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RE: Simplified Syntax (The Crux of the Matter!)

From: John Boyer <jboyer@uwi.com>
Date: Mon, 6 Dec 1999 09:01:59 -0800
To: "Peter Lipp" <Peter.Lipp@iaik.at>, "Tim Berners-Lee" <timbl@w3.org>, "DSig Group" <w3c-ietf-xmldsig@w3.org>
Message-ID: <NDBBLAOMJKOFPMBCHJOIEEIKCCAA.jboyer@uwi.com>
Hi Peter,

> Incorrect.  What is covered by the digest is ABDE, but within ABDE is a
> *signed* assertion that the only allowable difference between the document
> and ABDE is the addition of C between B and D.  Can you please
> state why you think this is insecure?  I don't think you can.

I think this overcomplicates things and nobody, or not many, will understand
that concept. This is as if we sign ABCDE and tell the user to ignore C.
Doesn't make sense. Either we want to sign ABDE, then we should sign ABDE,
and if we wnat to put C into the picture, why tell them that we don't want
to sign it, but still do in some obscure way, indirectly maybe.

<John>
Actually, we likely want to sign a document containing ABDE but ensure that
future persons can only make modifications of the form given by "C if
between B and D".  Note that C still contains sufficient variability to
allow the work necessary to 'close' or complete the document.  This could,
for example, be the act of filling out the 'office use only' section of a
form, or adding multiple signatures to the document, or the act of 'code
signing', where the code is represented by markup.  The scenarios document
contains more details on these examples.

As for whether document closure overcomplicates things, we are talking about
the same group of people that intellectually grasp the fact that
cryptographic security can result from things like modular exponentiation
and modular multiplicative inverse via GCD as well as details like the
cascade effect and and the possible need for a nonce with regard to digital
document 'fingerprinting' with an algorithm like SHA-1.

Whereas the purportedly 'obscure' signing methodology I've been proposing
amounts to little more than using cryptography to secure a message M which
happens to contain a self-referential statement of the form "This message
must originate from a document of the form ABCDE where C has the following
characteristics...".

Since university computer science coursework usually covers the
cryptographic material mentioned above *after* the basic issues of
computability such as the Turing halting problem and Godel's incompleteness
theorem (which arise from problems pertaining to self-reference), it seems
likely that the cryptography material is as complicated or *more* so, and
that anyone who buys into it will not have trouble grasping the use of
cryptography to secure a message M that contains a self-referential
statement.

John Boyer
Software Development Manager
UWI.Com -- The Internet Forms Company
</John>

Peter
Received on Monday, 6 December 1999 12:03:28 GMT

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