Copyright © 2003 Simon Josefsson.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being “Commercial Support” and “Criticism of GSS”, the Front-Cover texts being “A GNU Manual”, and with the Back-Cover Texts being “You have freedom to copy and modify this GNU Manual, like GNU software”. A copy of the license is included in the section entitled “GNU Free Documentation License”.
GSS is an implementation of the Generic Security Service Application Program Interface (GSS-API). GSS-API is used by network servers to provide security services, e.g., to authenticate SMTP/IMAP clients against SMTP/IMAP servers. GSS consists of a library and a manual.
GSS 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.
GSS is a GNU project, and is licensed under the GNU General Public License.
This manual documents the GSS programming interface. All functions and data types provided by the library are explained.
The reader is assumed to possess basic familiarity with GSS-API and
network programming in C or C++. For general GSS-API information, and
some programming examples, there is a guide available online at
<http://docs.sun.com/db/doc/816-1331>.
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.
GSS might have a couple of advantages over other libraries doing a similar job.
This section describes GSS-API from a protocol point of view.
The Generic Security Service Application Programming Interface provides security services to calling applications. It allows a communicating application to authenticate the user associated with another application, to delegate rights to another application, and to apply security services such as confidentiality and integrity on a per-message basis.
There are four stages to using the GSS-API:
To establish and maintain the shared information that makes up the security context, certain GSS-API calls will return a token data structure, which is an opaque data type that may contain cryptographically protected data. The caller of such a GSS-API routine is responsible for transferring the token to the peer application, encapsulated if necessary in an application- application protocol. On receipt of such a token, the peer application should pass it to a corresponding GSS-API routine which will decode the token and extract the information, updating the security context state information accordingly.
GSS has at some point in time been tested on the following platforms.
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.
GCC 2.95.1 and GNU Make. armv4l-unknown-linux-gnu.
Tru64 UNIX C compiler and Tru64 Make. alphaev67-dec-osf5.1,
alphaev68-dec-osf5.1.
GCC 2.96 and GNU Make. alphaev6-unknown-linux-gnu,
alphaev67-unknown-linux-gnu.
GCC 3.0 and GNU Make. ia64-unknown-linux-gnu.
GCC 2.96 and GNU Make. alphaev6-unknown-linux-gnu,
alphaev67-unknown-linux-gnu, ia64-unknown-linux-gnu.
GCC 3.2 and GNU Make. i686-pc-linux-gnu.
GCC 2.96 and GNU Make. i686-pc-linux-gnu.
GCC 2.95.3 and GNU Make. i686-pc-linux-gnu.
GCC 3.2 and GNU Make. i686-pc-linux-gnu.
MIPS C compiler, IRIX Make. mips-sgi-irix6.5.
IBM C for AIX compiler, AIX Make. rs6000-ibm-aix4.3.2.0.
GCC 3.2, GNU make. i686-pc-cygwin.
HP-UX C compiler and HP Make. ia64-hp-hpux11.22,
hppa2.0w-hp-hpux11.11.
Sun WorkShop Compiler C 6.0 and SUN Make. sparc-sun-solaris2.8.
GCC 2.95.3 and GNU Make. alpha-unknown-netbsd1.6,
i386-unknown-netbsdelf1.6.
GCC 2.95.3 and GNU Make. alpha-unknown-openbsd3.1,
i386-unknown-openbsd3.1.
GCC 2.95.4 and GNU Make. alpha-unknown-freebsd4.7,
i386-unknown-freebsd4.7.
If you use GSS on, or port GSS to, a new platform please report it to the author.
Commercial support is available for users of GNU GSS. 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 GSS and would like to be mentioned here, contact the author (see Bug Reports).
The package can be downloaded from several places, including
<http://josefsson.org/gss/releases/>. The latest version is
stored in a file, e.g., gss-0.0.7.tar.gz where the
0.0.7 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/gss/releases/gss-0.0.7.tar.gz
$ tar xfz gss-0.0.7.tar.gz
$ cd gss-0.0.7/
$ ./configure
...
$ make
...
$ make install
...
After that GSS should be properly installed and ready for use.
If you think you have found a bug in GSS, 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-gss@josefsson.orgIf 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:
If you normally code using another coding standard, there is no
problem, but you should use indent to reformat the code
(see GNU Indent) before submitting your work.
diff -u.
This is also known as the “todo list”. If you like to start working on anything, please let me know so work duplication can be avoided.
To use GSS, 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 GSS may be to look at the examples at the end of this manual.
All standard interfaces (data types and functions) of the official GSS
API are defined in the header file gss/api.h. The file is
taken verbatim from the RFC (after correcting a few typos) where it is
known as gssapi.h. However, to be able to co-exist gracefully
with other GSS-API implementation, the name gssapi.h was
changed.
The header file gss.h includes gss/api.h, add a few
non-standard extensions (by including gss/ext.h), takes care of
including header files related to all supported mechanisms (e.g.,
gss/krb5.h) and finally add C++ namespace protection of all
definitions. Therefore, including gss.h in your project is
recommended over gss/api.h. If using gss.h instead of
gss/api.h causes problems, it should be regarded a bug.
You must include either file in all programs using the library, either directly or through some other header file, like this:
#include <gss.h>
The name space of GSS is gss_* for function names, gss_*
for data types and GSS_* 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.
Each supported GSS mechanism may want to expose mechanism specific
functionality, and can do so through one or more header files under
the gss/ directory. The Kerberos 5 mechanism uses the file
gss/krb5.h, but again, it is included (with C++ namespace
fixes) from gss.h.
GSS does not need to be initialized before it can be used.
In order to take advantage of the internationalisation features in
GSS, e.g. translated error messages, the application must set the
current locale using setlocale() before calling, e.g.,
gss_display_status(). This is typically done in main()
as in the following example.
#include <gss.h>
#include <locale.h>
...
setlocale (LC_ALL, "");
It is often desirable to check that the version of GSS 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. The function is
called gss_check_version() and is described formally in
See Extended GSS API.
The normal way to use the function is to put something similar to the
following early in your main():
#include <gss.h>
...
if (!gss_check_version (GSS_VERSION))
{
printf ("gss_check_version() failed:\n"
"Header file incompatible with shared library.\n");
exit(1);
}
If you want to compile a source file that includes the gss.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, GSS 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 gss. The following
example shows how it can be used at the command line:
gcc -c foo.c `pkg-config gss --cflags`
Adding the output of pkg-config gss --cflags to the compilers
command line will ensure that the compiler can find the gss.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 gss can be used. For
convenience, this option also outputs all other options that are
required to link the program with the GSS libarary (for instance, the
-lshishi option). The example shows how to link foo.o
with GSS into a program foo.
gcc -o foo foo.o `pkg-config gss --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 gss --cflags --libs`
The GSS API does not have a standard error code for the out of memory error condition. Instead of adding a non-standard error code, this library has chosen to adopt a different strategy. Out of memory handling happens in rare situations, but performing the out of memory error handling after almost all API function invocations pollute your source code and might make it harder to spot more serious problems. The strategy chosen improve code readability and robustness.
For most applications, aborting the application with an error message when the out of memory situation occur is the best that can be wished for. This is how the library behaves by default.
However, we realize that some applications may not want to have the
GSS library abort execution in any situation. The GSS library support
a hook to let the application regain control and perform its own
cleanups when an out of memory situation has occured. The application
can define a function (having a void prototype, i.e., no return
value and no parameters) and set the library variable
xalloc_fail_func to that function. The variable should be
declared as follows.
extern void (*xalloc_fail_func) (void);
The GSS library will invoke this function if an out of memory error occurs. Note that after this the GSS library is in an undefined state, so you must unload or restart the application to continue call GSS library functions. The hook is only intended to allow the application to log the situation in a special way. Of course, care must be taken to not allocate more memory, as that will likely also fail.
Every GSS-API routine returns two distinct values to report status information to the caller: GSS status codes and Mechanism status codes.
GSS-API routines return GSS status codes as their OM_uint32 function value. These codes indicate errors that are independent of the underlying mechanism(s) used to provide the security service. The errors that can be indicated via a GSS status code are either generic API routine errors (errors that are defined in the GSS-API specification) or calling errors (errors that are specific to these language bindings).
A GSS status code can indicate a single fatal generic API error from the routine and a single calling error. In addition, supplementary status information may be indicated via the setting of bits in the supplementary info field of a GSS status code.
These errors are encoded into the 32-bit GSS status code as follows:
MSB LSB
|------------------------------------------------------------|
| Calling Error | Routine Error | Supplementary Info |
|------------------------------------------------------------|
Bit 31 24 23 16 15 0
Hence if a GSS-API routine returns a GSS status code whose upper 16 bits contain a non-zero value, the call failed. If the calling error field is non-zero, the invoking application's call of the routine was erroneous. Calling errors are defined in table 3-1. If the routine error field is non-zero, the routine failed for one of the routine- specific reasons listed below in table 3-2. Whether or not the upper 16 bits indicate a failure or a success, the routine may indicate additional information by setting bits in the supplementary info field of the status code. The meaning of individual bits is listed below in table 3-3.
Table 3-1 Calling Errors
Name Value in field Meaning
---- -------------- -------
GSS_S_CALL_INACCESSIBLE_READ 1 A required input parameter
could not be read
GSS_S_CALL_INACCESSIBLE_WRITE 2 A required output parameter
could not be written.
GSS_S_CALL_BAD_STRUCTURE 3 A parameter was malformed
Table 3-2 Routine Errors
Name Value in field Meaning
---- -------------- -------
GSS_S_BAD_MECH 1 An unsupported mechanism
was requested
GSS_S_BAD_NAME 2 An invalid name was
supplied
GSS_S_BAD_NAMETYPE 3 A supplied name was of an
unsupported type
GSS_S_BAD_BINDINGS 4 Incorrect channel bindings
were supplied
GSS_S_BAD_STATUS 5 An invalid status code was
supplied
GSS_S_BAD_MIC GSS_S_BAD_SIG 6 A token had an invalid MIC
GSS_S_NO_CRED 7 No credentials were
supplied, or the
credentials were
unavailable or
inaccessible.
GSS_S_NO_CONTEXT 8 No context has been
established
GSS_S_DEFECTIVE_TOKEN 9 A token was invalid
GSS_S_DEFECTIVE_CREDENTIAL 10 A credential was invalid
GSS_S_CREDENTIALS_EXPIRED 11 The referenced credentials
have expired
GSS_S_CONTEXT_EXPIRED 12 The context has expired
GSS_S_FAILURE 13 Miscellaneous failure (see
text)
GSS_S_BAD_QOP 14 The quality-of-protection
requested could not be
provided
GSS_S_UNAUTHORIZED 15 The operation is forbidden
by local security policy
GSS_S_UNAVAILABLE 16 The operation or option is
unavailable
GSS_S_DUPLICATE_ELEMENT 17 The requested credential
element already exists
GSS_S_NAME_NOT_MN 18 The provided name was not a
mechanism name
Table 3-3 Supplementary Status Bits
Name Bit Number Meaning
---- ---------- -------
GSS_S_CONTINUE_NEEDED 0 (LSB) Returned only by
gss_init_sec_context or
gss_accept_sec_context. The
routine must be called again
to complete its function.
See routine documentation for
detailed description
GSS_S_DUPLICATE_TOKEN 1 The token was a duplicate of
an earlier token
GSS_S_OLD_TOKEN 2 The token's validity period
has expired
GSS_S_UNSEQ_TOKEN 3 A later token has already been
processed
GSS_S_GAP_TOKEN 4 An expected per-message token
was not received
The routine documentation also uses the name GSS_S_COMPLETE, which is a zero value, to indicate an absence of any API errors or supplementary information bits.
All GSS_S_xxx symbols equate to complete OM_uint32 status codes, rather than to bitfield values. For example, the actual value of the symbol GSS_S_BAD_NAMETYPE (value 3 in the routine error field) is 3<<16. The macros GSS_CALLING_ERROR(), GSS_ROUTINE_ERROR() and GSS_SUPPLEMENTARY_INFO() are provided, each of which takes a GSS status code and removes all but the relevant field. For example, the value obtained by applying GSS_ROUTINE_ERROR to a status code removes the calling errors and supplementary info fields, leaving only the routine errors field. The values delivered by these macros may be directly compared with a GSS_S_xxx symbol of the appropriate type. The macro GSS_ERROR() is also provided, which when applied to a GSS status code returns a non-zero value if the status code indicated a calling or routine error, and a zero value otherwise. All macros defined by GSS-API evaluate their argument(s) exactly once.
A GSS-API implementation may choose to signal calling errors in a platform-specific manner instead of, or in addition to the routine value; routine errors and supplementary info should be returned via major status values only.
The GSS major status code GSS_S_FAILURE is used to indicate that the underlying mechanism detected an error for which no specific GSS status code is defined. The mechanism-specific status code will provide more details about the error.
GSS-API routines return a minor_status parameter, which is used to indicate specialized errors from the underlying security mechanism. This parameter may contain a single mechanism-specific error, indicated by a OM_uint32 value.
The minor_status parameter will always be set by a GSS-API routine, even if it returns a calling error or one of the generic API errors indicated above as fatal, although most other output parameters may remain unset in such cases. However, output parameters that are expected to return pointers to storage allocated by a routine must always be set by the routine, even in the event of an error, although in such cases the GSS-API routine may elect to set the returned parameter value to NULL to indicate that no storage was actually allocated. Any length field associated with such pointers (as in a gss_buffer_desc structure) should also be set to zero in such cases.
Table 2-1 GSS-API Credential-management Routines
Routine Section Function
------- ------- --------
gss_acquire_cred 5.2 Assume a global identity; Obtain
a GSS-API credential handle for
pre-existing credentials.
gss_add_cred 5.3 Construct credentials
incrementally
gss_inquire_cred 5.21 Obtain information about a
credential
gss_inquire_cred_by_mech 5.22 Obtain per-mechanism information
about a credential.
gss_release_cred 5.27 Discard a credential handle.
| OM_uint32 gss_acquire_cred (OM_uint32 *minor_status, const gss_name_t desired_name, OM_uint32 time_req, const gss_OID_set desired_mechs, gss_cred_usage_t cred_usage, gss_cred_id_t *output_cred_handle, gss_OID_set *actual_mechs, OM_uint32 *time_rec) | Function |
|
minor_status: Integer, modify. Mechanism specific status code. desired_name: gss_name_t, read. Name of principal whose credential should be acquired. time_req: Integer, read, optional number of seconds that credentials should remain valid. Specify GSS_C_INDEFINITE to request that the credentials have the maximum permitted lifetime. desired_mechs: Set of Object IDs, read, optional set of underlying security mechanisms that may be used. GSS_C_NO_OID_SET may be used to obtain an implementation-specific default. cred_usage: gss_cred_usage_t, read. GSS_C_BOTH - Credentials may be used either to initiate or accept security contexts. GSS_C_INITIATE - Credentials will only be used to initiate security contexts. GSS_C_ACCEPT - Credentials will only be used to accept security contexts. output_cred_handle: gss_cred_id_t, modify. The returned credential handle. Resources associated with this credential handle must be released by the application after use with a call to gss_release_cred(). actual_mechs: Set of Object IDs, modify, optional. The set of mechanisms for which the credential is valid. Storage associated with the returned OID-set must be released by the application after use with a call to gss_release_oid_set(). Specify NULL if not required. time_rec: Integer, modify, optional. Actual number of seconds for which the returned credentials will remain valid. If the implementation does not support expiration of credentials, the value GSS_C_INDEFINITE will be returned. Specify NULL if not required Allows an application to acquire a handle for a pre-existing credential by name. GSS-API implementations must impose a local access-control policy on callers of this routine to prevent unauthorized callers from acquiring credentials to which they are not entitled. This routine is not intended to provide a "login to the network" function, as such a function would involve the creation of new credentials rather than merely acquiring a handle to existing credentials. Such functions, if required, should be defined in implementation-specific extensions to the API. If desired_name is GSS_C_NO_NAME, the call is interpreted as a request for a credential handle that will invoke default behavior when passed to gss_init_sec_context() (if cred_usage is GSS_C_INITIATE or GSS_C_BOTH) or gss_accept_sec_context() (if cred_usage is GSS_C_ACCEPT or GSS_C_BOTH). Mechanisms should honor the desired_mechs parameter, and return a credential that is suitable to use only with the requested mechanisms. An exception to this is the case where one underlying credential element can be shared by multiple mechanisms; in this case it is permissible for an implementation to indicate all mechanisms with which the credential element may be used. If desired_mechs is an empty set, behavior is undefined. This routine is expected to be used primarily by context acceptors, since implementations are likely to provide mechanism-specific ways of obtaining GSS-API initiator credentials from the system login process. Some implementations may therefore not support the acquisition of GSS_C_INITIATE or GSS_C_BOTH credentials via gss_acquire_cred for any name other than GSS_C_NO_NAME, or a name produced by applying either gss_inquire_cred to a valid credential, or gss_inquire_context to an active context. If credential acquisition is time-consuming for a mechanism, the mechanism may choose to delay the actual acquisition until the credential is required (e.g. by gss_init_sec_context or gss_accept_sec_context). Such mechanism-specific implementation decisions should be invisible to the calling application; thus a call of gss_inquire_cred immediately following the call of gss_acquire_cred must return valid credential data, and may therefore incur the overhead of a deferred credential acquisition. Valid return values and their meaning:
|
| OM_uint32 gss_add_cred (OM_uint32 *minor_status, const gss_cred_id_t input_cred_handle, const gss_name_t desired_name, const gss_OID desired_mech, gss_cred_usage_t cred_usage, OM_uint32 initiator_time_req, OM_uint32 acceptor_time_req, gss_cred_id_t *output_cred_handle, gss_OID_set *actual_mechs, OM_uint32 *initiator_time_rec, OM_uint32 *acceptor_time_rec) | Function |
|
minor_status: Integer, modify. Mechanism specific status code. input_cred_handle: gss_cred_id_t, read, optional. The credential to which a credential-element will be added. If GSS_C_NO_CREDENTIAL is specified, the routine will compose the new credential based on default behavior (see description above). Note that, while the credential-handle is not modified by gss_add_cred(), the underlying credential will be modified if output_credential_handle is NULL. desired_name: gss_name_t, read. Name of principal whose credential should be acquired. desired_mech: Object ID, read. Underlying security mechanism with which the credential may be used. cred_usage: gss_cred_usage_t, read. GSS_C_BOTH - Credential may be used either to initiate or accept security contexts. GSS_C_INITIATE - Credential will only be used to initiate security contexts. GSS_C_ACCEPT - Credential will only be used to accept security contexts. initiator_time_req: Integer, read, optional. number of seconds that the credential should remain valid for initiating security contexts. This argument is ignored if the composed credentials are of type GSS_C_ACCEPT. Specify GSS_C_INDEFINITE to request that the credentials have the maximum permitted initiator lifetime. acceptor_time_req: Integer, read, optional. number of seconds that the credential should remain valid for accepting security contexts. This argument is ignored if the composed credentials are of type GSS_C_INITIATE. Specify GSS_C_INDEFINITE to request that the credentials have the maximum permitted initiator lifetime. output_cred_handle: gss_cred_id_t, modify, optional. The returned credential handle, containing the new credential-element and all the credential-elements from input_cred_handle. If a valid pointer to a gss_cred_id_t is supplied for this parameter, gss_add_cred creates a new credential handle containing all credential-elements from the input_cred_handle and the newly acquired credential-element; if NULL is specified for this parameter, the newly acquired credential-element will be added to the credential identified by input_cred_handle. The resources associated with any credential handle returned via this parameter must be released by the application after use with a call to gss_release_cred(). actual_mechs: Set of Object IDs, modify, optional. The complete set of mechanisms for which the new credential is valid. Storage for the returned OID-set must be freed by the application after use with a call to gss_release_oid_set(). Specify NULL if not required. initiator_time_rec: Integer, modify, optional. Actual number of seconds for which the returned credentials will remain valid for initiating contexts using the specified mechanism. If the implementation or mechanism does not support expiration of credentials, the value GSS_C_INDEFINITE will be returned. Specify NULL if not required acceptor_time_rec: Integer, modify, optional. Actual number of seconds for which the returned credentials will remain valid for accepting security contexts using the specified mechanism. If the implementation or mechanism does not support expiration of credentials, the value GSS_C_INDEFINITE will be returned. Specify NULL if not required Adds a credential-element to a credential. The credential-element is identified by the name of the principal to which it refers. GSS-API implementations must impose a local access-control policy on callers of this routine to prevent unauthorized callers from acquiring credential-elements to which they are not entitled. This routine is not intended to provide a "login to the network" function, as such a function would involve the creation of new mechanism-specific authentication data, rather than merely acquiring a GSS-API handle to existing data. Such functions, if required, should be defined in implementation-specific extensions to the API. If desired_name is GSS_C_NO_NAME, the call is interpreted as a request to add a credential element that will invoke default behavior when passed to gss_init_sec_context() (if cred_usage is GSS_C_INITIATE or GSS_C_BOTH) or gss_accept_sec_context() (if cred_usage is GSS_C_ACCEPT or GSS_C_BOTH). This routine is expected to be used primarily by context acceptors, since implementations are likely to provide mechanism-specific ways of obtaining GSS-API initiator credentials from the system login process. Some implementations may therefore not support the acquisition of GSS_C_INITIATE or GSS_C_BOTH credentials via gss_acquire_cred for any name other than GSS_C_NO_NAME, or a name produced by applying either gss_inquire_cred to a valid credential, or gss_inquire_context to an active context. If credential acquisition is time-consuming for a mechanism, the mechanism may choose to delay the actual acquisition until the credential is required (e.g. by gss_init_sec_context or gss_accept_sec_context). Such mechanism-specific implementation decisions should be invisible to the calling application; thus a call of gss_inquire_cred immediately following the call of gss_add_cred must return valid credential data, and may therefore incur the overhead of a deferred credential acquisition. This routine can be used to either compose a new credential containing all credential-elements of the original in addition to the newly-acquire credential-element, or to add the new credential- element to an existing credential. If NULL is specified for the output_cred_handle parameter argument, the new credential-element will be added to the credential identified by input_cred_handle; if a valid pointer is specified for the output_cred_handle parameter, a new credential handle will be created. If GSS_C_NO_CREDENTIAL is specified as the input_cred_handle, gss_add_cred will compose a credential (and set the output_cred_handle parameter accordingly) based on default behavior. That is, the call will have the same effect as if the application had first made a call to gss_acquire_cred(), specifying the same usage and passing GSS_C_NO_NAME as the desired_name parameter to obtain an explicit credential handle embodying default behavior, passed this credential handle to gss_add_cred(), and finally called gss_release_cred() on the first credential handle. If GSS_C_NO_CREDENTIAL is specified as the input_cred_handle parameter, a non-NULL output_cred_handle must be supplied. Valid return values and their meaning:
|
| OM_uint32 gss_inquire_cred (OM_uint32 *minor_status, const gss_cred_id_t cred_handle, gss_name_t *name, OM_uint32 *lifetime, gss_cred_usage_t *cred_usage, gss_OID_set *mechanisms) | Function |
|
minor_status: Integer, modify. Mechanism specific status code cred_handle: gss_cred_id_t, read. A handle that refers to the target credential. Specify GSS_C_NO_CREDENTIAL to inquire about the default initiator principal. name: gss_name_t, modify, optional. The name whose identity the credential asserts. Storage associated with this name should be freed by the application after use with a call to gss_release_name(). Specify NULL if not required. lifetime: Integer, modify, optional. The number of seconds for which the credential will remain valid. If the credential has expired, this parameter will be set to zero. If the implementation does not support credential expiration, the value GSS_C_INDEFINITE will be returned. Specify NULL if not required. cred_usage: gss_cred_usage_t, modify, optional. How the credential may be used. One of the following: GSS_C_INITIATE, GSS_C_ACCEPT, GSS_C_BOTH. Specify NULL if not required. mechanisms: gss_OID_set, modify, optional. Set of mechanisms supported by the credential. Storage associated with this OID set must be freed by the application after use with a call to gss_release_oid_set(). Specify NULL if not required. Obtains information about a credential. Valid return values and their meaning:
|
| OM_uint32 gss_inquire_cred_by_mech (OM_uint32 *minor_status, const gss_cred_id_t cred_handle, const gss_OID mech_type, gss_name_t *name, OM_uint32 *initiator_lifetime, OM_uint32 *acceptor_lifetime, gss_cred_usage_t *cred_usage) | Function |
|
minor_status: Integer, modify. Mechanism specific status code cred_handle: gss_cred_id_t, read. A handle that refers to the target credential. Specify GSS_C_NO_CREDENTIAL to inquire about the default initiator principal. mech_type: gss_OID, read. The mechanism for which information should be returned. name: gss_name_t, modify, optional. The name whose identity the credential asserts. Storage associated with this name must be freed by the application after use with a call to gss_release_name(). Specify NULL if not required. initiator_lifetime: Integer, modify, optional. The number of seconds for which the credential will remain capable of initiating security contexts under the specified mechanism. If the credential can no longer be used to initiate contexts, or if the credential usage for this mechanism is GSS_C_ACCEPT, this parameter will be set to zero. If the implementation does not support expiration of initiator credentials, the value GSS_C_INDEFINITE will be returned. Specify NULL if not required. acceptor_lifetime: Integer, modify, optional. The number of seconds for which the credential will remain capable of accepting security contexts under the specified mechanism. If the credential can no longer be used to accept contexts, or if the credential usage for this mechanism is GSS_C_INITIATE, this parameter will be set to zero. If the implementation does not support expiration of acceptor credentials, the value GSS_C_INDEFINITE will be returned. Specify NULL if not required. cred_usage: gss_cred_usage_t, modify, optional. How the credential may be used with the specified mechanism. One of the following: GSS_C_INITIATE, GSS_C_ACCEPT, GSS_C_BOTH. Specify NULL if not required. Obtains per-mechanism information about a credential. Valid return values and their meaning:
|
| OM_uint32 gss_release_cred (OM_uint32 * minor_status, gss_cred_id_t * cred_handle) | Function |
|
minor_status: Mechanism specific status code. cred_handle: Optional opaque handle identifying credential to be released. If GSS_C_NO_CREDENTIAL is supplied, the routine will complete successfully, but will do nothing. Informs GSS-API that the specified credential handle is no longer required by the application, and frees associated resources. Implementations are encouraged to set the cred_handle to GSS_C_NO_CREDENTIAL on successful completion of this call. Returns GSS_S_COMPLETE for successful completion, and GSS_S_NO_CRED for credentials could not be accessed. |
Table 2-2 GSS-API Context-Level Routines
Routine Section Function
------- ------- --------
gss_init_sec_context 5.19 Initiate a security context with
a peer application
gss_accept_sec_context 5.1 Accept a security context
initiated by a
peer application
gss_delete_sec_context 5.9 Discard a security context
gss_process_context_token 5.25 Process a token on a security
context from a peer application
gss_context_time 5.7 Determine for how long a context
will remain valid
gss_inquire_context 5.20 Obtain information about a
security context
gss_wrap_size_limit 5.34 Determine token-size limit for
gss_wrap on a context
gss_export_sec_context 5.14 Transfer a security context to
another process
gss_import_sec_context 5.17 Import a transferred context
| OM_uint32 gss_init_sec_context (OM_uint32 * minor_status, const gss_cred_id_t initiator_cred_handle, gss_ctx_id_t * context_handle, const gss_name_t target_name, const gss_OID mech_type, OM_uint32 req_flags, OM_uint32 time_req, const gss_channel_bindings_t input_chan_bindings, const gss_buffer_t input_token, gss_OID * actual_mech_type, gss_buffer_t output_token, OM_uint32 * ret_flags, OM_uint32 * time_rec) | Function |
|
minor_status: Mechanism specific status code. initiator_cred_handle: Optional handle for credentials claimed. Supply GSS_C_NO_CREDENTIAL to act as a default initiator principal. If no default initiator is defined, the function will return GSS_S_NO_CRED. context_handle: Context handle for new context. Supply
GSS_C_NO_CONTEXT for first call; use value returned by first call
in continuation calls. Resources associated with this
context-handle must be released by the application after use with a
call to target_name: Name of target. mech_type: Optional object ID of desired mechanism. Supply GSS_C_NO_OID to obtain an implementation specific default req_flags: Contains various independent flags, each of which requests that the context support a specific service option. Symbolic names are provided for each flag, and the symbolic names corresponding to the required flags should be logically-ORed together to form the bit-mask value. See below for details. time_req: Optional Desired number of seconds for which context should remain valid. Supply 0 to request a default validity period. input_chan_bindings: Optional Application-specified bindings. Allows application to securely bind channel identification information to the security context. Specify GSS_C_NO_CHANNEL_BINDINGS if channel bindings are not used. input_token: Optional (see text) Token received from peer application. Supply GSS_C_NO_BUFFER, or a pointer to a buffer containing the value GSS_C_EMPTY_BUFFER on initial call. actual_mech_type: Optional actual mechanism used. The OID returned via this parameter will be a pointer to static storage that should be treated as read-only; In particular the application should not attempt to free it. Specify NULL if not required. output_token: Token to be sent to peer application. If the length
field of the returned buffer is zero, no token need be sent to the
peer application. Storage associated with this buffer must be
freed by the application after use with a call to
ret_flags: Optional various independent flags, each of which indicates that the context supports a specific service option. Specify NULL if not required. Symbolic names are provided for each flag, and the symbolic names corresponding to the required flags should be logically-ANDed with the ret_flags value to test whether a given option is supported by the context. See below for details. time_rec: Optional number of seconds for which the context will remain valid. If the implementation does not support context expiration, the value GSS_C_INDEFINITE will be returned. Specify NULL if not required. Initiates the establishment of a security context between the application and a remote peer. Initially, the input_token parameter should be specified either as GSS_C_NO_BUFFER, or as a pointer to a gss_buffer_desc object whose length field contains the value zero. The routine may return a output_token which should be transferred to the peer application, where the peer application will present it to gss_accept_sec_context. If no token need be sent, gss_init_sec_context will indicate this by setting the length field of the output_token argument to zero. To complete the context establishment, one or more reply tokens may be required from the peer application; if so, gss_init_sec_context will return a status containing the supplementary information bit GSS_S_CONTINUE_NEEDED. In this case, gss_init_sec_context should be called again when the reply token is received from the peer application, passing the reply token to gss_init_sec_context via the input_token parameters. Portable applications should be constructed to use the token length and return status to determine whether a token needs to be sent or waited for. Thus a typical portable caller should always invoke int context_established = 0;
gss_ctx_id_t context_hdl = GSS_C_NO_CONTEXT;
...
input_token->length = 0;
while (!context_established) {
maj_stat = gss_init_sec_context(&min_stat,
cred_hdl,
&context_hdl,
target_name,
desired_mech,
desired_services,
desired_time,
input_bindings,
input_token,
&actual_mech,
output_token,
&actual_services,
&actual_time);
if (GSS_ERROR(maj_stat)) {
report_error(maj_stat, min_stat);
};
if (output_token->length != 0) {
send_token_to_peer(output_token);
gss_release_buffer(&min_stat, output_token)
};
if (GSS_ERROR(maj_stat)) {
if (context_hdl != GSS_C_NO_CONTEXT)
gss_delete_sec_context(&min_stat,
&context_hdl,
GSS_C_NO_BUFFER);
break;
};
if (maj_stat & GSS_S_CONTINUE_NEEDED) {
receive_token_from_peer(input_token);
} else {
context_established = 1;
};
};
Whenever the routine returns a major status that includes the value GSS_S_CONTINUE_NEEDED, the context is not fully established and the following restrictions apply to the output parameters:
If the initial call of gss_init_sec_context() fails, the implementation should not create a context object, and should leave the value of the context_handle parameter set to GSS_C_NO_CONTEXT to indicate this. In the event of a failure on a subsequent call, the implementation is permitted to delete the "half-built" security context (in which case it should set the context_handle parameter to GSS_C_NO_CONTEXT), but the preferred behavior is to leave the security context untouched for the application to delete (using gss_delete_sec_context). During context establishment, the informational status bits GSS_S_OLD_TOKEN and GSS_S_DUPLICATE_TOKEN indicate fatal errors, and GSS-API mechanisms should always return them in association with a routine error of GSS_S_FAILURE. This requirement for pairing did not exist in version 1 of the GSS-API specification, so applications that wish to run over version 1 implementations must special-case these codes. The
The
All other bits should be set to zero. Valid return values and their meaning:
|
| OM_uint32 gss_accept_sec_context (OM_uint32 *minor_status, gss_ctx_id_t *context_handle, const gss_cred_id_t acceptor_cred_handle, const gss_buffer_t input_token_buffer, const gss_channel_bindings_t input_chan_bindings, const gss_name_t *src_name, gss_OID *mech_type, gss_buffer_t output_token, OM_uint32 *ret_flags, OM_uint32 *time_rec, gss_cred_id_t *delegated_cred_handle) | Function |
|
minor_status: Integer, modify Mechanism specific status code. context_handle: gss_ctx_id_t, read/modify context handle for new context. Supply GSS_C_NO_CONTEXT for first call; use value returned in subsequent calls. Once gss_accept_sec_context() has returned a value via this parameter, resources have been assigned to the corresponding context, and must be freed by the application after use with a call to gss_delete_sec_context(). acceptor_cred_handle: gss_cred_id_t, read Credential handle claimed by context acceptor. Specify GSS_C_NO_CREDENTIAL to accept the context as a default principal. If GSS_C_NO_CREDENTIAL is specified, but no default acceptor principal is defined, GSS_S_NO_CRED will be returned. input_token_buffer: buffer, opaque, read token obtained from remote application. input_chan_bindings: channel bindings, read, optional Application- specified bindings. Allows application to securely bind channel identification information to the security context. If channel bindings are not used, specify GSS_C_NO_CHANNEL_BINDINGS. src_name: gss_name_t, modify, optional Authenticated name of context initiator. After use, this name should be deallocated by passing it to gss_release_name(). If not required, specify NULL. mech_type: Object ID, modify, optional Security mechanism used. The returned OID value will be a pointer into static storage, and should be treated as read-only by the caller (in particular, it does not need to be freed). If not required, specify NULL. output_token: buffer, opaque, modify Token to be passed to peer application. If the length field of the returned token buffer is 0, then no token need be passed to the peer application. If a non- zero length field is returned, the associated storage must be freed after use by the application with a call to gss_release_buffer(). ret_flags: bit-mask, modify, optional Contains various independent flags, each of which indicates that the context supports a specific service option. If not needed, specify NULL. Symbolic names are provided for each flag, and the symbolic names corresponding to the required flags should be logically-ANDed with the ret_flags value to test whether a given option is supported by the context. See below for the values. time_rec: Integer, modify, optional number of seconds for which the context will remain valid. Specify NULL if not required. delegated_cred_handle: gss_cred_id_t, modify, optional credential handle for credentials received from context initiator. Only valid if deleg_flag in ret_flags is true, in which case an explicit credential handle (i.e. not GSS_C_NO_CREDENTIAL) will be returned; if deleg_flag is false, gss_accept_context() will set this parameter to GSS_C_NO_CREDENTIAL. If a credential handle is returned, the associated resources must be released by the application after use with a call to gss_release_cred(). Specify NULL if not required. Allows a remotely initiated security context between the application and a remote peer to be established. The routine may return a output_token which should be transferred to the peer application, where the peer application will present it to gss_init_sec_context. If no token need be sent, gss_accept_sec_context will indicate this by setting the length field of the output_token argument to zero. To complete the context establishment, one or more reply tokens may be required from the peer application; if so, gss_accept_sec_context will return a status flag of GSS_S_CONTINUE_NEEDED, in which case it should be called again when the reply token is received from the peer application, passing the token to gss_accept_sec_context via the input_token parameters. Portable applications should be constructed to use the token length and return status to determine whether a token needs to be sent or waited for. Thus a typical portable caller should always invoke gss_accept_sec_context within a loop: gss_ctx_id_t context_hdl = GSS_C_NO_CONTEXT;
do {
receive_token_from_peer(input_token);
maj_stat = gss_accept_sec_context(&min_stat,
&context_hdl,
cred_hdl,
input_token,
input_bindings,
&client_name,
&mech_type,
output_token,
&ret_flags,
&time_rec,
&deleg_cred);
if (GSS_ERROR(maj_stat)) {
report_error(maj_stat, min_stat);
};
if (output_token->length != 0) {
send_token_to_peer(output_token);
gss_release_buffer(&min_stat, output_token);
};
if (GSS_ERROR(maj_stat)) {
if (context_hdl != GSS_C_NO_CONTEXT)
gss_delete_sec_context(&min_stat,
&context_hdl,
GSS_C_NO_BUFFER);
break;
};
} while (maj_stat & GSS_S_CONTINUE_NEEDED);
Whenever the routine returns a major status that includes the value GSS_S_CONTINUE_NEEDED, the context is not fully established and the following restrictions apply to the output parameters: The value returned via the time_rec parameter is undefined Unless the accompanying ret_flags parameter contains the bit GSS_C_PROT_READY_FLAG, indicating that per-message services may be applied in advance of a successful completion status, the value returned via the mech_type parameter may be undefined until the routine returns a major status value of GSS_S_COMPLETE. The values of the GSS_C_DELEG_FLAG, GSS_C_MUTUAL_FLAG,GSS_C_REPLAY_FLAG, GSS_C_SEQUENCE_FLAG, GSS_C_CONF_FLAG,GSS_C_INTEG_FLAG and GSS_C_ANON_FLAG bits returned via the ret_flags parameter should contain the values that the implementation expects would be valid if context establishment were to succeed. The values of the GSS_C_PROT_READY_FLAG and GSS_C_TRANS_FLAG bits within ret_flags should indicate the actual state at the time gss_accept_sec_context returns, whether or not the context is fully established. Although this requires that GSS-API implementations set the GSS_C_PROT_READY_FLAG in the final ret_flags returned to a caller (i.e. when accompanied by a GSS_S_COMPLETE status code), applications should not rely on this behavior as the flag was not defined in Version 1 of the GSS-API. Instead, applications should be prepared to use per-message services after a successful context establishment, according to the GSS_C_INTEG_FLAG and GSS_C_CONF_FLAG values. All other bits within the ret_flags argument should be set to zero. While the routine returns GSS_S_CONTINUE_NEEDED, the values returned via the ret_flags argument indicate the services that the implementation expects to be available from the established context. If the initial call of gss_accept_sec_context() fails, the implementation should not create a context object, and should leave the value of the context_handle parameter set to GSS_C_NO_CONTEXT to indicate this. In the event of a failure on a subsequent call, the implementation is permitted to delete the "half-built" security context (in which case it should set the context_handle parameter to GSS_C_NO_CONTEXT), but the preferred behavior is to leave the security context (and the context_handle parameter) untouched for the application to delete (using gss_delete_sec_context). During context establishment, the informational status bits GSS_S_OLD_TOKEN and GSS_S_DUPLICATE_TOKEN indicate fatal errors, and GSS-API mechanisms should always return them in association with a routine error of GSS_S_FAILURE. This requirement for pairing did not exist in version 1 of the GSS-API specification, so applications that wish to run over version 1 implementations must special-case these codes. The
All other bits should be set to zero. Return values:
|
| OM_uint32 gss_delete_sec_context (OM_uint32 * minor_status, gss_ctx_id_t * context_handle, gss_buffer_t output_token) | Function |
|
minor_status: Mechanism specific status code. context_handle: Context handle identifying context to delete. After deleting the context, the GSS-API will set this context handle to GSS_C_NO_CONTEXT. output_token: Optional token to be sent to remote application to instruct it to also delete the context. It is recommended that applications specify GSS_C_NO_BUFFER for this parameter, requesting local deletion only. If a buffer parameter is provided by the application, the mechanism may return a token in it; mechanisms that implement only local deletion should set the length field of this token to zero to indicate to the application that no token is to be sent to the peer. Delete a security context. In addition to deleting established security contexts,
The output_token parameter is retained for compatibility with
version 1 of the GSS-API. It is recommended that both peer
applications invoke Returns GSS_S_COMPLETE for successful completion, and GSS_S_NO_CONTEXT if no valid context was supplied. |
Table 2-3 GSS-API Per-message Routines
Routine Section Function
------- ------- --------
gss_get_mic 5.15 Calculate a cryptographic message
integrity code (MIC) for a
message; integrity service
gss_verify_mic 5.32 Check a MIC against a message;
verify integrity of a received
message
gss_wrap 5.33 Attach a MIC to a message, and
optionally encrypt the message
content;
confidentiality service
gss_unwrap 5.31 Verify a message with attached
MIC, and decrypt message content
if necessary.
| OM_uint32 gss_wrap (OM_uint32 * minor_status, const gss_ctx_id_t context_handle, int conf_req_flag, gss_qop_t qop_req, const gss_buffer_t input_message_buffer, int * conf_state, gss_buffer_t output_message_buffer) | Function |
|
minor_status: Mechanism specific status code. context_handle: Identifies the context on which the message will be sent conf_req_flag: Whether confidentiality is requested. qop_req: Specifies required quality of protection. A mechanism-specific default may be requested by setting qop_req to GSS_C_QOP_DEFAULT. If an unsupported protection strength is requested, gss_wrap will return a major_status of GSS_S_BAD_QOP. input_message_buffer: Message to be protected. conf_state: Optional output variable indicating if confidentiality services have been applied. output_message_buffer: Buffer to receive protected message.
Storage associated with this message must be freed by the
application after use with a call to Attaches a cryptographic MIC and optionally encrypts the specified input_message. The output_message contains both the MIC and the message. The qop_req parameter allows a choice between several cryptographic algorithms, if supported by the chosen mechanism. Since some application-level protocols may wish to use tokens
emitted by Returns GSS_S_COMPLETE Successful completion GSS_S_CONTEXT_EXPIRED The context has already expired GSS_S_NO_CONTEXT The context_handle parameter did not identify a valid context GSS_S_BAD_QOP The specified QOP is not supported by the mechanism. |
| OM_uint32 gss_unwrap (OM_uint32 * minor_status, const gss_ctx_id_t context_handle, const gss_buffer_t input_message_buffer, gss_buffer_t output_message_buffer, int * conf_state, gss_qop_t * qop_state) | Function |
|
minor_status: Mechanism specific status code. context_handle: Identifies the context on which the message arrived input_message_buffer: input protected message output_message_buffer: Buffer to receive unwrapped message.
Storage associated with this buffer must be freed by the
application after use use with a call to conf_state: optional output variable indicating if confidentiality protection was used. qop_state: optional output variable indicating quality of protection. Converts a message previously protected by gss_wrap back to a usable form, verifying the embedded MIC. The conf_state parameter indicates whether the message was encrypted; the qop_state parameter indicates the strength of protection that was used to provide the confidentiality and integrity services. Since some application-level protocols may wish to use tokens
emitted by Returns: GSS_S_COMPLETE Successful completion GSS_S_DEFECTIVE_TOKEN The token failed consistency checks GSS_S_BAD_SIG The MIC was incorrect GSS_S_DUPLICATE_TOKEN The token was valid, and contained a correct MIC for the message, but it had already been processed GSS_S_OLD_TOKEN The token was valid, and contained a correct MIC for the message, but it is too old to check for duplication. GSS_S_UNSEQ_TOKEN The token was valid, and contained a correct MIC for the message, but has been verified out of sequence; a later token has already been received. GSS_S_GAP_TOKEN The token was valid, and contained a correct MIC for the message, but has been verified out of sequence; an earlier expected token has not yet been received. GSS_S_CONTEXT_EXPIRED The context has already expired GSS_S_NO_CONTEXT The context_handle parameter did not identify a valid context |
Table 2-4 GSS-API Name manipulation Routines
Routine Section Function
------- ------- --------
gss_import_name 5.16 Convert a contiguous string name
to internal-form
gss_display_name 5.10 Convert internal-form name to
text
gss_compare_name 5.6 Compare two internal-form names
gss_release_name 5.28 Discard an internal-form name
gss_inquire_names_for_mech 5.24 List the name-types supported by
the specified mechanism
gss_inquire_mechs_for_name 5.23 List mechanisms that support the
specified name-type
gss_canonicalize_name 5.5 Convert an internal name to an MN
gss_export_name 5.13 Convert an MN to export form
gss_duplicate_name 5.12 Create a copy of an internal name
| OM_uint32 gss_import_name (OM_uint32 * minor_status, const gss_buffer_t input_name_buffer, const gss_OID input_name_type, gss_name_t * output_name) | Function |
|
minor_status: Mechanism specific status code input_name_buffer: buffer containing contiguous string name to convert input_name_type: Optional Object ID specifying type of printable name. Applications may specify either GSS_C_NO_OID to use a mechanism-specific default printable syntax, or an OID recognized by the GSS-API implementation to name a specific namespace. output_name: returned name in internal form. Storage associated
with this name must be freed by the application after use with a call
to Convert a contiguous string name to internal form. In general, the internal name returned (via the <output_name> parameter) will not be an MN; the exception to this is if the <input_name_type> indicates that the contiguous string provided via the <input_name_buffer> parameter is of type GSS_C_NT_EXPORT_NAME, in which case the returned internal name will be an MN for the mechanism that exported the name. Returns GSS_S_COMPLETE for successful completion, GSS_S_BAD_NAMETYPE when the input_name_type was unrecognized, GSS_S_BAD_NAME when the input_name parameter could not be interpreted as a name of the specified type, and GSS_S_BAD_MECH when the input name-type was GSS_C_NT_EXPORT_NAME, but the mechanism contained within the input-name is not supported. |
| OM_uint32 gss_display_name (OM_uint32 * minor_status, const gss_name_t input_name, gss_buffer_t output_name_buffer, gss_OID * output_name_type) | Function |
|
minor_status: Mechanism specific status code. input_name: Name to be displayed output_name_buffer: Buffer to receive textual name string. The
application must free storage associated with this name after use
with a call to output_name_type: Optional type of the returned name. The returned gss_OID will be a pointer into static storage, and should be treated as read-only by the caller (in particular, the application should not attempt to free it). Specify NULL if not required. Allows an application to obtain a textual representation of an opaque internal-form name for display purposes. The syntax of a printable name is defined by the GSS-API implementation. If input_name denotes an anonymous principal, the implementation should return the gss_OID value GSS_C_NT_ANONYMOUS as the output_name_type, and a textual name that is syntactically distinct from all valid supported printable names in output_name_buffer. If input_name was created by a call to gss_import_name, specifying GSS_C_NO_OID as the name-type, implementations that employ lazy conversion between name types may return GSS_C_NO_OID via the output_name_type parameter. Returns GSS_S_COMPLETE for successful completion, GSS_S_BAD_NAME when input_name was ill-formed. |
| OM_uint32 gss_compare_name (OM_uint32 * minor_status, const gss_name_t name1, const gss_name_t name2, int * name_equal) | Function |
|
minor_status: Mechanism specific status code. name1: Internal-form name. name2: Internal-form name. name_equal: non-zero if names refer to same entity. Allows an application to compare two internal-form names to determine whether they refer to the same entity. If either name presented to gss_compare_name denotes an anonymous principal, the routines should indicate that the two names do not refer to the same identity. Returns GSS_S_COMPLETE for successful completion, GSS_S_BAD_NAMETYPE when the two names were of incomparable types, and GSS_S_BAD_NAME if one or both of name1 or name2 was ill-formed. |
| OM_uint32 gss_release_name (OM_uint32 * minor_status, gss_name_t * name) | Function |
|
minor_status: Mechanism specific status code. name: The name to be deleted. Free GSSAPI-allocated storage associated with an internal-form name. Implementations are encouraged to set the name to GSS_C_NO_NAME on successful completion of this call. Returns GSS_S_COMPLETE for successful completion, and GSS_S_BAD_NAME when the name parameter did not contain a valid name. |
| OM_uint32 gss_canonicalize_name (OM_uint32 * minor_status, const gss_name_t input_name, const gss_OID mech_type, gss_name_t * output_name) | Function |
|
minor_status: Mechanism specific status code. input_name: The name for which a canonical form is desired. mech_type: The authentication mechanism for which the canonical form of the name is desired. The desired mechanism must be specified explicitly; no default is provided. output_name: The resultant canonical name. Storage associated
with this name must be freed by the application after use with a
call to Generate a canonical mechanism name (MN) from an arbitrary internal name. The mechanism name is the name that would be returned to a context acceptor on successful authentication of a context where the initiator used the input_name in a successful call to gss_acquire_cred, specifying an OID set containing <mech_type> as its only member, followed by a call to gss_init_sec_context, specifying <mech_type> as the authentication mechanism. Returns GSS_S_COMPLETE Successful completion. GSS_S_BAD_MECH The identified mechanism is not supported. GSS_S_BAD_NAMETYPE The provided internal name contains no elements that could be processed by the specified mechanism. GSS_S_BAD_NAME The provided internal name was ill-formed. |
| OM_uint32 gss_inquire_names_for_mech (OM_uint32 *minor_status, const gss_OID mechanism, gss_OID_set *name_types) | Function |
|
minor_status: Implementation specific status code. mechanism: The mechanism to be interrogated. name_types: Output set of name-types supported by the specified mechanism. The returned OID set must be freed by the application after use with a call to gss_release_oid_set(). Outputs the set of nametypes supported by the specified mechanism. Returns GSS_S_COMPLETE for successful completion. |
| OM_uint32 gss_inquire_mechs_for_name (OM_uint32 *minor_status, const gss_name_t input_name, gss_OID_set *mech_types) | Function |
|
minor_status: Implementation specific status code. input_name: The name to which the inquiry relates. mech_types: Output set of mechanisms that may support the specified name. The returned OID set must be freed by the caller after use with a call to gss_release_oid_set(). Outputs the set of mechanisms supported by the GSS-API implementation that may be able to process the specified name. Each mechanism returned will recognize at least one element within the name. It is permissible for this routine to be implemented within a mechanism-independent GSS-API layer, using the type information contained within the presented name, and based on registration information provided by individual mechanism implementations. This means that the returned mech_types set may indicate that a particular mechanism will understand the name when in fact it would refuse to accept the name as input to gss_canonicalize_name(), gss_init_sec_context(), gss_acquire_cred() or gss_add_cred() (due to some property of the specific name, as opposed to the name type). Thus this routine should be used only as a pre-filter for a call to a subsequent mechanism-specific routine. Returns GSS_S_COMPLETE for successful completion, GSS_S_BAD_NAME to indicate that the input_name parameter was ill-formed, and GSS_S_BAD_NAMETYPE to indicate that the input_name parameter contained an invalid or unsupported type of name. |
| OM_uint32 gss_canonicalize_name (OM_uint32 *minor_status, const gss_name_t input_name, const gss_OID mech_type, gss_name_t *output_name) | Function |
|
minor_status: Mechanism specific status code. input_name: The name for which a canonical form is desired. mech_type: The authentication mechanism for which the canonical form of the name is desired. The desired mechanism must be specified explicitly; no default is provided. output_name: The resultant canonical name. Storage associated with this name must be freed by the application after use with a call to gss_release_name(). Generate a canonical mechanism name (MN) from an arbitrary internal name. The mechanism name is the name that would be returned to a context acceptor on successful authentication of a context where the initiator used the input_name in a successful call to gss_acquire_cred, specifying an OID set containing <mech_type> as its only member, followed by a call to gss_init_sec_context, specifying <mech_type> as the authentication mechanism. Returns GSS_S_COMPLETE for successful completion, GSS_S_BAD_MECH to indicate that the identified mechanism is not supported, GSS_S_BAD_NAMETYPE to indicate that the provided internal name contains no elements that could be processed by the specified mechanism, and GSS_S_BAD_NAME to indicate that the provided internal name was ill-formed. |
| OM_uint32 gss_export_name (OM_uint32 *minor_status, const gss_name_t input_name, gss_buffer_t exported_name) | Function |
|
minor_status: Mechanism specific status code. input_name: The mechanism name to be exported. exported_name: Output variable with canonical contiguous string form of input_name. Storage associated with this string must freed by the application after use with gss_release_buffer(). To produce a canonical contiguous string representation of a mechanism name (MN), suitable for direct comparison (e.g. with memcmp) for use in authorization functions (e.g. matching entries in an access-control list). The input_name parameter must specify a valid MN (i.e. an internal name generated by gss_accept_sec_context or by gss_canonicalize_name). Returns GSS_S_COMPLETE for successful completion, GSS_S_NAME_NOT_MN to indicate that the provided internal name was not a mechanism name, GSS_S_BAD_NAME to indicate that the provided internal name was ill-formed, and GSS_S_BAD_NAMETYPE to indicate that the internal name was of a type not supported by the GSS-API implementation. |
| OM_uint32 gss_duplicate_name (OM_uint32 * minor_status, const gss_name_t src_name, gss_name_t * dest_name) | Function |
|
minor_status: Mechanism specific status code. src_name: Internal name to be duplicated. dest_name: The resultant copy of <src_name>. Storage associated
with this name must be freed by the application after use with a
call to Create an exact duplicate of the existing internal name src_name. The new dest_name will be independent of src_name (i.e. src_name and dest_name must both be released, and the release of one shall not affect the validity of the other). Returns GSS_S_COMPLETE for successful completion, and GSS_S_BAD_NAME when the src_name parameter was ill-formed. |
Table 2-5 GSS-API Miscellaneous Routines
Routine Section Function
------- ------- --------
gss_add_oid_set_member 5.4 Add an object identifier to
a set
gss_display_status 5.11 Convert a GSS-API status code
to text
gss_indicate_mechs 5.18 Determine available underlying
authentication mechanisms
gss_release_buffer 5.26 Discard a buffer
gss_release_oid_set 5.29 Discard a set of object
identifiers
gss_create_empty_oid_set 5.8 Create a set containing no
object identifiers
gss_test_oid_set_member 5.30 Determines whether an object
identifier is a member of a set.
| OM_uint32 gss_release_buffer (OM_uint32 * minor_status, gss_buffer_t buffer) | Function |
|
minor_status: Mechanism specific status code. buffer: The storage associated with the buffer will be deleted. The gss_buffer_desc object will not be freed, but its length field will be zeroed. Free storage associated with a buffer. The storage must have been allocated by a GSS-API routine. In addition to freeing the associated storage, the routine will zero the length field in the descriptor to which the buffer parameter refers, and implementations are encouraged to additionally set the pointer field in the descriptor to NULL. Any buffer object returned by a GSS-API routine may be passed to gss_release_buffer (even if there is no storage associated with the buffer). Returns GSS_S_COMPLETE for successful completion. |
| OM_uint32 gss_create_empty_oid_set (OM_uint32 * minor_status, gss_OID_set * oid_set) | Function |
|
minor_status: Mechanism specific status code oid_set: The empty object identifier set. The routine will
allocate the gss_OID_set_desc object, which the application must free
after use with a call to Create an object-identifier set containing no object identifiers, to
which members may be subsequently added using the
Returns GSS_S_COMPLETE for successful completion. |
| OM_uint32 gss_add_oid_set_member (OM_uint32 * minor_status, const gss_OID member_oid, gss_OID_set * oid_set) | Function |
|
minor_status: Mechanism specific status code member_oid: The object identifier to copied into the set. oid_set: The set in which the object identifier should be inserted. Add an Object Identifier to an Object Identifier set. This routine
is intended for use in conjunction with gss_create_empty_oid_set
when constructing a set of mechanism OIDs for input to
gss_acquire_cred. The oid_set parameter must refer to an OID-set
that was created by GSS-API (e.g. a set returned by
Returns GSS_S_COMPLETE for successful completion. |
| OM_uint32 gss_test_oid_set_member (OM_uint32 * minor_status, const gss_OID member, const gss_OID_set set, int * present) | Function |
|
minor_status: Mechanism specific status code member: The object identifier whose presence is to be tested. set: The Object Identifier set. present: output indicating if the specified OID is a member of the set, zero if not. Interrogate an Object Identifier set to determine whether a specified
Object Identifier is a member. This routine is intended to be used
with OID sets returned by Returns GSS_S_COMPLETE for successful completion. |
| OM_uint32 gss_release_oid_set (OM_uint32 * minor_status, gss_OID_set * set) | Function |
|
minor_status: Mechanism specific status code set: The storage associated with the gss_OID_set will be deleted. Free storage associated with a GSSAPI-generated gss_OID_set object.
The set parameter must refer to an OID-set that was returned from a
GSS-API routine. Implementations are encouraged to set the gss_OID_set parameter to GSS_C_NO_OID_SET on successful completion of this routine. Returns GSS_S_COMPLETE for successful completion. |
| OM_uint32 gss_indicate_mechs (OM_uint32 *minor_status, gss_OID_set *mech_set) | Function |
|
minor_status: Mechanism specific status code. mech_set: Output OID set with implementation-supported mechanisms. Allows an application to determine which underlying security mechanisms are available. The returned gss_OID_set value will be a dynamically-allocated OID set, that should be released by the caller after use with a call to gss_release_oid_set(). Returns GSS_S_COMPLETE for successful completion. |
| OM_uint32 gss_display_status (OM_uint32 *minor_status, OM_uint32 status_value, int status_type, const gss_OID mech_type, OM_uint32 *message_context, gss_buffer_t status_string) | Function |
|
minor_status: Mechanism specific status code. status_value Status value to be converted status_type: Type of status code. Valid values include GSS_C_GSS_CODE to indicate that status_value is a GSS status code, and GSS_C_MECH_CODE to indicate that status_value is a mechanism status code. mech_type: Optional OID of underlying mechanism (used to interpret a minor status value) Supply GSS_C_NO_OID to obtain the system default. message_context: Input/output variable that should be initialized to zero by the application prior to the first call. On return from gss_display_status(), a non-zero status_value parameter indicates that additional messages may be extracted from the status code via subsequent calls to gss_display_status(), passing the same status_value, status_type, mech_type, and message_context parameters. status_string: Output textual interpretation of the status_value. Storage associated with this parameter must be freed by the application after use with a call to gss_release_buffer(). Allows an application to obtain a textual representation of a GSS-API status code, for display to the user or for logging purposes. Since some status values may indicate multiple conditions, applications may need to call gss_display_status multiple times, each call generating a single text string. The message_context parameter is used by gss_display_status to store state information about which error messages have already been extracted from a given status_value; message_context must be initialized to 0 by the application prior to the first call, and gss_display_status will return a non-zero value in this parameter if there are further messages to extract. The message_context parameter contains all state information required by gss_display_status in order to extract further messages from the status_value; even when a non-zero value is returned in this parameter, the application is not required to call gss_display_status again unless subsequent messages are desired. The following code extracts all messages from a given status code and prints them to stderr: OM_uint32 message_context;
OM_uint32 status_code;
OM_uint32 maj_status;
OM_uint32 min_status;
gss_buffer_desc status_string;
...
message_context = 0;
do {
maj_status = gss_display_status (
&min_status,
status_code,
GSS_C_GSS_CODE,
GSS_C_NO_OID,
&message_context,
&status_string)
fprintf(stderr,
"%.*s\n",
(int)status_string.length,
(char *)status_string.value);
gss_release_buffer(&min_status, &status_string);
} while (message_context != 0);
Returns GSS_S_COMPLETE for successful completion, GSS_S_BAD_MECH to indicate that translation in accordance with an unsupported mechanism type was requested, and GSS_S_BAD_STATUS to indicate that the status value was not recognized, or the status type was neither GSS_C_GSS_CODE nor GSS_C_MECH_CODE. |
None of the following functions are standard GSS API functions. As
such, they are not declared in gss/api.h, but rather in
gss/ext.h (which is included from gss.h).
| const char * gss_check_version (const char * req_version) | Function |
|
req_version: version string to compare with, or NULL Check that the the version of the library is at minimum the one given
as a string in |
| int gss_oid_equal (gss_OID first_oid, gss_OID second_oid) | Function |
|
Compare two OIDs for equality. Compares actual content, not just pointer equality. Returns a boolean true iff the OIDs are equal. |
| OM_uint32 gss_copy_oid (OM_uint32 * minor_status, const gss_OID src_oid, gss_OID dest_oid); | Function |
|
Make an exact copy of the given OID, that shares no memory areas with the original. The contents of the copied OID must be deallocated by the caller. Returns GSS_S_COMPLETE on success. |
| OM_uint32 gss_duplicate_oid (OM_uint32 * minor_status, const gss_OID src_oid, gss_OID * dest_oid) | Function |
|
Allocate an exact copy of the given OID, that shares no memory areas with the original. The newly created OID, and its contents, must be deallocated by the caller. Returns GSS_S_COMPLETE on success. |
| int gss_encapsulate_token (gss_buffer_t input_message, gss_OID token_oid, gss_buffer_t output_message) | Function |
|
input_message: Message to be encapsulated. token_oid: OID of mechanism. input_message: Output buffer with encapsulated message. Wrap a buffer in the mechanism-independent token format. This is used for the initial token of a GSS-API context establishment sequence. It incorporates an identifier of the mechanism type to be used on that context, and enables tokens to be interpreted unambiguously at GSS-API peers. See further section 3.1 of RFC 2743. |
| int gss_decapsulate_token (gss_buffer_t input_message, gss_OID token_oid, gss_buffer_t output_message) | Function |
|
input_message: Message to decapsulated. token_oid: Output buffer with mechanism OID used in message. input_message: Output buffer with encapsulated message. Unwrap a buffer in the mechanism-independent token format. This is
the reverse of |
This manual borrows text from RFC 2743 and RFC 2744 that describe GSS API formally.
The author has doubts whether GSS is the best solution for free software projects looking for a implementation agnostic security framework. We express these doubts in this section, so that the reader can judge for herself if any of the potential problems discussed here are relevant for their project, or if the benefit outweigh the problems. GSS can be criticized on several levels. We start with the actual implementation.
GSS does not appear to be designed by experienced C programmers.
While generally this may be a good thing (C is not the best language),
but since they defined the API in C, it is unfortunate. The primary
evidence of this is the major_status and minor_status error code
solution. It is a complicated way to describe error conditions, but
what makes matters worse, the error condition is separated; half of
the error condition is in the function return value and the other half
is in the first argument to the function, which is always a pointer to
an integer. (The pointer is not even allowed to be NULL, if
the application doesn't care about the minor error code.) This makes
the API unreadable, and difficult to use. A better solutions would be
to return a struct containing the entire error condition, which can be
accessed using macros, although we acknowledge that the C language
used at the time GSS was designed may not have allowed this (this may
in fact be the reason the awkward solution was chosen). Instead, the
return value could have been passed back to callers using a pointer to
a struct, accessible using various macros, and the function could have
a void prototype. The fact that minor_status is placed first in the
parameter list increases the pain it is to use the API. Important
parameters should be placed first. A better place for minor_status (if
it must be present at all) would have been last in the prototypes.
Another evidence of the C inexperience are the memory management
issues; GSS provides functions to deallocate data stored within, e.g.,
gss_buffer_t but the caller is responsible of deallocating the
structure pointed at by the gss_buffer_t (i.e., the
gss_buffer_desc) itself. Memory management issues are error
prone, and this division easily leads to memory leaks (or worse).
Instead, the API should be the sole owner of all gss_ctx_id_t,
gss_cred_id_t, and gss_buffer_t structures: they should
be allocated by the library, and deallocated (using the utility
functions defined for this purpose) by the library.
TBA: thread issues
TBA: multiple mechanisms in a GSS library
TBA: high-level design criticism.
TBA: no credential forwarding.
TBA: internationalization
TBA: krb5: no way to access authorization-data
TBA: krb5: firewall/pre-IP: iakerb status?
TBA: krb5: single-DES only
TBA: the API may block, unusable in select() based servers. Especially if the servers contacted is decided by the, yet unauthenticated, remote client.
Finally we note that few free security applications uses GSS, perhaps the only major exception to this are Kerberos 5 implementations. While not substantial evidence, this do suggest that the GSS may not be the simplest solution available to solve actual problems, since otherwise more projects would have chosen to take advantage of the work that went into GSS instead of using another framework (or designing their own solution).
Our conclusion is that free software projects that are looking for a security framework should evaluate carefully whether GSS actually is the best solution before using it. In particular it is recommended to compare GSS with the Simple Authentication and Security Layer (SASL) framework, which in several situations provide the same feature as GSS does. The most compelling argument for SASL over GSS is, as its acronym suggest, Simple, whereas GSS is far from it.
However, that said, for free software projects that wants to support Kerberos 5, we do acknowledge that no other framework provides a more portable and interoperable interface into the Kerberos 5 system. If your project needs to use Kerberos 5 specifically, we do recommend you to use GSS instead of the Kerberos 5 implementation specific APIs.
gss_accept_sec_context: Context-Level Routines
gss_acquire_cred: Credential Management
gss_add_cred: Credential Management
gss_add_oid_set_member: Miscellaneous Routines
GSS_C_ANON_FLAG: Context-Level Routines
GSS_C_CONF_FLAG: Context-Level Routines
GSS_C_DELEG_FLAG: Context-Level Routines
GSS_C_INTEG_FLAG: Context-Level Routines
GSS_C_MUTUAL_FLAG: Context-Level Routines
GSS_C_PROT_READY_FLAG: Context-Level Routines
GSS_C_REPLAY_FLAG: Context-Level Routines
GSS_C_SEQUENCE_FLAG: Context-Level Routines
GSS_C_TRANS_FLAG: Context-Level Routines
GSS_CALLING_ERROR: Error Handling
gss_canonicalize_name: Name Manipulation
gss_check_version: Extended GSS API
gss_compare_name: Name Manipulation
gss_copy_oid: Extended GSS API
gss_create_empty_oid_set: Miscellaneous Routines
gss_decapsulate_token: Extended GSS API
gss_delete_sec_context: Context-Level Routines
gss_display_name: Name Manipulation
gss_display_status: Miscellaneous Routines
gss_duplicate_name: Name Manipulation
gss_duplicate_oid: Extended GSS API
gss_encapsulate_token: Extended GSS API
GSS_ERROR: Error Handling
gss_export_name: Name Manipulation
gss_import_name: Name Manipulation
gss_indicate_mechs: Miscellaneous Routines
gss_init_sec_context: Context-Level Routines
gss_inquire_cred: Credential Management
gss_inquire_cred_by_mech: Credential Management
gss_inquire_mechs_for_name: Name Manipulation
gss_inquire_names_for_mech: Name Manipulation
gss_oid_equal: Extended GSS API
gss_release_buffer: Miscellaneous Routines
gss_release_cred: Credential Management
gss_release_name: Name Manipulation
gss_release_oid_set: Miscellaneous Routines
GSS_ROUTINE_ERROR: Error Handling
GSS_S_...: Error Handling
GSS_SUPPLEMENTARY_INFO: Error Handling
gss_test_oid_set_member: Miscellaneous Routines
gss_unwrap: Per-Message Routines
gss_wrap: Per-Message Routines
xalloc_fail_func: Out of Memory handling