Subject: time-stamp-03: interaction of TSTTime and serialNumber values

From: [email-masked] (Terry Hayes)
Date: Wed, 22 Sep 1999 14:09:23 -0700

The current draft of TSP requires that responses include a monotonically
increasing integer to identify the token and to resolve ordering within
the precision of the time stamp value.  However, the draft is not clear
as to whether the serial number itself is sufficient to order all tokens
issued by a certain TSA.  In particular, the draft does not indicate
whether the order of serialNumbers must correspond with the order of the
time stamp values themselves.

For example, is it legal to issue the following time stamps?

  Token #1:
    genTime: 19990922233002Z
    serialNumber: 1

  Token #2:
    genTime: 19990922233001Z
    serialNumber: 2

  Token #3:
    genTime: 19990922233002Z
    serialNumber: 3

I think that this sequence should be legal.  The serial number field
still provides ordering within the same genTime value, and also provides
the required reference value for future queries about the token.  The
primary source of ordering information should always be the genTime
field.  If those values are the same, then the serialNumber MAY be used
to resolve the ordering of the tokens.

(As an aside, I think providing ordering information is really beyond
the scope of this protocol in any case, and so I don't see any
requirement for monotonically increasing values)

Terry

---

From: Denis Pinkas <[email-masked]>
Date: Thu, 23 Sep 1999 11:43:24 +0200

Terry,

The current text says:

The serialNumber field shall include a strictly monotonically 
increasing integer from one TimeStampToken to the next (e.g. 45,
236,
 245, 1023, ...). This guarantees that each token is unique and 
allows to compare the ordering of two time stamps from the same TSA 
bearing the same time. This field also provides the way to build a 
unique identifier to reference the token. It should be noticed that 
the monotonic property must remain valid even after a possible 
interruption (e.g. crash) of the service. 

Apparently it is not clear enough. The text was supposed to mean:

The serialNumber field shall include a strictly monotonically 
increasing integer from one TimeStampToken to the next (e.g. 45,
236,
 245, 1023, ...). This guarantees that each token is unique and 
allows to compare the ordering of two time stamps. This is 
useful in particular when two times stamps bear the same time. 
This field also provides the way to build a unique identifier 
to reference the token. It should be noticed that the monotonic 
property must remain valid even after a possible interruption 
(e.g. crash) of the service. 

As a consequence with this clarification, your example will become
invalid. I will include this clarification in the next draft.

Denis
 
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