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Re: [openpgp] Fingerprints and their collisions resistance

Daniel Kahn Gillmor <dkg@fifthhorseman.net> Thu, 03 January 2013 23:08 UTC

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Date: Thu, 03 Jan 2013 18:08:42 -0500
From: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
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To: Andrey Jivsov <openpgp@brainhub.org>
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Subject: Re: [openpgp] Fingerprints and their collisions resistance
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On 01/03/2013 05:33 PM, Andrey Jivsov wrote:
> In the process of writing such a draft I noticed that the only place in
> OpenPGP where SHA1 is used in collision resistance sensitive way without
> the possibility to change it is fingerprints.

As i mentioned on the discussion on the GnuPG discussion list, i remain
unconvinced that OpenPGP fingerprints need to be collision-resistant.
They certainly need to be able to resist preimage attacks, but i haven't
seen any convincing attacks that make me think collision resistance is
an issue.

Here's the recent GnuPG discussion:

 http://thread.gmane.org/gmane.comp.encryption.gpg.devel/17366/focus=17389

And here's earlier discussion from Daniel Nagy and myself on this list
suggesting that collision-resistance is an issue for fingerprints:

 http://thread.gmane.org/gmane.ietf.openpgp/6012/focus=6013
 http://thread.gmane.org/gmane.ietf.openpgp/7115/focus=7126

If anyone disagrees with this analysis, i would be interested in hearing
how failed collision-resistance of the fingerprint mechanism could lead
to practical attacks in OpenPGP.

> I have this Keccak in OpenPGP darft written, waiting to for the NIST to
> publish SHA-3 and the OIDs assigned.

thanks for doing this, i think this will be a useful contribution.

Regards,

	--dkg

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