Re: Microsoft's CryptoAPI - thoughts?

17 Dec 2003

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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!

Re: Microsoft's CryptoAPI - thoughts?

futplex＠pseudonym.com