DSSync encryption notes

Andrew Bartlett abartlet at samba.org
Fri Dec 23 00:09:29 GMT 2005

I just wanted to put some observations to the list about the encryptped
blobs in the DRSUAPI replication.

Firstly, this is the command I've been running:

bin/smbtorture ncacn_ip_tcp:win2k3dc.win2k3.abartlet.net RPC-DSSYNC
-Uadministrator%penguin --option=dssync:print_pwd_blobs=true
--option=realm=win2k3.abartlet.net --option=workgroup=win2k3ab

This particular setup ensures that the base encryption keys for NTLMSSP
remain constant, which is an important for the crypt-analysis of this

Interestingly, the output (in terms of encrypted blobs) varies between
runs.  I also note that attributes appear 20 bytes longer than I would
have expected.  My suspicion is that each value is encrypted with the
hash of a 16 or 20 byte 'confounder' and the session key, much like the
samr_set_password_ex call. 

I'm yet to figure out what algorithms are used for the hash, but I
strongly suspect that the actual data encryption is RC4 (due to
irregular length data blobs, which discount a block cipher).

At some point I'll write up a 'challenge' to narrow this down further.

Andrew Bartlett
Andrew Bartlett                                http://samba.org/~abartlet/
Authentication Developer, Samba Team           http://samba.org
Student Network Administrator, Hawker College  http://hawkerc.net
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