the protocol code TRANSFER ACK the encrypted session key and then the file itself The session key is stored in a variable for later use an
112. the original size of the file from the list If both sizes are identical the file was downloaded successfully so the session key is decrypted and used to decrypt the file If the file sizes do not match then the downloaded file is deleted The following code illustrates this process 4 3 6 Find the entry in the listview by using the function in modClient itemNumber modClient getDownloadListItem Index Set the filename to this strFileName lvwDownload ListItems itemNumber SubItems 1 Now test to see if this download completed if not exit If Download completed successfully filesize and received filesize should be the same If lvwDownload ListItems itemNumber SubItens 2 lt gt lvwDownload ListItems itemNumber SubItems 4 Then Delete and reset the temporary file Close DownloadingFile Index DownloadingFile Index 0 Kill strPath amp Temp amp strFileName resumeError Update the status of the download item in the ListView so the user can clear it at a later stage itemNumber modClient getDownloadListItem Index lvwDownload ListItems itemNumber Subltems 4 Failed Exit Sub End If The file was successfully downloaded so now close and reset the file that was written to by the winsock object Close DownloadingFile Index DownloadingFile Index 0 We now have the filepath and encrypted session key first recover the encrypted key decryptSess RSAvl dec sessionKey Index t
113. the protocol code SHARED START is received from a connected client This process is automatically performed when a client first logs in and can be performed again any number of times at the client s request The server then obtains the username of the client and deletes the current shared file list from the database The client then sends the names and sizes of their shared files which the server stores in the database until the client sends the protocol code SHARED END which indicates the end of the list To inform the client that the shared file list has been successfully received the protocol code SHARED ACK is sent to the client This is performed using the following code First get the client s username from the connected users table The index of the tcpServer winsock is used to find this client Set rsl New ADODB Recordset rs1 Open SELECT Username FROM ConnectedUsers Where SocketNumber amp Index amp LocalDb adOpenStatic adLockReadOnly if the recordset contains no records a major failure has occured If rsl EOF True Then Send the protocol command code to disconnect this client tcpServer Index SendData SESS NAK vbCr rsl Close Exit Sub End If Store the username of this client userName rsl Username rsl Close delete any files shared by this client from the table Set rs2 New ADODB Recordset rs2 Open SELECT Filename FROM SharedFiles Where Username amp userName amp
114. the requesting client losing their connection the status of the upload will change to ERROR The status of a download can be David Brown BSc Hons Computing 2002 79 e PROCESSING The target SDFS Client is encrypting the requested file This is then followed by a send progress indication as the amount of data sent is constantly updated and displayed e DECRYPTING SDFS Client has recovered the random session key with private key and is decrypting the received file with it e COMPLETED SDFS Client has successfully sent the file If an error occurs during the download process such as the target client losing their connection the status of the download will change to ERROR 12 6 Settings This section displays the current details of the user From this screen the user can change their password shared file directory and their public private amp modulus keys David Brown BSc Hons Computing 2002 13 Appendix 7 Project Gantt Chart 80 David Brown BSc Hons Computing 2002 81
115. um of four keys and so on Table 4 shows some examples of the number of key permutations for a given code size Code Size Total Number of Keys 1 2 2 4 4 16 8 256 16 65 536 20 1 048 576 24 16 777 216 26 67 108 864 28 268 435 456 32 4 294 967 296 Table 4 Key Permutations In the client application the file encryption is based on a 32 bit key which has over four billion different combinations 4 294 967 296 In order to discover the amount of time it would take for an unauthorised user to break a code of this size if they discovered the encryption algorithm a code breaking application was developed This application uses a 20 bit key giving over a million possible key combinations and contains the ciphertext of the plaintext Hello This ciphertext is encrypted with the value 1 048 576 which is the maximum value of a 20 bit key The application starts at the number 1 and continues to 1 048 576 using each key permutation to decrypt the ciphertext and comparing the decrypted string against the known plaintext The reason a 20 bit key was used rather than a 32 bit key was it would not take a great amount of time to crack the code and it would then be possible to calculate the amount of time it would take to break the 32 bit code through simple multiplication As a 32 bit key has 4 294 967 296 combinations and a 20 bit key has 1 048 576 combinations the 32 bit key contains 4 294 967 296 1 048 576 4096 more combinatio
116. ut Soc 2002 pp 99 100 Los Alamitos CA USA Scarlata V Levine B amp Shields C Responder anonymity and anonymous peer to peer file sharing Proceedings Ninth International Conference on Network Protocols ICNP 2001 IEEE Comput Soc 2001 pp 272 80 Los Alamitos CA USA Singh S 2000 The Code Book London Fourth Estate Sommerville I 2001 Software Engineering New York Addison Wesley Stallings W 2000 Data amp Computer Communications New Jersey Prentice Hall Tanenbaum A S Van Steen M 1996 Distributed Systems Principles and Paradigms New Jersey Prentice Hall Tulloch M 1996 Microsoft Encyclopaedia of Networking Redmond Microsoft Press Vrana G Peering through the peer to peer fog EDN vol 46 no 16 19 July 2001 pp 75 9 Cahners Publishing USA Waters JK Peer to peer computing the new old thing Application Development Trends vol 8 no 1 Jan 2001 pp 20 7 101communications LLC USA Yang B Garcia Molina H Comparing hybrid peer to peer systems Proceedings of the 27th International Conference on Very Large Databases Morgan Kaufmann Publishing 2001 pp 361 70 Orlando FL USA Zimmermann P R 1995 The Official PGP User s Guide Massachusetts IT Press David Brown BSc Hons Computing 2002 67 7 Appendix 1 Client Design Client Started Connect to a Server Register New Connect to a User Details Server Submit User Validated No Details Validated Yes Yes
117. ver Settings Server IP Settings ODBC Settings Enter ODBC Data Source Names Note these have to This Server s IP Address be set via Data Sources through Control Panel Server 1 IP Address Server 1 Local Db Server 2 IP Address Server 2 Local Db A 7 VU Server Port Settings This Server s Local Db This Server s Global Db Server 1 Connection Remote Port Connect Server 1 Connection Local Port Listen Server 2 Connection Remote Port Connect Server 2 Connection Local Port Listen Server Password OK Cancel This window contains three sections that require an entry from the user Server IP Settings Server Port Settings ODBC Settings and Server Password Server IP Settings This section requires the IP addresses of the other two SDFS Servers in the system if these addresses are currently unknown any values may be entered as they can be changed later and the system will still function SDFS Server automatically detects its own IP address Server Port Settings This section requires the port numbers for the connections to Server 1 and Server 2 In the same way as entering the Server IP settings if the port numbers are unknown any values may be entered as they can be changed later and the system will still function The remote port is the port number on the remote Server that will be listening for a connection from this Server The Local port is the port number on the lo
118. vl enc txtPasswd Text txtPrivate Text txtModulus Text first inform the server that a key change is being sent achieved by sending the code KEY CHNG If ServerConn State lt gt sckConnected Then Connection failed ServerConn Close Else ServerConn SendData KEY CHNG vbCr ServerConn SendData frmMain txtUser Text amp vbCr contents of username text box ServerConn SendData encryptPasswd vbCr encrypted password ServerConn SendData txtPublic Text vbCr new public key ServerConn SendData txtModulus Text amp vbCr new modulus key End If 4 3 8 Change Shared File Directory While logged on to the server a user can change their shared file directory at any time After selecting a new directory the client application checks if the new directory is different from the previous one If it is the Windows registry is updated and the new list of shared files is sent to the server 4 4 Server Implementation Figure 24 illustrates a high level view of the server application with each important section individually numbered This number corresponds directly to a sub section in this chapter where the functionality and corresponding code is explained in detail David Brown BSc Hons Computing 2002 46 Initialise Server 4 3 1 Accept client Connect to Challenge Perform file Update client connection server client session search file list 43 2 4 3 3 4 3 4 4 3 5 3 43 7 Figure 24 Server Application High Leve
119. work involves the transfer of bits from one machine to another Mackenzie 1998 points out that to create an David Brown BSc Hons Computing 2002 14 application to communicate in this manner would be an awkward task as it would take a large number of 0 s and 1 s to create a simple message Instead a high level interface for applications to communicate is provided by software running on the networked computers usually in the operating system itself All communicating entities on a network must agree on a set of rules and conventions to be used when sending information over the network medium These rules are called a network protocol which sets the format of messages and the appropriate actions required for each message and specifies how the data is packaged into messages The network protocol can also determine the following e Error checking to be used e Data compression method e How the sending device indicates a message is sent e How the receiving device indicates a message is received 2 4 1 Protocol Layered Model Instead of having one large protocol to specify the rules for any possible form of communication the problem was divided into subsections with a protocol required for each subsection To ensure that the protocols cooperate they are developed in complete sets called suites where each protocol in the suite tackles one part of the communication process As a protocol is required for each subsection in a suit
120. xtPrivate Text txtModulus Text Before decrypting the file inform the user of this by updating the status in the listview as decryption can take some time on big files lvwDownload ListItems itemNumber Subltems 4 Decrypting Now decrypt the received file using this information Call modBinaryEncrypt DecryptFile strPath amp Temp strFileName strPath amp Shared strFileName decryptSess Update the download listview for this item lvwDownload ListItems itemNumber SubItems 4 Completed Delete the old File from the temp directory Kill strPath amp Temp amp strFileName Authenticate Details This process begins when the protocol code SESS_CHALL is received from the server The client decrypts the received value using the private and modulus keys and sends the server the protocol code CHALL REPLY followed by the decrypted value This process is performed using the following code We now have a received encrypted value from the SDFS Server unencrypt it using the private key challVal RSAvl dec chall1String txtPrivate Text txtModulus Text Inform the server that the response is being sent and send the decrypted value to the server ServerConn SendData CHALL REPLY vbCr David Brown BSc Hons Computing 2002 45 ServerConn SendData challVal amp vbCr 4 3 7 Change Password Public key While logged on to the server a user can change their password or their pu
121. yptPasswd amp vbCr enc password frmMain ServerConn SendData ipAddressVal amp vbCr ip address End If If the logon attempt is successful the client then sends the shared file list to the server which is discussed in the next section 4 3 2 Send Shared File List The client application automatically sends the list of shared files to the server immediately after a successful logon attempt The user can also trigger this process at any time while logged on to the server This process uses an ADO record set to store the file list and comprises of two stages reading and sending The read process begins by clearing the ADO record set each file in the shared file directory is added to the record set with the exception of files that contain an apostrophe which are ignored as these characters cause an SQL error After the last file in the directory is processed the send process begins The read process is performed using the following code first clear any records in the recordset If rs RecordCount gt 0 Then rs MoveFirst Do While rs EOF False rs Delete rs MoveNext Loop End If Loop through the shared directory and populate the Recordset strPath txtDirList Text amp strName Dir strPath Do While strName lt gt If strName lt gt And strName lt gt Then Make sure the filename does not have a character in it SOL Error If InStr strName 0 Then FileSize Filelen strPath amp strName
122. ze FileLength Loc OpenedFileNbr lastdata True End If Make the temp variable equal to the size of the packet Temp Space packetsize Load the data into the empty Temp string Get OpenedFileNbr Temp If ClientSend Index State lt gt sckConnected Then The connection has failed so close the file delete it and update the listview Close OpenedFileNbr ill strEncFilePath itemNumber modClient getUploadListItem Index lvwUpload ListItems itemNumber SubItems 4 Failed Unload ClientSend Index Exit Sub End If This is used to keep track of how much data is sent doneBytes doneBytes Len Temp Get the best format for the amount of data sent FileSize modClient getFileSize doneBytes Find the position in the listview of this upload item and update the amount sent itemNumber modClient getUploadListItem Index Update the amount sent for this item acts as a send progress for the user lvwUpload ListItems itemNumber Subltems 4 FileSize Send the data to the remote client if still connected If ClientSend Index State sckConnected Then ClientSend Index SendData Temp Else The connection has failed so close the file delete it and update the listview Close OpenedFileNbr Kill strEncFilePath itemNumber modClient getUploadListItem Index lvwUpload ListItems itemNumber SubItems 4 Failed Exit Sub End If DoEvents Loop Close the file now that

A Secure and Distributed Architectural Model for File Sharing

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