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. ________________________________ _______________________________________________ ntpwg mailing list [email protected]<mailto:[email protected]> http://lists.ntp.org/listinfo/ntpwg
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