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Re: public key algorithm naming

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At 10:49 AM 3/12/98 -0800, Hal Finney wrote:
>If you don't put the hash algorithm in the key, then if there were a
>weak hash algorithm, people could forge signatures using that hash.
>They could take an existing signature and create a structure which hashes
>to the same value using the weak hash.
>
>The same thing could happen of course if the key had a weak hash
>algorithm, but probably there are fewer keys than signatures, hence more
>opportunities to use weak hashes if it is in the signature.  Someone can
>create his key with a strong hash algorithm and be sure that no hash
>substitutions are possible.
>
>If a hash is discovered to be weak, then either the key holder can replace
>it in his key, or the verifier can know to ignore signatures with the
>bad hash.  If hashes are in the signatures then only the latter course
>is available, so there is one less way to recover.

Hal,

	I believe that all 3 of the options I listed (I), (II) and (III)
prevent someone sneaking up with a weak hash algorithm and faking a claim
of signature on a document of their choice.  It's just that in (II) and
(III), there's an additional structure involved.

Next time I get to my LINUX machine, I'll generate examples of the three
ways and post them.

 - Carl

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|Carl M. Ellison  cme@cybercash.com   http://www.clark.net/pub/cme |
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