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Re: How to Calculate Signatures?

Konrad Rosenbaum <konrad@silmor.de> Sun, 03 April 2005 18:04 UTC

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From: Konrad Rosenbaum <konrad@silmor.de>
To: ietf-openpgp@imc.org
Subject: Re: How to Calculate Signatures?
Date: Sun, 03 Apr 2005 19:48:18 +0200
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On Sunday 03 April 2005 18:41, Ben Laurie wrote:
> Oh, yes. This left me with an unresolved issue: how does one use
> SHA{256,384,512} with DSA (which requires a 160 bit hash).

Simple: you don't. DSA was designed to be used with SHA-1, which is 160 bit. 
Since SHA-1 is theoretically broken (practically will probably follow in a 
few months) one should see what the NIST makes of it. Supplanting a broken 
hash with another hash doesn't make much sense with DSA, since it does not 
contain the ID of the hash (as PKCS#1 does for RSA) - so any attacker could 
find a collission with the broken hash and then simply change the hash ID 
in the signature packet.


	Konrad

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