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.Dd September  3, 2003
.Dt KRB5_425_CONV_PRINCIPAL 3
.Os
.Sh NAME
.Nm krb5_425_conv_principal ,
.Nm krb5_425_conv_principal_ext ,
.Nm krb5_524_conv_principal
.Nd converts to and from version 4 principals
.Sh LIBRARY
Kerberos 5 Library (libkrb5, -lkrb5)
.Sh SYNOPSIS
.In krb5/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 *principal"
.Ft krb5_error_code
.Fn 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"
.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 part (short hostname).  Because of these problems
the conversion between principals will have to be site customized.
.Pp
.Fn krb5_425_conv_principal_ext
will try to convert a version 4 principal, given by
.Fa name ,
.Fa instance ,
and
.Fa realm ,
to a version 5 principal. This can result in several possible
principals, and if
.Fa func
is non-NULL, it will be called for each candidate principal.
.Fa func
should return true if the principal was
.Dq good .
To accomplish this,
.Fn krb5_425_conv_principal_ext
will look up the name in
.Pa krb5.conf .
It first looks in the
.Li 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
.Li realms
section), or in the
.Li 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
.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), no further attempts
will be made to find a conversion if this fails (with
.Fa func ) .
If the
.Fa resolve
parameter is true, the instance will be looked up with
.Fn 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
.Li v4_domains
variable, which should contain a list of possible domains for the
specific realm.
.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
This list of default host-type conversions is compiled-in:
.Bd -literal -offset indent
v4_name_convert = {
	host = {
		ftp = ftp
		hprop = hprop
		imap = imap
		pop = pop
		rcmd = host
		smtp = smtp
	}
}
.Ed
.Pp
It will only be used if there isn't an entry for these names in the
config file, so you can override these defaults.
.Pp
.Fn krb5_425_conv_principal
will call
.Fn krb5_425_conv_principal_ext
with
.Dv NULL
as
.Fa func ,
and the value of
.Li v4_instance_resolve
(from the
.Li libdefaults
section) as
.Fa resolve .
.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_instance_resolve = yes
[realms]
	FOO.COM = {
		kdc = kerberos.foo.com
		v4_instance_convert = {
			foo = foo.com
		}
		v4_domains = 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	-\*(Gt host/a-host.foo.com
ftp.b-host	-\*(Gt ftp/b-host.bar.com
pop.foo		-\*(Gt pop/foo.com
ftp.other	-\*(Gt ftp/other.foo.com
other.a-host	-\*(Gt other/a-host
.Ed
.Pp
The first three are what you expect. If you remove the
.Dq v4_domains ,
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 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