Re: [pkix] Gen-ART review of draft-ietf-pkix-rfc2560bis-15

[Stefan Santesson <[e-mail]>]

Hi David,

Thanks for the review.
My reply in line.

On 3/26/13 1:25 AM, "Black, David" <[e-mail]> wrote:

>Authors,
>
>I am the assigned Gen-ART reviewer for this draft. For background on
>Gen-ART, please
>see the FAQ at <http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.
>
>Please resolve these comments along with any other Last Call comments you
>may receive.
>
>Document: draft-ietf-pkix-rfc2560bis-15
>Reviewer: David L. Black
>Review Date: March 25, 2013
>IETF LC End Date: March 27, 2013
>
>Summary:
>This draft is on the right track but has open issues, described in the
>review.
>
>This draft updates the OCSP protocol for obtaining certificate status
>with some minor extensions.
>
>Because this is a "bis" draft, I reviewed the diffs against RFC 2560.
>
>I did not check the ASN.1.  I also did not see a writeup for this draft
>in the data tracker, and so will rely on the document shepherd to
>ensure that the ASN.1 has been checked when the writeup is prepared.
>
>I found five open issues, all of which are minor, plus one idnits item
>that is probably ok, but should be double-checked.
>
>Minor issues:
>
>[1] Section 2.2:
>
>	NOTE: The "revoked" state for known non-issued certificate serial	
>		numbers is allowed in order to reduce the risk of relying	
>		parties using CRLs as a fall back mechanism, which would be	
>		considerably higher if an "unknown" response was returned.
>
>Given this explanation, I'm surprised that the use of "revoked" instead of
>"unknown" for a known non-issued certificate is a "MAY" requirement and
>not a "SHOULD" requirement.  Why is that the case?
>
>It appears that the reason is that the use of "revoked" in this situation
>may be dangerous when serial numbers can be predicted for certificates
>that
>will be issued in the future.  If that's what's going on, this concern is
>already explained in the security considerations section, but it should
>also be mentioned here for completeness.

No, this is not the main reason. The main reason is the one stated as a
Note: in this section:

NOTE: The "revoked" state for known non-issued certificate serial numbers
is allowed in order to reduce the risk of relying parties using CRLs as a
fall back mechanism, which would be considerably higher if an "unknown"
response was returned.


>
>[2] Section 4.2.2.2:
>
>	The key that signs a certificate's status information need not be the
>	same key that signed the certificate. It is necessary however to
>	ensure that the entity signing this information is authorized to do
>	so.  Therefore, a certificate's issuer MAY either sign the OCSP
>	responses itself or it MAY explicitly designate this authority to
>	another entity.
>
>The two instances of "MAY" in the above text were both "MUST" in RFC 2560.
>
>The RFC 2560 text construction of "MUST" or "MUST" is a bit odd, but the
>two
>"MAY"s in this draft are even worse, as they allow "MAY do something else
>entirely", despite being enclosed in an either-or construct.  I strongly
>suspect that the latter was not intended, so the following would be
>clearer:
>
>	The key that signs a certificate's status information need not be the
>	same key that signed the certificate. It is necessary however to
>	ensure that the entity signing this information is authorized to do
>	so.  Therefore, a certificate's issuer MUST do one of the following:
>		- sign the OCSP responses itself, or
>		- explicitly designate this authority to another entity.


I Agree. I will adopt your text.

>
>[3] Section 4.3:
>
>Is the "SHOULD" requirement still appropriate for the DSA with SHA-1 combo
>(vs. a "MAY" requirement)?  This requirement was a "MUST" in RFC 2560, but
>I wonder about actual usage of DSA in practice.

The change in algorithm requirements was provided by RFC 6277, and further
refined in this draft in accordance with requests from Sean Turner.

>
>[4] Section 5, last paragraph:
>
>	Responding a "revoked" state to certificate that has never been	
>	issued may enable someone to obtain a revocation response for a	
>	certificate that is not yet issued, but soon will be issued, if the	
>	CA issues certificates using sequential certificate serial number	
>	assignment.
>
>The above text after starting with the "if" is too narrow - it should say:
>
>	if the certificate serial number of the certificate that
>	will be issued can be predicted or guessed by the requester.
>	Such prediction is easy for a CA that issues certificates
>	using sequential certificate serial number assignment.
>
>There's also a nit in original text - its first line should be:
>
>	Responding with a "revoked" state for a certificate that has never been	

Good suggestions. I will update accordingly.

>
>[5] Section 5.1.1:
>
>	In archival applications it is quite possible that an OCSP responder	
>	might be asked to report the validity of a certificate on a date in	
>	the distant past. Such a certificate might employ a signing method	
>	that is no longer considered acceptably secure. In such	
>	circumstances the responder MUST NOT generate a signature using a	
>	signing mechanism that is not considered acceptably secure.
>
>This could use an additional warning that certificate archival should
>not rely solely on signatures in archived certificates for ensuring the
>validity and integrity of the archived certificates because the signature
>algorithm(s) may transition to no longer being considered acceptably
>secure at some point after the certificates are archived.

This note if I remember correctly is imported from RFC 6277, which is
incorporated into this document. The reason behind the text is only to
avoid usages of insecure algorithms.
Historical validation is a real can of worms that I really would like to
keep a tight lid on. I really want to avoid doing recommendations in this
space as it may trigger a whole flood of things that could be equally
important to say about this subject.

>
>Nits:
>
>idnits 2.12.15 said:
>
>  -- The document seems to lack a disclaimer for pre-RFC5378 work, but may
>     have content which was first submitted before 10 November 2008.  If
>you
>     have contacted all the original authors and they are all willing to
>grant
>     the BCP78 rights to the IETF Trust, then this is fine, and you can
>ignore
>     this comment.  If not, you may need to add the pre-RFC5378
>disclaimer. 
>     (See the Legal Provisions document at
>     http://trustee.ietf.org/license-info for more information.)
>
>This looks like it's ok because all the authors of RFC 2560 are also
>authors of
>this draft, but it should be double-checked.


I defer this one to Sean. I think he has this one under control.


Thanks again for the review.

/Stefan


>
>Thanks,
>--David
>----------------------------------------------------
>David L. Black, Distinguished Engineer
>EMC Corporation, 176 South St., Hopkinton, MA  01748
>[phone]             FAX: [phone]
>[e-mail]        Mobile: [phone]
>----------------------------------------------------
>
>