Non-repudiation (was RE: The PAIN mnemonic)

[Ben Laurie]

Amir Herzberg wrote:

> Ian proposes below two draft-definitions for non-repudiation - legal and 
> technical. Lynn also sent us a bunch of definitions. Let's focus on the 
> technical/crypto one for now - after all this is a crypto forum (I agree 
> the legal one is also somewhat relevant to this forum).
> 
> In my work on secure e-commerce, I use (technical, crypto) definitions 
> of non-repudiation, and consider these as critical to many secure 
> e-commerce problems/scenarios/requirements/protocols. Having spent 
> considerable time and effort on appropriate definitions and analysis 
> (proofs), I was/am a bit puzzled and alarmed to find that others in our 
> community seem so vehemently against non-repudiation.
> 
> Of course, like other technical terms, there can be many variant 
> definitions; that is not really a problem (the community will gradually 
> focus on few important and distinct variants). Also it's an unavoidable 
> fact of life (imho) that other communities (e.g. legal) use the same 
> term in somewhat different meaning.
> 
> So my question is only to people like Ben and Carl who have expressed, 
> if I understood correctly, objection to any form of technical, crypto 
> definition of non-repudiation. I repeat: do you really object and if so 
> why?

I object because its not a technical, crypto concept. It doesn't matter 
what you do to try to achieve non-repudiation technically, I can always 
repudiate it - all I have to do is say "I didn't sign that" or "it 
wasn't me that initiated that transaction".

> What of applications/scenarios that seem to require 
> non-repudiation, e.g. certified mail, payments, contract signing,...?

These do not require non-repudiation in the existing world, why do they 
suddenly need it when they become electronic?

What I presume you are trying to get at is to distinguish the use of a 
key with an intent to bind you rather than with an intent to provide 
authentication (or some other service signing can provide). This is not 
non-repudiation, it's something else, and it only confuses matters to 
use the wrong word for it.

Cheers,

Ben.

-- 
http://www.apache-ssl.org/ben.html       http://www.thebunker.net/

"There is no limit to what a man can do or how far he can go if he
doesn't mind who gets the credit." - Robert Woodruff

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