From: Randall Farmer <rfarmer@HiWAAY.net>
Date: Wed, 26 Nov 1997 10:00:58 +0800
Subject: Re: Quoting Portions of a Signed Document
In-Reply-To: <199711252109.WAA05443@basement.replay.com>
Message-ID: <Pine.OSF.3.96.971125185947.22431D-100000@fly.HiWAAY.net>
MIME-Version: 1.0
Content-Type: text/plain



> It would be neat if you could quote people and prove that they signed
> the particular paragraph quoted without supplying the entire text.  Is
> there a way to do this? 

Yes. To do it using standard proggies, hash each of your paragraphs and put the
results in a PGP-signed message. Quoter provides signature and signed hashes. 
Reader hashes your quoted paragraph and checks the signed message to see if it
was one of the original paragraphs. So simple I can do it. :) 

[Disclaimer: I think.]

A more cool-sounding solution would be to concatenate those hashes and sign
them (not a hash of them) as one packet. Since RSA sigs are secret-key
decryptions (right?), the reader can re-encrypt it and check any individual
hash. Not more secure, though, and it takes a lot of processor time.

No idea how to do it with bit-level granularity.

> (It seems impossible, but so does mental poker.) 

Mental poker? Easy.

> 
> A crude approach would be to sign every paragraph or line separately,
> but that's obviously inelegant.

Allows you a tad too much freedom with their quotes, too...

> 
> Monty Cantsin
> Editor in Chief
> Smile Magazine
> http://www.neoism.org/squares/smile_index.html
> http://www.neoism.org/squares/cantsin_10.htm

---------------------------------------------------------------------------
Randall Farmer
    rfarmer@hiwaay.net
    http://hiwaay.net/~rfarmer