User`s Manual - School of Engineering and Applied Science
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1. 05 19 12 56 gt Computer Inc build 1671 on darwin copyright credits or license for more information Figure 2 sython Starting Output 10 We will begin by allocating a new sython variable This is done via the line x syalloc i This line allocates a new variable x The variable is a handle for an integer that is stored on the Sython Daemon The value was randomly assigned The function syalloc is just one of a number of new built in functions Consult the reference manual in the next chapter for a complete list Try to determine the value of x by typing print x and hitting Return Only the memory location of the syobj handle is revealed The actual value isn t even stored in Sython it is in sythond s protected memory Next we will allocate another secure variable Type in y syalloc i 10 20 This will allocate a new variable y which will be a handle to another integer in the Sython Daemon This integer will be randomly chosen from the range ten to twenty Just like normal Python variables secure variables support mathematic operations type z x y The variable z now contains the sum of x and A useful debugging tool in Sython is the new built in function 1 The function returns a string representation of a secure variable The string will stay the same between calls as long as the secure variable itself does not change If the variable changes the return value may or may not change too To see2. in Sython Intepreter on machine B use the command sython comm dHost machineA local where machineA local is the hostname of the machine running the Sython Daemon instance In addition to host names IP addresses may be used Please note the protocol Sython uses to communicate with the Daemon is not encrypted As such it may be intercepted by third parties when used over a network To protect against this attack users are encouraged to use SSH port tunneling Please see the SSH man page for more information on port tunneling Sometimes when launching the Sython Daemon an error message will be displayed saying socket error 48 Address already in use This can happen in two cases The first and most obvious is when there is already a program bound to the port sythond is attempting to launch using To solve this problem exit the other program This error message can also happen when relaunching sythond immediately after exiting the program In this case simply wait a few minutes before relaunching sythond 22
3. now containing the results of syalloc i If is bound as an insecure variable a SySecurityException will be raised Sx abc Invalid syntax The dollar sign denotes a secure variable but the string abc is nota secure variable A SySecurityException will be raised Sx syalloc s x abc Valid syntax x is bound as a secure variable initially Itis then rebound as an insecure variable containing the string abc 12 5 2 SYTHON BUILT IN FUNCTIONS To support development using secure variables Sython adds a number of new built in functions This section will detail each new function syalloc type range len constraint sets gt syobj Allocates a new syobj Variables to hold syobj must be denoted with a dollar sign 5 when assigning a new syobj type is the type of sython variable to allocate either 1 for int or 5 for string range is a two element tuple containing the valid range of values from which to choose an initial value range is used with ints and must be a distance of ten or more units apart len is the initial length that str based syobj should constraint sets is a tuple containing strings of constraints Valid constraints are ALL for no constraints EVEN for only even numbers ODD for only odd numbers POSITIVE for numbers greater than zero NEGATIVE for numbers less than one fo
4. Os as SO ee Figure 2 sython Startins eds en ata wedged iii LIST OF TABLES Table Validity as SOc tures Com gS 12 Table 2 Sython Daemon Command Line 15 Table 3 Sython Daemon Log Pile ss cienne GB 16 Table 4 Sython Daemon Database 17 Table 5 Sython Daemon Input Text 17 Table 6 Sython Daemon Output Text 18 1 PRODUCT DESCRIPTION Sython adds the ability to specify certain variables in Python as secure The values of these secure variables are restricted and only acted upon in a black box like fashion This allows software development to be outsourced and testing to be performed upon live data while still protecting the data s sensitivity Sython accomplishes this data protection by separating the storage of secure variable into a different memory space The memory space belongs to Sython s sister application the Sython Daemon sythond Requests to modify secure variables are sent transparently to sythond Sythond will not allow any request that could lead to the values of secure variables being known by the client operator Secure variables in Sython are denoted in a specific fashion that visually separates them from regular variables This is in kee
5. enabled care must also be taken when maintaining SQLite Upgrades to SQLite can be found at http www sql org but should be tested for compatibility with PySQLite 19 7 TROUBLESHOOTING This chapter offers solutions to many common problems when working with Sython Please read through these solutions before contacting the manufacturer 7 1 INSTALLATION If you experience difficulties during the installation of Sython please follow this procedure if you re experiencing difficulties installing SQLite please visit their website at http www sqlite org The website has answers to various frequently asked questions There is also a special section dealing with installing SQLite on various architectures including MacOS X at http www sqlite org cvstrac wiki p HowToCompile Reading the README file that comes with the distribution can also provide installation hints If you re experiencing difficulties with installing PySQLite please visit their website at http initd org tracker pysqlite In addition the README file in the distribution is useful and points to a more complete usage manual in the doc rest subdirectory If you re experiencing installation difficulties with the Sython distribution the Python README in the main distribution directory has helpful installation tips The Python website at http www python org also features helpful installation documentation If you re experiencing difficulties installing the Sytho
6. syval in action type syval z This has been a brief tutorial on using the new features of Sython It has been far from exhaustive Users are urged to read the reference manual in the next chapter for a more complete description of all new Sython features Also the Python built in help is a valuable resource Simply type help syalloc into the Sython interpreter prompt to see help about syalloc or any other new Sython function 11 5 SYTHON REFERENCE MANUAL This chapter is the main reference for Sython It details all of the changes to the standard Python Interpreter as well as the various configuration options for sythond 5 1 SYTHON SYNTAX Sython adds one new syntactical construct to Python This construct is the use of the dollar sign to visually distinguish secure variables The dollar sign goes in front of the variable name It is required when declaring a new variable binding a new name but after that the dollar sign is optional while that variable is still secure specification See Table 1 for the complete Table 1 Sython Syntax Validity Syntax Validity 5 110 1 Valid syntax If x is unbound x will become a secure variable If x is bound it will be reassigned as a secure variable x syalloc i Ambiguous syntax If x is unbound this will raise SySecurityException 15 bound as a secure variable x will continue to be a secure variable
7. THE GEORGE WASHINGTON UNIVERSITY School of Engineering and Applied Science Department of Computer Science User s Manual For Sython A Security Addition to the Python Programming Language PRELIMINARY RELEASE EDITION TABLE OF CONTENTS EIST OF FIGURES e tu ill LISFOF TABLES iv PRODUCT DESCRIPTION 5 1 1 MODULE DESCRIPTIONS 5 22 PRODUCT SPECIFICATIONS 7 3 INSTALLATION 8 4 a 10 2 SYTHON REFERENCE MANU AU gs 12 Dele SYTHON SYNTAX E 12 2 SYPHON BUTE TEIN FUNCTIONS noemen an aenea n an 13 D5 SY THON OBJECT METHODS 14 5 4 SYTHON DAEMON CONFIGURATION OPTIONS 15 Se SY THON DAEMON FILES sii fiance 16 MAINTAINANCE OE tay ots er 19 ka TROUBLESHOOTING n a E E a dsanaueis 20 is SINS TATE eA HONG aa a 20 7 2 PROGRAMMING PROBLEMS wise 20 13 Sone 21 LIST OF FIGURES Figure 1 sythond Starting Output nera te es
8. ched The handler module is the most significant module within the daemon It consists of two sub modules the fetcher and the handler The fetcher receives each request from the interpreter and performs basic validity checks After passing those checks the request is forwarded to the handler for processing The last module within the daemon is the database module This module adds support for simple database functionality within Sython The database module is implemented as in interface to a SQLite database 2 PRODUCT SPECIFICATIONS This version of Sython was developed for the Apple MacOS X platform As such official testing has been conducted on Apple Macintosh computers Sython officially supports Macs with G4 processors with 512 MB of RAM or more In practice however any Macintosh that is able to run operating system versions 10 3 or above should be able to run Sython Note the Apple Developer Tools are required to install Sython on MacOS X Python version 2 3 4 from which Sython is derived runs on a number of platforms including Windows and Linux Care has been taken to use platform independent coding practices when constructing Sython as such Sython should be portable to any platform that Python supports Changes may need to be made to the installation scripts For database functionality Sython requires SQLite version 3 1 or above SQLite can be downloaded from http www sqlite org In addition Python SQLite bindings are requir
9. ed A package called PySQLite handles this task It can be found at http initd org tracker pysqlite Versions supporting SQLite 3 are required Note Sython will run without database support If database functionality is not required SQLite and PySQLite are not required 3 INSTALLATION This chapter will detail the installation procedure for Sython If database functionality is required SQLite and PySQLite will need to be installed before Sython can be installed To install these packages visit the sites listed in Chapter 2 Please refer to SQLite and PySQLite documentation for installation directions for those packages Installation of Sython is very similar to the installation of Python To install copy the Sython distribution found in the install sython directory of the distribution CD into a working directory such as the Desktop then unpack it using the tar zxvf Sython tgz command This will create a new folder containing the Sython distribution The following paragraphs detail the installation procedure for both the Sython Interpreter and the Sython Daemon From here there are two methods of installation Sython supports the traditional Python Unix style installation but it also supports the installation of a Darwin MacOS X Framework The Framework allows Sython to be embedded in MacOS X applications It is also less likely to be effected by operating system upgrades than the traditional Unix style installation The Unix style i
10. ename sydinput txt Purpose This file is used in coordination with the function syinput It is used to securely input fixed data into Sython secure variables The syinput function together with this file may be used to simulate user input during testing File format syinput reads one line of this file with each call preceded comments are supported and will not be included in the syinput results Example File start 1234 hello this is a string that was a string this is a comment Table 6 Sython Daemon Output Text File File Sython Daemon Output Text File Default filename Sydoutput txt Purpose This file is used in coordination with the function syoutput It is used to output the values of secure variables The syoutput function together with this file may be used to simulate screen output during testing File format The file is formatted into two line groups in this structure lt Date gt lt Time gt lt variable value gt 18 6 MAINTAINANCE Because Sython is derived from Python 2 3 4 it needs to be maintained similarly to regular Python installations The big difference is that Python patches should not be directly applied to the Sython source code as they may inadvertently disable Sython functionality Instead Sython specific updates which have been tested explicitly with Sython should be used If the Sython database functionality has been
11. lines and client A executes syinput then client B executes syinput and then finally client A executes syinput again client A will have variables containing the first and third lines while client B has a variable containing the second line The other main problem with threading is an internal Python issue There is only one interpreter thread within each Python process This generally isn t a problem but users may notice some slow down when the Sython Daemon is servicing many clients simultaneously 73 CONFIGURATION PROBLEMS By default Sython is configured to communicate with the Sython Daemon running on the same machine over TCP port 60123 This configuration can be changed If an alternative port is desired to steps are required First when launching sythond the command line argument p and then the alternative port number is required So to launch sythond on port 54321 type in sythond p 54321 in the command line and hit Return Next the Sython Interpreter needs to be configured to communicate on the alternative port This is done programmatically Simply 21 type sython comm dPort 54321 to change the port number to 54321 This should be done before creating any secure variables The change is for the current session only The steps are similar to use Sython on different machine than the Sython Daemon On machine A launch sythond using the command line argument g This enables non local or global clients Then
12. lt port number is 60123 o lt file gt Specify alternative output filename The default output filename is sydoutput txt 5 5 SYTHON DAEMON FILES The Sython Daemon interacts with four external files This section details the use and format of each file Section 5 4 details how to specify alternative files By default each file is searched for within the same directory as the sythond application System administrators should take precautions to limit access to all of these files as they can contain the actual values of secure variables Table 3 Sython Daemon Log File File Sython Daemon Log File Default filename syd 1og Note This filename cannot be changed at sythond runtime Purpose This file keeps a record of events in the Sython Daemon By default only request will be logged only new client sessions are logged but if debugging is turned on each client File format lt DATE gt lt TIME gt lt INFORMATION LEVEL gt lt MESSAGE gt 16 Table 4 Sython Daemon Database File File Sython Daemon Database File Default filename syd db Purpose This is a SQLite database file It is contains the database that is queried in the syquery command File format See the SQLite reference manual for more information about the file format Table 5 Sython Daemon Input Text File File Sython Daemon Input Text File Default fil
13. n Daemon you may need to carefully reread the installation directions Ensure that before running the install_syd script your current working directory is the same as that of sythond Additionally administrator privileges are required for installation 7 2 PROGRAMMING PROBLEMS This section details common difficulties when programming with certain parts of Sython 20 One of the main difficulties with the current Sython implementation is the limited support for secure variables as function or method arguments The obvious syntax of def x y z 18 not currently supported Secure variables may still be passed as function or method arguments but automatic enforcement of secure status is not currently available Developers are encouraged to use type testing as a temporary workaround Developers may notice that division operations never raise a ZeroDivisionError This is an intentional security decision A malicious user could write a script that would use the ZeroDivisionError to discover values of secure integers Instead ZeroDivisionErrors are transparently mapped to the value zero See Section 5 3 for more information For the most part the Sython Daemon transparently supports multiple simultaneous clients There are some caveats to this however The input and output files are shared between clients and there is only a single file descriptor that is shared This means that for example if an input file contains three
14. nable framework lt installation directory gt The last installation task is to install the Sython Daemon In the install directory of the distribution CD there is a subdirectory labeled sythond To install the Sython Daemon copy that directory into a more permanent place such as usr then from within the terminal application change into the moved sythond directory type install_syd and hit Return You may be prompted for the administrator password This script will write a script that launches the Sython Daemon in usr local bin allowing the user to invoke the daemon from any location In addition to the Daemon application itself the sythond folder contains sample input output and database files 4 TUTORIAL This chapter offers a brief run though using sython and sythond It does not seek to be exhaustive but rather touches upon the most used features of Sython To start the daemon type sythond c from the terminal window Typing sythond h will display all of the command line parameters The c parameter starts it in an interactive console mode The output of sythond when first started looks like Figure 1 Now open a new terminal window and type sython The output of sython when first started looks like Figure 2 Terminal python ttyp5 mgaiman Archy2 8 sythond c sythond 1 8 sythond accepting connections Figure 1 sythond Starting Output Terminal sython ttyp1 on
15. nstallation will be covered first In Terminal app or another terminal application change into the unpacked sython directory Once there three simple commands will install the Sython Interpreter Type configure and then hit Return This will create a MakeFile tailored to your environment Once the configure command has succeeded type make into the terminal and hit Return This will actually build Sython Once make has completed the one final command is needed to actually install Sython Type into the terminal sudo make install hit Return and type in your password if prompted Because Sython will install itself in the System s usr local directory administrator privileges are required Once this command has completed Sython has been successfully installed If during any of these steps you encountered an error please consult the troubleshooting chapter at the end of this manual The Framework installation of Sython is very similar to the Unix style installation In Terminal app or another terminal application change into the unpacked sython directory Once there follow the steps detailed in the Unix style installation but change the commands to the following configure becomes configur enable framework and sudo make install becomes sudo make frameworkinstall The Sython framework will be installed in the Library Frameworks directory To install in a different directory change the configure command to configure e
16. o ZeroDivisionError is raised Instead x 0 gt 0 for all values x This is done to protect the actual values of sythond variables When a string is represented Sython Objects support the concatenation and length operations 5 4 SYTHON DAEMON CONFIGURATION OPTIONS The Sython Daemon supports a number of configuration options These options are specified as command line arguments when launching the daemon Table 2 details each command line argument Note there is no specific command used to exit the Sython Daemon This unix command kill can be used when sythond is launched in non interactive mode Table 2 Sython Daemon Command Line Arguments Command Line Argument Argument Description b lt file gt Specify an alternative SQLite database filename See section 5 5 for more information about the database file c Launch sythond in interactive console mode To exit sythond when launched in this mode type control c Enable debugging mode logging The log file and console if in console mode will display additional information about each sythond request 15 Command Line Argument Argument Description g Enable global client support Without this argument sythond will only allow communications between clients on the localhost i lt file gt Specify alternative input filename The default input filename is sydinput txt ies Specify alternative port number The defau
17. ping with Python s philosophy of highly readable source code In addition Sython adds a number of new built in functions to operate on the secure variables This manual assumes basic familiarity with regular Python It details all changes to Python from the point of view of both the developer and the system administrator For a well written high level tutorial on Python Wikipedia is an excellent resource visit http en wikipedia org wiki Python_programming language 1 1 MODULE DESCRIPTIONS The Sython distribution consists of two main applications the Sython Interpreter sython and the Sython Daemon sythond Within each application there are a number of modules This section will discuss each module in detail The Sython interpreter consists of two modules the Python module and the communicator module The Python module is a modified version of the Python 2 3 4 distribution It has been modified to support the dollar sign as the indicator of secure variables and adds several new built in functions as detailed in Chapter 4 The communicator module handles communication with the daemon application via a well defined protocol It is implemented as a Python module called sython comm The Sython daemon consists of three modules These modules are the main module the handler module and the database module The daemon main module initializes the other modules based upon command line arguments supplied when the daemon is laun
18. query The sql statement should reference syobj by either 351 for syints or s for systrs Examples syquery select from users might return syobj syobj syobj if the table users was made up of three columns and contained one row syquery select from users where users id i x lt where x is a secure variable gt might return if the id column in the users table contained no entry that equaled the value of x 5 3 SYTHON OBJECT METHODS Internally Sython represents secure variables as Objects of the type syobj These objects have two methods in addition to support for various arithmetic operations Note Sython Objects can be handles for both integers and strings in the Sython Daemon syobj isstr gt bool Returns True if this syobj represents a string in the Sython Daemon syobj isint gt bool Returns True if this syobj represents an integer in the Sython Daemon 14 Sython Objects support the following arithmetic operations addition subtraction multiplication division modulus negation and absolute value These operations are only supported with the Sython Object represents an integer Operations can be mixed between two Sython Objects representing integers or one Sython Object representing an integer and one integer or long All arithmetic operations that support Sython Objects produce additional Sython Objects Please note unlike in division between two integers when dividing by zero n
19. r uppercase letters LOWER for lowercase letters PUNCT for punctuation letters SPACE for whitespace DIGITS for numerical digits The tuple can combine constraints where they make sense for exampl POSITIVE or UPPER LOWER Please note integer based constraints are restrictive whereas string based constraints are additive Examples Sx syalloc i 0 100 EVEN for an even integer between 0 and 100 Sy syalloc s 10 UPPER SPACE for a string containing uppercase letters and spaces that is 10 letters long Sz syalloc s None ODD NEGATIVE for an odd negative integer 13 syval syobj gt str Returns a string representing a sython variable The string will not change between syval calls if the syobj value does not change If the syobj value does change the string returned by syval may or may not change syinput gt syobj Returns syobj containing a line from the daemon s input file See Section 5 5 for more information about the input file syoutput syobj gt bool Writes the current value of to a new line at the end of the daemon s output file See Section 5 5 for more information about the output file True is returned if writing the output was successful False otherwise syquery sql syobj gt syobj Performs a database
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