Re: Decryption Transform

Joseph M. Reagle Jr. wrote:


> For example, Alice wishes to order and pay for a book from Bob using the 
> mutually trusted payment system ZipPay. Bob creates an order form 
> including the book title, price and his account info. He wants to sign 
> all of this information, but will subsequently encrypt his account info 
> for ZipPay only.


So far so good.

> He sends this to Alice who affirms the book title and 
> price, signs the form


Now on your "sign only what is seen" principle, shouldn't Alice sign the
title and price only?  Then we have a signature covering the
whole plaintext document, and another covering part of the plaintext
document.  ZipPay can decrypt Bob's info and then verify both
signatures: no need for verify-decrypt-verify, although of course that
will work as well.

-- 
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