Re: [pkix] New draft-ietf-pkix-rfc2560bis-06

["Peter Rybar" <[e-mail]>]

Well, yes, sort of. You can only be sure to validate a signature at the moment of production. 

 

What if the signature key was compromised at the moment of production but is not yet on a revocation list?

[PR] According to clause 2.4  -  thisUpdate: The time at which the status being indicated is known to be correct

It means when signature time-stamp time is X then any OCSP responses with thisUpdate time X+y are sufficient to validate because the status is correct. 

Y is in the interval <0, producedAt - X>

 

At any later point in time the signature key may be compromised, or the algorithms involved may have become to weak. (In which case the time of revocation in the OCSP response is worth nothing to you). The risk increases as time passes. And of course, the revocation information may not be kept around after the expiry of the certificate. 

 

That's why you should validate signatures as soon as possible. 

 

For these archival purposes wouldn't it be better to have the final revocation list before removed due to expiry?  In any case, you'd need verification information collected after some grace period following moment of production.

[PR] Grace period is not a fixed value of the time interval. 

Grace period is changeable because the first OCSP response with thisUpdate time value > than time of signature time-stamp contains correct status.

 

 



If you need to ascertain that a signature was valid at a later time, you have to trust your system that it performed the validation at the time it first received the signature. That trust must be established through some kind of mix of policies and technical measures (such as timestamping).

 

In the dark corner just beyond the dark corner that is SCVP, there's a spec (RFC 5276) that defines a binding of evidence records to artifacts that can be returned via SCVP.  This provides for timestamping.  

[PR] The validation is simplified when OCSP response with positive statement as a hash value of requested certificate is used.

Positive statement is evidence that OCSP know the status of certificate and also protect the integrity of certificate with a new more secure hash algorithm.

 

Peter Rybar

 



Simon Tardell, 

Technology Nexus.

On Fri, Oct 19, 2012 at 1:07 PM, Peter Rybar <[e-mail]> wrote:

Stefan,

I have a question about the present OCSP RFC and at the end of the mail about the new situation which will happen according to your new proposal.

The presence of the positive statement in OCSP response is important for electronic signature validations, especially for an expired certificate. Positive statement is the hash value of a certificate whose status is provided in OCSP response.

Electronic signature validation is usually about the signatures created in the past and validated now, when the certificate is expired.

When the certificate expires then revocation is usually removed from CRL and the revoked certificate can be provided as "good" in OCSP response.
Is it acceptable? I think not.

According to your new draft there is not defined a value of revocationTime.
RFC must also define the value of revocationTime when the certificate which was never issued is as "revoked".
http://www.ietf.org/rfcdiff?url2=draft-ietf-pkix-rfc2560bis-06

Have you also covered the situation when the certificate is expired, REMOVED FROM CRL and will be provided as revoked with incorrect revocationTime e.g. with the value before or after the revocationTime which was present in the removed record from CRL?
Because according to sentence in your draft ""revoked" - This state SHOULD also be returned if the responder knows that the requested certificate has never been issued." the following situation can happen: when certificate is removed from CRL after expiration and CA/OCSP responder is responsible for this certificate but have not record about expired certificate and for that reason it is identified as "never been issued".

...
revoked     [1]     IMPLICIT RevokedInfo,
...

   RevokedInfo ::= SEQUENCE {
       revocationTime              GeneralizedTime,
       revocationReason    [0]     EXPLICIT CRLReason OPTIONAL }

As you have mentioned in the mail:

"On the "revoked" state, the old spec did not even consider the case of a certificate being requested where the OCSP responder knows that the certificate was never issued."

"It simply recommend a known to be bad certificate to result
in "revoked" in order to prevent damage as far as possible. It also opens
for definition of new extensions through which such knowledge could be
obtained."

Peter Rybar
National Security Authority
Information Security and Electronic Signature Department
Budatinska 30, 850 07 Bratislava 57, Slovak Republic
e-mail: [e-mail]
e-mail: [e-mail]


-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf Of Stefan Santesson
Sent: Monday, October 15, 2012 1:49 AM
To: [e-mail]
Subject: [pkix] New draft-ietf-pkix-rfc2560bis-06

All,

I have just posted an update of rfc2560bis (OCSP update) after carefully
reviewing all comments on the list.

Some notes about the update:

- Added the previous OCSP editors with updated affiliations.
- Added some calcifications on ResponderID as suggested by Simon Josefsson.
- Updated the clarifications on Authorized responders. The requirements
have not changed. I just tried to improve the text.
- Updated a clarification on the "revoked" state to be the preferred
response if a certificate is known by the responder to never have been
issued.
- Some minor editorial nits.


Regarding backwards compatibility I mean that none of the clarifications
changes RFC 2560.

On Authorized responders it has always been the case that a responder
certificate issued with the same key as was used to issue the certificate
being checked for revocation, represents a valid Authorized responder.
There has never been an explicit requirement to support key rollover and
key rollover support has never been in the "spirit" of the original
standard as it clearly attempted to provide direct cryptographic binding
between the responder and the CA.

On the "revoked" state, the old spec did not even consider the case of a
certificate being requested where the OCSP responder knows that the
certificate was never issued. It is clearly counterproductive to respond
good when a certificate is known to be bad. A responder must pick one
response and picking "revoked" breaks nothing, but has the desired effect,
that is, to prevent the certificate from being accepted. The current text
makes clear that there is no mechanism in the current standard by which a
client can know how a responder will respond to a request for a not issued
certificate. It simply recommend a known to be bad certificate to result
in "revoked" in order to prevent damage as far as possible. It also opens
for definition of new extensions through which such knowledge could be
obtained.

The current updates also clearly opens a path for the CAB forum efforts to
define a suitable solution for server certificates.

I have not, even thug suggested, added any requirements on what clients
should do with the checked cert as a result of a particular response. I
don't believe such requirements are suitable as it is policy and not
protocol. We have no right to demand that all systems MUST reject any
certificate for any reason as they may have a local policy that overrules
the OCSP response. This protocol only provides information about the cert
status, it does not mandate validation policy.

I have not included any of the substantial changes i the Pinkas draft. I
want to wait for a list of motivation for each change before including any
of them. So there changed may be up for debate before this draft is ready
for WGLC.

/Stefan



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