Subject: RE: The need for two grades of time data.

From: Mathew Butler <[email-masked]>
Date: Thu, 14 Sep 2000 11:36:15 -0700

If this is the case, then the work that the IETF is attempting to do here is
going to be for naught, because nobody is going to use it for its intended
purpose.

(For that matter, what do you think the intended purpose of this
specification is?  If it's not to create a system that can be used simply
and reliably to verify assertions made within signatures [i.e., the person
who signed it is who he says he is, the signature was generated on the date
he said he generated it, and that the signature was applied to the data that
it is attached to] then we might as well give up now and save ourselves
further headache.  Shall I trot out some hypothetical examples of -why- this
level pedantism is necessary and useful?)

"Time-Stamping Authority" -- Okay, I can see your point.  However, at what
point does the TSA actually see the blob that it's expected to timestamp?
And perhaps more importantly, is there any way to verify that the TSA is
doing its job correctly, and not putting out bogus information (because
their clocks got skewed 24 minutes, for example)?  Is there a way to certify
the time that they have comes from a "reliable source"?  If there isn't, why
should we trust it?  If there is, then why not embed the trusted
certification?  It's a little more work, for a lot less hassle in the end.

(My opinion is that if we give the lawyers something that they -can't-
bicker over, then they can go off and leave us alone while we do other
things.  Otherwise, there will be demand in the future for the same type of
'certification of time' as I'm talking about -- which is exactly what the
TSA is supposed to provide, but which is not going to be certified
elsewise.)

-Mat

-----Original Message-----
From: Stephen Kent [mailto:[email-masked]]
Sent: Thursday, September 14, 2000 11:26 AM
To: Bob Jueneman
Cc: [email-masked]
Subject: Re: The need for two grades of time data.

Bob,

>I believe that what Todd is trying to say is that the question isn't,
>"What time is it?" but rather "What time is it, and who says so, and
>why should anyone believe them?"

Since Todd agrees with Bob's concise translation, I think this is really
easy:

	- by choosing to use the service of a given TSA, the client 
is relying on the TSA to state the time

	- the TSA has a cert to identity it, and that cert is issued 
by a CA, who vouches for the accuracy of the ID, consistent with our 
usual CA model

	- a TSA publishes the technical basis for its time keeping, 
which provides the basis for the last value judgement

So, if the goal is to answer Bob's questions, I think we're done.  If 
one believes that we should move on to establishing criteria for 
different grades of time stamps, you're probably subscribed to the 
wrong WG list, and the wrong standards body, i.e., the IETF is not in 
the business of generating assurance standards of this sort.

Steve

---

From: Ben Laurie <[email-masked]>
Date: Thu, 14 Sep 2000 19:50:09 +0100

> point does the TSA actually see the blob that it's expected to timestamp?

Presumably at the point it timestamps it.

> certification?  It's a little more work, for a lot less hassle in the end.

Errr ... we specify a way to check that a source you have chosen to
consider is reliable is actually the source of the timestamp. You still
have to do the choosing. Or am I missing something?

Cheers,

Ben.

--
http://www.apache-ssl.org/ben.html

Coming to ApacheCon Europe 2000? http://apachecon.com/

---

From: Stephen Kent <[email-masked]>
Date: Thu, 14 Sep 2000 15:14:24 -0400

Mat,

>level pedantism is necessary and useful?)

We are developing standards that support all of these functions. What 
we are not doing is establishing the parameters of what is good 
enough from an assurance perspective.

>certification?  It's a little more work, for a lot less hassle in the end.

A TSA NEVER sees the data on which the message imprint is calculated. 
That's a security feature of the model.  the specific measures a TSA 
employs to convince its clients that the time stampts are accurate is 
just the sort of assurance detail that we do not address, for the 
reasons already cited.

>TSA is supposed to provide, but which is not going to be certified

If you believe that we could define the mechanisms and operational 
procedures that would satisfy EVERY time stamping application, or 
even try to define the set of applications that are appropriate 
served by a TSA that implemented a specific set of mechanisms and 
procedures, then I think you would be creating a target for lawyers.

Let me give a simple, direct, analogy analogy. We don't say (in 2459) 
that a CA should or must use a FIPS 140-1 certified crypto module to 
protect its private signature keys. This is outside the scope of our 
standard, and it is a very significant aspect of the confidence that 
a client would place in a CA.

Steve

---

From: "todd glassey" <[email-masked]>
Date: Thu, 14 Sep 2000 12:22:03 -0700

More inline below -
----- Original Message -----
From: "Mathew Butler" <[email-masked]>
To: "'Stephen Kent'" <[email-masked]>; "Bob Jueneman" <[email-masked]>
Cc: <[email-masked]>
Sent: Thursday, September 14, 2000 11:36 AM
Subject: RE: The need for two grades of time data.

 SNIP

> Since Todd agrees with Bob's concise translation, I think this is really

One solution would be to add some data. perhaps in the Timestamp as a
content_header that is added to talk of whcih of these three classes of
items the TS contains and/or how to intrpret it. Myself I think this would
be very valuable and would be worth the overhead on the per marque basis.

Just a thought.

> by a CA, who vouches for the accuracy of the ID, consistent with our

One of the use issues here then is whether the proofing is internal to the
TS or whether the TS mandates an external Stamp Practices Statement to
process.

My vote is that stamps optionally be capable of standing on their own two
feet instead of requiring the external reference.

> which provides the basis for the last value judgement

Also the TSA may not be the source of the time and to make this TSA's,
marques comparable to those of other TSA's that needs to be addressed I
think.

I think that the TSA itself would not, from a trust perspective, want to be
its own source of time data. It would want to be a commercial or private
user of some higher timing authorites Time Resource like that provided by
the new PKI extensions to NTP.

Todd