Re: [Cfrg] A downside of deterministic DL signatures?

Tony Arcieri <bascule@gmail.com> Thu, 31 July 2014 17:09 UTC

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From: Tony Arcieri <bascule@gmail.com>
Date: Thu, 31 Jul 2014 10:08:58 -0700
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To: Michael Hamburg <mike@shiftleft.org>
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Cc: Dan Brown <dbrown@certicom.com>, IRTF Crypto Forum Research Group <cfrg@irtf.org>
Subject: Re: [Cfrg] A downside of deterministic DL signatures?
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On Thu, Jul 31, 2014 at 12:40 AM, Michael Hamburg <mike@shiftleft.org>
wrote:

> Indeed.  But collision attacks have also broken signature schemes *in
> practice*, for example the Flame malware.
>

Are there any other examples of collision attacks in the wild? Also note
this attack required a nationstate-level effort.

Attacks on bad nonces are comparatively common and relatively easy, e.g.
someone automated stealing of other's Bitcoins by detecting nonce reuse in
the BitCoin block chain:

https://bitcointalk.org/index.php?topic=271486.0


>  You can have any two of determinism, one-pass signatures, and protection
> from collision attacks.  So far as I know, you can’t have all three, at
> least not with a Schnorr scheme.  Please correct me if I’m wrong.
>

I think you're correct


> Or should we drop protection from collision attacks?


Probably, unless there's evidence they're a real threat.

-- 
Tony Arcieri