Re: [openpgp] Followup on fingerprints

[ianG <[e-mail]>]

On 4/08/2015 22:30 pm, Daniel Kahn Gillmor wrote:
> On Tue 2015-08-04 04:05:03 -0400, Nicholas Cole wrote:
>> I'm really struggling to follow what is going on with this whole
>> discussion!  Fingerprints need to be robust enough that creating aritrary
>> collisions is not feasible. That has always been central to OpenPGP.
>
> Why must fingerprints be collision-resistant?  We've always said that
> fingerprints need to be preimage-resistant -- that is, if i know your
> fingerprint, i should not be able to forge a new key that has the same
> fingerprint.
>
> But collision-resistance is a different property: if the fingerprint
> mechanism is not collision-resistant, then an attacker can create two
> keys with the same fingerprint.  Why is this a threat?


I'll bite:  A person with two keys can sign a document that holds him, 
then announce that it wasn't signed by him.  As proof, he can 
anonymously publish his other key...

(What does this prove?  Well, not a lot but it does spoil the normal 
narrative.  Part of the success of a system is that it eliminates 
spoilers...)

iang