This manual is last updated 19 December 2007 for version 0.0.23 of GNU GSS.
Copyright © 2003, 2004, 2005, 2006, 2007 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 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”.
Appendices
Indices
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.
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.
armv4l-unknown-linux-gnu.
alphaev67-dec-osf5.1,
alphaev68-dec-osf5.1.
alphaev6-unknown-linux-gnu,
alphaev67-unknown-linux-gnu.
ia64-unknown-linux-gnu.
alphaev6-unknown-linux-gnu,
alphaev67-unknown-linux-gnu, ia64-unknown-linux-gnu.
i686-pc-linux-gnu.
i686-pc-linux-gnu.
i686-pc-linux-gnu.
i686-pc-linux-gnu.
mips-sgi-irix6.5.
rs6000-ibm-aix4.3.2.0.
i686-pc-cygwin.
ia64-hp-hpux11.22,
hppa2.0w-hp-hpux11.11.
sparc-sun-solaris2.8.
alpha-unknown-netbsd1.6,
i386-unknown-netbsdelf1.6.
alpha-unknown-openbsd3.1,
i386-unknown-openbsd3.1.
alpha-unknown-freebsd4.7,
i386-unknown-freebsd4.7.
m68k-uclinux-elf.
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 Hagagatan 24 113 47 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-0.0.23.tar.gz’ where the ‘0.0.23’ 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-0.0.23.tar.gz
$ tar xfz gss-0.0.23.tar.gz
$ cd gss-0.0.23/
$ ./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:
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:
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.
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, and declares 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 adds 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. The rationale for the strategy chosen is that out of memory handling happens in rare situations, but performing the out of memory error handling after many API function invocations make source code harder to read. That may 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, or that the error
message should go somewhere else than to stderr.
To meet this need, the GSS library support a callback function to let
the application regain control, and perform its own cleanups, when an
out of memory situation has occurred. The application can define a
function and set the library variable gss_alloc_fail_function
to that function. This could be implemented as follows.
#include <gss/ext.h>
...
void my_gss_alloc_failer (void)
{
syslog (LOG_CRIT, "GSS library out of memory");
exit (1);
}
...
int
main (int argc, char *argv[])
{
...
gss_alloc_fail_function = my_gss_alloc_failer;
...
The GSS library will invoke gss_alloc_fail_function if an out
of memory error occurs. Note that after this all previously allocated
GSS library variables are in an undefined state, so you must not use
any previously allocated GSS variables again. You could discard all
previous GSS variable and start from scratch, though. 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.
As can be seen, the callback is a global variable, and is thus not
thread safe. It is assumed that if malloc fail in one thread,
it likely do the same for all threads within the application.
The following conventions are used by the GSS-API C-language bindings:
GSS-API uses the following integer data type:
OM_uint32 32-bit unsigned integer
Many of the GSS-API routines take arguments and return values that
describe contiguous octet-strings. All such data is passed between
the GSS-API and the caller using the gss_buffer_t data type.
This data type is a pointer to a buffer descriptor, which consists of
a length field that contains the total number of bytes in the datum,
and a value field which contains a pointer to the actual datum:
typedef struct gss_buffer_desc_struct {
size_t length;
void *value;
} gss_buffer_desc, *gss_buffer_t;
Storage for data returned to the application by a GSS-API routine
using the gss_buffer_t conventions is allocated by the GSS-API
routine. The application may free this storage by invoking the
gss_release_buffer routine. Allocation of the
gss_buffer_desc object is always the responsibility of the
application; unused gss_buffer_desc objects may be initialized
to the value GSS_C_EMPTY_BUFFER.
Certain multiple-word data items are considered opaque data types at
the GSS-API, because their internal structure has no significance
either to the GSS-API or to the caller. Examples of such opaque data
types are the input_token parameter to gss_init_sec_context
(which is opaque to the caller), and the input_message parameter to
gss_wrap (which is opaque to the GSS-API). Opaque data is
passed between the GSS-API and the application using the
gss_buffer_t datatype.
Certain multiple-word data items may be regarded as simple ISO Latin-1
character strings. Examples are the printable strings passed to
gss_import_name via the input_name_buffer parameter. Some
GSS-API routines also return character strings. All such character
strings are passed between the application and the GSS-API
implementation using the gss_buffer_t datatype, which is a
pointer to a gss_buffer_desc object.
When a gss_buffer_desc object describes a printable string, the
length field of the gss_buffer_desc should only count printable
characters within the string. In particular, a trailing NUL character
should NOT be included in the length count, nor should either the
GSS-API implementation or the application assume the presence of an
uncounted trailing NUL.
Certain GSS-API procedures take parameters of the type gss_OID,
or Object identifier. This is a type containing ISO-defined tree-
structured values, and is used by the GSS-API caller to select an
underlying security mechanism and to specify namespaces. A value of
type gss_OID has the following structure:
typedef struct gss_OID_desc_struct {
OM_uint32 length;
void *elements;
} gss_OID_desc, *gss_OID;
The elements field of this structure points to the first byte of an
octet string containing the ASN.1 BER encoding of the value portion of
the normal BER TLV encoding of the gss_OID. The length field
contains the number of bytes in this value. For example, the
gss_OID value corresponding to iso(1)
identified-organization(3) icd-ecma(12) member-company(2) dec(1011)
cryptoAlgorithms(7) DASS(5), meaning the DASS X.509 authentication
mechanism, has a length field of 7 and an elements field pointing to
seven octets containing the following octal values:
53,14,2,207,163,7,5. GSS-API implementations should provide constant
gss_OID values to allow applications to request any supported
mechanism, although applications are encouraged on portability grounds
to accept the default mechanism. gss_OID values should also be
provided to allow applications to specify particular name types (see
section 3.10). Applications should treat gss_OID_desc values
returned by GSS-API routines as read-only. In particular, the
application should not attempt to deallocate them with free().
Certain GSS-API procedures take parameters of the type
gss_OID_set. This type represents one or more object
identifiers (see Object Identifiers). A gss_OID_set object
has the following structure:
typedef struct gss_OID_set_desc_struct {
size_t count;
gss_OID elements;
} gss_OID_set_desc, *gss_OID_set;
The count field contains the number of OIDs within the set. The
elements field is a pointer to an array of gss_OID_desc
objects, each of which describes a single OID. gss_OID_set
values are used to name the available mechanisms supported by the
GSS-API, to request the use of specific mechanisms, and to indicate
which mechanisms a given credential supports.
All OID sets returned to the application by GSS-API are dynamic
objects (the gss_OID_set_desc, the "elements" array of the set,
and the "elements" array of each member OID are all dynamically
allocated), and this storage must be deallocated by the application
using the gss_release_oid_set routine.
A credential handle is a caller-opaque atomic datum that identifies a
GSS-API credential data structure. It is represented by the caller-
opaque type gss_cred_id_t.
GSS-API credentials can contain mechanism-specific principal authentication data for multiple mechanisms. A GSS-API credential is composed of a set of credential-elements, each of which is applicable to a single mechanism. A credential may contain at most one credential-element for each supported mechanism. A credential-element identifies the data needed by a single mechanism to authenticate a single principal, and conceptually contains two credential-references that describe the actual mechanism-specific authentication data, one to be used by GSS-API for initiating contexts, and one to be used for accepting contexts. For mechanisms that do not distinguish between acceptor and initiator credentials, both references would point to the same underlying mechanism-specific authentication data.
Credentials describe a set of mechanism-specific principals, and give their holder the ability to act as any of those principals. All principal identities asserted by a single GSS-API credential should belong to the same entity, although enforcement of this property is an implementation-specific matter. The GSS-API does not make the actual credentials available to applications; instead a credential handle is used to identify a particular credential, held internally by GSS-API. The combination of GSS-API credential handle and mechanism identifies the principal whose identity will be asserted by the credential when used with that mechanism.
The gss_init_sec_context and gss_accept_sec_context
routines allow the value GSS_C_NO_CREDENTIAL to be specified as
their credential handle parameter. This special credential-handle
indicates a desire by the application to act as a default principal.
The gss_ctx_id_t data type contains a caller-opaque atomic
value that identifies one end of a GSS-API security context.
The security context holds state information about each end of a peer communication, including cryptographic state information.
A token is a caller-opaque type that GSS-API uses to maintain
synchronization between the context data structures at each end of a
GSS-API security context. The token is a cryptographically protected
octet-string, generated by the underlying mechanism at one end of a
GSS-API security context for use by the peer mechanism at the other
end. Encapsulation (if required) and transfer of the token are the
responsibility of the peer applications. A token is passed between
the GSS-API and the application using the gss_buffer_t
conventions.
Certain GSS-API routines are intended to transfer data between
processes in multi-process programs. These routines use a
caller-opaque octet-string, generated by the GSS-API in one process
for use by the GSS-API in another process. The calling application is
responsible for transferring such tokens between processes in an
OS-specific manner. Note that, while GSS-API implementors are
encouraged to avoid placing sensitive information within interprocess
tokens, or to cryptographically protect them, many implementations
will be unable to avoid placing key material or other sensitive data
within them. It is the application's responsibility to ensure that
interprocess tokens are protected in transit, and transferred only to
processes that are trustworthy. An interprocess token is passed
between the GSS-API and the application using the gss_buffer_t
conventions.
A name is used to identify a person or entity. GSS-API authenticates the relationship between a name and the entity claiming the name.
Since different authentication mechanisms may employ different namespaces for identifying their principals, GSSAPI's naming support is necessarily complex in multi-mechanism environments (or even in some single-mechanism environments where the underlying mechanism supports multiple namespaces).
Two distinct representations are defined for names:
gss_name_t type. It is opaque to
GSS-API callers. A single gss_name_t object may contain
multiple names from different namespaces, but all names should refer
to the same entity. An example of such an internal name would be the
name returned from a call to the gss_inquire_cred routine, when
applied to a credential containing credential elements for multiple
authentication mechanisms employing different namespaces. This
gss_name_t object will contain a distinct name for the entity
for each authentication mechanism.
For GSS-API implementations supporting multiple namespaces, objects of
type gss_name_t must contain sufficient information to
determine the namespace to which each primitive name belongs.
Routines (gss_import_name and gss_display_name) are
provided to convert names between contiguous string representations
and the internal gss_name_t type. gss_import_name may
support multiple syntaxes for each supported namespace, allowing users
the freedom to choose a preferred name
representation. gss_display_name should use an
implementation-chosen printable syntax for each supported name-type.
If an application calls gss_display_name, passing the internal
name resulting from a call to gss_import_name, there is no
guarantee the the resulting contiguous string name will be the same as
the original imported string name. Nor do name-space identifiers
necessarily survive unchanged after a journey through the internal
name-form. An example of this might be a mechanism that authenticates
X.500 names, but provides an algorithmic mapping of Internet DNS names
into X.500. That mechanism's implementation of gss_import_name
might, when presented with a DNS name, generate an internal name that
contained both the original DNS name and the equivalent X.500 name.
Alternatively, it might only store the X.500 name. In the latter
case, gss_display_name would most likely generate a printable
X.500 name, rather than the original DNS name.
The process of authentication delivers to the context acceptor an
internal name. Since this name has been authenticated by a single
mechanism, it contains only a single name (even if the internal name
presented by the context initiator to gss_init_sec_context had
multiple components). Such names are termed internal mechanism names,
or "MN"s and the names emitted by gss_accept_sec_context are
always of this type. Since some applications may require MNs without
wanting to incur the overhead of an authentication operation, a second
function, gss_canonicalize_name, is provided to convert a
general internal name into an MN.
Comparison of internal-form names may be accomplished via the
gss_compare_name routine, which returns true if the two names
being compared refer to the same entity. This removes the need for
the application program to understand the syntaxes of the various
printable names that a given GSS-API implementation may support.
Since GSS-API assumes that all primitive names contained within a
given internal name refer to the same entity, gss_compare_name
can return true if the two names have at least one primitive name in
common. If the implementation embodies knowledge of equivalence
relationships between names taken from different namespaces, this
knowledge may also allow successful comparison of internal names
containing no overlapping primitive elements.
When used in large access control lists, the overhead of invoking
gss_import_name and gss_compare_name on each name from
the ACL may be prohibitive. As an alternative way of supporting this
case, GSS-API defines a special form of the contiguous string name
which may be compared directly (e.g. with memcmp()). Contiguous names
suitable for comparison are generated by the gss_export_name
routine, which requires an MN as input. Exported names may be re-
imported by the gss_import_name routine, and the resulting
internal name will also be an MN. The gss_OID constant
GSS_C_NT_EXPORT_NAME indentifies the "export name" type, and
the value of this constant is given in Appendix A. Structurally, an
exported name object consists of a header containing an OID
identifying the mechanism that authenticated the name, and a trailer
containing the name itself, where the syntax of the trailer is defined
by the individual mechanism specification. The precise format of an
export name is defined in the language-independent GSS-API
specification [GSSAPI].
Note that the results obtained by using gss_compare_name will
in general be different from those obtained by invoking
gss_canonicalize_name and gss_export_name, and then
comparing the exported names. The first series of operation
determines whether two (unauthenticated) names identify the same
principal; the second whether a particular mechanism would
authenticate them as the same principal. These two operations will in
general give the same results only for MNs.
The gss_name_t datatype should be implemented as a pointer
type. To allow the compiler to aid the application programmer by
performing type-checking, the use of (void *) is discouraged. A
pointer to an implementation-defined type is the preferred choice.
Storage is allocated by routines that return gss_name_t
values. A procedure, gss_release_name, is provided to free
storage associated with an internal-form name.
GSS-API supports the use of user-specified tags to identify a given context to the peer application. These tags are intended to be used to identify the particular communications channel that carries the context. Channel bindings are communicated to the GSS-API using the following structure:
typedef struct gss_channel_bindings_struct {
OM_uint32 initiator_addrtype;
gss_buffer_desc initiator_address;
OM_uint32 acceptor_addrtype;
gss_buffer_desc acceptor_address;
gss_buffer_desc application_data;
} *gss_channel_bindings_t;
The initiator_addrtype and acceptor_addrtype fields denote the type of addresses contained in the initiator_address and acceptor_address buffers. The address type should be one of the following:
GSS_C_AF_UNSPEC Unspecified address type GSS_C_AF_LOCAL Host-local address type GSS_C_AF_INET Internet address type (e.g. IP) GSS_C_AF_IMPLINK ARPAnet IMP address type GSS_C_AF_PUP pup protocols (eg BSP) address type GSS_C_AF_CHAOS MIT CHAOS protocol address type GSS_C_AF_NS XEROX NS address type GSS_C_AF_NBS nbs address type GSS_C_AF_ECMA ECMA address type GSS_C_AF_DATAKIT datakit protocols address type GSS_C_AF_CCITT CCITT protocols GSS_C_AF_SNA IBM SNA address type GSS_C_AF_DECnet DECnet address type GSS_C_AF_DLI Direct data link interface address type GSS_C_AF_LAT LAT address type GSS_C_AF_HYLINK NSC Hyperchannel address type GSS_C_AF_APPLETALK AppleTalk address type GSS_C_AF_BSC BISYNC 2780/3780 address type GSS_C_AF_DSS Distributed system services address type GSS_C_AF_OSI OSI TP4 address type GSS_C_AF_X25 X.25 GSS_C_AF_NULLADDR No address specified
Note that these symbols name address families rather than specific addressing formats. For address families that contain several alternative address forms, the initiator_address and acceptor_address fields must contain sufficient information to determine which address form is used. When not otherwise specified, addresses should be specified in network byte-order (that is, native byte-ordering for the address family).
Conceptually, the GSS-API concatenates the initiator_addrtype,
initiator_address, acceptor_addrtype, acceptor_address and
application_data to form an octet string. The mechanism calculates a
MIC over this octet string, and binds the MIC to the context
establishment token emitted by gss_init_sec_context. The same bindings
are presented by the context acceptor to gss_accept_sec_context, and a
MIC is calculated in the same way. The calculated MIC is compared with
that found in the token, and if the MICs differ,
gss_accept_sec_context will return a GSS_S_BAD_BINDINGS error, and the
context will not be established. Some mechanisms may include the
actual channel binding data in the token (rather than just a MIC);
applications should therefore not use confidential data as
channel-binding components.
Individual mechanisms may impose additional constraints on addresses
and address types that may appear in channel bindings. For example, a
mechanism may verify that the initiator_address field of the channel
bindings presented to gss_init_sec_context contains the correct
network address of the host system. Portable applications should
therefore ensure that they either provide correct information for the
address fields, or omit addressing information, specifying
GSS_C_AF_NULLADDR as the address-types.
Various parameters are described as optional. This means that they follow a convention whereby a default value may be requested. The following conventions are used for omitted parameters. These conventions apply only to those parameters that are explicitly documented as optional.
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.
In addition to the explicit major status codes for each API function,
the code GSS_S_FAILURE may be returned by any routine,
indicating an implementation-specific or mechanism-specific error
condition, further details of which are reported via the
minor_status parameter.
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.
GSS-API Credential-management Routines
Routine Function
------- --------
gss_acquire_cred Assume a global identity; Obtain
a GSS-API credential handle for
pre-existing credentials.
gss_add_cred Construct credentials
incrementally.
gss_inquire_cred Obtain information about a
credential.
gss_inquire_cred_by_mech Obtain per-mechanism information
about a credential.
gss_release_cred Discard a credential handle.
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.
Return value:
GSS_S_COMPLETE: Successful completion.
GSS_S_BAD_MECH: Unavailable mechanism requested.
GSS_S_BAD_NAMETYPE: Type contained within desired_name parameter is not supported.
GSS_S_BAD_NAME: Value supplied for desired_name parameter is ill formed.
GSS_S_CREDENTIALS_EXPIRED: The credentials could not be acquired Because they have expired.
GSS_S_NO_CRED: No credentials were found for the specified name.
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 text). 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.
Return value:
GSS_S_COMPLETE: Successful completion.
GSS_S_BAD_MECH: Unavailable mechanism requested.
GSS_S_BAD_NAMETYPE: Type contained within desired_name parameter is not supported.
GSS_S_BAD_NAME: Value supplied for desired_name parameter is ill-formed.
GSS_S_DUPLICATE_ELEMENT: The credential already contains an element for the requested mechanism with overlapping usage and validity period.
GSS_S_CREDENTIALS_EXPIRED: The required credentials could not be added because they have expired.
GSS_S_NO_CRED: No credentials were found for the specified name.
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.
Return value:
GSS_S_COMPLETE: Successful completion.
GSS_S_NO_CRED: The referenced credentials could not be accessed.
GSS_S_DEFECTIVE_CREDENTIAL: The referenced credentials were invalid.
GSS_S_CREDENTIALS_EXPIRED: The referenced credentials have expired. If the lifetime parameter was not passed as NULL, it will be set to 0.
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.
Return value:
GSS_S_COMPLETE: Successful completion.
GSS_S_NO_CRED: The referenced credentials could not be accessed.
GSS_S_DEFECTIVE_CREDENTIAL: The referenced credentials were invalid.
GSS_S_CREDENTIALS_EXPIRED: The referenced credentials have expired. If the lifetime parameter was not passed as NULL, it will be set to 0.
minor_status: (Integer, modify) Mechanism specific status code.
cred_handle: (gss_cred_id_t, modify, 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. The cred_handle is set to GSS_C_NO_CREDENTIAL on successful completion of this call.
Return value:
GSS_S_COMPLETE: Successful completion.
GSS_S_NO_CRED: Credentials could not be accessed.
GSS-API Context-Level Routines
Routine Function
------- --------
gss_init_sec_context Initiate a security context with
a peer application.
gss_accept_sec_context Accept a security context
initiated by a peer application.
gss_delete_sec_context Discard a security context.
gss_process_context_token Process a token on a security
context from a peer application.
gss_context_time Determine for how long a context
will remain valid.
gss_inquire_context Obtain information about a
security context.
gss_wrap_size_limit Determine token-size limit for
gss_wrap on a context.
gss_export_sec_context Transfer a security context to
another process.
gss_import_sec_context Import a transferred context.
minor_status: (integer, modify) Mechanism specific status code.
initiator_cred_handle: (gss_cred_id_t, read, 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: (gss_ctx_id_t, read/modify) 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 gss_delete_sec_context().
target_name: (gss_name_t, read) Name of target.
mech_type: (OID, read, optional) Object ID of desired mechanism. Supply GSS_C_NO_OID to obtain an implementation specific default.
req_flags: (bit-mask, read) 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 the flags.
time_req: (Integer, read, optional) Desired number of seconds for which context should remain valid. Supply 0 to request a default validity period.
input_chan_bindings: (channel bindings, read, 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: (buffer, opaque, read, optional) 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: (OID, modify, 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: (buffer, opaque, modify) 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 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. 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 the flags.
time_rec: (Integer, modify, 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 gss_init_sec_context within a loop:
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:
- 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 actual_mech_type parameter is 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. In particular, if the application has requested a service such as delegation or anonymous authentication via the req_flags argument, and such a service is unavailable from the underlying mechanism, gss_init_sec_context should generate a token that will not provide the service, and indicate via the ret_flags argument that the service will not be supported. The application may choose to abort the context establishment by calling gss_delete_sec_context (if it cannot continue in the absence of the service), or it may choose to transmit the token and continue context establishment (if the service was merely desired but not mandatory).
- 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_init_sec_context returns, whether or not the context is fully established.
- GSS-API implementations that support per-message protection are encouraged to 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). However, applications should not rely on this behavior as the flag was not defined in Version 1 of the GSS-API. Instead, applications should determine what per-message services are available 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.
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
req_flagsvalues:
GSS_C_DELEG_FLAG
- True - Delegate credentials to remote peer.
- False - Don't delegate.
GSS_C_MUTUAL_FLAG
- True - Request that remote peer authenticate itself.
- False - Authenticate self to remote peer only.
GSS_C_REPLAY_FLAG
- True - Enable replay detection for messages protected with gss_wrap or gss_get_mic.
- False - Don't attempt to detect replayed messages.
GSS_C_SEQUENCE_FLAG
- True - Enable detection of out-of-sequence protected messages.
- False - Don't attempt to detect out-of-sequence messages.
GSS_C_CONF_FLAG
- True - Request that confidentiality service be made available (via gss_wrap).
- False - No per-message confidentiality service is required.
GSS_C_INTEG_FLAG
- True - Request that integrity service be made available (via gss_wrap or gss_get_mic).
- False - No per-message integrity service is required.
GSS_C_ANON_FLAG
- True - Do not reveal the initiator's identity to the acceptor.
- False - Authenticate normally.
The
ret_flagsvalues:
GSS_C_DELEG_FLAG
- True - Credentials were delegated to the remote peer.
- False - No credentials were delegated.
GSS_C_MUTUAL_FLAG
- True - The remote peer has authenticated itself.
- False - Remote peer has not authenticated itself.
GSS_C_REPLAY_FLAG
- True - replay of protected messages will be detected.
- False - replayed messages will not be detected.
GSS_C_SEQUENCE_FLAG
- True - out-of-sequence protected messages will be detected.
- False - out-of-sequence messages will not be detected.
GSS_C_CONF_FLAG
- True - Confidentiality service may be invoked by calling gss_wrap routine.
- False - No confidentiality service (via gss_wrap) available. gss_wrap will provide message encapsulation, data-origin authentication and integrity services only.
GSS_C_INTEG_FLAG
- True - Integrity service may be invoked by calling either gss_get_mic or gss_wrap routines.
- False - Per-message integrity service unavailable.
GSS_C_ANON_FLAG
- True - The initiator's identity has not been revealed, and will not be revealed if any emitted token is passed to the acceptor.
- False - The initiator's identity has been or will be authenticated normally.
GSS_C_PROT_READY_FLAG
- True - Protection services (as specified by the states of the GSS_C_CONF_FLAG and GSS_C_INTEG_FLAG) are available for use if the accompanying major status return value is either GSS_S_COMPLETE or GSS_S_CONTINUE_NEEDED.
- False - Protection services (as specified by the states of the GSS_C_CONF_FLAG and GSS_C_INTEG_FLAG) are available only if the accompanying major status return value is GSS_S_COMPLETE.
GSS_C_TRANS_FLAG
- True - The resultant security context may be transferred to other processes via a call to gss_export_sec_context().
- False - The security context is not transferable.
All other bits should be set to zero.
Return value:
GSS_S_COMPLETE: Successful completion.
GSS_S_CONTINUE_NEEDED: Indicates that a token from the peer application is required to complete the context, and that gss_init_sec_context must be called again with that token.
GSS_S_DEFECTIVE_TOKEN: Indicates that consistency checks performed on the input_token failed.
GSS_S_DEFECTIVE_CREDENTIAL: Indicates that consistency checks performed on the credential failed.
GSS_S_NO_CRED: The supplied credentials were not valid for context initiation, or the credential handle did not reference any credentials.
GSS_S_CREDENTIALS_EXPIRED: The referenced credentials have expired.
GSS_S_BAD_BINDINGS: The input_token contains different channel bindings to those specified via the input_chan_bindings parameter.
GSS_S_BAD_SIG: The input_token contains an invalid MIC, or a MIC that could not be verified.
GSS_S_OLD_TOKEN: The input_token was too old. This is a fatal error during context establishment.
GSS_S_DUPLICATE_TOKEN: The input_token is valid, but is a duplicate of a token already processed. This is a fatal error during context establishment.
GSS_S_NO_CONTEXT: Indicates that the supplied context handle did not refer to a valid context.
GSS_S_BAD_NAMETYPE: The provided target_name parameter contained an invalid or unsupported type of name.
GSS_S_BAD_NAME: The provided target_name parameter was ill-formed.
GSS_S_BAD_MECH: The specified mechanism is not supported by the provided credential, or is unrecognized by the implementation.
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 flags.
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
ret_flagsvalues:
GSS_C_DELEG_FLAG
- True - Delegated credentials are available via the delegated_cred_handle parameter.
- False - No credentials were delegated.
GSS_C_MUTUAL_FLAG
- True - Remote peer asked for mutual authentication.
- False - Remote peer did not ask for mutual authentication.
GSS_C_REPLAY_FLAG
- True - replay of protected messages will be detected.
- False - replayed messages will not be detected.
GSS_C_SEQUENCE_FLAG
- True - out-of-sequence protected messages will be detected.
- False - out-of-sequence messages will not be detected.
GSS_C_CONF_FLAG
- True - Confidentiality service may be invoked by calling the gss_wrap routine.
- False - No confidentiality service (via gss_wrap) available. gss_wrap will provide message encapsulation, data-origin authentication and integrity services only.
GSS_C_INTEG_FLAG
- True - Integrity service may be invoked by calling either gss_get_mic or gss_wrap routines.
- False - Per-message integrity service unavailable.
GSS_C_ANON_FLAG
- True - The initiator does not wish to be authenticated; the src_name parameter (if requested) contains an anonymous internal name.
- False - The initiator has been authenticated normally.
GSS_C_PROT_READY_FLAG
- True - Protection services (as specified by the states of the GSS_C_CONF_FLAG and GSS_C_INTEG_FLAG) are available if the accompanying major status return value is either GSS_S_COMPLETE or GSS_S_CONTINUE_NEEDED.
- False - Protection services (as specified by the states of the GSS_C_CONF_FLAG and GSS_C_INTEG_FLAG) are available only if the accompanying major status return value is GSS_S_COMPLETE.
GSS_C_TRANS_FLAG
- True - The resultant security context may be transferred to other processes via a call to gss_export_sec_context().
- False - The security context is not transferable.
All other bits should be set to zero.
Return value:
GSS_S_CONTINUE_NEEDED: Indicates that a token from the peer application is required to complete the context, and that gss_accept_sec_context must be called again with that token.
GSS_S_DEFECTIVE_TOKEN: Indicates that consistency checks performed on the input_token failed.
GSS_S_DEFECTIVE_CREDENTIAL: Indicates that consistency checks performed on the credential failed.
GSS_S_NO_CRED: The supplied credentials were not valid for context acceptance, or the credential handle did not reference any credentials.
GSS_S_CREDENTIALS_EXPIRED: The referenced credentials have expired.
GSS_S_BAD_BINDINGS: The input_token contains different channel bindings to those specified via the input_chan_bindings parameter.
GSS_S_NO_CONTEXT: Indicates that the supplied context handle did not refer to a valid context.
GSS_S_BAD_SIG: The input_token contains an invalid MIC.
GSS_S_OLD_TOKEN: The input_token was too old. This is a fatal error during context establishment.
GSS_S_DUPLICATE_TOKEN: The input_token is valid, but is a duplicate of a token already processed. This is a fatal error during context establishment.
GSS_S_BAD_MECH: The received token specified a mechanism that is not supported by the implementation or the provided credential.
minor_status: (Integer, modify) Mechanism specific status code.
context_handle: (gss_ctx_id_t, modify) 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: (buffer, opaque, modify, 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. gss_delete_sec_context will delete the local data structures associated with the specified security context, and may generate an output_token, which when passed to the peer gss_process_context_token will instruct it to do likewise. If no token is required by the mechanism, the GSS-API should set the length field of the output_token (if provided) to zero. No further security services may be obtained using the context specified by context_handle.
In addition to deleting established security contexts, gss_delete_sec_context must also be able to delete "half-built" security contexts resulting from an incomplete sequence of gss_init_sec_context()/gss_accept_sec_context() calls.
The output_token parameter is retained for compatibility with version 1 of the GSS-API. It is recommended that both peer applications invoke gss_delete_sec_context passing the value GSS_C_NO_BUFFER for the output_token parameter, indicating that no token is required, and that gss_delete_sec_context should simply delete local context data structures. If the application does pass a valid buffer to gss_delete_sec_context, mechanisms are encouraged to return a zero-length token, indicating that no peer action is necessary, and that no token should be transferred by the application.
Return value:
GSS_S_COMPLETE: Successful completion.
GSS_S_NO_CONTEXT: No valid context was supplied.
minor_status: (Integer, modify) Implementation specific status code.
context_handle: (gss_ctx_id_t, read) Context handle of context on which token is to be processed
token_buffer: (buffer, opaque, read) Token to process.
Provides a way to pass an asynchronous token to the security service. Most context-level tokens are emitted and processed synchronously by gss_init_sec_context and gss_accept_sec_context, and the application is informed as to whether further tokens are expected by the GSS_C_CONTINUE_NEEDED major status bit. Occasionally, a mechanism may need to emit a context-level token at a point when the peer entity is not expecting a token. For example, the initiator's final call to gss_init_sec_context may emit a token and return a status of GSS_S_COMPLETE, but the acceptor's call to gss_accept_sec_context may fail. The acceptor's mechanism may wish to send a token containing an error indication to the initiator, but the initiator is not expecting a token at this point, believing that the context is fully established. Gss_process_context_token provides a way to pass such a token to the mechanism at any time.
Return value:
GSS_S_COMPLETE: Successful completion.
GSS_S_DEFECTIVE_TOKEN: Indicates that consistency checks performed on the token failed.
GSS_S_NO_CONTEXT: The context_handle did not refer to a valid context.
minor_status: (Integer, modify) Implementation specific status code.
context_handle: (gss_ctx_id_t, read) Identifies the context to be interrogated.
time_rec: (Integer, modify) Number of seconds that the context will remain valid. If the context has already expired, zero will be returned.
Determines the number of seconds for which the specified context will remain valid.
Return value:
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
minor_status: (Integer, modify) Mechanism specific status code.
context_handle: (gss_ctx_id_t, read) A handle that refers to the security context.
src_name: (gss_name_t, modify, optional) The name of the context initiator. If the context was established using anonymous authentication, and if the application invoking gss_inquire_context is the context acceptor, an anonymous name will be returned. 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.
targ_name: (gss_name_t, modify, optional) The name of the context acceptor. Storage associated with this name must be freed by the application after use with a call to gss_release_name(). If the context acceptor did not authenticate itself, and if the initiator did not specify a target name i