Re: [IETF-PKIX] Multiple certificates for same key?

["David P. Kemp" <dpkemp@xxxxxxxxxxxxxx>]

> From: Bill Burr <william.burr@NIST.GOV>
>
> If I have 50 or 100 certificates, each with some particular attributes
> bound with my keys, one for the auto club, one for the New York Times
> on-line, one for every pay site I subscribe to, etc., and I want to carry
> them around on my token and use them at home and at work, etc., maybe I've
> got a problem.
>
> Is does seem to me to simplify my life to use one key to sign everything;
> after all, I don't sign my name differently when I use my AMEX card than
> when I use my Visa.   This makes sense if we separate attributes from
> identity and use X9 style attribute certificates, that don't contain a key.
>  I'm far from convinced that such attribute certificates are practical.

I believe the analogy is flawed.  When you use your AMEX card, the
information extracted from the magstripe is different than the
information on your Visa magstripe.  You use the same handwritten
signature to authorize both cards, just as you use the same PIN to
activate your token.

I always cringe when people use the word "certificate" to mean both a
public key certificate and the associated private data, but from an
ergonomic point of view, there isn't much difference.  When you select
an X.509 certificate in your web browser to sign a message, the browser
automatically uses the private key associated with that certificate.
If you have 50 or 100 certificates to choose from, you have to choose
once, but you don't have to choose again to get the proper private key;
that part is automatic.

And if a token can store n certificates of 1K-2K bytes each, adding an
additional 128-256 bytes of private key for each certificate doesn't
significantly change the number of certs that can be carried on
the token.

Dave Kemp