Practical Considerations and Implementation Experiences in Securing Smart Object Networks
draft-ietf-lwig-crypto-sensors-06

From Eric Vyncke, as OPS DIR reviewer:
This informational draft is about the challenges associated with securing resource-constrained smart object devices (such as those using CoAP).  It describes a possible deployment model and some preliminary experiences. It is part of a set of documents (draft- arkko-core-security-arch).

The challenges section includes many operational aspects: provisioning, scalability, ... The document proposes a simple system to generate the device identity based on its public key. 

The authors made some tests using 6 different crypto-libraries on Arduino 8-bit processors, this is the main part of the document. Finally, sections 7 and 8 describe a simple test application and some considerations about implementations.

So, a rather practical document.

*My only regret is that ‘key pair renewal’ is mentioned twice in the document (section 4.1 and 8.1) but without any detail... Key renewal is a big operational issue and it deserves more text or be explicitly cited as a non-goal in the abstract.*

Review in context at:
https://mozphab-ietf.devsvcdev.mozaws.net/D4040


   both parties, there are some remaining vulnerabilities that may or
   may not be acceptable for the application in question.  For example,
   leap-of-faith or trust-on-first-use based pairing methods assume that
This is not strictly correct. SAS is an example that requires neither of these.



   the attacker is not present during the initial setup and are
   vulnerable to eavesdropping or man-in-the-middle (MitM) attacks.
You might be interested in 
Secure In-Band Wireless Pairing
Shyamnath Gollakota, Nabeel Ahmed, Nikolai Zeldovich, and Dina Katabi
USENIX Security 2011, San Francisco, CA, August 2011.



   not completely secure method where the last few digits of the
   identity are printed on a tiny device just a few millimeters across.
   Alternatively, the packaging for the device may include the full
This is subject to trivial attacks no?



      Igrp = h(Pdev1|Pdev2|...|Pdevm)
1.Where do you use Idev?

This does work, I guess, but requires you to have the public keys of every device. Why not use a Merkle tree?


      filtering, storage and other actions, again without impacting the
      security of the data being transmitted or stored.
It's not clear from this text why these benefits obtain (caching especially). Is that because the data is in self-contained PDUs which can be interpreted even if there is transport/network level modification?



      different symmetric key algorithms such as AES, triple DES and
      SkipJack.  It provides RSA as an asymmetric key algorithm.  Parts
      of the library were written in AVR-8 bit assembly language to
Skipjack? 3DES? Back to the future!



      of a large variety of cryptographic algorithms.  This not only
      includes RSA and ECC, but also pairing based asymmetric
      cryptography, Boneh-Lynn-Schacham, Boneh-Boyen short signatures
It might be useful to know whether it's just the NIST curves or also X25519 and X448.



      based public key cryptography on sensor networks.  It is written
      in nesC programming language and as such is designed for specific
      use on TinyOS.  However, the library can be ported to standard C
What is the nesC programming language? Maybe a cite?



      implementation as well as X509 certificate handling.  The library
      provides an intuitive API for developer with a minimal code
      footprint.  It is intended for various ARM platforms such as ARM
"intuitive" seems a bit subjective.



   +--------------+------------------------+---------------------------+
   | 2048         |                1587567 |                     1,280 |
   +--------------+------------------------+---------------------------+
The time value would be easier to read if you used comma separators, as you did with memory footprint.



   In Table 2 we present the results obtained by manually porting
   TinyECC into C99 standard and running ECDSA signature algorithm on
   the Arduino Uno board.  TinyECC supports a variety of SEC 2
Nit: "the ECDSA"



   | secp192k1   |          3425 | 1008            |              1536 |
   | secp192r1   |          3578 | 1008            |              1536 |
   +-------------+---------------+-----------------+-------------------+
Note: IETF's minimal size is 256-bit and we also wouldn't use any of the k1 curves probably.

Do you have a cite for the key length comparisons. Opinions vary a bit here. And I understood the consensus to be that 192-bit was rather stronger than 1536.



   | NIST K233       |         1736 | 3675           |            2048 |
   | NIST B233       |         4471 | 3261           |            2048 |
   +-----------------+--------------+----------------+-----------------+
You should use the same naming convention as with the precious tables.



   that the IETF community uses these curves for protocol specification
   and implementations.
I'm confused by this statement. I would in fact expect X25519 to be faster, but your table 6 show Relic out performing this:

NIST B233 | 6100 | 2737 | 2048 |



   did note that it is possible for such devices to generate a new key
   pair.  Given that this operation would only occur in rare
   circumstances (such as a factory reset or ownership change) and its
You should probably note that RSA key pair generation is very expensive compared to signing, whereas ECDSA key pair generation is quite cheap compared to signing (it is a fixed-base operation).



   Sequence numbers can wrap-around at their maximum value and,
   therefore, it is essential to ensure that sequence numbers are
Nit: no hyphen in wrap around because it' sbeing used as a verb.



      time it passes through an application level entity, it is not
      clear that there are attacks beyond denial-of-service.
This is very dependent on exactly how you build the data object protection protocol.



   ability to scale to hundreds of millions of devices, let alone
   billions.  But the authors do not believe scaling is an important
   differentiator when comparing the solutions.
I don't believe about PKs not scaling is true at this point. Even if you don't count TLS, here are several widely used PK-based IM protocols.

This document reads more like a research paper (especially as it often talks about „the authors“ and „we“). While I would find it more appropriate to publish the experimentation report as a research paper or maybe some kind of extended technical report and only document the resulting recommendations in a short informational RFC, I don’t object to the publication as it was at least an interesting read. I guess the authors could consider to move some parts to the appendix (I guess sections 5-7 and maybe even some more text) but it’s probably not worth the effort.