Transport Layer Security (TLS) / Datagram Transport Layer Security (DTLS) Profiles for the Internet of Things
draft-ietf-dice-profile-17

[Ballot comment]
Just some editorial comments here that the RFC Editor isn't likely to catch:

-- Section 1 --

  UDP is mainly used to carry CoAP messages but other
  transports can be utilized

This is worded oddly, as it looks as if it's saying that the main use of UDP is to carry CoAP messages.  Please consider this instead:

NEW
  CoAP messages are mainly carried over UDP, but other
  transports can be utilized
END

-- Section 3.1 --

  However, since DTLS operates on top of an unreliable datagram
  transport, it must explicitly cope with the reliable and ordered
  delivery assumptions made by TLS.

It must explicitly cope with the *absence of* reliable and ordered delivery.  Please consider re-wording this.

-- Section 4.4.4 --

  There are various algorithms used to sign digital certificates, such
  as RSA, the Digital Signature Algorithm (DSA), and the Elliptic Curve
  Digital Signature Algorithm (ECDSA).  As Table 1 indicates
  certificate are signed using ECDSA.

This initially confused me.  First, the "such as" modifier appears to apply to "digital certificates", when it's actually meant to apply to "algorithms".  Then the second sentence seemed to contradict the first, until I realized that it's incomplete.  Please consider this:

NEW
  There are various algorithms used to sign digital certificates; those
  algorithms include RSA, the Digital Signature Algorithm (DSA), and
  the Elliptic Curve Digital Signature Algorithm (ECDSA).  As Table 1
  shows, in this profile certificates are signed using ECDSA.
END

-- Section 4.4.6 --

  With certificate-based authentication a DTLS server conveys
  its end entity certificate to the client during the DTLS exchange
  provides.

Something's wrong with this sentence (the part that begins with "during"), but I can't figure out what.

-- Section 6 --

  All error messages marked as RESERVED are only supported for
  backwards compatibility with SSL MUST NOT be used with this profile.

You're missing "and" before "MUST NOT".

-- Section 13 --

  Implementations conformant to this specification MUST use AEAD
  ciphers.  Hence, RFC 7366 and the Truncated MAC extension of RFC 6066
  are not applicable to this specification and are NOT RECOMMENDED.

To me, "not applicable" says more than "NOT RECOMMENDED".  Why is this not "MUST NOT be used"?

-- Section 17 --

  To prevent the re-negotiation attack [RFC5746] this specification
  RECOMMENDS to disable the TLS renegotiation feature.  Clients MUST
  respond to server-initiated re-negotiation attempts with an alert
  message (no_renegotiation) and clients MUST NOT initiate them.

Doesn't the second sentence actually say that this specification REQUIRES (not "RECOMMENDS") disabling of the TLS renegotiation feature?

-- Section 18 --

  If at some time in the future this profile reaches the quality of SSL
  3.0 a software update is needed since constrained devices are
  unlikely to run multiple TLS/DTLS versions due to memory size
  restrictions.

I don't understand this.  What does "reaches the quality of SSL 3.0" mean?

[Ballot comment]
I really like this document. I wish more working groups produced similar guidance.

I did have a number of questions, that you might want to take a look at before the document is approved.

This text

  UDP is mainly used to carry CoAP messages but other
  transports can be utilized, such as SMS Appendix A or TCP
  [I-D.tschofenig-core-coap-tcp-tls].
 
is somewhat ambiguous - is this supposed to say that "Most CoAP messages are carried in UDP, but other transports can be utilized, such as ..."?

This document is pretty reference-rich, but

  For use with this profile the PSK identities
  SHOULD NOT assume a structured format (such as domain names,
  Distinguished Names, or IP addresses) and a constant time bit-by-bit
  comparison operation MUST be used by the server for any operation
  related to the PSK identity.
 
doesn't have a reference or a definition for "constant time bit-by-bit comparison operation". Could you provide one?

I wasn't quite sure what

  TLS/DTLS offers a lot of freedom for the use with ECC. 
 
means. At a minimum, "for the use with" needs help. I'm guessing from the rest of the paragraph that this is saying "TLS/DTLS offers a lot of choices when selecting ECC curves", or something like that. But I'm guessing.

Is there a missing word in

  For deployments
  where public key cryptography is acceptable the raw public might
                                      somewhere around here? ^
  offer an acceptable middle ground between the PSK ciphersuite in
  terms of out-of-band validation and the functionality offered by
  asymmetric cryptography.
 
I think I understand

  The use of PFS is a trade-off decision since on one hand the
  compromise of long-term secrets of embedded devices is more likely
  than with many other Internet hosts but on the other hand a Diffie-
  Hellman exchange requires ephemeral key pairs to be generated, which
  is demanding from a performance point of view.  For obvious
  performance improvement, some implementations re-use key pairs over
  multiple exchanges (rather than generating new keys for each
  exchange).  However, note that such key re-use over long periods
  voids the benefits of forward secrecy when an attack gains access to
  this DH key pair.

but, just to make sure - is this saying that when you gain access to a DH key pair, you can decrypt back to the last time the device generated new keys, but no further (so, "Imperfect Forward Secrecy")? I'm guessing that based on "trade-off" in the first sentence, but I'm not sure what's being traded for performance improvement.

In this text,

  On the other hand, the way DTLS handles
  retransmission, which is per-flight instead of per-segment, tends to
  interact poorly with low bandwidth networks.
 
I'm assuming you are using "per-flight" in the https://tools.ietf.org/html/rfc5681 sense of the term ("FLIGHT SIZE: The amount of data that has been sent but not yet cumulatively acknowledged"), but that's somewhat obscure, especially outside of TSV, and there's no definition or reference for it in this document. Perhaps you could say something like

  On the other hand, DTLS handles loss by retransmitting the
  entire amount of data that has been sent but has not been
  cumulatively acknowledged, and this tends to
  interact poorly with low bandwidth networks.
 
Just to make sure I understand,

  The ClientHello and the ServerHello messages contains the 'Random'
  structure, which has two components: gmt_unix_time and a sequence of
  28 random bytes. gmt_unix_time holds the current time and date in
  standard UNIX 32-bit format (seconds since the midnight starting Jan
  1, 1970, GMT).  Since many IoT devices do not have access to an
  accurate clock, it is RECOMMENDED to place a sequence of random bytes
  in the two components of the 'Random' structure when creating a
  ClientHello or ServerHello message and not to assume a structure when
  receiving these payloads.
 
is recommending that all IoT devices use a sequence of random bytes, even if they do have access to an accurate clock - is that right?

Could you help me understand why

  Implementing the Server Name Indication extension is RECOMMENDED
  unless it is known that a TLS/DTLS client does not interact with a
  server in a hosting environment.
 
isn't REQUIRED? This seems like a violation of the Principle of Least Astonishment ("we moved our server into a hosted environment to save money, and our sensor network quit working").

I don't understand this paragraph.

  To prevent the re-negotiation attack [RFC5746] this specification
  RECOMMENDS to disable the TLS renegotiation feature.  Clients MUST
  respond to server-initiated re-negotiation attempts with an alert
  message (no_renegotiation) and clients MUST NOT initiate them.
 
If you MUST tell the server you won't renegotiate, and you MUST not try to renegotiate yourself, how does these turn into a RECOMMENDS ("SHOULD")?

[Ballot comment]
Thanks for a clear, easy to read document. At the start, I considered complaining about the page count, but I think you used those pages well.

4.4.1, paragraph after first numbered list:
Can this be more precise than "breaks security"? Maybe something to the effect of "Comparing...is required to ensure the client is communicating with the intended server"?

4.4.3, and 23:
Are there bootstrapping concerns with software update mechanisms? For example, what if you need to revoke a trust anchor on which the update mechanism depends?

[Ballot comment]
Thanks for your work on this draft!  It is very well written and provides helpful guidance with appropriate pointers that I hope gets picked up by many IoT vendors.  I even tweeted about this one!  It would be good to raise awareness on this draft/RFC.

Nice job!

(Via drafts-lastcall@iana.org): IESG/Authors/WG Chairs:

IANA has reviewed draft-ietf-dice-profile-14, which is currently in Last Call, and has the following comments:

We understand that this document doesn't require any IANA actions.

While it's often helpful for a document's IANA Considerations section to remain in place upon publication even if there are no actions, if the authors strongly prefer to remove it, IANA does not object.

If this assessment is not accurate, please respond as soon as possible.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (TLS/DTLS Profiles for the Internet of Things) to Proposed Standard


The IESG has received a request from the DTLS In Constrained Environments
WG (dice) to consider the following document:
- 'TLS/DTLS Profiles for the Internet of Things'
  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
ietf@ietf.org mailing lists by 2015-09-04. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the
beginning of the Subject line to allow automated sorting.

Abstract


  A common design pattern in Internet of Things (IoT) deployments is
  the use of a constrained device that collects data via sensor or
  controls actuators for use in home automation, industrial control
  systems, smart cities and other IoT deployments.

  This document defines a Transport Layer Security (TLS) and Datagram
  TLS (DTLS) 1.2 profile that offers communications security for this
  data exchange thereby preventing eavesdropping, tampering, and
  message forgery.  The lack of communication security is a common
  vulnerability in Internet of Things products that can easily be
  solved by using these well-researched and widely deployed Internet
  security protocols.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-dice-profile/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-dice-profile/ballot/


No IPR declarations have been submitted directly on this I-D.

(1) What type of RFC is being requested (BCP, Proposed Standard,
Internet Standard, Informational, Experimental, or Historic)?  Why
is this the proper type of RFC?  Is this type of RFC indicated in the
title page header?

draft-ietf-dice-profile-13.txt is a Standards Track specification.
The intented status is indicated at the header page. The specification
defines different TLS/DTLS profiles for use with Internet of Things
devices.

(2) The IESG approval announcement includes a Document Announcement
Write-Up. Please provide such a Document Announcement Write-Up. Recent
examples can be found in the "Action" announcements for approved
documents. The approval announcement contains the following sections:

Technical Summary

  A common design pattern in Internet of Things (IoT) deployments is
  the use of a constrained device that collects data via sensor or
  controls actuators for use in home automation, industrial control
  systems, smart cities and other IoT deployments.

  This document defines a Transport Layer Security (TLS) and Datagram
  TLS (DTLS) 1.2 profile that offers communications security for this
  data exchange thereby preventing eavesdropping, tampering, and
  message forgery.  The lack of communication security is a common
  vulnerability in Internet of Things products that can easily be
  solved by using these well-researched and widely deployed Internet
  security protocols.

Working Group Summary

  Was there anything in WG process that is worth noting? For
  example, was there controversy about particular points or
  were there decisions where the consensus was particularly
  rough?

There was no controversy about this document.


Document Quality

  Are there existing implementations of the protocol? Have a
  significant number of vendors indicated their plan to
  implement the specification? Are there any reviewers that
  merit special mention as having done a thorough review,
  e.g., one that resulted in important changes or a
  conclusion that the document had no substantive issues? If
  there was a MIB Doctor, Media Type or other expert review,
  what was its course (briefly)? In the case of a Media Type
  review, on what date was the request posted?


The document has been reviewed by various DICE working group
participants. Due to the nature of the document additional
review from the security community is essential.

Various implementations of embedded TLS stacks exist on the market
(open source as well as closed source implementations) that
implement a subset of the functionality defined in the specification.

Personnel

  Who is the Document Shepherd? Who is the Responsible Area
  Director?

The responsible area director for DICE and for this document iks
Stephen Farrell.

(3) Briefly describe the review of this document that was performed by
the Document Shepherd.  If this version of the document is not ready
for publication, please explain why the document is being forwarded to
the IESG.

Zach Shelby is the document shepherd. Detailed reviews during the
lifetime of the document have been done by the shepherd.

(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

No, the document has gone through several iterations
due to review comments from various working group members. The
last few revisions and related have resulted in only minor editorial improvements.

(5) Do portions of the document need review from a particular or from
broader perspective, e.g., security, operational complexity, AAA, DNS,
DHCP, XML, or internationalization? If so, describe the review that
took place.

The document would benefit from further security reviews.


(6) Describe any specific concerns or issues that the Document Shepherd
has with this document that the Responsible Area Director and/or the
IESG should be aware of? For example, perhaps he or she is uncomfortable
with certain parts of the document, or has concerns whether there really
is a need for it. In any event, if the WG has discussed those issues and
has indicated that it still wishes to advance the document, detail those
concerns here.

There are no concerns with this document.



(7) Has each author confirmed that any and all appropriate IPR
disclosures required for full conformance with the provisions of BCP 78
and BCP 79 have already been filed. If not, explain why.

The authors have confirmed that any and all appropriate IPR disclosures have been filed.

(8) Has an IPR disclosure been filed that references this document?
If so, summarize any WG discussion and conclusion regarding the IPR
disclosures.

No IPR disclosures have been filed.

(9) How solid is the WG consensus behind this document? Does it
represent the strong concurrence of a few individuals, with others
being silent, or does the WG as a whole understand and agree with it? 

This document has wide working group support, and was the main focus
of the DICE charter.

(10) Has anyone threatened an appeal or otherwise indicated extreme
discontent? If so, please summarise the areas of conflict in separate
email messages to the Responsible Area Director. (It should be in a
separate email because this questionnaire is publicly available.)

No.

(11) Identify any ID nits the Document Shepherd has found in this
document. (See http://www.ietf.org/tools/idnits/ and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be
thorough.

The shepherd checked the document for nits. All identified problems have
been corrected.

(12) Describe how the document meets any required formal review
criteria, such as the MIB Doctor, media type, and URI type reviews.

No such formal reviews are required by this document.

(13) Have all references within this document been identified as
either normative or informative?

Yes. All references are separated into informative and normative.

(14) Are there normative references to documents that are not ready for
advancement or are otherwise in an unclear state? If such normative
references exist, what is the plan for their completion?

Yes, there are two documents that are still in draft state:

  [I-D.ietf-tls-cached-info]
              Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension", draft-ietf-tls-
              cached-info-19 (work in progress), March 2015.

  [I-D.ietf-tls-session-hash]
              Bhargavan, K., Delignat-Lavaud, A., Pironti, A., Langley,
              A., and M. Ray, "Transport Layer Security (TLS) Session
              Hash and Extended Master Secret Extension", draft-ietf-
              tls-session-hash-05 (work in progress), April 2015.

[I-D.ietf-tls-session-hash] has been submitted to the IESG for
publication and [I-D.ietf-tls-cached-info] will be submitted to the
IESG soon.

(15) Are there downward normative references references (see RFC 3967)?
If so, list these downward references to support the Area Director in
the Last Call procedure.

There are various downward references in this document.

The following specifications are non-IETF documents:



  [EUI64]    "GUIDELINES FOR 64-BIT GLOBAL IDENTIFIER (EUI-64)
              REGISTRATION AUTHORITY", April 2010,
              .

  [GSM-SMS]  ETSI, "3GPP TS 23.040 V7.0.1 (2007-03): 3rd Generation
              Partnership Project; Technical Specification Group Core
              Network and Terminals; Technical realization of the Short
              Message Service (SMS) (Release 7)", March 2007.

  [WAP-WDP]  Wireless Application Protocol Forum, "Wireless Datagram
              Protocol", June 2001.

This specification is an informational RFC:

  [RFC7251]  McGrew, D., Bailey, D., Campagna, M., and R. Dugal, "AES-
              CCM Elliptic Curve Cryptography (ECC) Cipher Suites for
              TLS", RFC 7251, June 2014.



(16) Will publication of this document change the status of any
existing RFCs? Are those RFCs listed on the title page header, listed
in the abstract, and discussed in the introduction? If the RFCs are not
listed in the Abstract and Introduction, explain why, and point to the
part of the document where the relationship of this document to the
other RFCs is discussed. If this information is not in the document,
explain why the WG considers it unnecessary.

This document will not change the status of any other RFC.

(17) Describe the Document Shepherd's review of the IANA considerations
section, especially with regard to its consistency with the body of the
document. Confirm that all protocol extensions that the document makes
are associated with the appropriate reservations in IANA registries.
Confirm that any referenced IANA registries have been clearly
identified. Confirm that newly created IANA registries include a
detailed specification of the initial contents for the registry, that
allocations procedures for future registrations are defined, and a
reasonable name for the new registry has been suggested (see RFC 5226).

This specification does not require actions by IANA.

(18) List any new IANA registries that require Expert Review for future
allocations. Provide any public guidance that the IESG would find
useful in selecting the IANA Experts for these new registries.

Not applicable.

(19) Describe reviews and automated checks performed by the Document
Shepherd to validate sections of the document written in a formal
language, such as XML code, BNF rules, MIB definitions, etc.


There are no formal languages used in this specification.