I have given this a go by expanding the note as follows:
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. The
"revoked" status is still optional in this context in order to
maintain backwards compatibility with deployments of RFC 2560.
For example, the responder may not have any knowledge about
whether a requested serial number has been assigned to any
issued certificate, or the responder may provide pre produced
responses in accordance with RFC 5019 and, for that reason, is
not capable of providing a signed response for all non-issued
certificate serial numbers.
Does this solve you issue.
I think this is as far as dare to go without risking a heated debate.
/Stefan
On 3/27/13 5:08 PM, "Black, David" <david.black@xxxxxxx> wrote:
>Stefan,
>
>> Is this important enough to do that?
>
>IMHO, yes - the "running code" aspects of existing responder
>behavior/limitations
>are definitely important enough for an RFC like this that revises a
>protocol spec,
>and the alternatives to "revoked" feel like an important complement to
>those
>aspects (discussion what to do instead when responder
>behavior/limitations are
>encountered).
>
>I appreciate the level of work that may be involved in capturing this, as
>I've had my share of contentious discussions in WGs that I chair - FWIW,
>I'm currently chairing my 4th and 5th WGs. OTOH, when a WG has put that
>much
>time/effort into reaching a (compromise) decision, it really is valuable
>to record why the decision was reached to avoid recovering that ground
>in the future and (specific to this situation) to give implementers some
>more context/information on how the protocol is likely to work in
>practice.
>
>Thanks,
>--David
>
>> -----Original Message-----
>> From: Stefan Santesson [mailto:stefan@xxxxxxxxxxx]
>> Sent: Wednesday, March 27, 2013 11:38 AM
>> To: Black, David; sts@xxxxxxxxxxx; mmyers@xxxxxxxxx; ambarish@xxxxxxxxx;
>> slava.galperin@xxxxxxxxx; cadams@xxxxxxxxxxxxxxx; gen-art@xxxxxxxx
>> Cc: pkix@xxxxxxxx; Sean Turner; ietf@xxxxxxxx
>> Subject: Re: Gen-ART review of draft-ietf-pkix-rfc2560bis-15
>>
>> I could.
>>
>> My worry is just that this is such a contentious subject and it took us
>>x
>> hundreds of emails to reach this state, that if I add more explanations,
>> people will start disagreeing with it and that we end up in a long
>>debate
>> on how to correctly express this.
>>
>> Is this important enough to do that?
>>
>> /Stefan
>>
>>
>> On 3/27/13 3:30 PM, "Black, David" <david.black@xxxxxxx> wrote:
>>
>> >Hi Stefan,
>> >
>> >> Does this answer your question?
>> >
>> >Yes, please add some of that explanation to the next version of the
>>draft
>> >;-).
>> >Coverage of existing responder behavior/limitations (important "running
>> >code"
>> >concerns, IMHO) and alternatives to using "revoked" ("have a number of
>> >tools
>> >to prevent the client from accepting a bad certificate") seem
>>particularly
>> >relevant.
>> >
>> >Thanks,
>> >--David
>> >
>> >> -----Original Message-----
>> >> From: Stefan Santesson [mailto:stefan@xxxxxxxxxxx]
>> >> Sent: Wednesday, March 27, 2013 7:44 AM
>> >> To: Black, David; sts@xxxxxxxxxxx; mmyers@xxxxxxxxx;
>>ambarish@xxxxxxxxx;
>> >> slava.galperin@xxxxxxxxx; cadams@xxxxxxxxxxxxxxx; gen-art@xxxxxxxx
>> >> Cc: pkix@xxxxxxxx; Sean Turner; ietf@xxxxxxxx
>> >> Subject: Re: Gen-ART review of draft-ietf-pkix-rfc2560bis-15
>> >>
>> >> Hi David,
>> >>
>> >> Yes I missed to respond to that aspect.
>> >>
>> >> This is a bit complicated, but we have a large legacy to take into
>> >>account
>> >> where some responders implements just RFC 2560, while some deliver
>> >> pre-generated responses according to RFC 5019 (Light-weight OCSP). LW
>> >> responders are not capable of producing a signed response at the
>>time of
>> >> responding and in case such responder finds a request for a
>>certificate
>> >> where no pre-produced response exists, it will reply with an unsigned
>> >> error response "unauthorized", which also is a legitimate way to
>> >>respond.
>> >> So the actual OCSP responder may actually know that the certificate
>>was
>> >> never issued, but since it delivers pre-produced responder through a
>> >>CDN,
>> >> it can not provide a revoked response in real time.
>> >>
>> >> So the major aim with the current writing is to declare that the
>>revoked
>> >> response is a MAY because there are other valid alternatives.
>> >>
>> >> We also want to avoid putting down a SHOULD respond revoked if a
>> >> certificate is known to be not-issued, because that would require us
>>to
>> >> define what "known to be non-issued" actually means. And that could
>>be
>> >> quite tricky as OCSP responders by no means are required to have this
>> >> knowledge.
>> >>
>> >> The OCSP responder simply have a number of tools to prevent the
>>client
>> >> from accepting a bad certificate.
>> >> This update of OCSP simply allows responders to use the "revoked"
>> >>response
>> >> as a preventive measure, without mandating it.
>> >>
>> >> This is also related to activities in the CA Browser Forum where they
>> >>put
>> >> down requirements on responders complying with CAB rules to not
>>respond
>> >> "good" to certificates that were never issued.
>> >> With this update in OCSP, they can now mandate in their policies both
>> >>the
>> >> fact that their responders MUST know if a certificate was never
>>issued
>> >>and
>> >> MUST respond "revoked".
>> >>
>> >> So we allow other communities to raise the bar even if the base
>>standard
>> >> defines the response as optional.
>> >>
>> >> In theory we could possibly say that responding revoked is optional,
>>but
>> >> if you choose between revoked and unknown then you SHOULD favour
>>revoked
>> >> over unknown. But such nested requirements just feels bad and
>>impossible
>> >> to test compliance against. I'd much rather just leave it optional. I
>> >> think the Note gives a clear recommendation on this and the rationale
>> >> without spelling it out as a requirement.
>> >>
>> >> Does this answer your question?
>> >>
>> >>
>> >> On 3/27/13 12:51 AM, "Black, David" <david.black@xxxxxxx> wrote:
>> >>
>> >> >Hi Stefan,
>> >> >
>> >> >This looks good - thank you for the prompt response.
>> >> >
>> >> >It looks like my speculation on item [1] was wrong, so could you
>> >>respond
>> >> >to the question below, please?:
>> >> >
>> >> >> >[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?
>> >> >
>> >> >--------------
>> >> >
>> >> >Beyond that, the proposed actions (or proposed non-actions) on items
>> >> >[2]-[5]
>> >> >are fine with me, Sean's taken care of the author permissions item
>>from
>> >> >idnits, and I assume someone has or will check the ASN.1 .
>> >> >
>> >> >Thanks,
>> >> >--David
>> >> >
>> >> >> -----Original Message-----
>> >> >> From: Stefan Santesson [mailto:stefan@xxxxxxxxxxx]
>> >> >> Sent: Monday, March 25, 2013 10:21 PM
>> >> >> To: Black, David; sts@xxxxxxxxxxx; mmyers@xxxxxxxxx;
>> >>ambarish@xxxxxxxxx;
>> >> >> slava.galperin@xxxxxxxxx; cadams@xxxxxxxxxxxxxxx; gen-art@xxxxxxxx
>> >> >> Cc: pkix@xxxxxxxx; Sean Turner; ietf@xxxxxxxx
>> >> >> Subject: Re: Gen-ART review of draft-ietf-pkix-rfc2560bis-15
>> >> >>
>> >> >> Hi David,
>> >> >>
>> >> >> Thanks for the review.
>> >> >> My reply in line.
>> >> >>
>> >> >> On 3/26/13 1:25 AM, "Black, David" <david.black@xxxxxxx> 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
>> >> >> >+1 (508) 293-7953 FAX: +1 (508) 293-7786
>> >> >> >david.black@xxxxxxx Mobile: +1 (978) 394-7754
>> >> >> >----------------------------------------------------
>> >> >> >
>> >> >> >
>> >> >>
>> >> >>
>> >> >
>> >>
>> >>
>> >
>>
>>
>