Re: [Dots] AD review of draft-ietf-dots-signal-channel-25 (5th Part)

["Konda, Tirumaleswar Reddy" <[e-mail]>]

> -----Original Message-----
> From: Dots <[e-mail]> On Behalf Of
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> Sent: Thursday, January 17, 2019 12:21 PM
> To: Benjamin Kaduk <[e-mail]>; draft-ietf-dots-signal-
> [e-mail]
> Cc: [e-mail]
> Subject: Re: [Dots] AD review of draft-ietf-dots-signal-channel-25 (5th Part)
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> 
> Hi Ben,
> 
> Please see inline.
> 
> Cheers,
> Med
> 
> > -----Message d'origine-----
> > De : Benjamin Kaduk [mailto:[e-mail]] Envoyé : mercredi 16
> > janvier 2019 01:14 À : [e-mail]
> > Cc : [e-mail]
> > Objet : AD review of draft-ietf-dots-signal-channel-25
> >
> > Section 7.2
> >
> > The TLS 1.3 handshake with 0-RTT diagram needs to be
> > revisited/refreshed, as RFC 8446 does not look like that.
> > Additionally, the usage of PSK as well as a certificate is not defined
> > until draft-housley-tls-tls13-cert-with-extern-psk is published.
> > I also note that in the diagram as presented, the client is not yet
> > known to be authenticated when the server sends its initial (0.5-RTT)
> > DOTS signal message.
> >
> 
> [Med] Noted. Thanks.

The DOTS signal channel draft is discussing PSK with (EC)DHE key establishment explained in RFC8446, and I don't see the need to refer to draft-housley-tls-tls13-cert-with-extern-psk-00. 
The 0-RTT diagram is a simplified version of 0-RTT just like the Figure 1 in https://tools.ietf.org/html/draft-ietf-quic-tls-17.

The only correction required to the diagram is end_of_early_data must be sent along with the client Finished message.

> 
> > Section 7.3
> >
> > This whole section seems to only be relevant for UDP usage, so
> > probably the "If UDP is used" clause can be dropped and an
> > introductory statement added earlier on.
> 
> [Med] Will consider that.
> 
> >
> >                               Path MTU MUST be greater than or equal to
> >    [CoAP message size + DTLS overhead of 13 octets + authentication
> >    overhead of the negotiated DTLS cipher suite + block padding]
> >    (Section 4.1.1.1 of [RFC6347]).  If the request size exceeds the path
> >    MTU then the DOTS client MUST split the DOTS signal into separate
> >    messages, for example the list of addresses in the 'target-prefix'
> >    parameter could be split into multiple lists and each list conveyed
> >    in a new PUT request.
> >
> > (DTLS 1.3 will have a short header for some packets, that is less than
> > 13 octets.)
> 
> [Med] The text is more about 1.2. We can add a 1.3 note if you think it is
> useful for the discussion.

We should say "DTLS 1.2 overhead of 13 octets"
In DTLS 1.3 DTLSCiphertext structure is variable length (full header is of size 6 octets). 

> 
> >
> > Section 8
> >
> > We've got some requirements in here about limiting behavior of
> > clients/servers when talking to gateways; is knowing about the
> > presence of a gateway something that's required to happen out of band
> > or is there an in-band way to identify that the peer is a gateway?
> 
> [Med] An agent does not necessary know that it peer is gateway. A gateway
> is seen as a server for the client, and a client for a server.
> 
> >
> >    messages from an authorized DOTS gateway, thereby creating a two-link
> >    chain of transitive authentication between the DOTS client and the
> >    DOTS server.
> >
> > This seems to ignore the possibility of setups that include both
> > client-domain and server-domain gateways.
> 
> [Med] I updated the text to mention this is only an example.
> 
> >
> >                  DOTS client certificate validation MUST be performed as
> >    per [RFC5280] and the DOTS client certificate MUST conform to the
> >    [RFC5280] certificate profile.  [...]
> >
> > This seems to duplicate a requirement already stated in Section 7.1;
> > it's probably best to only have normative language in one location,
> > even if we need to mention the topic in multiple locations.
> > Similarly for the mutual authentication requirement, which we
> > duplicate in the second and fourth paragraphs of this section.
> 
> [Med] Good point. Fixed.
> 
> >
> > If we don't want to use example.com vs. example.net as sample domains,
> > we can also use whateverwewant.example, per RFC 6761.
> 
> [Med] Will maintain the ones already in the draft. Thanks.
> 
> >
> > Section 9
> >
> > We should mention the media-type allocation in the top-level section.
> 
> [Med] Will fix that.
> 
> >
> > "mappings to CBOR" feels confusing to me, since it leaves empty what
> > we are mapping from.  Perhaps just talking about a registry of "CBOR
> > map keys" would be better, both here and in the Section 9.3 intro.
> >
> 
> [Med] Unless there is an objection, I can use "CBOR Map Keys".

I don't see "CBOR Map Keys" defined or used anywhere in the draft. 

> 
> > Section 9.3
> >
> > I suggest being very explicit about whether new requests for
> > registration should be directed to the mailing list or to IANA, as
> > we've had some confusion about this elsewhere.
> >
> > The criteria used by the experts also just lists things they should
> > consider, but does not provide full clarity on which answer to the
> > question is more likely to be approved.  (And yes, I know that this
> > text is largely copied from already published RFCs, but we can still
> > do
> > better.)
> 
> [Med] Will check this.
> 
> >
> > Section 9.3.1
> >
> > If we want the value 0 to be reserved we need to say so.
> 
> [Med] 0 is not part of the allocation range.
> 
> > Do we want to say anything about the usage of negative integers as map
> > keys?
> >
> > I suggest not mentioning the postal address, given the recent (e.g.)
> > GDPR requirements.
> 
> [Med] Good point. Done.
> 
> >
> > Section 9.3.2
> >
> > It may be worth mentioning Table 4 here as well.
> 
> [Med] OK.
> 
> >
> > Section 9.5.1
> >
> > We need to specify which range of values we are asking for an
> > allocation from.
> 
> [Med] Added a mention to 0-255 range.

As per https://www.iana.org/assignments/cbor-tags/cbor-tags.xhtml the allowed range is 23-255.

> 
> >
> > Section 9.6.1
> >
> > As above, specify what range we're asking about.
> 
> [Med] OK.

The range is already defined in section 9.6.1.1 

Cheers
-Tiru

> 
> >
> > I expect the current text to get some IESG (or directorate) feedback
> > that the Data Item and Semantics descriptions are repetitive and banal.
> >
> > Section 9.7
> >
> > IIUC, IANA is going to ask if we want this module to be "maintained by
> > IANA", so it would be good to have an answer ready even if we don't
> > put it in the document text.
> 
> [Med] This is discussed in -26.
> 
> >
> >    Rate-limiting DOTS requests, including those with new 'cuid' values,
> >    from the same DOTS client defends against DoS attacks that would
> >
> > With respect to "new" 'cuid' values, is the server required to
> > remember which ones it has seen in perpetuity, or can it time them out
> > eventually?
> 
> [Med] The attack vector is a DOTS client which changes frequently its cuid.
> The DOTS server can set an interval in which the same client cannot present
> a new cuid.
> 
> >
> > Section 10
> >
> > The security considerations seem to be taking a narrow focus on the
> > requirements for and consequences of specific bits on the wire in the
> > signal channel protocol.  I think it's appropriate to also include
> > some high-level thoughts about the functional behavior of the
> > protocol, allowing to signal that an attack is underway and trigger
> > mitigation, increasing the availability of services, etc., and the
> > risks that are posed by the protocol failing to work properly, whether
> > that means letting attack traffic through or improperly blocking
> > legitimate traffic.
> 
> [Med] Would a pointer to the architecture/requirements I-Ds be sufficient to
> cover to high-level aspects?
> 
> >
> > Section 13.1
> >
> > I think the IANA registries should be listed as Informational and not
> > Normative references.
> >
> 
> [Med] Done.
> 
> > Section 13.2
> >
> > Pending resolution of the question about using
> > draft-ietf-core-yang-cbor rules or RFC7951+RFC7049, the
> > draft-ietf-core-yang-cbor reference may need to be Normative.
> 
> [Med] Please refer to my answer to that question. draft-ietf-core-yang-cbor is
> informative.
> 
> >
> > Given that "URI" is a well-known abbreviation, we may be able to get
> > away with not citing RFC 3986.  On the other hand, it's not causing
> > any harm to leave it in...
> 
> [Med] Will leave it.
> 
> >
> > RFC 4632 needs to be Normative, since we need to know CIDR to
> > encode/decode target-prefixes.
> 
> [Med] Works for me.
> 
> >
> > Similarly, I think that RFCs 6234
> 
> [Med] This one is not listed as normative because other hash algos may be
> used.
> 
> , 7413
> [Med] The support if TFO is not mandatory.
> 
> , 7589
> [Med] This is a MAY in the spec. It is just fine to leave it as informative..
> 
> , 7918
> [Med] Idem as TFO.
> 
> , 7924
> [Med] Idem as TFO.
> 
> , and 7951
> [Med] this one was not listed as normative because the document lists two
> ways to do the mapping.
> 
> > should also be Normative.
> >
> >
> > -Ben
> 
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