Subject: RE: delta CRLs

From: "Housley, Russ" <[email-masked]>
Date: Mon, 07 May 2001 09:21:08 -0400

Santosh:

X.509 may allow the CRL number to wrap around, but I do not believe that 
PKIX does.

    5.2.3  CRL Number

    The CRL number is a non-critical CRL extension which conveys a
    monotonically increasing sequence number for each CRL issued by a CA.
    This extension allows users to easily determine when a particular CRL
    supersedes another CRL.  CAs conforming to this profile MUST include
    this extension in all CRLs.

    id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }

Russ

At 10:11 PM 5/5/2001 -0400, Santosh Chokhani wrote:

>Actually, the text allows for the wrap of the numbers.  Please see Annex B 
>of X.509.  Thus, it is not strictly increasing
>
>-----Original Message-----
>From: Peter Sylvester 
>[<mailto:[email-masked]>mailto:[email-masked]]
>Sent: Saturday, May 05, 2001 2:08 PM
>To: [email-masked]; [email-masked];
>[email-masked]
>Cc: [email-masked]
>Subject: RE: delta CRLs
>
> > Trevor:
> >
> > The 2000 version of X.509 is very clear on this.  For a given CRL stream
> > identifier, the CRL number is unique whether it is base or delta.  That is
> > why delta number has to be greater than the base.
>
>" 8.5.2.1 CRL number extension
>
>   This CRL extension field conveys a monotonically increasing sequence 
> number .."
>
>The text might be clearer IMHO if 'strictly increasing' would be used 
>instead.

---

From: "Carlin Covey" <[email-masked]>
Date: Tue, 8 May 2001 17:53:31 -0700

Russ,

A week or two ago we arrived at a consensus to remove the requirement
that a CA issue a full CRL whenever the CA issues a Delta-CRL.  If the
CA chooses to issue them simultaneously, why would they need to be numbered
the same?  If this requirement were lifted, it seems like requiring the CRL
number to be "strictly increasing" in a sequence would be preferable to
"monotonically increasing".  "Monotonically increasing" allows the
possibility
that the CRL number never changes, which seems undesirable.  I realize
that in either case the CRL number might wrap around at some point in the
future.
That is inevitable, given that that CRL number is defined as INTEGER
(0..MAX).
What else can a CA do when CRL number reaches MAX, stop issuing CRLs?

"monotonically increasing" - Definition: A function from a partially
order[ed]
domain to a partially ordered range such that x >= y implies f(x) >= f(y).

- From the NIST web site: http://hissa.nist.gov/dads/HTML/monotoncincr.html

Regards,

Carlin

____________________________

-  Carlin Covey
   Cylink Corporation

-----Original Message-----
From: Housley, Russ [mailto:[email-masked]]
Sent: Monday, May 07, 2001 6:21 AM
To: Santosh Chokhani
Cc: [email-masked]
Subject: RE: delta CRLs

Santosh:

    5.2.3  CRL Number

Russ

---

From: Denis Pinkas <[email-masked]>
Date: Wed, 09 May 2001 11:54:25 +0200

Carlin,

I agree. This is the point that Peter Sylvester mentionned. Taking the
definition of monotonically increasing, we do not expect CRLs to bear the
same number ! On the contrary we expect that using that number we can
uniquely identify a CRL. 

We need to fix of the text, as you point it out again, and change
"monotonically increasing" by "strictly increasing".

Denis

---

From: Dr S N Henson <[email-masked]>
Date: Wed, 09 May 2001 14:14:48 +0100

Carlin Covey wrote:
> the same?  

Its my understanding that the CRL number of the delta CRL serves an
additional purpose: it gives the CRL number of the equivalent full CRL
(which may not have been issued with the new rule) which can be
constructed by combining rhe delta with the base CRL (or a later CRL).
They have to be the same to convey this information.

See 5.2.4:

>    The constructed CRL has the CRL number specified in the CRL number
>    extension found in the delta CRL used in its construction.
> 

Another consequence of this appears to be that if a CA sometimes issues
deltas with no corresponding full CRLs then there will be gaps in the
numbering scheme of the full CRLs.

> If this requirement were lifted, it seems like requiring the CRL
> that the CRL number never changes, which seems undesirable.  

I'd say its not only undesirable but it also makes handling delta CRLs
difficult if not impossible.

> I realize

Well depends on the value of MAX I suppose. 

Something like 32 bits and assuming the CA issues a CRL every second
would mean that it wouldn't wrap around for 136 years or so, which is
hopfully tolerable.

Steve.
-- 
Dr Stephen N. Henson.   http://www.drh-consultancy.demon.co.uk/
Personal Email: [email-masked] 
Senior crypto engineer, Celo Communications: http://www.celocom.com/
Core developer of the   OpenSSL project: http://www.openssl.org/
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