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Re: [Ntp] Antw: Re: Adam Roach's No Objection on draft-ietf-ntp-mac-05: (with COMMENT)

Miroslav Lichvar <mlichvar@redhat.com> Thu, 22 November 2018 08:55 UTC

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Date: Thu, 22 Nov 2018 09:55:20 +0100
From: Miroslav Lichvar <mlichvar@redhat.com>
To: ntp@ietf.org
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References: <adam@nostrum.com> <154269649579.26521.17016787490324740775.idtracker@ietfa.amsl.com> <20181120200757.1BDB240605C@ip-64-139-1-69.sjc.megapath.net> <CAJU8_nUV+m-7f+1gLD4Uu__sNnkT1MTpY62hO2CmRLT2=N1Lmw@mail.gmail.com> <cd44b1d1-df40-eabf-8352-071c6c5431fb@nwtime.org> <5BF65E2F020000A10002E33A@gwsmtp1.uni-regensburg.de>
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Subject: Re: [Ntp] Antw: Re: Adam Roach's No Objection on draft-ietf-ntp-mac-05: (with COMMENT)
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On Thu, Nov 22, 2018 at 08:43:43AM +0100, Ulrich Windl wrote:
> While this may seem liberal, it's still problematic: For example HP-UX had
> shipped xntp V3 for a long time while Linux had NTP v4 where DES-keys were no
> longer supported, while the HP-UX still had them (as kind of default); as a
> consequence keys had to be moved to MD5.
> If now MD5 is no longer supported (would that be in conformance to the NTPv4
> RFC?), you'll have a similar problem (thinking of the many devices around with
> some old NTPv3 client in firmware).

NTPv3 has no extension fields, so length extension attacks won't work
unless the implementation is parsing them as NTPv4 packets.

I guess one possibility would be say that implementations should
ignore all extension fields in packets authenticated with an MD5 or
RIPEMD-160 (as Tim points out) key.

-- 
Miroslav Lichvar

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