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heimdal/lib/krb5/doxygen.c
Love Hörnquist Åstrand f911165af9 update (c) 
git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@22546 ec53bebd-3082-4978-b11e-865c3cabbd6b
2008-01-29 08:59:32 +00:00

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/*
* Copyright (c) 2007-2008 Kungliga Tekniska Högskolan
* (Royal Institute of Technology, Stockholm, Sweden).
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* 3. Neither the name of the Institute nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include "krb5_locl.h"
RCSID("$Id$");
/**
*
*/
/*! @mainpage Heimdal Kerberos 5 library
*
* @section intro Introduction
*
* Heimdal libkrb5 library is a implementation of the Kerberos
* protocol.
*
* Kerberos is a system for authenticating users and services on a
* network. It is built upon the assumption that the network is
* ``unsafe''. For example, data sent over the network can be
* eavesdropped and altered, and addresses can also be faked.
* Therefore they cannot be used for authentication purposes.
*
*
* - @ref page_introduction
* - @ref page_fileformats
*
* The project web page:\n
* http://www.h5l.org/
*
*/
/** @defgroup krb5 Heimdal Kerberos 5 library */
/** @defgroup krb5_address Heimdal Kerberos 5 address functions */
/** @defgroup krb5_ccache Heimdal Kerberos 5 credential cache functions */
/** @defgroup krb5_credential Heimdal Kerberos 5 credential handing functions */
/** @defgroup krb5_deprecated Heimdal Kerberos 5 deprecated functions */
/** @defgroup krb5_digest Heimdal Kerberos 5 digest service */
/** @defgroup krb5_error Heimdal Kerberos 5 error reporting functions */
/** @defgroup krb5_v4compat Heimdal Kerberos 4 compatiblity functions */
/** @defgroup krb5_support Heimdal Kerberos 5 support functions */
/*!
@page page_introduction Introduction to the Kerberos 5 API
@section api_overview Kerberos 5 API Overview
All functions are documented in manual pages. This section tries to
give an overview of the major components used in Kerberos library, and
point to where to look for a specific function.
@subsection krb5_context Kerberos context
A kerberos context (krb5_init_context()) holds all per thread state. All global variables that
are context specific are stored in this structure, including default
encryption types, credential cache (for example, a ticket file), and default realms.
See the manual pages for krb5_init_context().
@subsection krb5_auth_context Kerberos authentication context
Kerberos authentication context (krb5_auth_context) holds all
context related to an authenticated connection, in a similar way to the
kerberos context that holds the context for the thread or process.
The krb5_auth_context is used by various functions that are
directly related to authentication between the server/client. Example of
data that this structure contains are various flags, addresses of client
and server, port numbers, keyblocks (and subkeys), sequence numbers,
replay cache, and checksum types.
@subsection krb5_principal Kerberos principal
The Kerberos principal is the structure that identifies a user or
service in Kerberos. The structure that holds the principal is the
krb5_principal. There are function to extract the realm and
elements of the principal, but most applications have no reason to
inspect the content of the structure.
The are several ways to create a principal (with different degree of
portability), and one way to free it.
See manual page for krb5_principal for more information
about the functions.
@subsection krb5_ccache Credential cache
A credential cache holds the tickets for a user. A given user can have
several credential caches, one for each realm where the user have the
initial tickets (the first krbtgt).
The credential cache data can be stored internally in different way, each of them for
different proposes. File credential (FILE) caches and processes based
(KCM) caches are for permanent storage. While memory caches (MEMORY)
are local caches to the local process.
Caches are opened with krb5_cc_resolve() or created with
krb5_cc_gen_unique.
If the cache needs to be opened again (using
krb5_cc_resolve()) krb5_cc_close() will close the
handle, but not the remove the cache. krb5_cc_destroy() will
zero out the cache, remove the cache so it can no longer be
referenced.
See also manual page for krb5_ccache.
@subsection krb5_error_code Kerberos errors
Kerberos errors are based on the com_err library. All error codes are
32-bit signed numbers, the first 24 bits define what subsystem the
error originates from, and last 8 bits are 255 error codes within the
library. Each error code have fixed string associated with it. For
example, the error-code -1765328383 have the symbolic name
KRB5KDC_ERR_NAME_EXP, and associated error string ``Client's entry in
database has expired''.
This is a great improvement compared to just getting one of the unix
error-codes back. However, Heimdal have an extention to pass back
customised errors messages. Instead of getting ``Key table entry not
found'', the user might back ``failed to find
host/host.example.com\@EXAMLE.COM(kvno 3) in keytab /etc/krb5.keytab
(des-cbc-crc)''. This improves the chance that the user find the
cause of the error so you should use the customised error message
whenever it's available.
See also manual page for krb5_get_error_string and
krb5_get_err_text.
@subsection krb5_keytab Keytab management
A keytab is a storage for locally stored keys. Heimdal includes keytab
support for Kerberos 5 keytabs, Kerberos 4 srvtab, AFS-KeyFile's,
and for storing keys in memory.
Keytabs are used for servers and long-running services.
See also manual page for krb5_kt_resolve().
@subsection krb5_crypto Kerberos crypto
Heimdal includes a implementation of the Kerberos crypto framework,
all crypto operations.
See also manual page for krb5_crypto_init(), krb5_create_checksum(),
and krb5_encrypt().
@section kerberos5_client Walkthrough of a sample Kerberos 5 client
This example contains parts of a sample TCP Kerberos 5 clients, if you
want a real working client, please look in appl/test directory in
the Heimdal distribution.
All Kerberos error-codes that are returned from kerberos functions in
this program are passed to krb5_err, that will print a
descriptive text of the error code and exit. Graphical programs can
convert error-code to a human readable error-string with the
krb5_get_err_text function.
Note that you should not use any Kerberos function before
krb5_init_context() have completed successfully. That is the
reason err() is used when krb5_init_context() fails.
First the client needs to call krb5_init_context to initialise
the Kerberos 5 library. This is only needed once per thread
in the program. If the function returns a non-zero value it indicates
that either the Kerberos implementation is failing or it's disabled on
this host.
@code
#include <krb5.h>
int
main(int argc, char **argv)
{
krb5_context context;
if (krb5_context(&context))
errx (1, "krb5_context");
@endcode
Now the client wants to connect to the host at the other end. The
preferred way of doing this is using getaddrinfo (for
operating system that have this function implemented), since getaddrinfo
is neutral to the address type and can use any protocol that is available.
@code
struct addrinfo *ai, *a;
struct addrinfo hints;
int error;
memset (&hints, 0, sizeof(hints));
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
error = getaddrinfo (hostname, "pop3", &hints, &ai);
if (error)
errx (1, "%s: %s", hostname, gai_strerror(error));
for (a = ai; a != NULL; a = a->ai_next) {
int s;
s = socket (a->ai_family, a->ai_socktype, a->ai_protocol);
if (s < 0)
continue;
if (connect (s, a->ai_addr, a->ai_addrlen) < 0) {
warn ("connect(%s)", hostname);
close (s);
continue;
}
freeaddrinfo (ai);
ai = NULL;
}
if (ai) {
freeaddrinfo (ai);
errx ("failed to contact %s", hostname);
}
@endcode
Before authenticating, an authentication context needs to be
created. This context keeps all information for one (to be) authenticated
connection (see krb5_auth_context).
@code
status = krb5_auth_con_init (context, &auth_context);
if (status)
krb5_err (context, 1, status, "krb5_auth_con_init");
@endcode
For setting the address in the authentication there is a help function
krb5_auth_con_setaddrs_from_fd that does everything that is needed
when given a connected file descriptor to the socket.
@code
status = krb5_auth_con_setaddrs_from_fd (context,
auth_context,
&sock);
if (status)
krb5_err (context, 1, status,
"krb5_auth_con_setaddrs_from_fd");
@endcode
The next step is to build a server principal for the service we want
to connect to. (See also krb5_sname_to_principal.)
@code
status = krb5_sname_to_principal (context,
hostname,
service,
KRB5_NT_SRV_HST,
&server);
if (status)
krb5_err (context, 1, status, "krb5_sname_to_principal");
@endcode
The client principal is not passed to krb5_sendauth
function, this causes the krb5_sendauth function to try to figure it
out itself.
The server program is using the function krb5_recvauth to
receive the Kerberos 5 authenticator.
In this case, mutual authentication will be tried. That means that the server
will authenticate to the client. Using mutual authentication
is good since it enables the user to verify that they are talking to the
right server (a server that knows the key).
If you are using a non-blocking socket you will need to do all work of
krb5_sendauth yourself. Basically you need to send over the
authenticator from krb5_mk_req and, in case of mutual
authentication, verifying the result from the server with
krb5_rd_rep.
@code
status = krb5_sendauth (context,
&auth_context,
&sock,
VERSION,
NULL,
server,
AP_OPTS_MUTUAL_REQUIRED,
NULL,
NULL,
NULL,
NULL,
NULL,
NULL);
if (status)
krb5_err (context, 1, status, "krb5_sendauth");
@endcode
Once authentication has been performed, it is time to send some
data. First we create a krb5_data structure, then we sign it with
krb5_mk_safe using the auth_context that contains the
session-key that was exchanged in the
krb5_sendauth/krb5_recvauth authentication
sequence.
@code
data.data = "hej";
data.length = 3;
krb5_data_zero (&packet);
status = krb5_mk_safe (context,
auth_context,
&data,
&packet,
NULL);
if (status)
krb5_err (context, 1, status, "krb5_mk_safe");
@endcode
And send it over the network.
@code
len = packet.length;
net_len = htonl(len);
if (krb5_net_write (context, &sock, &net_len, 4) != 4)
err (1, "krb5_net_write");
if (krb5_net_write (context, &sock, packet.data, len) != len)
err (1, "krb5_net_write");
@endcode
To send encrypted (and signed) data krb5_mk_priv should be
used instead. krb5_mk_priv works the same way as
krb5_mk_safe, with the exception that it encrypts the data
in addition to signing it.
@code
data.data = "hemligt";
data.length = 7;
krb5_data_free (&packet);
status = krb5_mk_priv (context,
auth_context,
&data,
&packet,
NULL);
if (status)
krb5_err (context, 1, status, "krb5_mk_priv");
@endcode
And send it over the network.
@code
len = packet.length;
net_len = htonl(len);
if (krb5_net_write (context, &sock, &net_len, 4) != 4)
err (1, "krb5_net_write");
if (krb5_net_write (context, &sock, packet.data, len) != len)
err (1, "krb5_net_write");
@endcode
The server is using krb5_rd_safe and
krb5_rd_priv to verify the signature and decrypt the packet.
@section krb5_verify_user Validating a password in an application
See the manual page for krb5_verify_user.
@section mit_differences API differences to MIT Kerberos
This section is somewhat disorganised, but so far there is no overall
structure to the differences, though some of the have their root in
that Heimdal uses an ASN.1 compiler and MIT doesn't.
@subsection mit_krb5_principal Principal and realms
Heimdal stores the realm as a krb5_realm, that is a char *.
MIT Kerberos uses a krb5_data to store a realm.
In Heimdal krb5_principal doesn't contain the component
name_type; it's instead stored in component
name.name_type. To get and set the nametype in Heimdal, use
krb5_principal_get_type and
krb5_principal_set_type.
For more information about principal and realms, see
krb5_principal.
@subsection mit_krb5_error_code Error messages
To get the error string, Heimdal uses
krb5_get_error_string or, if NULL is returned,
krb5_get_err_text. This is to return custom error messages
(like ``Can't find host/datan.example.com\@CODE.COM in
/etc/krb5.conf.'' instead of a ``Key table entry not found'' that
error_message returns.
Heimdal uses a threadsafe(r) version of the com_err interface; the
global com_err table isn't initialised. Then
error_message returns quite a boring error string (just
the error code itself).
*/
/*!
@page page_fileformats File formats
@section fileformats File formats
This section documents the diffrent file formats that are used in
Heimdal and other Kerberos implementations.
@subsection file_keytab keytab
The keytab binary format is not a standard format. The format has
evolved and may continue to. It is however understood by several
Kerberos implementations including Heimdal, MIT, Sun's Java ktab and
are created by the ktpass.exe utility from Windows. So it has
established itself as the defacto format for storing Kerberos keys.
The following C-like structure definitions illustrate the MIT keytab
file format. All values are in network byte order. All text is ASCII.
@code
keytab {
uint16_t file_format_version; # 0x502
keytab_entry entries[*];
};
keytab_entry {
int32_t size;
uint16_t num_components; # subtract 1 if version 0x501
counted_octet_string realm;
counted_octet_string components[num_components];
uint32_t name_type; # not present if version 0x501
uint32_t timestamp;
uint8_t vno8;
keyblock key;
uint32_t vno; #only present if >= 4 bytes left in entry
};
counted_octet_string {
uint16_t length;
uint8_t data[length];
};
keyblock {
uint16_t type;
counted_octet_string;
};
@endcode
All numbers are stored in network byteorder (big endian) format.
The keytab file format begins with the 16 bit file_format_version which
at the time this document was authored is 0x502. The format of older
keytabs is described at the end of this document.
The file_format_version is immediately followed by an array of
keytab_entry structures which are prefixed with a 32 bit size indicating
the number of bytes that follow in the entry. Note that the size should be
evaluated as signed. This is because a negative value indicates that the
entry is in fact empty (e.g. it has been deleted) and that the negative
value of that negative value (which is of course a positive value) is
the offset to the next keytab_entry. Based on these size values alone
the entire keytab file can be traversed.
The size is followed by a 16 bit num_components field indicating the
number of counted_octet_string components in the components array.
The num_components field is followed by a counted_octet_string
representing the realm of the principal.
A counted_octet_string is simply an array of bytes prefixed with a 16
bit length. For the realm and name components, the counted_octet_string
bytes are ASCII encoded text with no zero terminator.
Following the realm is the components array that represents the name of
the principal. The text of these components may be joined with slashs
to construct the typical SPN representation. For example, the service
principal HTTP/www.foo.net\@FOO.NET would consist of name components
"HTTP" followed by "www.foo.net".
Following the components array is the 32 bit name_type (e.g. 1 is
KRB5_NT_PRINCIPAL, 2 is KRB5_NT_SRV_INST, 5 is KRB5_NT_UID, etc). In
practice the name_type is almost certainly 1 meaning KRB5_NT_PRINCIPAL.
The 32 bit timestamp indicates the time the key was established for that
principal. The value represents the number of seconds since Jan 1, 1970.
The 8 bit vno8 field is the version number of the key. This value is
overridden by the 32 bit vno field if it is present. The vno8 field is
filled with the lower 8 bits of the 32 bit protocol kvno field.
The keyblock structure consists of a 16 bit value indicating the
encryption type and is a counted_octet_string containing the key. The
encryption type is the same as the Kerberos standard (e.g. 3 is
des-cbc-md5, 23 is arcfour-hmac-md5, etc).
The last field of the keytab_entry structure is optional. If the size of
the keytab_entry indicates that there are at least 4 bytes remaining,
a 32 bit value representing the key version number is present. This
value supersedes the 8 bit vno8 value preceeding the keyblock.
Older keytabs with a file_format_version of 0x501 are different in
three ways:
- All integers are in host byte order [1].
- The num_components field is 1 too large (i.e. after decoding, decrement by 1).
- The 32 bit name_type field is not present.
[1] The file_format_version field should really be treated as two
separate 8 bit quantities representing the major and minor version
number respectively.
@subsection file_hdb_dump Heimdal database dump file
Format of the Heimdal text dump file as of Heimdal 0.6.3:
Each line in the dump file is one entry in the database.
Each field of a line is separated by one or more spaces, with the
exception of fields consisting of principals containing spaces, where
space can be quoted with \ and \ is quoted by \.
Fields and their types are:
@code
Quoted princial (quote character is \) [string]
Keys [keys]
Created by [event]
Modified by [event optional]
Valid start time [time optional]
Valid end time [time optional]
Password end valid time [time optional]
Max lifetime of ticket [time optional]
Max renew time of ticket [integer optional]
Flags [hdb flags]
Generation number [generation optional]
Extensions [extentions optional]
@endcode
Fields following these silently are ignored.
All optional fields will be skipped if they fail to parse (or comprise
the optional field marker of "-", w/o quotes).
Example:
@code
fred\@CODE.COM 27:1:16:e8b4c8fc7e60b9e641dcf4cff3f08a701d982a2f89ba373733d26ca59ba6c789666f6b8bfcf169412bb1e5dceb9b33cda29f3412:-:1:3:4498a933881178c744f4232172dcd774c64e81fa6d05ecdf643a7e390624a0ebf3c7407a:-:1:2:b01934b13eb795d76f3a80717d469639b4da0cfb644161340ef44fdeb375e54d684dbb85:-:1:1:ea8e16d8078bf60c781da90f508d4deccba70595258b9d31888d33987cd31af0c9cced2e:- 20020415130120:admin\@CODE.COM 20041221112428:fred\@CODE.COM - - - 86400 604800 126 20020415130120:793707:28 -
@endcode
Encoding of types are as follows:
- keys
@code
kvno:[masterkvno:keytype:keydata:salt]{zero or more separated by :}
@endcode
kvno is the key version number.
keydata is hex-encoded
masterkvno is the kvno of the database master key. If this field is
empty, the kadmin load and merge operations will encrypt the key data
with the master key if there is one. Otherwise the key data will be
imported asis.
salt is encoded as "-" (no/default salt) or
@code
salt-type /
salt-type / "string"
salt-type / hex-encoded-data
@endcode
keytype is the protocol enctype number; see enum ENCTYPE in
include/krb5_asn1.h for values.
Example:
@code
27:1:16:e8b4c8fc7e60b9e641dcf4cff3f08a701d982a2f89ba373733d26ca59ba6c789666f6b8bfcf169412bb1e5dceb9b33cda29f3412:-:1:3:4498a933881178c744f4232172dcd774c64e81fa6d05ecdf643a7e390624a0ebf3c7407a:-:1:2:b01934b13eb795d76f3a80717d469639b4da0cfb644161340ef44fdeb375e54d684dbb85:-:1:1:ea8e16d8078bf60c781da90f508d4deccba70595258b9d31888d33987cd31af0c9cced2e:-
@endcode
@code
kvno=27,{key: masterkvno=1,keytype=des3-cbc-sha1,keydata=..., default salt}...
@endcode
- time
Format of the time is: YYYYmmddHHMMSS, corresponding to strftime
format "%Y%m%d%k%M%S".
Time is expressed in UTC.
Time can be optional (using -), when the time 0 is used.
Example:
@code
20041221112428
@endcode
- event
@code
time:principal
@endcode
time is as given in format time
principal is a string. Not quoting it may not work in earlier
versions of Heimdal.
Example:
@code
20041221112428:bloggs\@CODE.COM
@endcode
- hdb flags
Integer encoding of HDB flags, see HDBFlags in lib/hdb/hdb.asn1. Each
bit in the integer is the same as the bit in the specification.
- generation:
@code
time:usec:gen
@endcode
usec is a the microsecond, integer.
gen is generation number, integer.
The generation can be defaulted (using '-') or the empty string
- extensions:
@code
first-hex-encoded-HDB-Extension[:second-...]
@endcode
HDB-extension is encoded the DER encoded HDB-Extension from
lib/hdb/hdb.asn1. Consumers HDB extensions should be aware that
unknown entires needs to be preserved even thought the ASN.1 data
content might be unknown. There is a critical flag in the data to show
to the KDC that the entry MUST be understod if the entry is to be
used.
*/
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