PrincipalName principalName = convertPrincipal(principal);
        EncryptionKey[] keys = Krb5Util.keysFromJavaxKeyTab(keytab, principalName);

        if ( keys == null || keys.length == 0 ) {
            throw new KrbException("Could not find any keys in keytab for " + principalName); //$NON-NLS-1$
        }

        KrbAsReqBuilder builder = new KrbAsReqBuilder(principalName, keytab);