[Fwd: Re: Non-repudiation (was RE: The PAIN mnemonic)]

[Anton Stiglic]

----- Original Message ----- 
From: "Jerrold Leichter" <jerrold.leichter at smarts.com>
Cc: "Cryptography" <cryptography at metzdowd.com>
Sent: Wednesday, January 07, 2004 7:14 AM
Subject: Re: [Fwd: Re: Non-repudiation (was RE: The PAIN mnemonic)]


> Now that we've trashed non-repudiation ... just how is it different from
> authentication?

I don't think the word "authentication" has the same problem as
"non-repudiation",
but you do need to be careful how you define it.

So here we are talking about entity authentication (as opposed to data
authentication,
the latter really has a unambiguous definition, at least I hope it does!).

The way you should define entity authentication
is by stating that it is a process of verifying that an entity possesses the
authentication
credentials associated to a user that entity claims to be.  This entity
might be the rightful
user, or it might be someone who stole the credentials from the rightful
user.   If someone
stole my ATM card and my PIN, he/she can successfully authenticate
him/herself to an
ATM and withdraw money.  The word "authenticate" is appropriate in this last
phrase.

But I see that most definitions that have been collected here:
http://www.garlic.com/~lynn/secgloss.htm#t523
are not careful about this.

The thing about non-repudiation is that it is something that even most laws
do not
permit.  See for example:
http://www.firstmonday.dk/issues/issue5_8/mccullagh/

Non-repudiation applied to digital signatures implies that the definition
states that
only one person possibly had possession of the private signing key and was
conscious
about the fact that it was used to sign something.

In most jurisdictions a person has the right to repudiate a signature
(had-written
or electronic), and thus non-repudiation does not work.  People have the
right to
repudiate signatures since it might be the result of a forgery, fraud, the
signer might have
been drunk or something at the time of signing or forced to sign (like with
a gun to his
head).    Repudiation is possible but non-repudiation is not.

I know some people who use the term "accountability" instead of
"non-repudiation"
to express the property needed in certain systems (commercial
infrastructures where
users login and need to be accountable for their acts).  This seems like a
better term
to be used in certain contexts, but I'm still thinking about it...

--Anton







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