Subject: RE: Post-facto queries [Was: RE: DPD & DPV requirements]

From: Peter Sylvester <[email-masked]>
Date: Thu, 1 Feb 2001 15:32:49 +0100 (MET)

> yuriy> To support non-repudiation, all you need is the ability to retrieve
> evidence to show that the signature was valid/invalid at the time in
> question.  Where that is done should not matter, although some approaches
> are better than others, and may be easier to prove in court.

You need an evidence that the document in question was signed at the
time in question by the entity in question. 

The validity of the signing certificate may not be sufficient for that.

> 
> > RPs should have a
> > capability to rely on a service to do this for them, especially smaller
> > institutions that do not want to go through the effort to implement such a
> > capability within their organization.
> 
> At the time you first receive a signature you had better to make sure that
> it is a valid one. So at the time you make the first verification, either
> yourself or using a remote server (like DPV), it is easy to grasp the proof
> and save it either locally or remotely. There is thus no need for
> post-validation.

> yuriy> I understand your solution, and I agree that some RPs will operate
> this way.  But in some communities that I am working in, like mortgages,
> smaller institutions desire the capability to perform a post-facto query.

Wouldn't your environment better be suited by a service that does not
ask for a validity of a certificate chain, but for the validity of a
signed document?  

> 
> > In addition, I think it is helpful to have a capability to perform
> > post-facto queries when for some reason the DPV service is originally
> > unavailable.
> 
> Making a query an hour later is fairly different from making the query 10
> years later.
> yuriy> But in essence, it is the same sort of query.  Was this signature
> valid/invalid at some time before the present?

That is not the question you have asked with DPV.

> yuriy> Some solutions I have seen don't send the receipt until the signature
> has been validated.  Until then, the sender is told that a receipt is
> pending.  Nonetheless, you still need to validate the signature at some time
> before the present, regardless of how you handled the receipt.

What can happen in the (short) time between these events? 

- The certificate expires. Well, a user should probalby not make the
  request with a cert that has a lifetime of 2 minutes left.

- The certificate gets revoked. This is an exceptional case, and
  it is not clear in advance whether the sent message should be treated
  as valid or invalid. If the revocation is initiated by the user
  of the cert, then you fall into the previous case. 

- Nothing happens. Then the two validations deliver the same result. 
 
> > When it comes back up, the agency will want
> > to know if my signature was valid when the proposal was submitted (at
> > 11:55A), and not when the service comes back up.
> 
> If the service was down for only a few hours, this can easily be be done.
> Doing it, 10 years later is a different story.
> yuriy> Again, I think the request is not different, in that you are asking a
> server to tell you if a signature was valid at some time before the present.
> It should not matter if it is 10 hours before present, or 10 years before
> present.  I understand the additional storage requirements on the server to
> support requests that date back 10 years, but why would we say it is
> acceptable to define a protocol that supports post-facto queries up to some
> amount of time before present?

Again, this is not the question you make to the DPV server. 

The current logic of path validation takes as an input a date value. 
Thus, in a strictly formal way, it seems to me that a DPV server has to
support some date as an input. 

The format of asking 10 years later or 2 hours may be the same, but it
doesn't seem to make much sense to me to make an INITIAL verification
10 years later.

---

From: "Yuriy Dzambasow" <[email-masked]>
Date: Mon, 5 Feb 2001 08:46:59 -0500

Peter,

Thanks for the response.  Comments below.

Yuriy

...snip...

The validity of the signing certificate may not be sufficient for that.
yuriy> It may not be sufficient, but it is part of the evidence that will
surely be required.

...snip...

Wouldn't your environment better be suited by a service that does not
ask for a validity of a certificate chain, but for the validity of a
signed document?
yuriy> In some cases, yes.  But I was not under the impression that we were
pursuing this functionality for DPV.

That is not the question you have asked with DPV.
yuriy> Sorry for the confusion.  I have inadvertently confused certificate
validation with signature validation.  The two are indeed different.  I was
talking about certificate validation throughout this thread.

What can happen in the (short) time between these events?
yuriy> The certificate can expire or be revoked.

- The certificate expires. Well, a user should probalby not make the
  request with a cert that has a lifetime of 2 minutes left.
yuriy> Do you know how many users I have talked to who were not aware that
their certificate was going to expire because of poor policy around renewal
notifications?  I don't think we can dismiss this case.

- The certificate gets revoked. This is an exceptional case, and
  it is not clear in advance whether the sent message should be treated
  as valid or invalid. If the revocation is initiated by the user
  of the cert, then you fall into the previous case.
yuriy> Revocation can still occur, and it should not jeopardize the fact
that I signed a document at a given time using a valid certificate.

yuriy> Agree.

Again, this is not the question you make to the DPV server.
yuriy> Again, I apologize for the confusion.  I was talking about
certificate validation.

The format of asking 10 years later or 2 hours may be the same, but it
doesn't seem to make much sense to me to make an INITIAL verification
10 years later.
yuriy> I am not saying that an INITIAL verification takes place 10 years
later.  What I provided in this thread were two different examples for why
one would make a post-facto query to a DPV server.