oss-security - Prime example of a can of worms

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Message-ID: <CANO=Ty18_pMLco8RdabsEbhs9sLahRhT_U93PGhDVwhcRaqzpQ@mail.gmail.com>
Date: Sun, 18 Oct 2015 22:06:13 -0600
From: Kurt Seifried <kseifried@...hat.com>
To: CVE ID Requests <cve-assign@...re.org>, oss-security <oss-security@...ts.openwall.com>
Subject: Prime example of a can of worms

So in light of:

https://weakdh.org/imperfect-forward-secrecy-ccs15.pdf

and

https://www.eff.org/deeplinks/2015/10/how-to-protect-yourself-from-nsa-attacks-1024-bit-DH

I would suggest we minimally have a conversation about DH prime security
(e.g. using larger 2048 primes, and/or a better mix of primes to make
pre-computation attacks harder). Generating good primes is not easy from
what I've seen of several discussions, my fear would be that people try to
fix this by finding new primes that turn out to be problematic.

Secondly I would also suggest we seriously look at assigning a CVE to the
use of suspected compromised DH primes. Despite the fact we don't have
conclusive direct evidence (that I'm aware of, correct me if there is any
conclusive evidence) I think in this case:

1) the attack is computationally feasible for an organization with
sufficient funding
2) the benefit of such an attack far, far, FAR outweighs the cost for
certain orgs, from the paper:

A small
number of fixed or standardized groups are used by millions
of servers; performing precomputation for a single 1024-bit
group would allow passive eavesdropping on 18% of popular
HTTPS sites, and a second group would allow decryption
of traffic to 66% of IPsec VPNs and 26% of SSH servers.

--
Kurt Seifried -- Red Hat -- Product Security -- Cloud
PGP A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993
Red Hat Product Security contact: secalert@...hat.com

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