.\" Copyright (c) 1997 Kungliga Tekniska Högskolan
.\" $Id$
.Dd August 8, 1997
.Dt KRB5_425_CONV_PRINCIPAL 3
.Os HEIMDAL
.Sh NAME
.Nm krb5_425_conv_principal ,
.Nm krb5_524_conv_principal
.Nd Converts to and from version 4 principals

.Sh SYNOPSIS
.Fd #include <krb5.h>

.Ft krb5_error_code
.Fn krb5_425_conv_principal "krb5_context context" "const char *name" "const char *instance" "const char *realm" "krb5_principal *princ"

.Ft krb5_error_code
.Fn krb5_524_conv_principal "krb5_context context" "const krb5_principal principal" "char *name" "char *instance" "char *realm"

.Sh DESCRIPTION

Converting between version 4 and version 5 principals can at best be
described as a mess.
.Pp
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 component.  Because of these problems the conversion
between principals will have to be site customized.
.Pp
.Fn krb5_425_conv_principal
will try to convert a version 4 principal, given by
.Fa name ,
.Fa instance ,
and
.Fa realm ,
to a version 5 principal. To do this it will look up the name in 
.Pa krb5.conf .
It first looks in the 
.Li v4_name_convert/host
binding, 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
.Li realms
section), or in the
.Li libdefaults
section.  If the name is found the first component of the principal
will be value of this binding. The instance is then first looked up in
.Li v4_instance_convert 
for the specified realm. If found the resulting value will be used as
instance (this can be used for special cases). If not found you can
optionally have the instance looked up (with
.Fn gethostbyname ) .
This is a time consuming, error prone, and unsafe operation, and it is
not turned on by default. You can turn on this feature by setting
.Li v4_instance_resolve 
to true in the 
.Li libdefaults 
section. As a final fallback you can, for each realm, include a
.Li default_realm
that will be appended to the instance without further checks.
.Pp
On the other hand, if the name is not found in a
.Li host
section, it is looked up in a 
.Li v4_name_convert/plain
binding. If found here the name will be converted, but the instance
will be untouched.
.Pp
.Fn krb5_524_conv_principal
basically does the opposite of 
.Fn 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
.Fa name , 
.Fa instance , 
and 
.Fa realm
should be at least 40 characters long.

.Sh EXAMPLES

Since this is confusing an example is in place.
.Pp
Assume that we have the 
.Dq foo.com , 
and 
.Dq bar.com  
domains that have shared a single version 4 realm, FOO.COM. The version 4 
.Pa krb.realms 
file looked like:
.Bd -literal -offset indent
foo.com		FOO.COM
\&.foo.com	FOO.COM
\&.bar.com	FOO.COM
.Ed
.Pp
A
.Pa krb5.conf
file that covers this case might look like:
.Bd -literal -offset indent
[libdefaults]
	v4_name_convert = {
		host = {
			rcmd = host
			ftp = ftp
			pop = pop
		}
	}
	v4_instance_resolve = yes
[realms]
	FOO.COM = {
		kdc = kerberos.foo.com
		v4_instance_convert = {
			foo = foo.com
		}
		default_domain = foo.com
	}
.Ed
.Pp
With this setup and the following host table:
.Bd -literal -offset indent
foo.com
a-host.foo.com
b-host.bar.com
.Ed
the following conversions will be made:
.Bd -literal -offset indent
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
.Ed
.Pp
The first three are what you expect. If you remove the 
.Dq default_domain ,
the fourth entry will result in an error (since the host
.Dq other
can't be found). Even if 
.Dq a-host 
is a valid host name, the last entry will not be converted, since the
.Dq other
name is not known to represent a host-type principal.
If you turn off
.Dq v4_instance_resolve
the second example will result in
.Dq 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.

.Sh BUGS
You have to set up your
.Pa krb5.conf
correctly to have any of this work.

.Sh SEE ALSO
.Xr krb5_build_principal 3 ,
.Xr krb5_free_principal 3 ,
.Xr krb5_parse_name 3 ,
.Xr krb5_sname_to_principal 3 ,
.Xr krb5_unparse_name 3 ,
.Xr krb5.conf 5