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Date: Tue, 20 Oct 2015 10:22:40 -0600
From: Kurt Seifried <kseifried@...hat.com>
To: oss-security <oss-security@...ts.openwall.com>
Subject: Re: Prime example of a can of worms

So some new questions arise:

1) in openssl does the -2/-5 option matter with respect to security? I read
http://security.stackexchange.com/questions/54359/what-is-the-difference-between-diffie-hellman-generator-2-and-5
and some other things and I have no idea if there is a real impact on
security. I bet the other tools have similar switches for which very few
people seem to understand what they actually do, and if they actually
impact security meaningfully.

2) Openssl/gnutls (and likely others) all apparently have slight variations
on how they generate/test primes. E.g.
http://nmav.gnutls.org/2011/12/generating-diffie-hellman-parameters.html
this worries me, diversity is good, but if not implemented correctly. Do
any best practices actually exist?

3) in testing for primeness how sure are we? Reading
https://en.wikipedia.org/wiki/Miller%E2%80%93Rabin_primality_test and so on
these tests are all "probably prime" but I can't find any data to show that
e.g. given this set of large primes, tested against the various traditional
primality methods, and then brute forced to confirm they are prime/not
prime, what % failed?


--
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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