Re: Microsoft's CryptoAPI - thoughts?

[futplex@pseudonym.com (Futplex)]

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James A. Donald writes:
> http://www.jim.com/jamesd/mscryptoapi.html

Thank you :)

> A notable misfeature of the API is that it assumes that in general 
> you will have two key pairs.  One for signing and one for encrypting.
> 
> Since in the most common case you are encrypting something related to a
> signed message by the person you are encrypting to this is a
> bad idea, 

Could you elaborate ?  I haven't heard of any known interaction
effects between a strong encryption algorithm and a distinct strong digital
signature algorithm (with or without distinct keys), although such an effect
is certainly conceivable. 

Using "bare" RSA for both encryption and signing, problems can of course arise 
because signing with a private key amounts to decrypting the plaintext to be
signed with that key. Thus you can be tricked into decrypting some
ciphertext by signing it. But this is the sort of problem addressed by the 
crypto object format standards like PKCS. No-one recommends using "bare" RSA.

Actually, using separate keys for signing and encrypting is another way to
avoid this issue.

> and protocols that require two key pairs to avoid protocol
> failure are hazardous and inconvenient.  I think Microsoft should 
> not have chosen to support such protocols.

(I disagree)

Futplex <futplex@pseudonym.com>
It takes a budget of billions to hold us back....

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