Re: WG Last Call: AIA CRL extension

[Russ Housley <[e-mail]>]

Julien & Tom:

Two points:

1.  I understand this scenario.  The change that you advocate as a 
countermeasure will prevent Indirect CRLs from working in scenarios that 
are intended.

2.  This observation has noting to do with the CRL AIA extension.  The 
attacker is inserting the bogus revocation information into the 
repository.  Any relying party that uses that repository (when using the 
CRL AIA extension or any other configuration information to locate it) will 
get the bogus revocation information.

If this is a concern, then it needs to be addressed in RFC3280bis, not here.

Russ

At 12:38 PM 5/24/2005, Julien Stern wrote:

>On Tue, May 24, 2005 at 10:36:16AM -0400, Tom Gindin wrote:
> >
> >         There is one scenario permitted by the "same trust anchor" rule
> > for CRL signers which seems to me to be a serious security hole.  Let us
> > assume a valid CA which is a direct subordinate of one of the RP's trust
> > anchors.  This CA issues separate CRL's and ARL's, in a quite usual way,
> > and issues cross certificates.  After months or years of operation, it
> > revokes one of its cross certificates because the subject's operator has
> > gone rogue.  That rogue subject then issues a fraudulent CRL Signing
> > certificate with the DN that the superior certificate has been using to
> > sign ARL's, a public key which it has newly generated, and various
> > extensions including an SKID.  It then issues an updated copy of an old
> > ARL under the fraudulent CRL signer's certificate and with an AKID
> > matching the fraudulent signer's SKID.  If the rogue can break into the
> > repository where the CRL is expected, this fraudulently issued CRL will
> > probably be validated whether it contains an AIA or not.  It will
> > certainly pass the "same trust anchor" condition.
> >         This scenario, in which a rogue CA issues an ARL certifiying that
> > its primary certificate has not been revoked and gets the ARL accepted, is
> > possible under "same trust anchor" but not under "signed by path member".
>
>I agree with the validity of this scenario. I believe this is very
>close to the issue I attempted to bring on the list a short time ago.
>Of course, it assumes the existence of a rogue CA at some point in time.
>
>Note that the CRL could be directly inserted into a "long term"
>signature (according to RFC3126 for example). This does not require
>a repository break-in and makes the "attack" even more realistic.
>
>Regards.
>
>--
>Julien Stern
>
> >
> >                 Tom Gindin
> >
> > ----- Forwarded by Tom Gindin/Watson/IBM on 05/24/2005 10:13 AM -----
> >
> >
> > Tom Gindin
> > 05/23/2005 10:46 PM
> >
> >         To:     [e-mail]
> >         cc:     [e-mail], [e-mail], [e-mail],
> > [e-mail]
> >         From:   Tom Gindin/Watson/IBM@IBMUS
> >         Subject:        Re: WG Last Call: AIA CRL extension
> >
> >         Tim:
> >
> >         I should probably have brought this up earlier, but are we certain
> > that "same trust anchor" is a strong enough check that the CRL signer is
> > the one expected by the issuing CA?  While I was not in San Diego when
> > this wording was included in the 3280 series, I do not really think that
> > that check is strong enough.  I would suggest instead that the CRL
> > signer's certificate needs to be directly issued by one of the CA's in the
> > certification path back to the trust anchor used for the certificate's
> > verification, or by that anchor itself, unless people have practical
> > experience with CA structures which that rule would prohibit.  Forcing the
> > CRL to be issued by the CA itself (as I understand Denis to have
> > suggested) prohibits the reasonable case where the CRL is issued by a
> > hierarchical superior, so it is IMHO too strict.
> >         I am personally not sure, FWIW, that a CRL should be permitted to
> > be signed by a second-cousin certificate of the issuer's certificate.  By
> > analogy to the use of the terms in families, "sibling" certificates would
> > have the same issuer, "first-cousin" certificates would be issued by
> > siblings, and "second-cousin" certificates would be issued by first
> > cousins - so they are both three levels down from the same trust anchor,
> > or from the last common CA in their paths.  This issue is not newly caused
> > by CRL AIA, since the same issue can arise with CRL's containing only
> > AKID.  AIA only allows RP's to build a path (whether right or wrong) more
> > quickly.
> >         In any case, nothing more than a note in Security Considerations
> > is appropriate in any of our RFC's other than 3280 and its successor.
> >
> >         Tom Gindin
> > P.S. -  The above views are mine, and not necessarily those of my employer
> >
> >
> >
> >
> >
> > Tim Polk <[e-mail]>
> > Sent by: [e-mail]
> > 05/10/2005 05:27 PM
> >
> >         To:     [e-mail]
> >         cc:     [e-mail], [e-mail], [e-mail]
> >         Subject:        WG Last Call: AIA CRL extension
> >
> >
> >
> >
> > This message initiates working group Last Call for the specification
> > "Internet X.509 Public Key Infrastructure: Authority Information Access
> > CRL
> > Extension".  While some issues raised in the working group are unresolved,
> >
> > the editors believe that rough consensus supports the current
> > specification.
> >
> > The URL for this Internet-Draft is:
> >
> > http://www.ietf.org/internet-drafts/draft-ietf-pkix-crlaia-01.txt
> >
> > Last Call will run for (at least) two weeks. That is, Last Call will not
> > close before May 24.
> >
> > Thanks,
> >
> > Tim Polk
> >
> >
> >