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Re: [Ntp] Antw: Re: Antw: [EXT] Re: Benjamin Kaduk's Discuss on draft-ietf-ntp-mode-6-cmds-09: (with DISCUSS and COMMENT)

Hal Murray <hmurray@megapathdsl.net> Mon, 31 August 2020 22:52 UTC

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To: Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de>
cc: Hal Murray <hmurray@megapathdsl.net>, "ntp@ietf.org" <ntp@ietf.org>
From: Hal Murray <hmurray@megapathdsl.net>
In-Reply-To: Message from "Ulrich Windl" <Ulrich.Windl@rz.uni-regensburg.de> of "Mon, 31 Aug 2020 10:58:49 +0200." <5F4CBBC9020000A10003B009@gwsmtp.uni-regensburg.de>
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Date: Mon, 31 Aug 2020 15:52:43 -0700
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Subject: Re: [Ntp] Antw: Re: Antw: [EXT] Re: Benjamin Kaduk's Discuss on draft-ietf-ntp-mode-6-cmds-09: (with DISCUSS and COMMENT)
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Ulrich.Windl@rz.uni-regensburg.de said:
> Original comment from NTP source:
>         /*
>          * Parse the extension field if present. We figure out whether
>          * an extension field is present by measuring the MAC size. If
>          * the number of words following the packet header is 0, no MAC
>          * is present and the packet is not authenticated. If 1, the
>          * packet is a crypto-NAK; if 3, the packet is authenticated
>          * with DES; if 5, the packet is authenticated with MD5; if 6,
>          * the packet is authenticated with SHA. If 2 or * 4, the packet
>          * is a runt and discarded forthwith. If greater than 6, an
>          * extension field is present, so we subtract the length of the
>          * field and go around again.
>          */ 

I think that comment is out of date.

ntpsec gets the algorithm from the keys file.  I am less familiar with the 
reference implementation, but I'm pretty sure it does the same.

If nothing else, the above comment won't work with AES, RFC-8573, which is the 
same length as MD5.

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