GNU Simple Authentication and Security Layer 0.0.14

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GNU Simple Authentication and Security Layer

This manual is last updated 18 January 2004 for version 0.0.14 of GNU SASL.

Copyright © 2002, 2003, 2004 Simon Josefsson.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with the Invariant Sections being "Commercial Support", no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

Appendices

Indices


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1 Introduction

GNU SASL is an implementation of the Simple Authentication and Security Layer framework and a few common SASL mechanisms. SASL is used by network servers (e.g., IMAP, SMTP) to request authentication from clients, and in clients to authenticate against servers.

GNU SASL contains of a library (`libgsasl'), a command line utility (`gsasl') to access the library from the shell, and a manual. The library includes support for the framework (with authentication functions and application data privacy and integrity functions) and at least partial support for the CRAM-MD5, EXTERNAL, GSSAPI, ANONYMOUS, PLAIN, SECURID, DIGEST-MD5, LOGIN, and NTLM mechanisms.

The library is easily ported because it does not do network communication by itself, but rather leaves it up to the calling application. The library is flexible with regards to the authorization infrastructure used, as it utilizes callbacks into the application to decide whether a user is authorized or not.

GNU SASL is developed for the GNU/Linux system, but runs on over 20 platforms including most major Unix platforms and Windows, and many kind of devices including iPAQ handhelds and S/390 mainframes.

GNU SASL is written in pure ANSI C89 to be portable to embedded and otherwise limited platforms. The entire library, with full support for ANONYMOUS, EXTERNAL, PLAIN, LOGIN and CRAM-MD5, and the front-end that support client and server mode, and the IMAP and SMTP protocols, fits in under 60kb on an Intel x86 platform, without any modifications to the code. (This figure was accurate as of version 0.0.13.)

GNU SASL is licensed under the GNU General Public License.


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1.1 Getting Started

This manual documents the `Libgsasl' library programming interface. All functions and data types provided by the library are explained.

The reader is assumed to possess basic familiarity with SASL and network programming in C or C++.

This manual can be used in several ways. If read from the beginning to the end, it gives a good introduction into the library and how it can be used in an application. Forward references are included where necessary. Later on, the manual can be used as a reference manual to get just the information needed about any particular interface of the library. Experienced programmers might want to start looking at the examples at the end of the manual, and then only read up those parts of the interface which are unclear.


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1.2 Features

`Libgsasl' might have a couple of advantages over other libraries doing a similar job.

It's Free Software
Anybody can use, modify, and redistribute it under the terms of the GNU General Public License.
It's thread-safe
No global variables are used and multiple library handles and session handles may be used in parallell.
It's internationalized
It handles non-ASCII username and passwords and user visible strings used in the library (error messages) can be translated into the users' language.
It's portable
It should work on all Unix like operating systems, including Windows. The library itself should be portable to any C89 system, not even POSIX is required.

Note that the library do not implement any policy to decide whether a certain user is “authenticated” or “authorized” or not. Rather, it uses callbacks back into the application to answer these questions.


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1.3 SASL Overview

This section describes SASL from a protocol point of view.

The Simple Authentication and Security Layer (SASL) is a method for adding authentication support to connection-based protocols. A protocol includes a command for identifying and authenticating a user to a server and for optionally negotiating a security layer for subsequent protocol interactions.

The command has a required argument identifying a SASL mechanism. SASL mechanisms are named by strings, from 1 to 20 characters in length, consisting of upper-case letters, digits, hyphens, and/or underscores.

If a server supports the requested mechanism, it initiates an authentication protocol exchange. This consists of a series of server challenges and client responses that are specific to the requested mechanism. The challenges and responses are defined by the mechanisms as binary tokens of arbitrary length. The protocol's profile then specifies how these binary tokens are then encoded for transfer over the connection.

After receiving the authentication command or any client response, a server may issue a challenge, indicate failure, or indicate completion. The protocol's profile specifies how the server indicates which of the above it is doing.

After receiving a challenge, a client may issue a response or abort the exchange. The protocol's profile specifies how the client indicates which of the above it is doing.

During the authentication protocol exchange, the mechanism performs authentication, transmits an authorization identity (frequently known as a userid) from the client to server, and negotiates the use of a mechanism-specific security layer. If the use of a security layer is agreed upon, then the mechanism must also define or negotiate the maximum cipher-text buffer size that each side is able to receive.

The transmitted authorization identity may be different than the identity in the client's authentication credentials. This permits agents such as proxy servers to authenticate using their own credentials, yet request the access privileges of the identity for which they are proxying. With any mechanism, transmitting an authorization identity of the empty string directs the server to derive an authorization identity from the client's authentication credentials.

If use of a security layer is negotiated, it is applied to all subsequent data sent over the connection. The security layer takes effect immediately following the last response of the authentication exchange for data sent by the client and the completion indication for data sent by the server. Once the security layer is in effect, the protocol stream is processed by the security layer into buffers of cipher-text. Each buffer is transferred over the connection as a stream of octets prepended with a four octet field in network byte order that represents the length of the following buffer. The length of the cipher-text buffer must be no larger than the maximum size that was defined or negotiated by the other side.


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1.4 Supported Platforms

Libgsasl has at some point in time been tested on the following platforms.

  1. Debian GNU/Linux 3.0 (Woody)

    GCC 2.95.4 and GNU Make. This is the main development platform. alphaev67-unknown-linux-gnu, alphaev6-unknown-linux-gnu, arm-unknown-linux-gnu, hppa-unknown-linux-gnu, hppa64-unknown-linux-gnu, i686-pc-linux-gnu, ia64-unknown-linux-gnu, m68k-unknown-linux-gnu, mips-unknown-linux-gnu, mipsel-unknown-linux-gnu, powerpc-unknown-linux-gnu, s390-ibm-linux-gnu, sparc-unknown-linux-gnu.

  2. Debian GNU/Linux 2.1

    GCC 2.95.1 and GNU Make. armv4l-unknown-linux-gnu.

  3. Tru64 UNIX

    Tru64 UNIX C compiler and Tru64 Make. alphaev67-dec-osf5.1, alphaev68-dec-osf5.1.

  4. SuSE Linux 7.1

    GCC 2.96 and GNU Make. alphaev6-unknown-linux-gnu, alphaev67-unknown-linux-gnu.

  5. SuSE Linux 7.2a

    GCC 3.0 and GNU Make. ia64-unknown-linux-gnu.

  6. RedHat Linux 7.2

    GCC 2.96 and GNU Make. alphaev6-unknown-linux-gnu, alphaev67-unknown-linux-gnu, ia64-unknown-linux-gnu.

  7. RedHat Linux 8.0

    GCC 3.2 and GNU Make. i686-pc-linux-gnu.

  8. RedHat Advanced Server 2.1

    GCC 2.96 and GNU Make. i686-pc-linux-gnu.

  9. Slackware Linux 8.0.01

    GCC 2.95.3 and GNU Make. i686-pc-linux-gnu.

  10. Mandrake Linux 9.0

    GCC 3.2 and GNU Make. i686-pc-linux-gnu.

  11. IRIX 6.5

    MIPS C compiler, IRIX Make. mips-sgi-irix6.5.

  12. AIX 4.3.2

    IBM C for AIX compiler, AIX Make. rs6000-ibm-aix4.3.2.0.

  13. Microsoft Windows 2000 (Cygwin)

    GCC 3.2, GNU make. i686-pc-cygwin.

  14. HP-UX 11

    HP-UX C compiler and HP Make. ia64-hp-hpux11.22, hppa2.0w-hp-hpux11.11.

  15. SUN Solaris 2.8

    Sun WorkShop Compiler C 6.0 and SUN Make. sparc-sun-solaris2.8.

  16. SUN Solaris 2.9

    Sun Forte Developer 7 C compiler and GNU Make. sparc-sun-solaris2.9.

  17. NetBSD 1.6

    GCC 2.95.3 and GNU Make. alpha-unknown-netbsd1.6, i386-unknown-netbsdelf1.6.

  18. OpenBSD 3.1 and 3.2

    GCC 2.95.3 and GNU Make. alpha-unknown-openbsd3.1, i386-unknown-openbsd3.1.

  19. FreeBSD 4.7

    GCC 2.95.4 and GNU Make. alpha-unknown-freebsd4.7, i386-unknown-freebsd4.7.

If you use Libgsasl on, or port Libgsasl to, a new platform please report it to the author.


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1.5 Commercial Support

Commercial support is available for users of GNU SASL. The kind of support that can be purchased may include:

If you are interested, please write to:

Simon Josefsson Datakonsult
Drottningholmsv. 70
112 42 Stockholm
Sweden

E-mail: simon@josefsson.org

If your company provide support related to GNU SASL and would like to be mentioned here, contact the author (see Bug Reports).


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1.6 Downloading and Installing

The package can be downloaded from several places, including:

<http://josefsson.org/gsasl/releases/>

The latest version is stored in a file, e.g., gsasl-0.0.42.tar.gz where the 0.0.42 indicate the highest version number.

The package is then extracted, configured and built like many other packages that use Autoconf. For detailed information on configuring and building it, refer to the INSTALL file that is part of the distribution archive.

Here is an example terminal session that download, configure, build and install the package. You will need a few basic tools, such as sh, make and cc.

     $ wget -q http://josefsson.org/gsasl/releases/gsasl-0.0.8.tar.gz
     $ tar xfz gsasl-0.0.8.tar.gz
     $ cd gsasl-0.0.8/
     $ ./configure
     ...
     $ make
     ...
     $ make install
     ...

After that gsasl should be properly installed and ready for use.

A few configure options may be relevant, summarized in the table.

--disable-client
--disable-server
If your target system require a minimal implementation, you may wish to disable the client or the server part of the code. This do not remove symbols from the library, so if you attempt to call an application that uses server functions in a libgsasl built with --disable-server, the function will return an error code.
--disable-anonymous
--disable-external
--disable-plain
--disable-login
--disable-securid
--disable-ntlm
--disable-cram-md5
--disable-digest-md5
--disable-gssapi
--disable-kerberos_v5
Disable individual mechanisms (see Mechanisms).
--without-stringprep
Disable internationalized string processing. Note that this will result in a SASL library that is only compatible with RFC 2222.

For the complete list, refer to the output from configure --help.


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1.7 Bug Reports

If you think you have found a bug in Libgsasl, please investigate it and report it.

Please make an effort to produce a self-contained report, with something definite that can be tested or debugged. Vague queries or piecemeal messages are difficult to act on and don't help the development effort.

If your bug report is good, we will do our best to help you to get a corrected version of the software; if the bug report is poor, we won't do anything about it (apart from asking you to send better bug reports).

If you think something in this manual is unclear, or downright incorrect, or if the language needs to be improved, please also send a note.

Send your bug report to:

bug-gsasl@gnu.org


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1.8 Contributing

If you want to submit a patch for inclusion – from solve a typo you discovered, up to adding support for a new feature – you should submit it as a bug report (see Bug Reports). There are some things that you can do to increase the chances for it to be included in the official package.

Unless your patch is very small (say, under 10 lines) we require that you assign the copyright of your work to the Free Software Foundation. This is to protect the freedom of the project. If you have not already signed papers, we will send you the necessary information when you submit your contribution.

For contributions that doesn't consist of actual programming code, the only guidelines are common sense. Use it.

For code contributions, a number of style guides will help you:


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2 Preparation

To use `Libgsasl', you have to perform some changes to your sources and the build system. The necessary changes are small and explained in the following sections. At the end of this chapter, it is described how the library is initialized, and how the requirements of the library are verified.

A faster way to find out how to adapt your application for use with `Libgsasl' may be to look at the examples at the end of this manual (see Examples).


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2.1 Header

All interfaces (data types and functions) of the library are defined in the header file `gsasl.h'. You must include this in all programs using the library, either directly or through some other header file, like this:

     #include <gsasl.h>

The name space of `Libgsasl' is gsasl_* for function names, Gsasl* for data types and GSASL_* for other symbols. In addition the same name prefixes with one prepended underscore are reserved for internal use and should never be used by an application.


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2.2 Initialization

`Libgsasl' must be initialized before it can be used. The library is initialized by calling gsasl_init (see Global Functions). The resources allocated by the initialization process can be released if the application no longer has a need to call `Libgsasl' functions, this is done by calling gsasl_done.

In order to take advantage of the internationalisation features in `Libgsasl', such as translated error messages, the application must set the current locale using setlocale before initializing `Libgsasl'.

In order to take advantage of the secure memory features in `Libgcrypt', which subsequently makes sensitive key material used in `Libgsasl' be allocated in secure memory, you need to initialize secure memory in your application, and for some platforms even make your application setuid root. See the libgcrypt documentation for more information. Example code to initialize secure memory in your code:

     #include <gcrypt.h>
     ...

     int
     main (int argc, char *argv[])
     {
     ...

       /* Check version of libgcrypt. */
       if (!gcry_check_version (GCRYPT_VERSION))
         die ("version mismatch\n");

       /* Allocate a pool of 16k secure memory.  This also drops priviliges
          on some systems. */
       gcry_control (GCRYCTL_INIT_SECMEM, 16384, 0);

       /* Tell Libgcrypt that initialization has completed. */
       gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
       ...

If you do not do this, keying material will not be allocated in secure memory, which for most application is not the biggest secure problem. Note that `Libgsasl' has not been audited to make sure it only ever stores passwords or keys in secure memory.


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2.3 Version Check

It is often desirable to check that the version of `Libgsasl' used is indeed one which fits all requirements. Even with binary compatibility new features may have been introduced but due to problem with the dynamic linker an old version is actually used. So you may want to check that the version is okay right after program startup.

— Function: const char * gsasl_check_version (const char * req_version)

req_version: version string to compare with, or NULL

Check library version.

Return value: Check that the the version of the library is at minimum the one given as a string in req_version and return the actual version string of the library; return NULL if the condition is not met. If NULL is passed to this function no check is done and only the version string is returned. It is a pretty good idea to run this function as soon as possible, because it may also intializes some subsystems. In a multithreaded environment if should be called before any more threads are created.

The normal way to use the function is to put something similar to the following early in your main:

       if (!gsasl_check_version (GSASL_VERSION))
         {
           printf ("gsasl_check_version failed:\n"
                   "Header file incompatible with shared library.\n");
           exit(1);
         }


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2.4 Building the source

If you want to compile a source file including the `gsasl.h' header file, you must make sure that the compiler can find it in the directory hierarchy. This is accomplished by adding the path to the directory in which the header file is located to the compilers include file search path (via the -I option).

However, the path to the include file is determined at the time the source is configured. To solve this problem, `Libgsasl' uses the external package pkg-config that knows the path to the include file and other configuration options. The options that need to be added to the compiler invocation at compile time are output by the --cflags option to pkg-config libgsasl. The following example shows how it can be used at the command line:

     gcc -c foo.c `pkg-config libgsasl --cflags`

Adding the output of pkg-config libgsasl --cflags to the compilers command line will ensure that the compiler can find the `gsasl.h' header file.

A similar problem occurs when linking the program with the library. Again, the compiler has to find the library files. For this to work, the path to the library files has to be added to the library search path (via the -L option). For this, the option --libs to pkg-config libgsasl can be used. For convenience, this option also outputs all other options that are required to link the program with the `libgsasl' libarary (for instance, the -lidn option). The example shows how to link foo.o with the `libgsasl' library to a program foo.

     gcc -o foo foo.o `pkg-config libgsasl --libs`

Of course you can also combine both examples to a single command by specifying both options to pkg-config:

     gcc -o foo foo.c `pkg-config libgsasl --cflags --libs`


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2.5 Autoconf tests

If you work on a project that uses Autoconf (see GNU Autoconf) to help find installed libraries, the suggestions in the previous section are not the entire story. There are a few methods to detect and incorporate Libgsasl into your Autoconf based package. The preferred approach, is to use Libtool in your project, and use the normal Autoconf header file and library tests.

2.5.1 Autoconf test via pkg-config

If your audience is a typical GNU/Linux desktop, you can often assume they have the pkg-config tool installed, in which you can use its Autoconf M4 macro to find and set up your package for use with Libgsasl. The following illustrate this scenario.

     AC_ARG_ENABLE(gsasl,
     	AC_HELP_STRING([--disable-gsasl], [don't use GNU SASL]),
     	gsasl=$enableval)
     if test "$gsal" != "no" ; then
     	PKG_CHECK_MODULES(GSASL, libgsasl >= 0.0.8,
     			[gsasl=yes],
                             [gsasl=no])
     	if test "$gsasl" != "yes" ; then
     		sal=no
     		AC_MSG_WARN([Cannot find GNU SASL, disabling])
     	else
     		gsasl=yes
     		AC_DEFINE(USE_GSASL, 1, [Define to 1 if you want GNU SASL.])
     	fi
     fi
     AC_MSG_CHECKING([if GNU SASL should be used])
     AC_MSG_RESULT($gsasl)

2.5.2 Standalone Autoconf test using Libtool

If your package uses Libtool(see GNU Libtool), you can use the normal Autoconf tests to find Libgsasl and rely on the Libtool dependency tracking to include the proper dependency libraries (e.g., Libidn). The following illustrate this scenario.

     AC_CHECK_HEADER(gsasl.h,
     	AC_CHECK_LIB(gsasl, gsasl_check_version,
     		[gsasl=yes AC_SUBST(GSASL_LIBS, -lgsasl)],
     		gsasl=no),
     	gsasl=no)
     AC_ARG_ENABLE(gsasl,
     	AC_HELP_STRING([--disable-gsasl], [don't use GNU SASL]),
     	gsasl=$enableval)
     if test "$gsasl" != "no" ; then
     	AC_DEFINE(USE_SASL, 1, [Define to 1 if you want GNU SASL.])
     else
     	AC_MSG_WARN([Cannot find GNU SASL, diabling])
     fi
     AC_MSG_CHECKING([if GNU SASL should be used])
     AC_MSG_RESULT($gsasl)


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3 Using the Library

After initialization of the library, the core part of the library is run within a loop until it has finished. The library is handed input from the other protocol entity and results in output which is to be sent to the other entity, or an error code. The library does not send data to the server itself, but only return it in buffers. The main interface to the library uses binary data, but since many common protocols uses Base 64 encoded data, a wrapper around the main function is also provided.

The following pseudo code illustrates how the library is used in a simple client. All the functions used are explained later on in this manual.

     main()
     {
       Gsasl_ctx          *ctx;
       Gsasl_session_ctx  *cctx;
       char *input, output[BUFFERSIZE];
       size_t output_len;
       int rc;

       rc = gsasl_init (&ctx);
       if (rc != GSASL_OK)
         die(gsasl_strerror(rc));

       /* XXX Set callbacks here */

       /* Read supported SASL mechanism from server */
       input = read_from_client();

       /* Select a good mechanism */
       mech = gsasl_client_suggest_mechanism (ctx, input);
       if (mech == NULL)
         die("Cannot find any commonly agreed SASL mechanism...");

       /* Start to use it */
       res = gsasl_client_start (ctx, mech, &cctx);
       if (res != GSASL_OK)
         die(gsasl_strerror (rc));

       input = NULL;
       do
         {
           /* Do one SASL step and unless we're done, send the output to
              server and read new data from server */

           rc = gsasl_client_step_base64 (cctx, input, output, BUFFERSIZE);
           if (rc != GSASL_NEEDS_MORE && rc != GSASL_OK)
             break;

           write_to_server(output);

           if (rc == GSASL_OK)
             break;

           input = read_from_server();
         }
       while (rc == GSASL_NEEDS_MORE);

       if (rc != GSASL_OK)
         die("Authentication failed... %s\n", gsasl_strerror(rc);

       /* Client is now authenticated -- proceed with actual protocol... */

       gsasl_client_finish (cctx);
       gsasl_done (ctx);
     }

Notice the XXX comment that said you should specify the callbacks to use there. `Libgsasl' depend on callbacks to implement user interaction (in the client) and user validation (in the server). If you don't specify any callbacks, very few mechanisms will be supported (like EXTERNAL that don't need any additional information, see EXTERNAL). Since we are building a simple client, we define callbacks which are used by several SASL mechanisms to get username and password. We start by defining the function for querying the username, following the prototype for Gsasl_client_callback_authentication_id for the LOGIN mechanism (see LOGIN) .

     int
     callback_username (Gsasl_session_ctx *ctx,
                        char *out,
                        size_t *outlen)
     {
       char username[BUFFERSIZE];

       if (out == NULL)
         *outlen = BUFFERSIZE;
       else
         {
           fprintf(stdout, "Enter username: ");
           fgets(username, BUFFERSIZE, stdin);
           *outlen = strlen(BUFFERSIZE);
         }

       return GSASL_OK;
     }

As you can see, this is a simplistic function that reads a username from the user. The callback for entering the password is similar and follows the Gsasl_client_callback_password prototype:

     int
     callback_password (Gsasl_session_ctx *ctx,
                        char *out,
                        size_t *outlen)
     {
       char password[BUFFERSIZE];

       if (out == NULL)
         *outlen = BUFFERSIZE;
       else
         {
           fprintf(stdout, "Enter password: ");
           fgets(password, BUFFERSIZE, stdin);
           *outlen = strlen(BUFFERSIZE);
         }

       return GSASL_OK;
     }

In reality, the program should probably inhibit echo of the password to the terminal, but that is left as an exercise for the reader.

Now having implemented the callbacks, we are ready to replace the XXX comment with real code that set the callbacks (see Callback Functions). The following does it.

       gsasl_client_callback_authentication_id_set(ctx, callback_username);
       gsasl_client_callback_authorization_id_set(ctx, callback_username);
       gsasl_client_callback_password_set(ctx, callback_password);

Notice that we use the same callback for the authentication identity and the authorization identity. In reality, this may be too simplistic, but will do for an example.

The simple client is now complete, and will be able to support SASL mechanisms such as PLAIN and CRAM-MD5.

Implementing a server is very similar to the client, the only difference is that you use gsasl_server_* functions instead of gsasl_client_* and instead of implementing Gsasl_client_* callbacks implement some Gsasl_server_* callbacks. See each mechanism (see Mechanisms) for details on which callbacks are required and their prototype.

A note for server authors is in place, on the optional initial client output (discussed in section 5.1 of RFC 2222). In a server looking similar to the code above, the first call to gsasl_server_step_base64 would have a input set to NULL. The mechanisms interprete this as your protocol do not support initial client output. If the protocol in which you implement SASL supports initial client output, the first call to gsasl_server_step_base64 should include a real buffer with the initial client data.

One note for client authors is in place. The code above aborts processing if `Libgsasl' did not come out of the loop with a GSASL_OK exit code. It is a mistake to not require this, and instead only look at what the server is sending you. Even if the server said you are authenticated, it does not always mean that the SASL mechanism is satisfied. This is specifically true for SASL client mechanisms which perform server authentication. Thus, if you only trust what the server replied instead of requireing a GSASL_OK result, you may open up for fake servers. Don't shortcut the loop with a positive server response.


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4 Mechanisms

Different SASL mechanisms have different requirements on the application using it. Some simpler mechanisms, such as LOGIN and PLAIN, are straight forward to hook into existing authentication systems (such as /etc/passwd via PAM). The client callback for these mechanisms is easy to implement, the user is simply queried for the username and password. The server callbacks pass on the username and password into the policy deciding authentication system (e.g. PAM).

Other mechanism like CRAM-MD5, DIGEST-MD5, and SRP uses hashed passwords. The client callback are the same as for PLAIN and LOGIN. However, the server do not receive the plaintext password via the network but rather a hash of it. Existing policy deciding systems like PAM cannot handle this, so the server callback for these mechanisms are more complicated.

Further mechanisms like GSSAPI (Kerberos 5) assume a specific authentication system. In theory this means that `Libgsasl' would not need to interact with the application, but rather call this specific authentication system directly. However, some callbacks are supported anyway, to modify the behaviour of how the specific authentication system is used.

Special mechanisms like EXTERNAL and ANONYMOUS are entirely dependent on callbacks.


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4.1 The EXTERNAL mechanism

The EXTERNAL mechanism is used to authenticate a user to SASL when SASL is used in an environment which has already authenticated the user. It is often used within TLS or IPSEC protected channels.

This mechanism is only enabled in the server if you implement the callback below and set them in the library (see Callback Functions). It is always enabled in the client as there are no client callbacks.

— Prototype: int (*Gsasl_server_callback_external) (Gsasl_session_ctx * ctx)

ctx: libgsasl handle.

Type of callback function the application implements. It should return GSASL_OK if user is authenticated by out of band means, otherwise GSASL_AUTHENTICATION_ERROR.


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4.2 The ANONYMOUS mechanism

The ANONYMOUS mechanism is used to “authenticate” clients to anonymous services; or rather just indicate that the client wishes to use the service anonymously. The client sends a token, usually her email address.

This mechanism is only enabled in the client and server if you implement the respectively callbacks below and set them in the library (see Callback Functions).

— Prototype: int (*Gsasl_client_callback_anonymous) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with client token.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with some input from the user and set the output array length, and return GSASL_OK, or fail with an error code.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_server_callback_anonymous) (Gsasl_session_ctx * ctx, const char * token)

ctx: libgsasl handle.

ctx: output array with client token.

ctx: on input the maximum size of the output array, on output contains the actual size of the output array. If OUT is

Type of callback function the application implements. It should return GSASL_OK if user should be permitted anonymous access, otherwise GSASL_AUTHENTICATION_ERROR.


Next: , Previous: ANONYMOUS, Up: Mechanisms

4.3 The PLAIN mechanism

The PLAIN mechanism uses username (authentication identity and authorization identity) and password to authenticate users. Two ways of validating the user is provided, either by having the SASL mechanism retrieve the raw password from the application and perform the validation internally, or by calling the application with authentication identity, authorization identity and password and let it decide. If both the validating and the retrieving callbacks are specified by the application, the validating one will be used.

This mechanism is only enabled in the client and server if you implement the respectively callbacks below and set them in the library (see Callback Functions).

— Prototype: int (*Gsasl_client_callback_authorization_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authorization identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authorization identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authorization identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_authentication_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authentication identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authentiction identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authentication identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_password) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with password.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with password of user and set the output array length, and return GSASL_OK, or fail with an error code. The password must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_server_callback_validate) (Gsasl_session_ctx * ctx, char * authorization_id, char * authentication_id, char * password)

ctx: libgsasl handle.

authorization_id: input array with authorization identity.

authentication_id: input array with authentication identity.

password: input array with password.

Type of callback function the application implements. It should return GSASL_OK if and only if the validation of the provided credential was succesful. GSASL_AUTHENTICATION_ERROR is a good failure if authentication failed, but any available return code may be used.

— Prototype: int (*Gsasl_server_callback_retrieve) (Gsasl_session_ctx * ctx, char * authentication_id, char * authorization_id, char * realm, char * key, size_t * keylen)

ctx: libgsasl handle.

authentication_id: input array with authentication identity.

authorization_id: input array with authorization identity, or NULL.

realm: input array with realm of user, or NULL.

key: output array with key for authentication identity.

keylen: on input the maximum size of the key output array, on output contains the actual size of the key output array.

Type of callback function the application implements. It should retrieve the password for the indicated user and return GSASL_OK, or an error code such as GSASL_AUTHENTICATION_ERROR. The key must be encoded in UTF-8, but need not be normalized in any way.

If KEY is NULL, the function should only populate the KEYLEN output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.


Next: , Previous: PLAIN, Up: Mechanisms

4.4 The LOGIN mechanism

The LOGIN mechanism uses username (authorization identity only) and password to authenticate users. Two ways of validating the user is provided, either by having the SASL mechanism retrieve the raw password from the application and perform the validation internally, or by calling the application with authorization identity and password and let it decide. If both the validating and the retrieving callbacks are specified by the application, the validating one will be used.

This mechanism is only enabled in the client and server if you implement the respectively callbacks below and set them in the library (see Callback Functions).

— Prototype: int (*Gsasl_client_callback_authorization_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authorization identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authorization identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authorization identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_password) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with password.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with password of user and set the output array length, and return GSASL_OK, or fail with an error code. The password must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_server_callback_validate) (Gsasl_session_ctx * ctx, char * authorization_id, char * authentication_id, char * password)

ctx: libgsasl handle.

authorization_id: input array with authorization identity.

authentication_id: input array with authentication identity.

password: input array with password.

Type of callback function the application implements. It should return GSASL_OK if and only if the validation of the provided credential was succesful. GSASL_AUTHENTICATION_ERROR is a good failure if authentication failed, but any available return code may be used.

— Prototype: int (*Gsasl_server_callback_retrieve) (Gsasl_session_ctx * ctx, char * authentication_id, char * authorization_id, char * realm, char * key, size_t * keylen)

ctx: libgsasl handle.

authentication_id: input array with authentication identity.

authorization_id: input array with authorization identity, or NULL.

realm: input array with realm of user, or NULL.

key: output array with key for authentication identity.

keylen: on input the maximum size of the key output array, on output contains the actual size of the key output array.

Type of callback function the application implements. It should retrieve the password for the indicated user and return GSASL_OK, or an error code such as GSASL_AUTHENTICATION_ERROR. The key must be encoded in UTF-8, but need not be normalized in any way.

If KEY is NULL, the function should only populate the KEYLEN output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.


Next: , Previous: LOGIN, Up: Mechanisms

4.5 The CRAM-MD5 mechanism

The CRAM-MD5 mechanism uses username (authorization identity only) and password to authenticate users. Only a hashed password is transfered, which means that you cannot use normal policy deciding authentication systems such as PAM which do not support extraction of passwords. Two ways of validating the user is provided, either by having the SASL mechanism retrieve the raw password from the application and perform the validation internally, or by calling the application with the CRAM-MD5 challenge and response and let it decide. If both the validating and the retrieving callbacks are specified by the application, the validating one will be used.

While not documented in the original CRAM-MD5 specification, this implementation normalizes the username and the authorization identity using the Unicode 3.2 NFKC form according to the proposed update of CRAM-MD5.

This mechanism is only enabled in the client and server if you implement the respectively callbacks below and set them in the library (see Callback Functions).

— Prototype: int (*Gsasl_client_callback_authorization_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authorization identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authorization identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authorization identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_password) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with password.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with password of user and set the output array length, and return GSASL_OK, or fail with an error code. The password must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_server_callback_retrieve) (Gsasl_session_ctx * ctx, char * authentication_id, char * authorization_id, char * realm, char * key, size_t * keylen)

ctx: libgsasl handle.

authentication_id: input array with authentication identity.

authorization_id: input array with authorization identity, or NULL.

realm: input array with realm of user, or NULL.

key: output array with key for authentication identity.

keylen: on input the maximum size of the key output array, on output contains the actual size of the key output array.

Type of callback function the application implements. It should retrieve the password for the indicated user and return GSASL_OK, or an error code such as GSASL_AUTHENTICATION_ERROR. The key must be encoded in UTF-8, but need not be normalized in any way.

If KEY is NULL, the function should only populate the KEYLEN output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_server_callback_cram_md5) (Gsasl_session_ctx * ctx, char * username, char * challenge, char * response)

ctx: libgsasl handle.

username: input array with username.

challenge: input array with CRAM-MD5 challenge.

response: input array with CRAM-MD5 response.

Type of callback function the application implements. It should return GSASL_OK if and only if the validation of the provided credential was succesful. GSASL_AUTHENTICATION_ERROR is a good failure if authentication failed, but any available return code may be used.


Next: , Previous: CRAM-MD5, Up: Mechanisms

4.6 The DIGEST-MD5 mechanism

The DIGEST-MD5 mechanism is based on the same cryptographic operation as CRAM-MD5 but supports more features, such as an authorization identity (proxy authentication) and cryptographic protection of data. Like CRAM-MD5, only a hashed password is transfered, which means that you cannot use e.g. PAM as a backend since it does not support extraction of passwords. Two ways of validating the user is provided, either by having the SASL mechanism retrieve the raw password from the application and perform the validation internally, or by having the SASL mechanism retrieve a hashed version of the secret. The advantage of using the latter method is that you do not need to store plain text user passwords on the server, but rather a one-way hash of the username, realm and password. Still, this one-way hash of the secret should be handled the same way as a clear text password. The advantage is that if someone steals the one-way hash she cannot immediately read users' password. If both the callbacks are specified by the application, the one which retrieve the secret hash will be used.

While not documented in the original DIGEST-MD5 specification, this implementation normalizes the username and the authentication identity using the Unicode 3.2 NFKC form according to the proposed update of DIGEST-MD5.

This mechanism is only enabled in the client and server if you implement the respectively callbacks below and set them in the library (see Callback Functions).

— Prototype: int (*Gsasl_client_callback_authentication_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authentication identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authentiction identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authentication identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_authorization_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authorization identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authorization identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authorization identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_password) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with password.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with password of user and set the output array length, and return GSASL_OK, or fail with an error code. The password must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_service) (Gsasl_session_ctx * ctx, char * service, size_t * servicelen, char * hostname, size_t * hostnamelen, char * servicename, size_t * servicenamelen)

ctx: libgsasl handle.

service: output array with name of service.

servicelen: on input the maximum size of the service output array, on output contains the actual size of the service output array.

hostname: output array with hostname of server.

hostnamelen: on input the maximum size of the hostname output array, on output contains the actual size of the hostname output array.

servicename: output array with generic name of server in case of replication (DIGEST-MD5 only).

servicenamelen: on input the maximum size of the servicename output array, on output contains the actual size of the servicename output array.

Type of callback function the application implements. It should retrieve the service (which should be a registered GSSAPI host based service name, such as “imap”) on the server, hostname of server (usually canoncial DNS hostname) and optionally generic service name of server in case of replication (e.g. “mail.example.org” when the hostname is “mx42.example.org”, see the RFC 2831 for more information). It should return GSASL_OK, or an error such as GSASL_AUTHENTICATION_ERROR if it fails.

If SERVICE, HOSTNAME or SERVICENAME is NULL, the function should only populate SERVICELEN, HOSTNAMELEN or SERVICENAMELEN with the output length of the respective field, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size. Furthermore, SERVICENAMELEN may also be NULL, indicating that the mechanism is not interested in this field.

— Prototype: int (*Gsasl_server_callback_retrieve) (Gsasl_session_ctx * ctx, char * authentication_id, char * authorization_id, char * realm, char * key, size_t * keylen)

ctx: libgsasl handle.

authentication_id: input array with authentication identity.

authorization_id: input array with authorization identity, or NULL.

realm: input array with realm of user, or NULL.

key: output array with key for authentication identity.

keylen: on input the maximum size of the key output array, on output contains the actual size of the key output array.

Type of callback function the application implements. It should retrieve the password for the indicated user and return GSASL_OK, or an error code such as GSASL_AUTHENTICATION_ERROR. The key must be encoded in UTF-8, but need not be normalized in any way.

If KEY is NULL, the function should only populate the KEYLEN output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_server_callback_digest_md5) (Gsasl_session_ctx * ctx, char * username, char * realm, char * secrethash)

ctx: libgsasl handle.

username: input array with authentication identity of user.

realm: input array with realm of user.

secrethash: output array that should contain hash of username, realm and password as described for the DIGEST-MD5 mechanism.

Type of callback function the application implements. It should retrieve the secret hash for the given user in given realm and return GSASL_OK, or an error such as GSASL_AUTHENTICATION_ERROR if it fails. The secrethash buffer is guaranteed to have size for the fixed length MD5 hash.


Next: , Previous: DIGEST-MD5, Up: Mechanisms

4.7 The NTLM mechanism

The NTLM mechanism uses username (authorization identity only) and password to authenticate users. Only the client side is implemented. This mechanism is only enabled in the client if you implement the callbacks below and set them in the library (see Callback Functions).

Note: Libntlm uses assert in some places, it may thus crash your client if it is given bad input.

— Prototype: int (*Gsasl_client_callback_authorization_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authorization identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authorization identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authorization identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_password) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with password.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with password of user and set the output array length, and return GSASL_OK, or fail with an error code. The password must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.


Next: , Previous: NTLM, Up: Mechanisms

4.8 The SECURID mechanism

The SECURID mechanism uses authentication and authorization identity and a passcode from a hardware token to authenticate users. This mechanism is only enabled in the client and server if you implement the respectively callbacks below and set them in the library (see Callback Functions).

— Prototype: int (*Gsasl_client_callback_authentication_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authentication identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authentiction identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authentication identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_authorization_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authorization identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authorization identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authorization identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_passcode) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with passcode.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with passcode of user and set the output array length, and return GSASL_OK, or fail with an error code.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_server_callback_validate) (Gsasl_session_ctx * ctx, char * authentication_id, char * authorization_id, char * passcode, char * pin, char * suggestpin, size_t * suggestpinlen)

ctx: libgsasl handle.

authorization_id: input array with authorization identity.

authentication_id: input array with authentication identity.

passcode: input array with passcode.

pin: input array with new pin (this may be NULL).

suggestpin: output array with new suggested PIN.

suggestpinlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should return GSASL_OK if and only if the validation of the provided credential was succesful. GSASL_AUTHENTICATION_ERROR is a good failure if authentication failed, but any available return code may be used.

Two SECURID specific error codes also exists. The function can return GSASL_SECURID_SERVER_NEED_ADDITIONAL_PASSCODE to request that the client generate a new passcode. It can also return GSASL_SECURID_SERVER_NEED_NEW_PIN to request that the client generate a new PIN. If the server wishes to suggest a new PIN it can populate the SUGGESTPIN field.

If SUGGESTPIN is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.


Next: , Previous: SECURID, Up: Mechanisms

4.9 The GSSAPI mechanism

The GSSAPI mechanism uses a framework similar to SASL for authenticating the user. While GSSAPI can be implemented using many techniques, libgsasl currently links with GSS, Heimdal or MIT Kerberos and is limited to Kerberos 5 only. The GSSAPI client mechanism assumes the user acquired credentials (kerberos tickets) before it is invoked (it will fail if this has not been done). The client need (via callbacks) the name of the service and the name of the user. The server needs the name of the service and a function that authorizes a user. This mechanism is only enabled in the client and server if you implement the respectively callbacks below and set them in the library (see Callback Functions).

— Prototype: int (*Gsasl_client_callback_authentication_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authentication identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authentiction identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authentication identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_service) (Gsasl_session_ctx * ctx, char * service, size_t * servicelen, char * hostname, size_t * hostnamelen, char * servicename, size_t * servicenamelen)

ctx: libgsasl handle.

service: output array with name of service.

servicelen: on input the maximum size of the service output array, on output contains the actual size of the service output array.

hostname: output array with hostname of server.

hostnamelen: on input the maximum size of the hostname output array, on output contains the actual size of the hostname output array.

servicename: output array with generic name of server in case of replication (DIGEST-MD5 only).

servicenamelen: on input the maximum size of the servicename output array, on output contains the actual size of the servicename output array.

Type of callback function the application implements. It should retrieve the service (which should be a registered GSSAPI host based service name, such as “imap”) on the server, hostname of server (usually canoncial DNS hostname) and optionally generic service name of server in case of replication (e.g. “mail.example.org” when the hostname is “mx42.example.org”, see the RFC 2831 for more information). It should return GSASL_OK, or an error such as GSASL_AUTHENTICATION_ERROR if it fails.

If SERVICE, HOSTNAME or SERVICENAME is NULL, the function should only populate SERVICELEN, HOSTNAMELEN or SERVICENAMELEN with the output length of the respective field, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size. Furthermore, SERVICENAMELEN may also be NULL, indicating that the mechanism is not interested in this field.

— Prototype: int (*Gsasl_server_callback_service) (Gsasl_session_ctx * ctx, char * service, size_t * servicelen, char * hostname, size_t * hostnamelen)

ctx: libgsasl handle.

service: output array with name of service.

servicelen: on input the maximum size of the service output array, on output contains the actual size of the service output array.

hostname: output array with hostname of server.

hostnamelen: on input the maximum size of the hostname output array, on output contains the actual size of the hostname output array.

Type of callback function the application implements. It should retrieve the service (which should be a registered GSSAPI host based service name, such as “imap”) the server provides and hostname of server (usually canoncial DNS hostname). It should return GSASL_OK, or an error such as GSASL_AUTHENTICATION_ERROR if it fails.

If SERVICE or HOSTNAME is NULL, the function should only populate SERVICELEN or HOSTNAMELEN with the output length of the respective field, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_server_callback_gssapi) (Gsasl_session_ctx * ctx, char * clientname, char * authentication_id)

ctx: libgsasl handle.

clientname: input array with GSSAPI client name.

authentication_id: input array with authentication identity.

Type of callback function the application implements. It should return GSASL_OK if and only if the GSSAPI user is authorized to log on as the given authentication_id. GSASL_AUTHENTICATION_ERROR is a good failure if authentication failed, but any available return code may be used. This callback is usually implemented in the application as a call to krb5_kuserok(), such as:

          int
          callback_gssapi (Gsasl_session_ctx *ctx,
          		 char *clientname,
          		 char *authentication_id)
          {
            int rc = GSASL_AUTHENTICATION_ERROR;

            krb5_principal p;
            krb5_context kcontext;

            krb5_init_context (&kcontext);

            if (krb5_parse_name (kcontext, clientname, &p) != 0)
              return -1;
            if (krb5_kuserok (kcontext, p, authentication_id))
              rc = GSASL_OK;
            krb5_free_principal (kcontext, p);

            return rc;
          }
     


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4.10 The KERBEROS_V5 mechanism

The KERBEROS_V5 is an experimental mechanism, the protocol specification is available on the GNU SASL homepage. It can operate in three modes, non-infrastructure mode, infrastructure mode and proxied infrastructure mode. Currently only non-infrastructure mode is supported.

In the non-infrastructure mode, it works as a superset of most features provided by PLAIN, CRAM-MD5, DIGEST-MD5 and GSSAPI while at the same time building on what is believed to be proven technology (the RFC 1510 network security system). The non-infrastructure mode is chosen when the Gsasl_client_callback_authorization_id callback prototype is implemented by the application. In non-infrastructure mode, the client must specify (via callbacks) the name of the user, and optionally the server name and realm. The server must be able to retrieve passwords given the name of the user.

In the infrastructure mode (proxied or otherwise), it allows clients and servers to authenticate via SASL in an RFC 1510 environment, using a trusted third party, a “Key Distribution Central”. In the normal mode, clients aquire tickets out of band and then invokes a one roundtrip AP-REQ and AP-REP exchange. In the proxied mode, which can be used by clients without IP addresses or without connectivity to the KDC (e.g., when the KDC is IPv4 and the client is IPV6-only), the client uses the server to proxy ticket requests and finishes with the AP-REQ/AP-REP exchange. In infrastructure mode (proxied or otherwise), the client nor server need to implement any callbacks (this will likely change later, to allow a server to authorize users, similar to the GSSAPI callback).

— Prototype: int (*Gsasl_client_callback_authentication_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authentication identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authentiction identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authentication identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_authorization_id) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with authorization identity.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with authorization identity of user and set the output array length, and return GSASL_OK, or fail with an error code. The authorization identity must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_client_callback_password) (Gsasl_session_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output array with password.

outlen: on input the maximum size of the output array, on output contains the actual size of the output array.

Type of callback function the application implements. It should populate the output array with password of user and set the output array length, and return GSASL_OK, or fail with an error code. The password must be encoded in UTF-8, but need not be normalized in any way.

If OUT is NULL, the function should only populate the output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.

— Prototype: int (*Gsasl_server_callback_retrieve) (Gsasl_session_ctx * ctx, char * authentication_id, char * authorization_id, char * realm, char * key, size_t * keylen)

ctx: libgsasl handle.

authentication_id: input array with authentication identity.

authorization_id: input array with authorization identity, or NULL.

realm: input array with realm of user, or NULL.

key: output array with key for authentication identity.

keylen: on input the maximum size of the key output array, on output contains the actual size of the key output array.

Type of callback function the application implements. It should retrieve the password for the indicated user and return GSASL_OK, or an error code such as GSASL_AUTHENTICATION_ERROR. The key must be encoded in UTF-8, but need not be normalized in any way.

If KEY is NULL, the function should only populate the KEYLEN output length field with the length, and return GSASL_OK. This usage may be used by the caller to allocate the proper buffer size.


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5 Global Functions

— Function: int gsasl_init (Gsasl ** ctx)

ctx: pointer to libgsasl handle.

This functions initializes libgsasl. The handle pointed to by ctx is valid for use with other libgsasl functions iff this function is successful.

Return value: GSASL_OK iff successful, otherwise GSASL_MALLOC_ERROR.

— Function: void gsasl_done (Gsasl * ctx)

ctx: libgsasl handle.

This function destroys a libgsasl handle. The handle must not be used with other libgsasl functions after this call.

— Function: int gsasl_client_mechlist (Gsasl * ctx, char ** out)

ctx: libgsasl handle.

out: newly allocated output character array.

Return a newly allocated string containing SASL names, separated by space, of mechanisms supported by the libgsasl client. out is allocated by this function, and it is the responsibility of caller to deallocate it.

Return value: Returns GSASL_OK if successful, or error code.

— Function: int gsasl_server_mechlist (Gsasl * ctx, char ** out)

ctx: libgsasl handle.

out: newly allocated output character array.

Return a newly allocated string containing SASL names, separated by space, of mechanisms supported by the libgsasl server. out is allocated by this function, and it is the responsibility of caller to deallocate it.

Return value: Returns GSASL_OK if successful, or error code.

— Function: int gsasl_client_support_p (Gsasl * ctx, const char * name)

ctx: libgsasl handle.

name: name of SASL mechanism.

Return value: Returns 1 if the libgsasl client supports the named mechanism, otherwise 0.

— Function: int gsasl_server_support_p (Gsasl * ctx, const char * name)

ctx: libgsasl handle.

name: name of SASL mechanism.

Return value: Returns 1 if the libgsasl server supports the named mechanism, otherwise 0.

— Function: const char * gsasl_client_suggest_mechanism (Gsasl * ctx, const char * mechlist)

ctx: libgsasl handle.

mechlist: input character array with SASL mechanism names, separated by invalid characters (e.g. SPC).

Return value: Returns name of "best" SASL mechanism supported by the libgsasl client which is present in the input string.

— Function: const char * gsasl_server_suggest_mechanism (Gsasl * ctx, const char * mechlist)

ctx: libgsasl handle.

mechlist: input character array with SASL mechanism names, separated by invalid characters (e.g. SPC).

Return value: Returns name of "best" SASL mechanism supported by the libgsasl server which is present in the input string.


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6 Callback Functions

— Function: Gsasl * gsasl_ctx_get (Gsasl_session * sctx)

sctx: libgsasl session handle

Return value: Returns the libgsasl handle given a libgsasl session handle.

— Function: void gsasl_application_data_set (Gsasl * ctx, void * appdata)

ctx: libgsasl handle.

appdata: opaque pointer to application specific data.

Store application specific data in the libgsasl handle. The application data can be later (for instance, inside a callback) be retrieved by calling gsasl_application_data_get(). It is normally used by the application to maintain state between the main program and the callback.

— Function: void * gsasl_application_data_get (Gsasl * ctx)

ctx: libgsasl handle.

Retrieve application specific data from libgsasl handle. The application data is set using gsasl_appdata_set(). It is normally used by the application to maintain state between the main program and the callback.

Return value: Returns the application specific data, or NULL.

— Function: void gsasl_appinfo_set (Gsasl_session * sctx, void * appdata)

sctx: libgsasl session handle.

appdata: opaque pointer to application specific data.

Store application specific data in the libgsasl session handle. The application data can be later (for instance, inside a callback) be retrieved by calling gsasl_application_session_data_get(). It is normally used by the application to maintain state between the main program and the callback.

— Function: void * gsasl_appinfo_get (Gsasl_session * sctx)

sctx: libgsasl client handle.

Retrieve application specific data from libgsasl session handle. The application data is set using gsasl_application_session_data_set(). It is normally used by the application to maintain state between the main program and the callback.

Return value: Returns the application specific data, or NULL.

— Function: void gsasl_server_callback_validate_set (Gsasl * ctx, Gsasl_server_callback_validate cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server for deciding if user is authenticated using authentication identity, authorization identity and password. The function can be later retrieved using gsasl_server_callback_validate_get().

— Function: Gsasl_server_callback_validate gsasl_server_callback_validate_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_validate_set().

— Function: void gsasl_server_callback_retrieve_set (Gsasl * ctx, Gsasl_server_callback_retrieve cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server for deciding if user is authenticated using authentication identity, authorization identity and password. The function can be later retrieved using gsasl_server_callback_retrieve_get().

— Function: Gsasl_server_callback_retrieve gsasl_server_callback_retrieve_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_retrieve_set().

— Function: void gsasl_server_callback_cram_md5_set (Gsasl * ctx, Gsasl_server_callback_cram_md5 cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server for deciding if user is authenticated using CRAM-MD5 challenge and response. The function can be later retrieved using gsasl_server_callback_cram_md5_get().

— Function: Gsasl_server_callback_cram_md5 gsasl_server_callback_cram_md5_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_cram_md5_set().

— Function: void gsasl_server_callback_digest_md5_set (Gsasl * ctx, Gsasl_server_callback_digest_md5 cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server for retrieving the secret hash of the username, realm and password for use in the DIGEST-MD5 mechanism. The function can be later retrieved using gsasl_server_callback_digest_md5_get().

— Function: Gsasl_server_callback_digest_md5 gsasl_server_callback_digest_md5_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Return the callback earlier set by calling gsasl_server_callback_digest_md5_set().

— Function: void gsasl_server_callback_external_set (Gsasl * ctx, Gsasl_server_callback_external cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server for deciding if user is authenticated out of band. The function can be later retrieved using gsasl_server_callback_external_get().

— Function: Gsasl_server_callback_external gsasl_server_callback_external_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_external_set().

— Function: void gsasl_server_callback_anonymous_set (Gsasl * ctx, Gsasl_server_callback_anonymous cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server for deciding if user is permitted anonymous access. The function can be later retrieved using gsasl_server_callback_anonymous_get().

— Function: Gsasl_server_callback_anonymous gsasl_server_callback_anonymous_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_anonymous_set().

— Function: void gsasl_server_callback_realm_set (Gsasl * ctx, Gsasl_server_callback_realm cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server to know which realm it serves. The realm is used by the user to determine which username and password to use. The function can be later retrieved using gsasl_server_callback_realm_get().

— Function: Gsasl_server_callback_realm gsasl_server_callback_realm_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_realm_set().

— Function: void gsasl_server_callback_qop_set (Gsasl * ctx, Gsasl_server_callback_qop cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server to know which quality of protection it accepts. The quality of protection eventually used is selected by the client though. It is currently used by the DIGEST-MD5 mechanism. The function can be later retrieved using gsasl_server_callback_qop_get().

— Function: Gsasl_server_callback_qop gsasl_server_callback_qop_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_qop_set().

— Function: void gsasl_server_callback_maxbuf_set (Gsasl * ctx, Gsasl_server_callback_maxbuf cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server to inform the client of the largest buffer the server is able to receive when using the DIGEST-MD5 "auth-int" or "auth-conf" Quality of Protection (qop). If this directive is missing, the default value 65536 will be assumed. The function can be later retrieved using gsasl_server_callback_maxbuf_get().

— Function: Gsasl_server_callback_maxbuf gsasl_server_callback_maxbuf_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_maxbuf_set().

— Function: void gsasl_server_callback_cipher_set (Gsasl * ctx, Gsasl_server_callback_cipher cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server to inform the client of the cipher suites supported. The DES and 3DES ciphers must be supported for interoperability. It is currently used by the DIGEST-MD5 mechanism. The function can be later retrieved using gsasl_server_callback_cipher_get().

— Function: Gsasl_server_callback_cipher gsasl_server_callback_cipher_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_cipher_set().

— Function: void gsasl_server_callback_securid_set (Gsasl * ctx, Gsasl_server_callback_securid cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server for validating a user via the SECURID mechanism. The function should return GSASL_OK if user authenticated successfully, GSASL_SECURID_SERVER_NEED_ADDITIONAL_PASSCODE if it wants another passcode, GSASL_SECURID_SERVER_NEED_NEW_PIN if it wants a PIN change, or an error. When (and only when) GSASL_SECURID_SERVER_NEED_NEW_PIN is returned, suggestpin can be populated with a PIN code the server suggests, and suggestpinlen set to the length of the PIN. The function can be later retrieved using gsasl_server_callback_securid_get().

— Function: Gsasl_server_callback_securid gsasl_server_callback_securid_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_securid_set().

— Function: void gsasl_server_callback_gssapi_set (Gsasl * ctx, Gsasl_server_callback_gssapi cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server for checking if a GSSAPI user is authorized for username (by, e.g., calling krb5_userok()). The function should return GSASL_OK if the user should be permitted access, or an error code such as GSASL_AUTHENTICATION_ERROR on failure. The function can be later retrieved using gsasl_server_callback_gssapi_get().

— Function: Gsasl_server_callback_gssapi gsasl_server_callback_gssapi_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_gssapi_set().

— Function: void gsasl_server_callback_service_set (Gsasl * ctx, Gsasl_server_callback_service cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the server to set the name of the service. The service buffer should be a registered GSSAPI host-based service name, hostname the name of the server. The function can be later retrieved using gsasl_server_callback_service_get().

— Function: Gsasl_server_callback_service gsasl_server_callback_service_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_server_callback_service_set().

— Function: void gsasl_client_callback_authentication_id_set (Gsasl * ctx, Gsasl_client_callback_authentication_id cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the client to set the authentication identity. The function can be later retrieved using gsasl_client_callback_authentication_id_get().

— Function: Gsasl_client_callback_authentication_id gsasl_client_callback_authentication_id_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_client_callback_authentication_id_set().

— Function: void gsasl_client_callback_authorization_id_set (Gsasl * ctx, Gsasl_client_callback_authorization_id cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the client to set the authorization identity. The function can be later retrieved using gsasl_client_callback_authorization_id_get().

— Function: Gsasl_client_callback_authorization_id gsasl_client_callback_authorization_id_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_client_callback_authorization_id_set().

— Function: void gsasl_client_callback_password_set (Gsasl * ctx, Gsasl_client_callback_password cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the client to set the password. The function can be later retrieved using gsasl_client_callback_password_get().

— Function: Gsasl_client_callback_password gsasl_client_callback_password_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_client_callback_password_set().

— Function: void gsasl_client_callback_passcode_set (Gsasl * ctx, Gsasl_client_callback_passcode cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the client to set the passcode. The function can be later retrieved using gsasl_client_callback_passcode_get().

— Function: Gsasl_client_callback_passcode gsasl_client_callback_passcode_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_client_callback_passcode_set().

— Function: void gsasl_client_callback_pin_set (Gsasl * ctx, Gsasl_client_callback_pin cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the client to chose a new pin, possibly suggested by the server, for the SECURID mechanism. This is not normally invoked, but only when the server requests it. The function can be later retrieved using gsasl_client_callback_pin_get().

— Function: Gsasl_client_callback_pin gsasl_client_callback_pin_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_client_callback_pin_set().

— Function: void gsasl_client_callback_service_set (Gsasl * ctx, Gsasl_client_callback_service cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the client to set the name of the service. The service buffer should be a registered GSSAPI host-based service name, hostname the name of the server. Servicename is used by DIGEST-MD5 and should be the name of generic server in case of a replicated service. The function can be later retrieved using gsasl_client_callback_service_get().

— Function: Gsasl_client_callback_service gsasl_client_callback_service_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_client_callback_service_set().

— Function: void gsasl_client_callback_anonymous_set (Gsasl * ctx, Gsasl_client_callback_anonymous cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the client to set the anonymous token, which usually is the users email address. The function can be later retrieved using gsasl_client_callback_anonymous_get().

— Function: Gsasl_client_callback_anonymous gsasl_client_callback_anonymous_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_client_callback_anonymous_set().

— Function: void gsasl_client_callback_qop_set (Gsasl * ctx, Gsasl_client_callback_qop cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the client to determine the qop to use after looking at what the server offered. The function can be later retrieved using gsasl_client_callback_qop_get().

— Function: Gsasl_client_callback_qop gsasl_client_callback_qop_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_client_callback_qop_set().

— Function: void gsasl_client_callback_maxbuf_set (Gsasl * ctx, Gsasl_client_callback_maxbuf cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the client to inform the server of the largest buffer the client is able to receive when using the DIGEST-MD5 "auth-int" or "auth-conf" Quality of Protection (qop). If this directive is missing, the default value 65536 will be assumed. The function can be later retrieved using gsasl_client_callback_maxbuf_get().

— Function: Gsasl_client_callback_maxbuf gsasl_client_callback_maxbuf_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_client_callback_maxbuf_set().

— Function: void gsasl_client_callback_realm_set (Gsasl * ctx, Gsasl_client_callback_realm cb)

ctx: libgsasl handle.

cb: callback function

Specify the callback function to use in the client to know which realm it belongs to. The realm is used by the server to determine which username and password to use. The function can be later retrieved using gsasl_client_callback_realm_get().

— Function: Gsasl_client_callback_realm gsasl_client_callback_realm_get (Gsasl * ctx)

ctx: libgsasl handle.

Return value: Returns the callback earlier set by calling gsasl_client_callback_realm_set().


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7 Session Functions

— Function: int gsasl_client_start (Gsasl * ctx, const char * mech, Gsasl_session ** sctx)

ctx: libgsasl handle.

mech: name of SASL mechanism.

sctx: pointer to client handle.

This functions initiates a client SASL authentication. This function must be called before any other gsasl_client_*() function is called.

Return value: Returns GSASL_OK if successful, or error code.

— Function: int gsasl_server_start (Gsasl * ctx, const char * mech, Gsasl_session ** sctx)

ctx: libgsasl handle.

mech: name of SASL mechanism.

sctx: pointer to server handle.

This functions initiates a server SASL authentication. This function must be called before any other gsasl_server_*() function is called.

Return value: Returns GSASL_OK if successful, or error code.

— Function: int gsasl_step (Gsasl_session * sctx, const char * input, size_t input_len, char ** output, size_t * output_len)

sctx: libgsasl session handle.

input: input byte array.

input_len: size of input byte array.

output: newly allocated output byte array.

output_len: pointer to output variable with size of output byte array.

Perform one step of SASL authentication. This reads data from the other end (from input and input_len), processes it (potentially invoking callbacks to the application), and writes data to server (into newly allocated variable output and output_len that indicate the length of output).

The contents of the output buffer is unspecified if this functions returns anything other than GSASL_OK or GSASL_NEEDS_MORE. If this function return GSASL_OK or GSASL_NEEDS_MORE, however, the output buffer is allocated by this function, and it is the responsibility of caller to deallocate it by calling free (output).

Return value: Returns GSASL_OK if authenticated terminated successfully, GSASL_NEEDS_MORE if more data is needed, or error code.

— Function: int gsasl_step64 (Gsasl_session * sctx, const char * b64input, char ** b64output)

sctx: libgsasl client handle.

b64input: input base64 encoded byte array.

b64output: newly allocated output base64 encoded byte array.

This is a simple wrapper around gsasl_step() that base64 decodes the input and base64 encodes the output.

The contents of the b64output buffer is unspecified if this functions returns anything other than GSASL_OK or GSASL_NEEDS_MORE. If this function return GSASL_OK or GSASL_NEEDS_MORE, however, the b64output buffer is allocated by this function, and it is the responsibility of caller to deallocate it by calling free (b64output).

Return value: Returns GSASL_OK if authenticated terminated successfully, GSASL_NEEDS_MORE if more data is needed, or error code.

— Function: void gsasl_finish (Gsasl_session * sctx)

sctx: libgsasl session handle.

Destroy a libgsasl client or server handle. The handle must not be used with other libgsasl functions after this call.

— Function: int gsasl_encode (Gsasl_session * sctx, const char * input, size_t input_len, char * output, size_t * output_len)

sctx: libgsasl session handle.

input: input byte array.

input_len: size of input byte array.

output: output byte array.

output_len: size of output byte array.

Encode data according to negotiated SASL mechanism. This might mean that data is integrity or privacy protected.

Return value: Returns GSASL_OK if encoding was successful, otherwise an error code.

— Function: int gsasl_decode (Gsasl_session * sctx, const char * input, size_t input_len, char * output, size_t * output_len)

sctx: libgsasl session handle.

input: input byte array.

input_len: size of input byte array.

output: output byte array.

output_len: size of output byte array.

Decode data according to negotiated SASL mechanism. This might mean that data is integrity or privacy protected.

Return value: Returns GSASL_OK if encoding was successful, otherwise an error code.


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8 Utilities

— Function: char * gsasl_stringprep_nfkc (const char * in, ssize_t len)

in: a UTF-8 encoded string.

len: length of str, in bytes, or -1 if str is nul-terminated.

Converts a string into canonical form, standardizing such issues as whether a character with an accent is represented as a base character and combining accent or as a single precomposed character.

The normalization mode is NFKC (ALL COMPOSE). It standardizes differences that do not affect the text content, such as the above-mentioned accent representation. It standardizes the "compatibility" characters in Unicode, such as SUPERSCRIPT THREE to the standard forms (in this case DIGIT THREE). Formatting information may be lost but for most text operations such characters should be considered the same. It returns a result with composed forms rather than a maximally decomposed form.

Return value: Return a newly allocated string, that is the NFKC normalized form of str, o NULL on error.

— Function: char * gsasl_stringprep_saslprep (const char * in, int * stringprep_rc)

in: input ASCII or UTF-8 string with data to prepare according to SASLprep.

stringprep_rc: pointer to output variable with stringprep error code, or NULL to indicate that you don't care about it.

Process a Unicode string for comparison, according to the "SASLprep" stringprep profile. This function is intended to be used by Simple Authentication and Security Layer (SASL) mechanisms (such as PLAIN, CRAM-MD5, and DIGEST-MD5) as well as other protocols exchanging user names and/or passwords.

Return value: Return a newly allocated string that is the "SASLprep" processed form of the input string, or NULL on error, in which case stringprep_rc contain the stringprep library error code.

— Function: char * gsasl_stringprep_trace (const char * in, int * stringprep_rc)

in: input ASCII or UTF-8 string with data to prepare according to "trace".

stringprep_rc: pointer to output variable with stringprep error code, or NULL to indicate that you don't care about it.

Process a Unicode string for use as trace information, according to the "trace" stringprep profile. The profile is designed for use with the SASL ANONYMOUS Mechanism.

Return value: Return a newly allocated string that is the "trace" processed form of the input string, or NULL on error, in which case stringprep_rc contain the stringprep library error code.

— Function: int gsasl_base64_encode (char const * src, size_t srclength, char * target, size_t targsize)

src: input byte array

srclength: size of input byte array

target: output byte array

targsize: size of output byte array

Encode data as base64. Converts characters, three at a time, starting at src into four base64 characters in the target area until the entire input buffer is encoded.

Return value: Returns the number of data bytes stored at the target, or -1 on error.

— Function: int gsasl_base64_decode (char const * src, char * target, size_t targsize)

src: input byte array

target: output byte array

targsize: size of output byte array

Decode Base64 data. Skips all whitespace anywhere. Converts characters, four at a time, starting at (or after) src from Base64 numbers into three 8 bit bytes in the target area.

Return value: Returns the number of data bytes stored at the target, or -1 on error.

— Function: int gsasl_md5pwd_get_password (const char * filename, const char * username, char * key, size_t * keylen)

filename: filename of file containing passwords.

username: username string.

key: output character array.

keylen: input maximum size of output character array, on output contains actual length of output array.

Retrieve password for user from specified file. To find out how large the output array must be, call this function with out=NULL.

The file should be on the UoW "MD5 Based Authentication" format, which means it is in text format with comments denoted by # first on the line, with user entries looking as username\tpassword. This function removes \r and \n at the end of lines before processing.

Return value: Return GSASL_OK if output buffer contains the password, GSASL_AUTHENTICATION_ERROR if the user could not be found, or other error code.

— Function: int gsasl_randomize (int strong, char * data, size_t datalen)

strong: 0 iff operation should not block, non-0 for very strong randomness.

data: output array to be filled with random data.

datalen: size of output array.

Store cryptographically random data of given size in the provided buffer.

Return value: Returns GSASL_OK iff successful.

— Function: int gsasl_md5 (const char * in, size_t inlen, char * out[MD5_DIGEST_SIZE])

in: input character array of data to hash.

inlen: length of input character array of data to hash.

Compute hash of data using MD5. The out buffer must be deallocated by the caller.

Return value: Returns GSASL_OK iff successful.

— Function: int gsasl_hmac_md5 (const char * key, size_t keylen, const char * in, size_t inlen, char * outhash[MD5_DIGEST_SIZE])

key: input character array with key to use.

keylen: length of input character array with key to use.

in: input character array of data to hash.

inlen: length of input character array of data to hash.

Compute keyed checksum of data using HMAC-MD5. The outhash buffer must be deallocated by the caller.

Return value: Returns GSASL_OK iff successful.


Next: , Previous: Session Functions, Up: Top

9 Old Functions

As GNU SASL is still under heavy development, some API functions have been found to be less useful. Those old API functions will be supported during a transition period. Refer to the NEWS file to find out since when a function has been deprecated.

— Function: int gsasl_client_listmech (Gsasl_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output character array.

outlen: input maximum size of output character array, on output contains actual length of output array.

Write SASL names, separated by space, of mechanisms supported by the libgsasl client to the output array. To find out how large the output array must be, call this function with out=NULL.

Note that this function is obsolete and may be removed in the future.

Return value: Returns GSASL_OK if successful, or error code.

— Function: int gsasl_server_listmech (Gsasl_ctx * ctx, char * out, size_t * outlen)

ctx: libgsasl handle.

out: output character array.

outlen: input maximum size of output character array, on output contains actual length of output array.

Write SASL names, separated by space, of mechanisms supported by the libgsasl server to the output array. To find out how large the output array must be, call this function with out=NULL.

Note that this function is obsolete and may be removed in the future.

Return value: Returns GSASL_OK if successful, or error code.

— Function: int gsasl_client_step (Gsasl_session_ctx * sctx, const char * input, size_t input_len, char * output, size_t * output_len)

sctx: libgsasl client handle.

input: input byte array.

input_len: size of input byte array.

output: output byte array.

output_len: size of output byte array.

Perform one step of SASL authentication in client. This reads data from server (specified with input and input_len), processes it (potentially invoking callbacks to the application), and writes data to server (into variables output and output_len).

The contents of the output buffer is unspecified if this functions returns anything other than GSASL_NEEDS_MORE.

Note that this function is obsolete and may be removed in the future.

Return value: Returns GSASL_OK if authenticated terminated successfully, GSASL_NEEDS_MORE if more data is needed, or error code.

— Function: int gsasl_server_step (Gsasl_session_ctx * sctx, const char * input, size_t input_len, char * output, size_t * output_len)

sctx: libgsasl server handle.

input: input byte array.

input_len: size of input byte array.

output: output byte array.

output_len: size of output byte array.

Perform one step of SASL authentication in server. This reads data from client (specified with input and input_len), processes it (potentially invoking callbacks to the application), and writes data to client (into variables output and output_len).

The contents of the output buffer is unspecified if this functions returns anything other than GSASL_NEEDS_MORE.

Note that this function is obsolete and may be removed in the future.

Return value: Returns GSASL_OK if authenticated terminated successfully, GSASL_NEEDS_MORE if more data is needed, or error code.

— Function: int gsasl_client_step_base64 (Gsasl_session_ctx * sctx, const char * b64input, char * b64output, size_t b64output_len)

sctx: libgsasl client handle.

b64input: input base64 encoded byte array.

b64output: output base64 encoded byte array.

b64output_len: size of output base64 encoded byte array.

This is a simple wrapper around gsasl_client_step() that base64 decodes the input and base64 encodes the output.

Note that this function is obsolete and may be removed in the future.

Return value: See gsasl_client_step().

— Function: int gsasl_server_step_base64 (Gsasl_session_ctx * sctx, const char * b64input, char * b64output, size_t b64output_len)

sctx: libgsasl server handle.

b64input: input base64 encoded byte array.

b64output: output base64 encoded byte array.

b64output_len: size of output base64 encoded byte array.

This is a simple wrapper around gsasl_server_step() that base64 decodes the input and base64 encodes the output.

Note that this function is obsolete and may be removed in the future.

Return value: See gsasl_server_step().

— Function: void gsasl_client_finish (Gsasl_session_ctx * sctx)

sctx: libgsasl client handle.

Destroy a libgsasl client handle. The handle must not be used with other libgsasl functions after this call.

Note that this function is obsolete and may be removed in the future.

— Function: void gsasl_server_finish (Gsasl_session_ctx * sctx)

sctx: libgsasl server handle.

Destroy a libgsasl server handle. The handle must not be used with other libgsasl functions after this call.

Note that this function is obsolete and may be removed in the future.

— Function: Gsasl_ctx * gsasl_client_ctx_get (Gsasl_session_ctx * sctx)

sctx: libgsasl client handle

Note that this function is obsolete and may be removed in the future.

Return value: Returns the libgsasl handle given a libgsasl client handle.

— Function: void gsasl_client_application_data_set (Gsasl_session_ctx * sctx, void * application_data)

sctx: libgsasl client handle.

application_data: opaque pointer to application specific data.

Store application specific data in the libgsasl client handle. The application data can be later (for instance, inside a callback) be retrieved by calling gsasl_client_application_data_get(). It is normally used by the application to maintain state between the main program and the callback.

Note that this function is obsolete and may be removed in the future.

— Function: void * gsasl_client_application_data_get (Gsasl_session_ctx * sctx)

sctx: libgsasl client handle.

Retrieve application specific data from libgsasl client handle. The application data is set using gsasl_client_application_data_set(). It is normally used by the application to maintain state between the main program and the callback.

Note that this function is obsolete and may be removed in the future.

Return value: Returns the application specific data, or NULL.

— Function: Gsasl_ctx * gsasl_server_ctx_get (Gsasl_session_ctx * sctx)

sctx: libgsasl server handle

Note that this function is obsolete and may be removed in the future.

Return value: Returns the libgsasl handle given a libgsasl server handle.

— Function: void gsasl_server_application_data_set (Gsasl_session_ctx * sctx, void * application_data)

sctx: libgsasl server handle.

application_data: opaque pointer to application specific data.

Store application specific data in the libgsasl server handle. The application data can be later (for instance, inside a callback) be retrieved by calling gsasl_server_application_data_get(). It is normally used by the application to maintain state between the main program and the callback.

Note that this function is obsolete and may be removed in the future.

— Function: void * gsasl_server_application_data_get (Gsasl_session_ctx * sctx)

sctx: libgsasl server handle.

Retrieve application specific data from libgsasl server handle. The application data is set using gsasl_server_application_data_set(). It is normally used by the application to maintain state between the main program and the callback.

Note that this function is obsolete and may be removed in the future.

Return value: Returns the application specific data, or NULL.


Next: , Previous: Utilities, Up: Top

10 Error Handling

Most functions in `Libgsasl' are returning an error if they fail. For this reason, the application should always catch the error condition and take appropriate measures, for example by releasing the resources and passing the error up to the caller, or by displaying a descriptive message to the user and cancelling the operation.

Some error values do not indicate a system error or an error in the operation, but the result of an operation that failed properly.


Next: , Up: Error Handling

10.1 Error values

Errors are returned as an int. Except for the OK case an application should always use the constants instead of their numeric value. Applications are encouraged to use the constants even for OK as it improves readability. Possible values are:

GSASL_OK
This value indicates success. The value of this error is guaranteed to always be 0 so you may use it in boolean constructs.
GSASL_NEEDS_MORE
SASL mechanisms needs more data
GSASL_UNKNOWN_MECHANISM
Unknown SASL mechanism
GSASL_MECHANISM_CALLED_TOO_MANY_TIMES
SASL mechanism called too many times
GSASL_TOO_SMALL_BUFFER
SASL function need larger buffer (internal error)
GSASL_FOPEN_ERROR
Could not open file in SASL library
GSASL_FCLOSE_ERROR
Could not close file in SASL library
GSASL_MALLOC_ERROR
Memory allocation error in SASL library
GSASL_BASE64_ERROR
Base 64 coding error in SASL library
GSASL_GCRYPT_ERROR
Gcrypt error in SASL library
GSASL_GSSAPI_RELEASE_BUFFER_ERROR
GSSAPI library could not deallocate memory in gss_release_buffer() in SASL library. This is a serious internal error.
GSASL_GSSAPI_IMPORT_NAME_ERROR
GSSAPI library could not understand a peer name in gss_import_name() in SASL library. This may be due to incorrect user supplied data.
GSASL_GSSAPI_INIT_SEC_CONTEXT_ERROR
GSSAPI error in client while negotiating security context in gss_init_sec_context() in SASL library. This is most likely due insufficient credentials or malicious interactions.
GSASL_GSSAPI_ACCEPT_SEC_CONTEXT_ERROR
GSSAPI error in server while negotiating security context in gss_init_sec_context() in SASL library. This is most likely due insufficient credentials or malicious interactions.
GSASL_GSSAPI_UNWRAP_ERROR
GSSAPI error while decrypting or decoding data in gss_unwrap() in SASL library. This is most likely due to data corruption.
GSASL_GSSAPI_WRAP_ERROR
GSSAPI error while encrypting or encoding data in gss_wrap() in SASL library.
GSASL_GSSAPI_ACQUIRE_CRED_ERROR
GSSAPI error acquiring credentials in gss_acquire_cred() in SASL library. This is most likely due to not having the proper Kerberos key available in /etc/krb5.keytab on the server.
GSASL_GSSAPI_DISPLAY_NAME_ERROR
GSSAPI error creating a display name denoting the client in gss_display_name() in SASL library. This is probably because the client suplied bad data.
GSASL_GSSAPI_UNSUPPORTED_PROTECTION_ERROR
Other entity requested integrity or confidentiality protection in GSSAPI mechanism but this is currently not implemented.
GSASL_NEED_CLIENT_ANONYMOUS_CALLBACK
SASL mechanism needs gsasl_client_callback_anonymous() callback (application error)
GSASL_NEED_CLIENT_PASSWORD_CALLBACK
SASL mechanism needs gsasl_client_callback_password() callback (application error)
GSASL_NEED_CLIENT_PASSCODE_CALLBACK
SASL mechanism needs gsasl_client_callback_passcode() callback (application error)
GSASL_NEED_CLIENT_PIN_CALLBACK
SASL mechanism needs gsasl_client_callback_pin() callback (application error)
GSASL_NEED_CLIENT_AUTHORIZATION_ID_CALLBACK
SASL mechanism needs gsasl_client_callback_authorization_id() callback (application error)
GSASL_NEED_CLIENT_AUTHENTICATION_ID_CALLBACK
SASL mechanism needs gsasl_client_callback_authentication_id() callback (application error)
GSASL_NEED_CLIENT_SERVICE_CALLBACK
SASL mechanism needs gsasl_client_callback_service() callback (application error)
GSASL_NEED_SERVER_VALIDATE_CALLBACK
SASL mechanism needs gsasl_server_callback_validate() callback (application error)
GSASL_NEED_SERVER_CRAM_MD5_CALLBACK
SASL mechanism needs gsasl_server_callback_cram_md5() callback (application error)
GSASL_NEED_SERVER_DIGEST_MD5_CALLBACK
SASL mechanism needs gsasl_server_callback_digest_md5() callback (application error)
GSASL_NEED_SERVER_ANONYMOUS_CALLBACK
SASL mechanism needs gsasl_server_callback_anonymous() callback (application error)
GSASL_NEED_SERVER_EXTERNAL_CALLBACK
SASL mechanism needs gsasl_server_callback_external() callback (application error)
GSASL_NEED_SERVER_REALM_CALLBACK
SASL mechanism needs gsasl_server_callback_realm() callback (application error)
GSASL_NEED_SERVER_SECURID_CALLBACK
SASL mechanism needs gsasl_server_callback_securid() callback (application error)
GSASL_NEED_SERVER_SERVICE_CALLBACK
SASL mechanism needs gsasl_server_callback_service() callback (application error)
GSASL_NEED_SERVER_GSSAPI_CALLBACK
SASL mechanism needs gsasl_server_callback_gssapi() callback (application error)
GSASL_NEED_SERVER_RETRIEVE_CALLBACK
SASL mechanism needs gsasl_server_callback_retrieve() callback (application error)
GSASL_MECHANISM_PARSE_ERROR
SASL mechanism could not parse input
GSASL_AUTHENTICATION_ERROR
Error authentication user
GSASL_CANNOT_GET_CTX
Cannot get internal library handle (library error)
GSASL_INTEGRITY_ERROR
Integrity error in application payload
GSASL_NO_MORE_REALMS
No more realms available (non-fatal)
GSASL_NO_CLIENT_CODE
Client-side functionality not available in library (application error)
GSASL_NO_SERVER_CODE
Server-side functionality not available in library (application error)
GSASL_INVALID_HANDLE
The provided library handle was invalid (application error)


Previous: Error values, Up: Error Handling

10.2 Error strings

— Function: const char * gsasl_strerror (int err)

err: libgsasl error code

Return value: Returns a pointer to a statically allocated string containing a description of the error with the error value err. This string can be used to output a diagnostic message to the user.


Next: , Previous: Error Handling, Up: Top

11 Examples

This chapter contains example code which illustrate how `Libgsasl' can be used when writing your own application.


Up: Examples

11.1 Example 1

This is the minimal program which uses `Libgsasl' (including internationalization features) without doing anything.

     #include <locale.h>
     #include <stdio.h>
     #include <gsasl.h>

     /* Build using the following command:
      * gcc -o foo foo.c `libgsasl-config --cflags --libs`
      */

     int
     main (int argc, char *argv[])
     {
       Gsasl_ctx *ctx;
       int res;

       setlocale (LC_ALL, "");

       if (gsasl_check_version(GSASL_VERSION) == NULL)
         {
           fprintf(stderr, "Libgsasl is %s expected %s\n",
     	      gsasl_check_version(NULL), GSASL_VERSION);
           return 1;
         }

       res = gsasl_init (&ctx);
       if (res != GSASL_OK)
         {
           fprintf(stderr, "Cannot initialize libgsasl: %s\n",
     	      gsasl_strerror(res));
           return 1;
         }

       /* Do things here ... */

       gsasl_done(ctx);

       return 0;
     }


Next: , Previous: Examples, Up: Top

12 Acknowledgements

The makefiles, manuals, etc borrowed much from Libgcrypt written by Werner Koch.

Cryptographic functions for some SASL mechanisms uses Libgcrypt by Werner Koch et al. The NTLM mechanism uses Libntlm by Grant Edwards et al, using code from Samba written by Andrew Tridgell, and now maintained by Simon Josefsson. The KERBEROS_V5 mechanism uses Shishi by Simon Josefsson. The GSSAPI mechanism uses a GSS-API implementation, such as GSSLib by Simon Josefsson.

This manual borrows text from the SASL specification.


Next: , Previous: Acknowledgements, Up: Top

13 Invoking gsasl

Name

GNU SASL (gsasl) – Command line interface to libgsasl.

Description

gsasl is the main program of GNU SASL.

This section only lists the commands and options available.

Mandatory or optional arguments to long options are also mandatory or optional for any corresponding short options.

Commands

gsasl recognizes these commands:

  -c, --client               Act as client.
      --client-mechanisms    Write name of supported client mechanisms
                             separated by space to stdout.
  -s, --server               Act as server.
      --server-mechanisms    Write name of supported server mechanisms
                             separated by space to stdout.

Network Options

Normally the SASL negotiation is performed on the terminal, with reading from stdin and writing to stdout. It is also possible to perform the negotiation with a server over a TCP network connection.

      --connect=HOSTNAME[:SERVICE]
                             Connect to TCP server and negotiate on stream
                             instead of stdin/stdout. SERVICE is the protocol
                             service, or an integer denoting the port, and
                             defaults to 143 (imap) if not specified. Also sets
                             the --hostname default.

Miscellaneous Options:

These parameters affect overall behaviour.

  -d, --application-data     After authentication, read data from stdin and run
                             it through the mechanism's security layer and
                             print it base64 encoded to stdout. The default is
                             to terminate after authentication.
      --imap                 Use a IMAP-like logon procedure (client only).
                             Also sets the --service default to "imap".
  -m, --mechanism=STRING     Mechanism to use.
      --no-client-first      Disallow client to send data first (client only).

SASL Mechanism Options

These options modify the behaviour of the callbacks (see Callback Functions) in the library. The default is the query the user on the terminal.

  -a, --authentication-id=STRING   Identity of credential owner.
      --disable-cleartext-validate
                             Disable cleartext validate hook, forcing server to
                             prompt for password.
      --enable-cram-md5-validate   Validate CRAM-MD5 challenge and response
                             interactively.
      --hostname=STRING      Set the name of the server with the requested
                             service.
  -n, --anonymous-token=STRING   Token for anonymous authentication, usually
                             mail address (ANONYMOUS only).
  -p, --password=STRING      Password for authentication (insecure for
                             non-testing purposes).
      --passcode=NUMBER      Passcode for authentication (SECURID only).
      --quality-of-protection=<auth | auth-int | auth-conf>
                             How application payload will be protected.  "auth"
                             means no protection, "auth-int" means integrity
                             protection, "auth-conf" means integrity and
                             confidentialiy protection.  Currently only used by
                             DIGEST-MD5, where the default is "auth-conf".
  -r, --realm=STRING         Realm (may be given more than once iff server).
                             Defaults to hostname.
      --service=STRING       Set the requested service name (should be a
                             registered GSSAPI host based service name).
      --service-name=STRING  Set the generic server name in case of a
                             replicated server (DIGEST-MD5 only).
  -x, --maxbuf=NUMBER        Indicate maximum buffer size (DIGEST-MD5 only).
  -z, --authorization-id=STRING   Identity to request service for.

Other Options

These are some standard parameters.

  -q, --quiet, --silent      Don't produce any diagnostic output.
  -v, --verbose              Produce verbose output.

  -?, --help                 Give this help list
      --usage                Give a short usage message
  -V, --version              Print program version


Next: , Previous: Invoking gsasl, Up: Top

Appendix A Copying This Manual


Up: Copying This Manual

A.1 GNU Free Documentation License

Version 1.2, November 2002
     Copyright © 2000,2001,2002 Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA  02111-1307, USA

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.
  1. PREAMBLE

    The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

    This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

    We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

  2. APPLICABILITY AND DEFINITIONS

    This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

    A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

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    The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

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    The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

    A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.

    The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

  3. VERBATIM COPYING

    You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

    You may also lend copies, under the same conditions stated above, and you may publicly display copies.

  4. COPYING IN QUANTITY

    If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

    If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

    If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

    It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

  5. MODIFICATIONS

    You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

    1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
    2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
    3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
    4. Preserve all the copyright notices of the Document.
    5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
    6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
    7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
    8. Include an unaltered copy of this License.
    9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
    10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
    11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
    12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
    13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
    14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
    15. Preserve any Warranty Disclaimers.

    If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

    You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

    You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

    The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

  6. COMBINING DOCUMENTS

    You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

    The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

    In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”

  7. COLLECTIONS OF DOCUMENTS

    You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

    You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

  8. AGGREGATION WITH INDEPENDENT WORKS

    A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

  9. TRANSLATION

    Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

    If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

  10. TERMINATION

    You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

  11. FUTURE REVISIONS OF THIS LICENSE

    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

A.1.1 ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

       Copyright (C)  year  your name.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:

         with the Invariant Sections being list their titles, with
         the Front-Cover Texts being list, and with the Back-Cover Texts
         being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.


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