Re: Certificates: limiting your liability with reuse limitations

[Adam Shostack <adam@lighthouse.homeport.org>]

A. Michael Froomkin writes:
> I know I can put an expiration date on the certificate, but that's not
> enough.  I can accumulate a lot of exposure in a few seconds, much less
> weeks.
>
> I know I can put a reliance limit in the X.509 ver 3 certificate, but
> that's not enough.  Even a $1 limit could be used many millions of times.
>
> Is it feasabile to say: Can only be relied on once per day/week/month?

	Undeniable digital signatures.  They're not 'undeniable'
differently from normal digital signatures, but they do require the
cooperation of the signer to confirm the signature.  Thus, a KCA could
decide only to verify a signature 50 times, or once per day (or once
per being paid the $10 signature verification fee.)

	Schneier has a decent amount on undeniable digital signatures.

Adam


-- 
"It is seldom that liberty of any kind is lost all at once."
					               -Hume