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

[Jerrold Leichter]

| 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.
There is absolutely *no* cryptographic or mathematical content to this
definition!  It could as well apply to key locks, to signatures on paper,
or whatever.  It's in no way a property of a cryptographic system, or of
*any* system.  Nor, as written, is there even any possible set of evidence
that could be adduced to prove this:  After all, someone might, just by
chance, have guessed the private key.

Granted, there are significant issues with non-repudiation - so significant
that it probably isn't a very useful concept.  But it there *is* some
cryptographic content behind it!  Otherwise, what are we to make, for example,
of the various "evolving signature key" schemes that detect stolen keys?

							-- Jerry

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