Subject: Re: Attributes within PK certs? [draft-ietf-pkix-ac509prof-00.txt]

From: [email-masked]
Date: Sun, 16 May 1999 13:07:23 +0300

Hello,

I have been reading this thread about AttributeCertificates and I can't
understand why the X509v3  can't serve for issuing short lived
certificates?
Why is it neccessary to define new format for AC which does not include a
public key, but just points to it?

Best, Yosi Mass,
IBM Haifa Research Lab

"Bob Blakley" <[email-masked]> on 05/15/99 01:29:09 AM

Please respond to "Bob Blakley" <[email-masked]>

To:   "Linn, John" <[email-masked]>, "Russ Housley"
      <[email-masked]>
cc:   [email-masked]
Subject:  Re: Attributes within PK certs?
      [draft-ietf-pkix-ac509prof-00.txt]

Russ,

>Steve Kent's Rule of Revocation: "The effective lifetime of a certificate
>is inversely proportional to the square of the number of attributes."
>
>I agree with Steve's rule.

Steve's rule is actually not correct. The correct formula can actually be
easily demonstrated.

Assume that a certificate has "n" attributes, all with pairwise mutually
independent lifetimes.

Assume that the certificate's key's lifetime starts at t=0 and ends at t=E,
where E>0.

Look at attribute number 1.  Its lifetime ends at t1.  This divides the
timeline into 2 pieces
(The interval from t=0 to t=t1, and the interval from t=t1 to t=E.)  On
average
each of these pieces will be the same length - that is, half the length of
the
interval from
t=0 to t=E.

Now look at attribute number 2.  With probability 1, it doesn't expire
exactly
at t1.  Instead,
it expires at some other time t2.  This adds one more interval to the
timeline; it doesn't matter,
so let's say attribute 2 expires first.  This divides the timeline into
three
segments -
t=0 to t=t2, t=t2 to t=t1, and t=t1 to t=E.  On average, these three
segments
will have equal
lengths, each one-third of the length of the interval from t=0 to t=E.

Continue the process; each new attribute results in exactly one more
segment,
and (assuming
independent lifetimes) all segments on average have equal length.  This
means
that
the real formula is

    lifetime of cert with attributes = lifetime of cert without attributes
*
(1/n)

    where n is the number of attributes with pairwise mutually independent
expiry intervals.

Hence I propose Bob & Steve's (corrected) rule of attribute certificate
lifetimes:

"The effective lifetime of a certificate is inversely proportional to the
number of attributes
in the certificate, if all attributes' lifetimes are pairwise mutually
independent."

--bob

Bob Blakley ([email-masked])
Chief Scientist, Dascom

---

From: Russ Housley <[email-masked]>
Date: Mon, 17 May 1999 13:00:30 -0400

There are many cases where attributes are short lived.  For example, a web
server may grant access to a particular page only after a previous page is
viewed.  This has nothing to do with the lifetime of the X.509 identity
certificate, and there is no reason to duplicate the public key.

Russ