On Mon, 28 Jan 2002 20:08:37 +0900 (JST), Kazu Yamamoto (³Ü§) said:
I don't understand this. I think you are talking about verification,
not creating a signature.
Right. When you create a signature, you know in advance what hash
algorithm to use.
Would you tell me how the micalg parameter is useful for S/MIME
application on verification more concretely? Probably I should
understand what 2-stage hashing method is.
S/MIME usually hashes the text and store the hash value inside the so
called signedAttributes. The signedAttributes, which are usually
small and contain various things like the signature creation time, are
then hashed again and that value is the input to the PK verification
algorithm.
OpenPGP hashes everything as one big block. The problem is that you
can't feed the hash value to OpenPGP because it is not possible to
hash more stuff after a hash as been finalized (i.e. the hash value
calculated) - well it would be possible to use the intermediate values
(the hash context) to the verification process, so that it can hash
more data in, but I don't consider this a clean design.
Werner
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