Hi Paul,
Thank you for sharing the paper.
A conclusion of the paper was "Our results are yet another reminder that
1024-bit primes should be considered insecure for the security of cryptosystems
based on the hardness of discrete logarithms. The discrete logarithm
computation for our backdoored prime was only feasible because of the 1024-bit
size, and the most effective protection against any backdoor of this type has
always been to use key sizes for which any computation is infeasible. NIST
recommended transitioning away from 1024-bit key sizes for DSA, RSA, and
Diffie-Hellman in 2010 [6]."
NIST has been urging users to move away from groups with 1024- bit p and
160-bit q for many years now.
In our document, we stated that group generators "should" provide their seeds.
The reason for having "should" instead of "shall (must)" was that anyone could
run our suggested method to generate their own group. A user who generates
his/her own group for her/his own application could have a choice of publishing
the seed or not. If a user had a contractor/third party to generate a group
for him/her, he or she could ask for all documentation about the whole process.
Quynh.
________________________________
From: IPsec <ipsec-boun...@ietf.org> on behalf of Paul Wouters <p...@nohats.ca>
Sent: Sunday, October 9, 2016 5:26 PM
To: ipsec@ietf.org WG
Cc: s...@ietf.org
Subject: [IPsec] trapdoor'ed DH (and RFC-5114 again)
Released a few days ago:
http://eprint.iacr.org/2016/961
A kilobit hidden SNFS discrete logarithm computation
Joshua Fried and Pierrick Gaudry and Nadia Heninger and Emmanuel Thomé
We perform a special number field sieve discrete logarithm
computation in a 1024-bit prime field. To our knowledge, this
is the first kilobit-sized discrete logarithm computation ever
reported for prime fields. This computation took a little over
two months of calendar time on an academic cluster using the
open-source CADO-NFS software.
Basically, this paper shows how to make a DH group of 1024 modp
with a backdoor, in two months of academic computing resources,
The paper mentions 5114 a few times:
RFC 5114 [33] specifies a number of groups for use with
Diffie-Hellman, and states that the parameters were drawn
from NIST test data, but neither the NIST test data [39] nor
RFC 5114 itself contain the seeds used to generate the finite
field parameters
And concludes:
Both from this perspective, and from our more modern one, dismissing
the
risk of trapdoored primes in real usage appears to have been a mistake,
as the apparent difficulties encountered by the trapdoor designer in
1992
turn out to be easily circumvented. A more conservative design decision
for FIPS 186 would have required mandatory seed publication instead of
making it optional. As a result, there are opaque, standardized
1024-bit
and 2048-bit primes in wide use today that cannot be properly verified.
This is the strongest statement yet that I've seen to not trust any
of the RFC-5114 groups.
The latest 4307bis document has these groups (22-24) as SHOULD NOT,
stating:
Group 22, 23 and 24 or 1024-bit MODP Group with 160-bit, and
2048-bit MODP Group with 224-bit and 256-bit Prime Order Subgroup
have small subgroups, which means that checks specified in the
"Additional Diffie-Hellman Test for the IKEv2" [RFC6989] section
2.2 first bullet point MUST be done when these groups are used.
These groups are also not safe-primes. The seeds for these groups
have not been publicly released, resulting in reduced trust in
these groups. These groups were proposed as alternatives for
group 2 and 14 but never saw wide deployment. It is expected
in the near future to be further downgraded to MUST NOT.
I'm proposing it is time to change this to MUST NOT for 4307bis.
Possibly, we should do this via SAAG in general, and then follow SAAG's
advise in IPSECME.
Is there _any_ reason why group 22-24 should not be MUST NOT ?
Paul
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