Re: [Ntp] Last Call: <draft-ietf-ntp-yang-data-model-10.txt> (A YANG Data Model for NTP) to Proposed Standardsecurity

Dhruv Dhody <> Mon, 08 February 2021 17:05 UTC

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From: Dhruv Dhody <>
Date: Mon, 08 Feb 2021 22:35:08 +0530
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To: tom petch <>
Cc:,,, NTP WG <>, Dieter Sibold <>,
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Subject: Re: [Ntp] Last Call: <draft-ietf-ntp-yang-data-model-10.txt> (A YANG Data Model for NTP) to Proposed Standardsecurity
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Hi Tom,

Thanks for your detailed review. Lets discuss the security first -

On Mon, Feb 8, 2021 at 6:07 PM tom petch <> wrote:
> This is my second response to this Last Call, about a possible security
> issue.
> RFC8573 seems clear that MD5 must not be used to effect security for NTP
> but this I-D imports iana-crypt-hash which allows MD5 without any
> restriction, so is MD5 allowed or not?

Good question. While it is easy to restrict the use of MD5 by adding a
must statement, I want to check if it is a good idea. The YANG model
is written in such a way that it supports older versions of NTP as
well. Would barring MD5 configuration be an issue if there are older
implementations in the network still? I think perhaps adding a warning
in the description is a good idea. I did a quick search and dont see
other YANG models doing a check either. Would be good to get some
guidance on this.

> There are features defined which allow the hash in iana-crypt-hash to be
> restricted but this I-D does not use them.

I didn't see any reason to use them in the NTP Yang. Can you?

> Probably iana-crypt-hash should be updated - I will raise that on the
> NETMOD WG list.
> The I-D also uses MD5 in a way that would appear not to be security
> related, to hash an IPv6 address.

This is as per RFC 5905 -

   If using the IPv4 address family, the identifier is the four-
   octet IPv4 address.  If using the IPv6 address family, it is the
   first four octets of the MD5 hash of the IPv6 address.

> In passing, this I-D has three references to RFC7317.  This is wrong -
> the module is IANA-maintained and so the references should be to the
> IANA website.

But even the iana-crypt-hash YANG model put RFC 7317 as a reference -

     revision 2014-08-06 {
         "Initial revision.";
         "RFC 7317: A YANG Data Model for System Management";

I will start working on your other comments and prepare a new version.


> The secdir reviewer might be interested in my thoughts.
> Tom Petch
> On 29/01/2021 22:39, The IESG wrote:
> >
> > The IESG has received a request from the Network Time Protocol WG (ntp) to
> > consider the following document: - 'A YANG Data Model for NTP'
> >    <draft-ietf-ntp-yang-data-model-10.txt> as Proposed Standard
> >
> > The IESG plans to make a decision in the next few weeks, and solicits final
> > comments on this action. Please send substantive comments to the
> > mailing lists by 2021-02-12. Exceptionally, comments may
> > be sent to instead. In either case, please retain the beginning
> > of the Subject line to allow automated sorting.
> >
> > Abstract
> >
> >
> >     This document defines a YANG data model for Network Time Protocol
> >     (NTP) implementations.  The data model includes configuration data
> >     and state data.
> >
> >