Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 20 Jan 2016 13:00:15 -0500
From: Daniel Kahn Gillmor <dkg@...thhorseman.net>
To: Kurt Seifried <kseifried@...hat.com>
Cc: oss-security <oss-security@...ts.openwall.com>
Subject: Re: Prime example of a can of worms

On Wed 2016-01-20 12:25:42 -0500, Kurt Seifried wrote:
> Sorry yes, although this also applies equally to keys/etc.

sure, though i hope we're not in a "few keys" scenario, that would
definitely be bad :)

> [dkg wrote:]
>> For one, the writeup addresses probabilistic primality tests, but
>> doesn't describe proofs of primality, which are significantly more
>> expensive to generate (and still probably more expensive to verify than
>> a short Miller-Rabin test).  But these proofs provide certainty in a way
>> that probabilistic tests might not.  If we're talking about runtime
>> primality checking when communicating with a potential adversary, are
>> there proofs about the (im)possibility of generating a pseudoprime that
>> is more or less likely to pass a miller-rabin test?
>
> I looked at this a bit and quite honestly the computational time involved
> is just to much to be useful, unless we're talking about generating a small
> set of highly trusted primes. For normal people, this just isn't feasible
> (witness prime generation taking between less then a second, and more than
> 10 minutes, nobody wants to wait 10 minutes...).

right, i'm not suggesting that proof generation be done at runtime, just
that it is an example of a stronger guarantee than we have for runtime
checks, and that it *only* applies to the "generating a small set of
highly-trusted primes" case.

> Agreed, I listed the diversity more as a stop-gap for the cases where
> people have older hard/software (e.g. Java) that will never support larger
> primes/keys. At least then you don't get caught in dragnets for the
> default/commonly used primes.

I agree with this analysis, but the chart in the middle of your paper
makes it looks like the diversity is "best", while the "small set of
heavily-evaluated primes" (i'm assuming that's what's meant with the
"few keys" side of the X axis) is merely "good".

     --dkg

Powered by blists - more mailing lists

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.