Signing and Encrypting with the same key?

Jorge López | 29 Nov 2008 13:01

Re: Signing and Encrypting with the same key?

Hi all,

This mail was intented for the past discussion about if using the same key pair for encrypting and signing may derive in a reduction of the security of the scheme. Sorry if it's too late for that, but I haven't had the URL to the paper so far. The URL points to the recent results of a research (preprint version) made by a spanish colleague of mine where they actually prove the security or insecurity of using the same key pair in both encryption and signature schemes, depending on the specific situation.

http://eprint.iacr.org/2008/466

Hope this (still) help a bit

Regards,

Jorge L. Hernandez-Ardieta

2008/11/17 Kemp, David P. <DPKemp <at> missi.ncsc.mil>

-----Original Message-----
> From: Stephen Wilson
>
> I'd like to know the precise
> history of the NR bit in X.509. Who actually thought of it, were they
> an engineer or a lawyer, and what if any debate went on at the time?

Trust me, you really, REALLY don't want to know .

Those on one side of the argument thought that the NR bit set should be used for signatures that could be validated indefinitely (i.e. for what one normally thinks of as "signing"), and signatures with the NR bit clear could be used only for session authentication. That way a signed object created as part of a login session could not be misrepresented as a signed document.

Those on the other side thought that the NR bit actually had something to do with "repudiating" signatures, which IMHO is a ridiculous idea for the reasons you suggest. Those who believe in the current X.509 interpretation may defend it if they wish, or spare us the discussion.

Dave