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

[<[e-mail]>]

Hi Ben, all, 

Please see inline.

Cheers,
Med

> -----Message d'origine-----
> De : Konda, Tirumaleswar Reddy [mailto:[e-mail]]
> Envoyé : samedi 19 janvier 2019 07:32
> À : Benjamin Kaduk; BOUCADAIR Mohamed TGI/OLN
> Cc : [e-mail]; [e-mail]
> Objet : RE: [Dots] AD review of draft-ietf-dots-signal-channel-25 (5th Part)
> 
> Hi Ben,
> 
> Please see inline
> 
> > -----Original Message-----
> > From: Dots <[e-mail]> On Behalf Of Benjamin Kaduk
> > Sent: Saturday, January 19, 2019 2:33 AM
> > To: [e-mail]
> > Cc: [e-mail]; [e-mail]
> > Subject: Re: [Dots] AD review of draft-ietf-dots-signal-channel-25 (5th
> Part)
> >
> > This email originated from outside of the organization. Do not click links
> or
> > open attachments unless you recognize the sender and know the content is
> safe.
> >
> > Hi all,
> >
> > Thanks for all the edits and the published -27.
> > Assuming I'm actually caught up on all the review/response threads, I think
> > we're pretty close to being able to go to IETF LC -- here's what I see as
> still left:
> >
> > - We need to settle the risk of needing normative downrefs called out for
> >   the last call

[Med] I updated the text to:
* cite 7618/7624 as normative (+ indicate that a similar mechanism to false start may also be defined for DTLS).
* tweak the TFO text to maintain it as informative. 

> > - I just noticed while reviewing the diff that we also need to say a
> >   little more about (D)TLS 1.3 0-RTT data (more below)
> > - It looks like we lost the guidance to the Experts and text about the
> >   review mailing list from the IANA Considerations, during the reshuffling
> >   around having IANA manage more things
> >

[Med] That was on purpose. We would like to rely on RFC8126 rules for deigned expert reviews. 

> > Regarding the (D)TLS 1.3 0-RTT data, RFC 8446 notes that "Application
> > protocols MUST NOT use 0-RTT data without a profile that defines its use.
> > That profile needs to identify which messages or interactions are safe to
> use
> > with 0-RTT and how to handle the situation when the server rejects 0-RTT
> and
> > falls back to 1-RTT."  So we either need to say which client requests are
> 0-RTT
> > safe (and why) or defer that profile to another document.  draft-ietf-
> dnsop-
> > session-signal is perhaps an example of a document that specifies which
> > messages are/aren't allowed in early data.
> > (draft-ietf-acme-acme is another, but an uninteresting one, since they make
> > every request include a single-use nonce, and all messages are 0-RTT safe.)
> > Our use of increasing 'mid' values may help here, in terms of allowing
> DELETEs
> > to be safe, but I'd have to think a little more to be sure that requesting
> > mitigation would be safe.  (On first glance the session-managemnet bits
> would
> > not be safe, but I may be missing something.)
> 
> The draft only uses idempotent requests (GET, PUT and DELETE), and CoAP is
> capable of detecting message duplication (see
> https://tools.ietf.org/html/rfc7252#section-4.5) for both confirmable and
> non-confirmable messages.
>  [1] An attacker replaying DELETE will not have any adverse impact, 2.02
> (Deleted) Response Code is returned even if the mitigation request does not
> exist.
> [2] The techniques discussed in Section 8 of RFC8446 should suffice to handle
> anti-replay (e.g. an attacker replaying a 0-RTT data carrying an old
> mitigation request replaced by a new mitigation scope).
> 

[Med] FWIW, we do already have this text in the draft: 

      Section 8 of [RFC8446] discusses some mechanisms to implement to
      limit the impact of replay attacks on 0-RTT data.  If the DOTS
      server accepts 0-RTT, it MUST implement one of these mechanisms.
      A DOTS server can reject 0-RTT by sending a TLS HelloRetryRequest.

> >
> > Further notes inline.
> >
> > On Thu, Jan 17, 2019 at 06:51:04AM +0000, [e-mail]
> > wrote:
> > > 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.
> > >
> > > > 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.
> > >
> > > >
> > > > 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".
> > >
> > > > 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.
> > >
> > > >
> > > > Section 9.6.1
> > > >
> > > > As above, specify what range we're asking about.
> > >
> > > [Med] OK.
> > >
> > > >
> > > > 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?
> >
> > Those documents' security considerations do seem to cover the relevant
> points,
> > yes.
> >
> > > >
> > > > 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.
> >
> > It's a lower-case "recommended", which can probably eke by as descriptive
> and
> > not a "protocol feature" (see below).
> >
> > > , 7413
> > > [Med] The support if TFO is not mandatory.
> >
> > It's a SHOULD ("SHOULD implement all of the following items"), though...
> >
> > > , 7589
> > > [Med] This is a MAY in the spec. It is just fine to leave it as
> informative.
> >
> > ....per
> > https://www.ietf.org/blog/iesg-statement-normative-and-informative-
> > references/
> > note 1, "Even references that are relevant only for optional features must
> be
> > classified as normative if they meet the above conditions for normative
> > references."
> >
> > This does seem to be something we actually need to care about before IETF
> LC,
> > though, as 7413 is Experimental and not listed in the downref registry
> > (https://datatracker.ietf.org/doc/downref/), so if we leave it as
> Informational
> > and have to change it later, we'd need to also restart/re-run the IETF LC.
> >
> > > , 7918
> > > [Med] Idem as TFO.
> >
> > This is Informational (i.e., also susceptible to the downref issue).
> >
> > > , 7924
> > > [Med] Idem as TFO.
> >
> > (idem x2), though this is standards-track at least, so we have more leeway
> to
> > move things around later.
> >
> >
> >
> > I think the most expedient thing to do here would just be to relax the
> > requirement for TLS Falst STart, TFO, and Cached Information, perhaps to
> text
> > like "The following items are additional mechanisms that can reduce the
> delay
> > required to deliver a DOTS signal channel message, which implementations
> are
> > encouraged to implement as possible.", but I am open to other suggestions
> for
> > what to do.
> 
> TLS False Start and Cached Information can be made normative references (just
> like we referenced these items in our spec
> https://tools.ietf.org/html/rfc8310)
> TFO is for TCP only and that too for exception scenarios where UDP is
> blocked. TFO can removed from the list of items the DOTS agents SHOULD
> implement.
> 
> NEW:
> Compared to UDP, DOTS signal channel over TCP requires an additional round-
> trip time (RTT) of latency to establish a TCP connection.  Implementations
> are encouraged to implement TCP
> Fast Open [RFC7413] to eliminate that RTT when information exists from prior
> TCP connection.
> 
> -Tiru
> 
> >
> >
> > > , and 7951
> > > [Med] this one was not listed as normative because the document lists two
> > ways to do the mapping.
> >
> > Agreed.
> >
> > -Ben
> >
> > > > should also be Normative.
> > > >
> > > >
> > > > -Ben
> > >
> >
> > _______________________________________________
> > Dots mailing list
> > [e-mail]
> > https://www.ietf.org/mailman/listinfo/dots