Michael
-
In regards to storing all generated CRLs for n period of
time to address the non-repudiation issues; yes this would deal with the
problem. However CRL validity windows commonly overlap; so determining how
would some one know (without CRLNumbers which most CAs do not include yet) if
they had them all? Additionally the process of looking at ALL CRLs and
determining which one is the "most recent" match would be an expensive
one.
For these reasons it
would be "nice" if CRLs were only used by servers and contained all revoked
certificates; but this means that clients would not want to use CRLs due to
the expense associated with acquiring the recent
CRL.
I believe the overall
goal of CRLs was not to deal with NR, but to instead have a simple mechanism
to distribute bulk "current" revocation information to the broadest set of
clients. For this reason; I think its best to remove the expired certificates
and deal with NR through another mechanism, probably service
based.
After reading every
ones posts on this topic, I guess I do not think we should mandate the removal
of the entries; we may wish recommend this be done though. This of coarse is a
mute point due to the last-call already taking place
;)
Ryan
-----Original
Message-----
From: Flynn,
Michael [mailto:MFlynn@xxxxxxxxxxxx]
Sent: Wednesday, September 05,
2001 10:03
AM
To: 'Ryan Hurst'; IETF-PKIX
Subject: RE: Removing expired
certificates from CRLs.....
Now logically it makes sense to
remove certificates that are expired from CRLs to control size, yes this has a
negative point specifically it prevents CRLs from being used as a
non-repudiation source; but this is mute due to many other
issues.
At least regarding removing
expired certs from CRLs, I would think that non-repudiation can be satisfied
by keeping the old CRLs in back up storage for some length of time. That time
being how far back in time a contract dispute might go; ten years, twenty?
So long as you could get them off tape for the lawyers to look at
the legal process would be satisfied, they don't need to be online
forever.
Michael
-----Original
Message-----
From: Ryan
Hurst [mailto:ryanh@xxxxxxxxxxxx]
Sent: Tuesday, September 04, 2001 8:50
PM
To:
IETF-PKIX
Subject: Removing
expired certificates from CRLs.....
I was speaking with
Peter
Williams today about the removal of
expired certificates from CRLs; I have always been under the belief that
this behavior was optional, I vaguely remembered reading text in 2459 along
those lines; additionally I know of several commercial CAs that do not
remove the expired certificates from their CRLs. Peter on the other hand was
under the impression that it was a mandate to remove CRLs; he too remembered
reading text in 2459 to support is position.
So we each pulled out the RFC
and found that we were both right! Specifically both sections 3.3 and
8.6.2.2 have text on this subject:
3.3
Revocation
When a
certificate is issued, it is expected to be in use for its entire validity
period. However, various
circumstances may cause a certificate to become invalid prior to the
expiration of the validity period.
....
An entry
is added to the CRL as part of the next update following notification of
revocation. An
entry may be removed from the CRL after appearing on one regularly scheduled
CRL issued beyond the revoked certificate's validity
period.
8.6.2.2
Issuing distribution point extension
This CRL extension
field identifies the CRL distribution point for this particular CRL, and
indicates if the CRL is limited to revocations for end-entity certificates
only, for authority certificates only, or for a limited set of reasons only.
The CRL is signed by the CRL issuer's key- CRL distribution points do not
have their own key pairs. However, for a CRL distributed via the Directory,
the CRL is stored in the entry of the CRL distribution point, which may not
be the directory entry of the CRL issuer. If this field
is absent, the CRL shall contain entries for all revoked unexpired
certificates issued by the CRL
issuer.
....
The
distributionPoint
component contains the name of
the distribution point in one or more name forms. If this field is absent,
the CRL shall contain entries for all revoked certificates issued by the CRL
issuer. After a
certificate appears on a CRL, it is deleted from a subsequent CRL after the
certificate's expiry.
Although section 8.6.2.2 is
specifically in regards to CRLdps, any difference between full CRLs and
CRLdps in this case I feel would be an arbitrary one.
Now logically it makes sense to
remove certificates that are expired from CRLs to control size, yes this has
a negative point specifically it prevents CRLs from being used as a
non-repudiation source; but this is mute due to many other
issues.
That being the case I think; and
I believe Peter would agree the correct thing to do is to remove these
expired/revoked entries from the CRL.
The question now is what is the
PKIX stance on this matter?
Ryan M.
Hurst
ValiCert,
Inc.
"It may
roundly be asserted that human ingenuity cannot concoct a cipher which
human ingenuity cannot resolve."
-Edgar Allan
Poe