Re: Microsoft's CryptoAPI - thoughts?

[futplex@pseudonym.com (Futplex)]

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James Donald writes:
> I was concerned about a different issue:
> 
> Suppose you have some signed information:  You wish to send some encrypted
> information to the person who wrote that signed information.
> 
> If the signing key and the encrypting key are the same, your software can
> locally ensure that you encrypt with the right key, (The correct key is the
> same public key that you used to check the signature on the message.)
> 
> If the signing key and the encrypting key are different, then in order to
> ensure that you are not spoofed into using the wrong public key, the
> whole protocol must work correctly, exposing many more points of attack, 
> since key management is the most complex and most vulnerable area.

OK, I think I understand the concern. I was assuming a model where the 
signing and encrypting keys are bound together in a certificate in some 
fashion. Presumably the encrypting key is signed by the signing key. The
certificates are distributed & managed according to some protocols and 
policies that are orthogonal to the number of keys in a single certificate.

Things get slightly more complicated if you want to update the encrypting and
signing keys independently of each other. But offhand I don't see any new
thorny issues arising.

Disclaimer: I haven't read enough of the MSCAPI to have any idea how it 
proposes to handle the purpose-specific keys. 

Futplex <futplex@pseudonym.com>		GO COWBOYS!

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