OpenVPN local/remote options string differs in keydir

catkin

What is the meaning of "keydir" in messages like these:

Apr 30 10:12:58 LS1 ovpn-client.BLAV[1579]: Local Options String: 'V4,dev-type tun,link-mtu 1542,tun-mtu 1500,proto UDPv4,comp-lzo,keydir 1,cipher BF-CBC,auth SHA1,keysize 128,tls-auth,key-method 2,tls-client'
Apr 30 10:12:58 LS1 ovpn-client.BLAV[1579]: Expected Remote Options String: 'V4,dev-type tun,link-mtu 1542,tun-mtu 1500,proto UDPv4,comp-lzo,keydir 0,cipher BF-CBC,auth SHA1,keysize 128,tls-auth,key-method 2,tls-server'

The only difference between the strings is the keydir value.

What I tried:

Searched on the 'net but found nothing (many pages include logs containing similar messages).
Searched the openvpn man page for keydir (one hit, essentially about messages lie these), "key-" (only key-method and key-server) and "key d" (not found).
Searched the /usr/sbin/openvpn binary for keydir but found only a format string (keydir %s), presumably for messages like these.

Searched openvpn --help output for keydir (nothing), "key-" (nothing) and "key d" and found:

Data Channel Encryption Options (must be compatible between peers):
(These options are meaningful for both Static Key & TLS-mode)
--secret f [d]  : Enable Static Key encryption mode (non-TLS).
                  Use shared secret file f, generate with --genkey.
                  The optional d parameter controls key directionality.
                  If d is specified, use separate keys for each
                  direction, set d=0 on one side of the connection,
                  and d=1 on the other side.

From the openvpn man page:

--secret file [direction]
       Enable Static Key encryption mode (non-TLS).  Use pre-shared secret file which was
       generated  with --genkey.
       [snip]
       The  direction parameter should always be complementary on either side of the
       connection, i.e. one side should use "0" and the other should use "1", or both sides
       should omit it altogether.

That excerpt from the man page looks promising:

"keydir" could be short for "key direction".
It has values 0 and 1.
Each side of the connection should use a different value.

But:

It sounds as if it is only applies when TLS is not being used.

AFAIK TLS is being used:

>  grep tls /etc/openvpn/server.conf 
tls-auth /etc/openvpn/keys/ta.key 0 #Full path to TLS key file
>  grep tls /etc/openvpn/client.BLAV.conf
tls-auth /etc/openvpn/bl-keys/ta.key 1

Note: there's a 0 and a 1 on those which also indicate "direction".

AFAIK "secret" is not being used:

>  grep secret /etc/openvpn/server.conf
[no output]
> grep secret /etc/openvpn/client.BLAV.con
[no output]

catkin

I have examined the source code and concluded that the keydir values printed in the messages are always the same and they are not derived from the OpenVPN configuration.

With reference to the OpenVPN 2.3.1 source code ...

The messages are generated by function do_print_data_channel_mtu_parms defined in init.c:

2670 /*
2671  * Get local and remote options compatibility strings.
2672  */
2673 static void
2674 do_compute_occ_strings (struct context *c)
2675 {
2676   struct gc_arena gc = gc_new ();
2677 
2678   c->c2.options_string_local =
2679     options_string (&c->options, &c->c2.frame, c->c1.tuntap, false, &gc);
2680   c->c2.options_string_remote =
2681     options_string (&c->options, &c->c2.frame, c->c1.tuntap, true, &gc);
2682 
2683   msg (D_SHOW_OCC, "Local Options String: '%s'", c->c2.options_string_local);
2684   msg (D_SHOW_OCC, "Expected Remote Options String: '%s'",
2685        c->c2.options_string_remote);

The values are populated by the options_string function defined in options.c:

2901 options_string (const struct options *o,
2902         const struct frame *frame,
2903         struct tuntap *tt,
2904         bool remote,
2905         struct gc_arena *gc)
2906 
[snip]
2981   /*
2982    * Key direction
2983    */
2984   {
2985     const char *kd = keydirection2ascii (o->key_direction, remote);
2986     if (kd)
2987       buf_printf (&out, ",keydir %s", kd);
2988   }{

Thus it's clear that keydir is a "key direction" not a "key directory".

Function keydirection2ascii is defined in crypto.c:

1180 keydirection2ascii (int kd, bool remote)
1181 {
1182   if (kd == KEY_DIRECTION_BIDIRECTIONAL)
1183     return NULL;
1184   else if (kd == KEY_DIRECTION_NORMAL)
1185     return remote ? "1" : "0";
1186   else if (kd == KEY_DIRECTION_INVERSE)
1187     return remote ? "0" : "1";
1188   else
1189     {
1190       ASSERT (0);
1191     }
1192   return NULL; /* NOTREACHED */
1193 }

Thus the value of keydir in the messages is decided by function keydirection2ascii according to the value of remote. The value of remote is set by do_compute_occ_strings in the two calls to options_string -- invariantly once to true and once to false.