On 12/13/2011 6:06 AM, Brian Utterback wrote:
Dave, in a email message to the ntpwg list on July 14, you wrote to
Todd Glassey and said:
"A careful read of the specification should give you comfort that the
parsing rules do distinguish between an extension field and a MAC. In
particular, the rules permit one or more extension fields without a
MAC. The only requirement is that a MAC, if present, must be the last
field."
Speaking of which Dave I also took your suggestion and our new Patent
Applied For version of NTP (which also serves PTP too) last Sunday and
its now on file with US PTO... he he he - as is the GPUniverse
application for the Trillion-+ timestamp server... (filed a week
earlier) oh and I forgot to mention just because Dave and I slap each
other around once in a while for fun doesnt mean we don't respect or
admire each others work. Dave is a Research Timekeeper (as is much of
this list) - I am a Production Timekeeper and tis a very different
world therein.
So folks - we will be looking for parties who want to test this new
system and will of course make them available to USNO and NIST T&F for
review as well per our discussion with USNO last week in DC. For those
of you with commercial systems - you are seriously going to want this
new secured system since it can be used to create a reference clock
system which can replace the SYSLOG or OS Logging model as the
repository of the timestamps - that's right, its fast enough to allow
application level access to the reference clock system at HOST OS Event
speeds.
Booya!
Todd
Which is it?
Personally, I would love for the extension field to be independent of
the MAC field.
On 12/12/11 13:53, David L. Mills wrote:
Tai,
All I can say is read my message again. Doing without the MAC is a
very special case and unintended by the specification.
Dave
Tal Mizrahi wrote:
Hi Dave,
So you are saying that according to the current spec it is possible
in some configurations to have an extension field without the
existence of a MAC?
Tal.
*From:*David L. Mills [mailto:[email protected]]
*Sent:* Monday, December 12, 2011 6:01 AM
*To:* Tal Mizrahi
*Cc:* [email protected]; [email protected]
*Subject:* Re: [ntpwg] [TICTOC] NTP Extension Field without
Authentication
Tal ,
It's a little more complicated than it seems. The parsing rules
assume that a message digest is always present if an extension field
is present. The NT$ packet header, extension fields and MAC are
multiples of 32-bit words. The minimum MAC length is 5 words and
maximum length is 6 words. The minimum extension field length is 2
words. If the remaining number of words during the parse is less
than 7, the remainder is the MAC. If not, an extension field is
present. The parser updates the parser pointer folloowing the
extension field and tries again.
Thus, if there are at least 7 words remaining and the extension
field eats up all those words, the MAC could be assumed absent .
This is a rather hokey design, but would in principle work.
Dave
Tal Mizrahi wrote:
Hi,
Revisiting an issue that was raised a few months ago and is yet to
be resolved:
RFC 5905 defines an extension field. The RFC states that a MAC must
be present when there is an extension field.
Obviously, it would be beneficial for various purposes to allow
Extension Fields independent of whether the MAC is present.
Some people thought this is a mistake in the spec, and that it
should be included in the errata. Others thought that Extension
Fields without MAC are something new that needs to be defined in a
new document.
This was discussed in IETF 81, and then revisited in the ad-hoc
meeting in October, but no conclusion was reached.
It would be great to hear the opinion of the WG and the chairs about
how to proceed with this.
Thanks,
Tal.
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