Re: [Cfrg] Progress on curve recommendations for TLS WG

Dan Brown <dbrown@certicom.com> Fri, 15 August 2014 17:59 UTC

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From: Dan Brown <dbrown@certicom.com>
To: "'cfrg@irtf.org'" <cfrg@irtf.org>
Thread-Topic: [Cfrg] Progress on curve recommendations for TLS WG
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Date: Fri, 15 Aug 2014 17:59:27 +0000
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Subject: Re: [Cfrg] Progress on curve recommendations for TLS WG
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From: Cfrg [mailto:cfrg-bounces@irtf.org] On Behalf Of Watson Ladd
> The reason Dan Brown's example isn't convincing is that having only  prime 
> factors of not that small size is common.

Right about it being common: Dickman's function says the chance of the largest 
prime factor of that size is about 15%.

Wrong about it being unconvincing: the severity of the attack is what matters, 
not how common it is.  Why would anybody care whether it took six or 
one-million trials to a find a weak 56-bit curve?

Also, I assume that you are not referring to my BARC example, in which the 
largest prime factor is two.   Maybe BARC is unconvincing for another reason, 
which is?