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NAME

     krb5_425_conv_principal, krb5_425_conv_principal_ext,
     krb5_524_conv_principal - converts to and from version 4 principals

LIBRARY

     Kerberos 5 Library (libkrb5, -lkrb5)

SYNOPSIS

     #include <krb5.h>

     krb5_error_code
     krb5_425_conv_principal(krb5_context context, const char *name,
             const char *instance, const char *realm,
             krb5_principal *principal);

     krb5_error_code
     krb5_425_conv_principal_ext(krb5_context context, const char *name,
             const char *instance, const char *realm,
             krb5_boolean (*func)(krb5_context, krb5_principal),
             krb5_boolean resolve, krb5_principal *principal);

     krb5_error_code
     krb5_524_conv_principal(krb5_context context,
             const krb5_principal principal, char *name, char *instance,
             char *realm);

DESCRIPTION

     Converting between version 4 and version 5 principals can at best be
     described as a mess.

     A version 4 principal consists of a name, an instance, and a realm. A
     version 5 principal consists of one or more components, and a realm. In
     some cases also the first component/name will differ between version 4
     and version 5.  Furthermore the second component of a host principal will
     be the fully qualified domain name of the host in question, while the
     instance of a version 4 principal will only contain the first part (short
     hostname).  Because of these problems the conversion between principals
     will have to be site customized.

     krb5_425_conv_principal_ext() will try to convert a version 4 principal,
     given by name, instance, and realm, to a version 5 principal. This can
     result in several possible principals, and if func is non-NULL, it will
     be called for each candidate principal.  func should return true if the
     principal was “good”.  To accomplish this, krb5_425_conv_principal_ext()
     will look up the name in krb5.conf.  It first looks in the
     v4_name_convert/host subsection, which should contain a list of version 4
     names whose instance should be treated as a hostname. This list can be
     specified for each realm (in the realms section), or in the libdefaults
     section.  If the name is found the resulting name of the principal will
     be the value of this binding. The instance is then first looked up in
     v4_instance_convert for the specified realm. If found the resulting value
     will be used as instance (this can be used for special cases), no further
     attempts will be made to find a conversion if this fails (with func).  If
     the resolve parameter is true, the instance will be looked up with
     gethostbyname().  This can be a time consuming, error prone, and unsafe
     operation.  Next a list of hostnames will be created from the instance
     and the v4_domains variable, which should contain a list of possible
     domains for the specific realm.

     On the other hand, if the name is not found in a host section, it is
     looked up in a v4_name_convert/plain binding. If found here the name will
     be converted, but the instance will be untouched.

     This list of default host-type conversions is compiled-in:

           v4_name_convert = {
                   host = {
                           ftp = ftp
                           hprop = hprop
                           imap = imap
                           pop = pop
                           rcmd = host
                           smtp = smtp
                   }
           }

     It will only be used if there isn’t an entry for these names in the
     config file, so you can override these defaults.

     krb5_425_conv_principal() will call krb5_425_conv_principal_ext() with
     NULL as func, and the value of v4_instance_resolve (from the libdefaults
     section) as resolve.

     krb5_524_conv_principal() basically does the opposite of
     krb5_425_conv_principal(), it just doesn’t have to look up any names, but
     will instead truncate instances found to belong to a host principal. The
     name, instance, and realm should be at least 40 characters long.

EXAMPLES

     Since this is confusing an example is in place.

     Assume that we have the “foo.com”, and “bar.com” domains that have shared
     a single version 4 realm, FOO.COM. The version 4 krb.realms file looked
     like:

           foo.com         FOO.COM
           .foo.com        FOO.COM
           .bar.com        FOO.COM

     A krb5.conf file that covers this case might look like:

           [libdefaults]
                   v4_instance_resolve = yes
           [realms]
                   FOO.COM = {
                           kdc = kerberos.foo.com
                           v4_instance_convert = {
                                   foo = foo.com
                           }
                           v4_domains = foo.com
                   }

     With this setup and the following host table:

           foo.com
           a-host.foo.com
           b-host.bar.com
     the following conversions will be made:

           rcmd.a-host     -> host/a-host.foo.com
           ftp.b-host      -> ftp/b-host.bar.com
           pop.foo         -> pop/foo.com
           ftp.other       -> ftp/other.foo.com
           other.a-host    -> other/a-host

     The first three are what you expect. If you remove the “v4_domains”, the
     fourth entry will result in an error (since the host “other” can’t be
     found). Even if “a-host” is a valid host name, the last entry will not be
     converted, since the “other” name is not known to represent a host-type
     principal.  If you turn off “v4_instance_resolve” the second example will
     result in “ftp/b-host.foo.com” (because of the default domain). And all
     of this is of course only valid if you have working name resolving.

SEE ALSO

     krb5_build_principal(3), krb5_free_principal(3), krb5_parse_name(3),
     krb5_sname_to_principal(3), krb5_unparse_name(3), krb5.conf(5)