Use of two private/public key pairs, Sign only and Encrypt only

[Robert J. Hansen]

On 9/26/2013 5:17 PM, Hank Ivy wrote:
> What articles exist on having two private/public key pairs, and
> using one to only sign a document, and the other only for
> encryption?

That depends on which context you're looking for.  In terms of
cryptographic articles about using separate keys, that one goes back to
the early '80s; I think Dorothy Denning had one in _Communications of
the ACM_.  (Five minutes with Google Scholar revealed "Digital
Signatures with RSA and other public-key cryptosystems," April 1984.)

In terms of legal articles about the consequences of using separate
keys, that one is currently badly unaddressed.

> Have there been any courts that subpoenaed the private key and its 
> pass phrase of a user? Would they make a distinction if a user had 
> two pairs, and used them uniquely for signature or encryption?

This has happened in the United Kingdom.  To my knowledge it has not
happened in the United States.  However, as this is a legal question,
you will be best served by asking a lawyer.  :(