Subject: RE: Huge CRLs

From: "David P. Kemp" <[email-masked]>
Date: Tue, 14 Sep 1999 17:29:11 -0400 (EDT)

> From: "Phillip M Hallam-Baker" <[email-masked]>
> 
> > Not all the world is the financial services sector.  Criticisms of CRL use
> > models based primarily on difficulties encountered in employing them in
> > that environment, or based on poor implementations, or based on poor
> > management parameter choices, etc.  do not necessarily mean that CRLs are
> > unworkable.
> 
> Steve,
> 
> 	I agree with your sentiments but I would prefer to see you saying
> something of the form 'this argument is irrelevant' or 'this argument
> is unproductive'.
> 
> 	We have already argued the case for supporting both online
> and blacklist style revocation. There are applications in which both
> approaches have specific advantages which may well prove critical.
> 
> 	I don't see how the current argument is going to lead to any
> substantive change to the WG drafts or RFCs. We have already advanced
> both sets of drafts to proposed standard status. 
> 
> 	Tempting though it may be to answer the numerous minor and minor
> fallacies in the argument presented I suggest that we just refer the
> combatants to the discussions we had on this topic over a year ago.

Phill,

Referring to last year's discussion is fine, but repeating last year's
fallacies is not helpful when the topic resurfaces .

There is no dichotomy between "online" and "blacklist" style revocation.
Online is on one axis, the opposite end of which is store-and-forward.
"List" is on an independent axis, namely the integers 1..N.

An OCSP response is online, and it covers a list of exactly one certificate.

A CRL could be generated and retrieved online, or could be generated
and stored for later retreival.  A CRL can cover any number of
certificates, from N down to one. The requirement space covered
is thus:
                 OCSP  CRL
                 ----  ----
Online, 1 cert    y     y
Online, N certs         y
Stored, 1 cert          y
Stored, N certs         y

---------- [from a later message] ----------

> The significance of OCSP is this. It is not sensible, practical or
> ecconomic to build a revocation infrastructure which addresses
> the planetary scale PKI at present while the size of the largest
> PKIs is in the small millions. OCSP permits a decoupling of the
> revocation/validation problem from the client implementation.

How is OCSP unique in this respect?  If you posit the existence of
a revocation server findable by and trusted by the client, that server
could return a CRL, or it could return an OCSP response.  The
advantage of returning a list is that the client might not have to
query as frequently.

--------- [Lynn Wheeler adds] ----------

> Also, CRL operation tends to be a scaleup issue proportional to the
> size of the population ...

Again, a matter of implementation.  The population covered by a CRL is
a tunable parameter which can be set anywhere between 1 and the entire
population.