Improper use of Hash for MAC

[Donald Stufft]

I noticed that within python-keystone client the memcache_crypt middleware uses a simple sha1 as a MAC. This is bad to do because a general hash function is not designed to work as a MAC and thus are often vulnerable to a number of attacks. I suggest that instead the hmac library in the python stdlib is used.

The code in question is here:
    https://github.com/openstack/python-keystoneclient/blob/master/keystoneclient/middleware/memcache_crypt.py#L89-L106

[Thierry Carrez (ttx)]

Several improvements are being rolled up in a security advisory going out Wednesday. We'll see if this still applies after that one is disclosed.

[Thierry Carrez (ttx)]

@Donald: could you check that the vulnerability still applies with the recent change in memcache hashing implementation ?

See https://review.openstack.org/#/c/33661 for details

[Donald Stufft (dstufft)]

It appears this issue, and the timing attack issue have both been resolved with that changeset.

[Thierry Carrez (ttx)]

Awesome. I'll close this bug and make it public in a short while.