[tor-bugs] #11611 [Obfsproxy]: obfs2/obfs3 AES counter initialization is incorrect.

[Tor Bug Tracker & Wiki]

#11611: obfs2/obfs3 AES counter initialization is incorrect.
---------------------------+-----------------
     Reporter:  yawning    |      Owner:  asn
         Type:  defect     |     Status:  new
     Priority:  normal     |  Milestone:
    Component:  Obfsproxy  |    Version:
   Resolution:             |   Keywords:
Actual Points:             |  Parent ID:
       Points:             |
---------------------------+-----------------

Comment (by yawning):

 PyCrypto will increment the counter by one per every block size worth of
 data processed.

 ScrambleSuit actually uses a `prefix | counter` style non-wrapping
 counter, but the code explicitly sets `allow_wraparound` to `False` (and
 doesn't use `common/aes.py`).  I do not see why future protocols could not
 use pycrypto's AES directly if they want different behavior like
 ScrambleSuit does.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/11611#comment:2>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online