From: "William H. Geiger III" <whgiii@invweb.net>
Date: Wed, 26 Nov 1997 07:14:13 +0800
To: cypherpunks@Algebra.COM
Subject: Re: Quoting Portions of a Signed Document
In-Reply-To: <199711252109.WAA05443@basement.replay.com>
Message-ID: <199711252306.SAA24052@users.invweb.net>
MIME-Version: 1.0
Content-Type: text/plain



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In <199711252109.WAA05443@basement.replay.com>, on 11/25/97 
   at 10:09 PM, nobody@REPLAY.COM (Anonymous) said:


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

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

Well this could be done by creating a document signature and then a
collection of sub signatures but it can get ugly real quick.

What level of granularity does one use for the sub signature?

Paragraph: Contentious block of text separated by a line of white space.
Line:      Block of text ending with a CRLF.
Word:      Block of text separated by a white space.

Then what does the sub signature really tell you? Yes you can verify that
the quote was written by someone but it may be taken completely out of
context. How about when several blocks of text from different messages are
combined. Each individual block checks out but by combining them the text
has a completely different meaning than the original document.

The best thing right now is for a user to lookup the referring document in
the archives and verify the signature. It also give him the advantage of
reading the quote in its full context.

In an environment where a public archive of messages are not available
then other means of obtaining the source document are available (contact
the original author, contact the person quoting the original document). In
some environments it may be beneficial to attach the original document to
the message when sending.

Considering that a signed quote would require the Author to format his
signatures in this way I for one would not do so nor could I see a reason
for doing so.

Side Note: The above is in reference to small documents and E-Mail. In
large documents it may be desirable to sign every page or sign each
chapter in addition to signing the entire document. A case may be made for
subsignatures in a E-Mail message in which there are separate signatures
for the text of a message and accompanying attachments. In both cases
there should be a meta-signature that covers the entire document.

- -- 
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William H. Geiger III  http://users.invweb.net/~whgiii
Geiger Consulting    Cooking With Warp 4.0

Author of E-Secure - PGP Front End for MR/2 Ice
PGP & MR/2 the only way for secure e-mail.
OS/2 PGP 2.6.3a at: http://users.invweb.net/~whgiii/pgpmr2.html                        
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