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Re: public key algorithm naming
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At 06:10 PM 4/6/98 -0400, Matt Fredette wrote:
>Right. To take the "informational" idea a little bit farther, I think that
><sig-val> should *never* hold the hash algorithm name when it can be inferred
>(= it was specified as part of the signing key's name) or recovered (= the
>encoding used by the signing key includes it). I.e., I think that the part
>of Section 3.8.3.1 <sig-val> in draft-ietf-spki-cert-structure-05.txt that
>reads:
>
> For rsa-pkcs1 (should that option be preferred by the working group
> over the specification of hash algorithm in the <pub-sig-alg-id>),
> <sig-val> would need to be:
>
> <sig-val>:: "(" "rsa-pkcs1-sig" <hash-alg-name> <byte-string> ")" ;
>
>should be removed. This keeps all old signatures and signature parsers valid.
Matt,
the reason to provide this outside the interior of an RSA block would be if
the hash needs to be computed by one computer while another does the RSA
operation. I have seen crypto processor designs that want the hash value
(or the name of the hash algorithm and the actual message body) before they
receive the signature value. BSAFE, for example, is constructed this way.
So is RSAREF. Hardware devices that imitate those end up acting this way.
With such an architecture, you need to know the hash algorithm before you
have done the RSA operation.
- Carl
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