+++ /dev/null
-The gss-api authentication mechanism implementation for racoon was
-based on the ietf draft draft-ietf-ipsec-isakmp-gss-auth-06.txt.
-
-The implementation uses the Heimdal gss-api library, i.e. gss-api
-on top of Kerberos 5. The Heimdal gss-api library had to be modified
-to meet the requirements of using gss-api in a daemon. More specifically,
-the gss_acquire_cred() call did not work for other cases than
-GSS_C_NO_CREDENTIAL ("use default creds"). Daemons are often started
-as root, and have no Kerberos 5 credentials, so racoon explicitly
-needs to acquire its credentials. The usual method (already used
-by login authentication daemons) in these situations is to add
-a set of special credentials to be used. For example, authentication
-by daemons concerned with login credentials, uses 'host/fqdn' as
-its credential, where fqdn is the hostname on the interface that
-is being used. These special credentials need to be extracted into
-a local keytab from the kdc. The default value used in racoon
-is 'ike/fqdn', but it can be overridden in the racoon config file.
-
-The modification to the Heimdal gss-api library implements the
-mechanism above. If a credential other than GSS_C_NO_CREDENTIAL
-is specified to gss_acquire_cred(), it first looks in the default
-credential cache if it its principal matches the desired credential.
-If not, it extracts it from the default keytab file, and stores
-it in a memory-based credential cache, part of the gss credential
-structure.
-
-
-
-The modifcations to racoon itself are as follows:
-
- * The racoon.conf config file accepts a new keyword, "gssapi_id",
- to be used inside a proposal specification. It specifies
- a string (a Kerberos 5 principal in this case), specifying the
- credential that racoon will try to acquire. The default value
- is 'ike/fqdn', where fqdn is the hostname for the interface
- being used for the exchange. If the id is not specified, no
- GSS endpoint attribute will be specified in the first SA sent.
- However, if the initiator does specify a GSS endpoint attribute,
- racoon will always respond with its own GSS endpoint name
- in the SA (the default one if not specified by this option).
-
- * The racoon.conf file accepts "gssapi_krb" as authentication
- method inside a proposal specification. The number used
- for this method is 65001, which is a temporary number as
- specified in the draft.
-
- * The cftoken.l and cfparse.y source files were modified to
- pick up the configuration options. The original sources
- stored algorithms in bitmask, which unfortunately meant
- that the maximum value was 32, clearly not enough for 65001.
- After consulting with the author (sakane@kame.net), it turned
- out that method was a leftover, and no longer needed. I replaced
- it with plain integers.
-
- * The gss-api specific code was concentrated as much as possible
- in gssapi.c and gssapi.h. The code to call functions defined
- in these files is conditional on HAVE_GSSAPI, except for the
- config scan code. Specifying this flag on the compiler commandline
- is conditional on the --enable-gssapi option to the configure
- script.
-
- * Racoon seems to want to send accepted SA proposals back to
- the initiator in a verbatim fashion, leaving no room to
- insert the (variable-length) GSS endpoint name attribute.
- I worked around this by re-assembling the extracted SA
- into a new SA if the gssapi_krb method is used, and the
- initiator sent the name attribute. This scheme should
- possibly be re-examined by the racoon maintainers, storing
- the SAs (the transformations, to be more precise) in a different
- fashion to allow for variable-length attributes to be
- re-inserted would be a good change, but I considered it to be
- beyond the scope of this project.
-
- * The various state functions for aggressive and main mode
- (in isakmp_agg.c and isakmp_ident.c respectively) were
- changed to conditionally change their behavior if the
- gssapi_krb method is specified.
-
-
-This implementation tried to follow the specification in the ietf draft
-as close as possible. However, it has not been tested against other
-IKE daemon implementations. The only other one I know of is Windows 2000,
-and it has some caveats. I attempted to be Windows 2000 compatible.
-Should racoon be tried against Windows 2000, the gssapi_id option in
-the config file must be used, as Windows 2000 expects the GSS endpoint
-name to be sent at all times. I have my doubts as to the W2K compatibility,
-because the spec describes the GSS endpoint name sent by W2K as
-an unicode string 'xxx@domain', which doesn't seem to match the
-required standard for gss-api + kerberos 5 (i.e. I am fairly certain
-that such a string will be rejected by the Heimdal gss-api library, as it
-is not a valid Kerberos 5 principal).
-
-With the Heimdal gss-api implementation, the gssapi_krb authentication
-method will only work in main mode. Aggressive mode does not allow
-for the extra round-trips needed by gss_init_sec_context and
-gss_accept_sec_context when mutual authentication is requested.
-The draft specifies that the a fallback should be done to main mode,
-through the return of INVALID-EXCHANGE-TYPE if it turns out that
-the gss-api mechanisms needs more roundtrips. This is implemented.
-Unfortunately, racoon does not seem to properly fall back to
-its next mode, and this is not specific to the gssapi_krb method.
-So, to avoid problems, only specify main mode in the config file.
-
-
- -- Frank van der Linden <fvdl@wasabisystems.com>
-
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