[cryptography] Proving knowledge of a message with a given SHA-1 without disclosing it?

William Whyte wwhyte at securityinnovation.com
Wed Feb 1 07:32:05 EST 2012


You can obviously prove it in the case where Alice claims she knows
SHA-1(SHA-1(m)), which seems to be the same claim.

William

> -----Original Message-----
> From: cryptography-bounces at randombit.net [mailto:cryptography-
> bounces at randombit.net] On Behalf Of Francois Grieu
> Sent: Wednesday, February 01, 2012 4:49 AM
> To: cryptography at randombit.net
> Subject: [cryptography] Proving knowledge of a message with a given
SHA-1
> without disclosing it?
>
> Alice discloses a 160-bit value h and claims that she (or
parties/devices she
> has access to) knows a message m with h=SHA-1(m).
>
> Can she convince Bob of her claim using some protocol, without letting
Bob
> find m, and without a third party or device that Bob trusts?
>
> At a Crypto'98 rump session, Hal Finney made a 7-minutes presentation "A
> zero-knowledge proof of possession of a pre-image of a SHA-1 hash"
> claiming a feasible protocol for this.
> http://video.google.com/videoplay?docid=-5745972992365920864
>
> This talk mentions using the protocol in the Crypto'98 paper of Ronald
Cramer
> and Ivan B. Damgård: "Zero-Knowledge Proofs for Finite Field Arithmetic
or:
> Can Zero-Knowledge be for Free?"
> http://www.springerlink.com/content/0l4734h77615u161/
> ftp://ftp.inf.ethz.ch/pub/crypto/publications/CraDam98.pdf
> http://www.brics.dk/RS/97/27/BRICS-RS-97-27.pdf
>
> The talk does not give much details, and I failed to locate any article
with a
> similar claim.
> I would find that result truly remarkable, and it is against my
intuition.
>
> Any info on the Hal Finney protocol, or a protocol giving a similar
result, or the
> (in)feasibility of such a protocol?
>
> TIA,
>   Francois Grieu
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