Re: [openpgp] "SHA-1 is a Shambles" and forging PGP WoT signatures

Damien Goutte-Gattat <dgouttegattat@incenp.org> Fri, 24 January 2020 21:21 UTC

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Date: Fri, 24 Jan 2020 21:21:28 +0000
From: Damien Goutte-Gattat <dgouttegattat@incenp.org>
To: Michael Richardson <mcr@sandelman.ca>
Cc: openpgp@ietf.org
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Subject: Re: [openpgp] "SHA-1 is a Shambles" and forging PGP WoT signatures
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On Fri, Jan 24, 2020 at 11:57:09AM -0500, Michael Richardson wrote:
>I guess, maybe if the key is big enough (rsa 8K, bigger), that the 
>bytes could be in the prime itself.  Are you saying that?

Yes.


> If so, I wonder what the smallest key for which this is true is.

The collision found by the authors used 9 near-collision blocks (4608 
bits). They believe it would have been possible to find a collision with 
7 near-collision blocks (3584 bits), which could fit into a 4096-bit RSA 
key.


- Damien