Next: Introduction, Up: (dir) [Contents][Index]
This manual is last updated 6 August 2022 for version 1.0.4 of GNU GSS.
Copyright © 2003–2022 Simon Josefsson.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 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”.
| • Introduction | How to use this manual. | |
| • Preparation | What you should do before using the library. | |
| • Standard GSS API | Reference documentation for the Standard API. | |
| • Extended GSS API | Non-standard functions. | |
| • Invoking gss | Command line interface to the library. | |
| • Acknowledgements | Whom to blame. | |
Appendices | ||
|---|---|---|
| • Criticism of GSS | Why you maybe shouldn’t use GSS. | |
| • Copying Information | How you can copy and share GSS. | |
Indices | ||
| • Concept Index | Index of concepts and programs. | |
| • API Index | Index of functions, variables and data types. | |
Next: Preparation, Previous: Top, Up: Top [Contents][Index]
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 works on many platforms including most major Unix and Windows systems.
| • Getting Started | ||
| • Features | ||
| • GSS-API Overview | ||
| • Supported Platforms | ||
| • Commercial Support | ||
| • Downloading and Installing | ||
| • Bug Reports | ||
| • Contributing | ||
| • Planned Features |
Next: Features, Up: Introduction [Contents][Index]
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.
Next: GSS-API Overview, Previous: Getting Started, Up: Introduction [Contents][Index]
GSS might have a couple of advantages over other libraries doing a similar job.
Anybody can use, modify, and redistribute it under the terms of the LGPLv3|GPLv2+ license.
No global variables are used and multiple library handles and session handles may be used in parallell.
It handles non-ASCII names and user visible strings used in the library (e.g., error messages) can be translated into the users’ language.
It should work on all Unix like operating systems, including Windows.
Next: Supported Platforms, Previous: Features, Up: Introduction [Contents][Index]
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.
Next: Commercial Support, Previous: GSS-API Overview, Up: Introduction [Contents][Index]
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.
GCC 3.4 and GNU Make m68k-uclinux-elf.
If you use GSS on, or port GSS to, a new platform please report it to the author.
Next: Downloading and Installing, Previous: Supported Platforms, Up: Introduction [Contents][Index]
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 AB Hagagatan 24 113 47 Stockholm Sweden E-mail: simon@josefsson.org
If your company provides support related to GNU GSS and would like to be mentioned here, contact the author (see Bug Reports).
Next: Bug Reports, Previous: Commercial Support, Up: Introduction [Contents][Index]
The package can be downloaded from several places, including:
The latest version is stored in a file, e.g., ‘gss-1.0.4.tar.gz’ where the ‘1.0.4’ 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 downloads, configures, builds and installs the package. You will need a few basic tools, such as ‘sh’, ‘make’ and ‘cc’.
$ wget -q ftp://ftp.gnu.org/gnu/gss/gss-1.0.4.tar.gz $ tar xfz gss-1.0.4.tar.gz $ cd gss-1.0.4/ $ ./configure ... $ make ... $ make install ...
After that GSS should be properly installed and ready for use.
Next: Contributing, Previous: Downloading and Installing, Up: Introduction [Contents][Index]
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:
Next: Planned Features, Previous: Bug Reports, Up: Introduction [Contents][Index]
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 (indent)GNU Indent) before submitting your work.
Previous: Contributing, Up: Introduction [Contents][Index]
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.
Next: Standard GSS API, Previous: Introduction, Up: Top [Contents][Index]
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.
| • Header | ||
| • Initialization | ||
| • Version Check | ||
| • Building the source | ||
| • Out of Memory handling |
Next: Initialization, Up: Preparation [Contents][Index]
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.
Next: Version Check, Previous: Header, Up: Preparation [Contents][Index]
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, "");
Next: Building the source, Previous: Initialization, Up: Preparation [Contents][Index]
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(EXIT_FAILURE);
}
Next: Out of Memory handling, Previous: Version Check, Up: Preparation [Contents][Index]
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`
Previous: Building the source, Up: Preparation [Contents][Index]
The GSS API does not have a standard error code for the out of memory
error condition. This library will return GSS_S_FAILURE and
set minor_status to ENOMEM.
Next: Extended GSS API, Previous: Preparation, Up: Top [Contents][Index]
| • Simple Data Types | About integers, strings, OIDs, and OID sets. | |
| • Complex Data Types | About credentials, contexts, names, etc. | |
| • Optional Parameters | What value to use when you don’t want one. | |
| • Error Handling | How errors in GSS are reported and handled. | |
| • Credential Management | Standard GSS credential functions. | |
| • Context-Level Routines | Standard GSS context functions. | |
| • Per-Message Routines | Standard GSS per-message functions. | |
| • Name Manipulation | Standard GSS name manipulation functions. | |
| • Miscellaneous Routines | Standard miscellaneous functions. | |
| • SASL GS2 Routines | Standard SASL GS2 related functions. |
Next: Complex Data Types, Up: Standard GSS API [Contents][Index]
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.
Next: Optional Parameters, Previous: Simple Data Types, Up: Standard GSS API [Contents][Index]
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 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.
Next: Error Handling, Previous: Complex Data Types, Up: Standard GSS API [Contents][Index]
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.
Next: Credential Management, Previous: Optional Parameters, Up: Standard GSS API [Contents][Index]
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.
Next: Context-Level Routines, Previous: Error Handling, Up: Standard GSS API [Contents][Index]
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: desired_name: time_req: desired_mechs: cred_usage: output_cred_handle: actual_mechs: time_rec:
minor_status: input_cred_handle: desired_name: desired_mech: cred_usage: initiator_time_req: acceptor_time_req: output_cred_handle: actual_mechs: initiator_time_rec: acceptor_time_rec:
minor_status: cred_handle: name: lifetime: cred_usage: mechanisms:
minor_status: cred_handle: mech_type: name: initiator_lifetime: acceptor_lifetime: cred_usage:
minor_status: cred_handle:
Next: Per-Message Routines, Previous: Credential Management, Up: Standard GSS API [Contents][Index]
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: initiator_cred_handle: context_handle: target_name: mech_type: req_flags: time_req: input_chan_bindings: input_token: actual_mech_type: output_token: ret_flags: time_rec:
minor_status: context_handle: acceptor_cred_handle: input_token_buffer: input_chan_bindings: src_name: mech_type: output_token: ret_flags: time_rec: delegated_cred_handle:
minor_status: context_handle: output_token:
minor_status: context_handle: token_buffer:
minor_status: context_handle: time_rec:
minor_status: context_handle: src_name: targ_name: lifetime_rec: mech_type: ctx_flags: locally_initiated: open:
minor_status: context_handle: conf_req_flag: qop_req: req_output_size: max_input_size:
minor_status: context_handle: interprocess_token:
minor_status: interprocess_token: context_handle:
Next: Name Manipulation, Previous: Context-Level Routines, Up: Standard GSS API [Contents][Index]
GSS-API Per-message Routines
Routine Function
------- --------
gss_get_mic Calculate a cryptographic message
integrity code (MIC) for a
message; integrity service.
gss_verify_mic Check a MIC against a message;
verify integrity of a received
message.
gss_wrap Attach a MIC to a message, and
optionally encrypt the message
content.
confidentiality service
gss_unwrap Verify a message with attached
MIC, and decrypt message content
if necessary.
minor_status: context_handle: qop_req: message_buffer: message_token:
minor_status: context_handle: message_buffer: token_buffer: qop_state:
minor_status: context_handle: conf_req_flag: qop_req: input_message_buffer: conf_state: output_message_buffer:
minor_status: context_handle: input_message_buffer: output_message_buffer: conf_state: qop_state:
Next: Miscellaneous Routines, Previous: Per-Message Routines, Up: Standard GSS API [Contents][Index]
GSS-API Name manipulation Routines
Routine Function
------- --------
gss_import_name Convert a contiguous string name
to internal-form.
gss_display_name Convert internal-form name to
text.
gss_compare_name Compare two internal-form names.
gss_release_name Discard an internal-form name.
gss_inquire_names_for_mech List the name-types supported by.
the specified mechanism.
gss_inquire_mechs_for_name List mechanisms that support the
specified name-type.
gss_canonicalize_name Convert an internal name to an MN.
gss_export_name Convert an MN to export form.
gss_duplicate_name Create a copy of an internal name.
minor_status: input_name_buffer: input_name_type: output_name:
minor_status: input_name: output_name_buffer: output_name_type:
minor_status: name1: name2: name_equal:
minor_status: name:
minor_status: mechanism: name_types:
minor_status: input_name: mech_types:
minor_status: input_name: mech_type: output_name:
minor_status: input_name: exported_name:
minor_status: src_name: dest_name:
Next: SASL GS2 Routines, Previous: Name Manipulation, Up: Standard GSS API [Contents][Index]
GSS-API Miscellaneous Routines
Routine Function
------- --------
gss_add_oid_set_member Add an object identifier to
a set.
gss_display_status Convert a GSS-API status code
to text.
gss_indicate_mechs Determine available underlying
authentication mechanisms.
gss_release_buffer Discard a buffer.
gss_release_oid_set Discard a set of object
identifiers.
gss_create_empty_oid_set Create a set containing no
object identifiers.
gss_test_oid_set_member Determines whether an object
identifier is a member of a set.
gss_encapsulate_token Encapsulate a context token.
gss_decapsulate_token Decapsulate a context token.
gss_oid_equal Compare two OIDs for equality.
minor_status: member_oid: oid_set:
minor_status: status_value: status_type: mech_type: message_context: status_string:
minor_status: mech_set:
minor_status: buffer:
minor_status: set:
minor_status: oid_set:
minor_status: member: set: present:
input_token: token_oid: output_token:
input_token: token_oid: output_token:
first_oid: second_oid:
Previous: Miscellaneous Routines, Up: Standard GSS API [Contents][Index]
minor_status: sasl_mech_name: mech_type:
minor_status: desired_mech: sasl_mech_name: mech_name: mech_description:
Next: Invoking gss, Previous: Standard GSS API, Up: Top [Contents][Index]
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). See Header.
req_version:
name: username:
Next: Acknowledgements, Previous: Extended GSS API, Up: Top [Contents][Index]
GNU GSS (gss) – Command line interface to the GSS Library.
gss is the main program of GNU GSS.
Mandatory or optional arguments to long options are also mandatory or optional for any corresponding short options.
gss recognizes these commands:
-l, --list-mechanisms
List information about supported mechanisms
in a human readable format.
-m, --major=LONG Describe a `major status' error code value.
-a, --accept-sec-context
Accept a security context as server.
-i, --init-sec-context=MECH
Initialize a security context as client.
MECH is the SASL name of mechanism, use -l
to list supported mechanisms.
-n, --server-name=SERVICE@HOSTNAME
For -i, set the name of the remote host.
For example, "imap@mail.example.com".
These are some standard parameters.
-h, --help Print help and exit -V, --version Print version and exit -q, --quiet Silent operation (default=off)
To list the supported mechanisms, use gss -l like this:
$ src/gss -l
Found 1 supported mechanisms.
Mechanism 0:
Mechanism name: Kerberos V5
Mechanism description: Kerberos V5 GSS-API mechanism
SASL Mechanism name: GS2-KRB5
$
To initialize a Kerberos V5 security context, use the
--init-sec-context parameter. Kerberos V5 needs to know the name
of the remote entity, so you need to supply the --server-name
parameter as well. That will provide the name of the server. For
example, use imap@mail.example.com to setup a security context
with the imap service on the host mail.example.com. The
Kerberos V5 client will use your ticket-granting ticket (which needs to
be available) and acquire a server ticket for the service. The KDC must
know about the server for this to work. The tool will print the GSS-API
context tokens base64 encoded on standard output.
$ gss -i GS2-KRB5 -n host@interop.josefsson.org Context token (protection is available): 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 Input context token:
The tool is waiting for the final Kerberos V5 context token from the server. Note the status text informing you that message protection is available.
To accept a Kerberos V5 context, the process is similar. The server
needs to know its name, so that it can find the host key from
(typically) /etc/shishi/shishi.keys. Once started it will wait
for a context token from the client. Below we’ll paste in the token
printed above.
$ gss -a -n host@interop.josefsson.org Importing name "host@interop.josefsson.org"... Acquiring credentials... Input context token: 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 Context has been accepted. Final context token: YHEGCSqGSIb3EgECAgIAb2IwYKADAgEFoQMCAQ+iVDBSoAMCARKhAwIBAKJGBESy1Zoy9DrG+DuV/6aWmAp79s9d+ofGXC/WKOzRuxAqo98vMRWbsbILW8z9aF1th4GZz0kjFz/hZAmnWyomZ9JiP3yQvg== $
Returning to the client, you may now cut’n’paste the final context token as shown by the server. The client has then authenticated the server as well. The output from the client is shown below.
YHEGCSqGSIb3EgECAgIAb2IwYKADAgEFoQMCAQ+iVDBSoAMCARKhAwIBAKJGBESy1Zoy9DrG+DuV/6aWmAp79s9d+ofGXC/WKOzRuxAqo98vMRWbsbILW8z9aF1th4GZz0kjFz/hZAmnWyomZ9JiP3yQvg== Context has been initialized. $
Next: Criticism of GSS, Previous: Invoking gss, Up: Top [Contents][Index]
This manual borrows text from RFC 2743 and RFC 2744 that describe GSS API formally.
Next: Copying Information, Previous: Acknowledgements, Up: Top [Contents][Index]
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. We are aware that some of the opinions are highly subjective, but we offer them in the hope they can serve as anecdotal evidence.
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: specification is unclear how memory for OIDs are managed. For
example, who is responsible for deallocate potentially newly allocated
OIDs returned as actual_mechs in gss_acquire_cred?
Further, are OIDs deeply copied into OID sets? In other words, if I
add an OID into an OID set, and modify the original OID, will the OID
in the OID set be modified too?
Another illustrating example is the sample GSS header file given in the RFC, which contains:
/* * We have included the xom.h header file. Verify that OM_uint32 * is defined correctly. */ #if sizeof(gss_uint32) != sizeof(OM_uint32) #error Incompatible definition of OM_uint32 from xom.h #endif
The C pre-processor does not know about the sizeof function, so
it is treated as an identifier, which maps to 0. Thus, the expression
does not check that the size of OM_uint32 is correct. It
checks whether the expression 0 != 0 holds.
TBA: thread issues
TBA: multiple mechanisms in a GSS library
TBA: high-level design criticism.
TBA: no credential forwarding.
TBA: internationalization
TBA: dynamically generated OIDs and memory deallocation issue. I.e., should gss_import_name or gss_duplicate_name allocate memory and copy the OID provided, or simply copy the pointer? If the former, who would deallocate that memory? If the latter, the application may deallocate or modify the OID, which seem unwanted.
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.
TBA: krb5: no support for GSS_C_PROT_READY_FLAG. We support it anyway, though.
TBA: krb5: gssapi-cfx differ from rfc 1964 in the reply token in that the latter require presence of sequence numbers whereas the former doesn’t.
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.
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Previous: Concept Index, Up: Top [Contents][Index]
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