Wireshark · Wireshark-dev: [Wireshark-dev] Question regarding decryption of ikev1 ISAKMP messages

[Susanne Goldammer <Susanne.Goldammer@xxxxxx>]

Hi all,

today i was trying to use this feature to decrypt IKEv1 messages
exchanged during Main Mode. Herefor i added the Initiator Cookie and the
Encryption Key to the IKEv1 Decryption Table. Unfortunately this did not
help. I used Wireshark version 1.8.0.

A source code analysis then showed up, that the code is checking whether
the connection is using Authentication-Method: PSK. In my case it does
not use a PSK but RSA-SIG method. So i changed the code

epan/dissectors/packet-isakmp.c:1728

if (!decr ||
    decr->is_psk == FALSE ||          <-- removed this line
    decr->gi_len == 0 ||
    decr->gr_len == 0)
  return NULL;  

and deactivated the line checking for is_psk.
Then it was possible to decode the ISAKMP payload (Encrypted data). So
the code seems to work for non PSK connections, too.

Now i was wondering about the reason for this check. Is it possible to
remove this for future versions to make the IKEv1 decryption work for
non PSK connections?

Thanks a lot for your replies.
Susanne