Subject: RE: Time Stamp: Usage of TDTs

From: [email-masked]
Date: Wed, 30 Jun 1999 16:10:01 +1000

Must admit it makes more sense now.

However, the question is why would a TSA's client require or be generally
interested in a "certified evidence of the TSA's diligence"?. This is what
you propose, isn't it? Sorry if I misunderstood it.

Would it be sufficient for the TSA just to claim (out of band, using legal
policy statement or else) that it is using such and such time source(s),
with a timePrecision field present in each TST?

A client would then decide, based on the policy information (clock
resolution, synchronization with NTA, reliability, etc), if that particular
TSA is suitable for use.

I can anticipate an argument that the TDT can be requested by the client
just once, to check how good is the TSA's timing. But this does not
guarantee that the consequent TSTs will be issued using the same clock, or
using the same clock-to-NTA synchronisation. If this is guaranteed by the
TSA's policy, and we are going to trust to what the policy promises, then as
well we can trust the rest of it (i.e. when/if it states that the clock IS
synchronised with NTA).

Probably, there are business cases where having TDT in a time stamp would be
a nice feature. Looking forward to hear more.

Regards
MichaelZ

-----Original Message-----
From: Bill Lattin [mailto:[email-masked]]
Sent: Wednesday, June 30, 1999 5:21 AM
To: [email-masked]
Cc: Dave Robinson; Ron Holm; Mike Duren; Greg Dowd
Subject: Time Stamp: Usage of TDTs

All,

Over the last few weeks, there has been considerable discussion on the need
for TDAs and their corresponding TDTs.  Much of the debate has been on
whether or not TDAs really add anything essential.  The heart of the issue
is whether or not the TSA is producing suitably trusted and accurate time.
It has been argued that if the time is accurate and trusted, then TDAs are
redundant (de la Vega and Zolotarev) and therefore should be eliminated.

Rather than use TDAs to provide secondary non-time information to
substantiate a TST, an alternative use is for a TDT to convey traceable
trusted time certification from a National Timing Authority (NTA) (e.g.
NIST) to the TSAs.  Rather than conveying something indirect like stock
market closing data, this new type of TDT could be used to show, in a
non-repudiatable manner, that: (i) a TSA's clock is accurately synchronized
to the NTA's clock ; and/or (ii) the time of creation of a TST embedding
such a TDT is traceable to the NTA.

We are working with the S/Time group to create a protocol to reliably
distribute time from an NTA to allow lower clocks in a timing hierarchy to
be accurately and reliably synchronized to the NTA's clock.  The result of
this process is a digitally signed certification that a clock is properly
synchronized to the NTA.  This certification can be embedded in a TDT to
prove that the time in the TDT or TST comes from a clock which has been
synchronized to an NTA.

Use of a TDT in this manner accomplishes a number of things:

1.  It directly enhances the quality of the TST by providing both a link to
UTC and traceability to NIST (or appropriate NTA);
2.  It can be used to synchronize multiple TSA's to an NTA so that the TSAs
can produce timestamps per NIST UTC (for instance) rather than their local
clock.
3.  It will aid certain electronic commerce implementations since the TSA's
clock can be shown to be directly traceable to an NTA.

Thus, we urge the group not to abandon TDAs and TDTs, but to consider an
alternative use for them that would contribute additional, directly relevant
timing information to enhance the operation of the TSA and the quality of
its TSTs.

Regards,

Bill

---

From: "Bill Lattin" <[email-masked]>
Date: Wed, 30 Jun 1999 14:11:59 -0700

Michael,

Thanks for the feedback.

Depending on the application, a client could be very interested in
"certified evidence" being located in a TST.  For example, in a currency
arbitrage or stock trade situation one coud envisage being able to prove
that a trade was placed at a certain time.  The real question is what
evidence is good enough?  Is it a contractual agreement that the local
TSA's clock is sufficently accurate and precise or is will there be a
mandate to use the clock from a National Timing Authority?

The answer is both.  We are not advocating that this type of TDT replace a
local TSA clock; both models are valid.  We just want to enable the use of
the National Timing Authority clocks since we believe that a number of
applications will insist on having time traceable to them.  As a current
example (although one for which PKIX time stamps will be too late for the
initial phases) is the NASDAQ OATS system.  This order tracking system is
required to use timing from NIST (the US' NTA).  The healthcare system in
the US is also extremely sensitive to time, and we expect that many new
applications will need to be linked to an NTA timing source rather than a
local source.

Further, I'm sure we all agree that the timeStampToken needs to be a
persistent data object.  For example, e-mail would normally be considered to
have low requirements for time-stamp trust.  However, 3 years down the road,
a given e-mail and its time of origin may be pivotal in a legal case.  If
the trust of the time in the timeStampToken can be embodied with a party in
addition to the entity possessing the TSA, the timeStampToken can better
meet the requirement to be a persistent data object.

You are right that a request of a single TDT does not guarantee future
performance from the TSA.  For applications that need traceability to NIST,
a TDT will be needed per time stamp.  This is an important extra benefit, a
TST with its own instance of a TDT can provide 'guaranteed' time independent
of the clock within the TSA.  Other applications, which are not as
sensitive, can operate as you have suggested - by agreement on policy that
the TSA is doing the right thing.

The bottom line is that the use of a TDT in this manner enables a new class
of applications which require explicit, provable traceability (with
associated audit trails) to an NTA.  The TSA operation is enhanced because
it can offer multiple types of service.

Cheers,

Bill

> From: [email-masked] [mailto:[email-masked]]
> Sent: Tuesday, June 29, 1999 23:10
> To: [email-masked]; "Denis.Pinkas[Denis.Pinkas"@bull.net];
> [email-masked]
> Cc: [email-masked]; [email-masked]; [email-masked];
> [email-masked]
> Subject: RE: Time Stamp: Usage of TDTs
>
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