From: "James A. Donald" <jamesd@echeque.com>
Date: Sun, 28 Jan 1996 22:47:56 +0800
To: cypherpunks@toad.com
Subject: Re: Microsoft's CryptoAPI - thoughts?
Message-ID: <199601281436.GAA22473@mailx.best.com>
MIME-Version: 1.0
Content-Type: text/plain


>James A. Donald writes:

> > 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, 

At 07:59 AM 1/27/96 -0500, Futplex wrote:

> 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),

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.

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