Using WPA2 DK PSK (derrived Key) instead of 4Way Handshake

[magnum]

Either way, I'm trying to follow the RFC's for the four way handshake to understand if, armed with the hash already, I could create a four way handshake capture which hashcat would be happy with. Can you think of any reason this wouldn't be physically possible?

The problem with that approach (apart from being tedious) is you only get half the possible speed. Aimed with the actual derived key and not just a sniffed handshake, we can exploit the inner workings of PBKDF2: We can create the first 160 bits of the key with half of the work compared to cracking a sniffed handshake - and then do early rejection. So a generic non-naive PBKDF2 format will be exactly twice as fast as the sniffed-handshake WPAPSK format.

We already had a generic pbkdf2-hmac-sha1 format in John the Ripper (bleeding-jumbo branch) so I tested this today. I had to tweak it a little to allow for longer salts etc. After verifying the concept I threw an OpenCL format together too. There should be a Trac ticket for implementing generic PBKDF2 formats in Hashcat - if not, just add one.

Here's how to crack such a hash in JtR now (provided you have the very latest source from GitHub):

Let's say you have an ESSID of "Harkonen" (I made this from a well known test vector) and a DK of ee51883793a6f68e9615fe73c80a3aa6f2dd0ea537bce627b929183cc6e57925. The password for this key is "12345678".

Convert the ESSID to hex (this is because the format is generic so it can take binary salts). For example like this:

Code:

$ perl -e 'print unpack("H*", "Harkonen"), "\n"'
4861726b6f6e656e

The iteration count is always 4096. Now just put the pieces together:

Code:

$ echo 'Harkonen:$pbkdf2-hmac-sha1$4096$4861726b6f6e656e$ee51883793a6f68e9615fe73c80a3aa6f2dd0ea537bce627b929183cc6e57925' > wpapsk-dk.in

(the "Harkonen:" in this line is just a "username" that will be output if/when the hash is cracked. It's not part of the hash itself and can be omitted).

Now fire away. Note that I add the -min-length option because WPAPSK has a minimum length of 8 so we don't want to try shorter candidates:

Code:

$ ../run/john wpapsk-dk.in -inc:digits -min-len=8
Loaded 1 password hash (PBKDF2-HMAC-SHA1 [PBKDF2-SHA1 8x SSE2])
Press 'q' or Ctrl-C to abort, almost any other key for status
12345678         (Harkonen)
1g 0:00:00:00 DONE (2014-09-04 19:35) 2.500g/s 10240p/s 10240c/s 10240C/s 029258369..20011212
Use the "--show" option to display all of the cracked passwords reliably
Session completed

(the speed figures shown here are way low because the password was cracked immediately)