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Versions: 00 01

  SUIT Working Group                                           P. Urien
  Internet Draft                                      Telecom ParisTech
  Intended status: Experimental

                                                         April 21, 2019
  Expires: October 2019

               Security Classes For Software Updates for IoT
                  draft-urien-suit-security-classes-01.txt


Abstract

   This draft attempts to define security classes for devices targeted
   by SUIT protocols. A device security is characterized by five
   Boolean security attributes: firmware loader (FLD), one time
   programmable memory (OTP), secure firmware loader (FLD-SEC), tamper
   resistant key (TRT-KEY) and diversified key (DIV-KEY). This
   classification creates 18 device classes.


Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF). Note that other groups may also distribute
   working documents as Internet-Drafts. The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 2019.

   .








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Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
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  Security Classes For Software Updates for IoT          April 2019

Table of Contents
   Abstract........................................................... 1
   Requirements Language.............................................. 1
   Status of this Memo................................................ 1
   Copyright Notice................................................... 2
   1 Overview......................................................... 4
   2 Security Considerations for Firmware Update...................... 5
      2.1 Firmware Loader, FLD........................................ 5
      2.2 One Time Programmable Memory, OTP........................... 5
      2.3 Secure Firmware Loader, FLD-SEC............................. 5
      2.4 Tamper Resistant Key, TRT-KEY............................... 6
      2.5 Diversified Key, DIV-KEY.................................... 6
   3 IANA Considerations.............................................. 6
   4 Security Considerations.......................................... 6
   5 References....................................................... 6
      5.1 Normative References........................................ 6
      5.2 Informative References...................................... 6
   6 Authors' Addresses............................................... 6


































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1 Overview

   The [SUIT] working focuses on firmware update for Class 1 (as
   defined in RFC 7228) devices, i.e., devices with ~10 KB RAM and ~100
   KB flash.

   This draft attempts to define security classes for devices targeted
   by SUIT protocols. The goal is to provide a qualitative estimation
   of risk induced by firmware remote updates according to device
   logical and hardware security resources.

   According to this draft a device comprises a main processor (MP), an
   optional communication processor (CP), actuators and/or sensors. The
   communication task MAY be handled by the main processor. The main
   processor SHOULD manage the update of other processor.

   The main processor embeds several types of memories:
   - One Time Programmable Memory (OTP)
   - Non Volatile Memory (NVR)
   The logical architecture of the optional communication processor is
   similar to those of the main processor.

                                                Optional
                Main Processor          Communication Processor
            +---------------------+     +---------------------+
            |                     |     |                     |
            |  +---- +   +-----+  |     |  +---- +   +-----+  |
            |  | NVM |   | OTP |  |     |  | NVM |   | OTP |  |
            |  +-----+   +-----+  |     |  +-----+   +-----+  |
            |                     | <=> |                     |
            | +-----------------+ |     | +-----------------+ |
            | | Firmware Loader + |     | | Firmware Loader + |
            | +-----------------+ |     | +-----------------+ |
            |                     |     |                     |
            +---------------------+     +---------------------+
   Figure1. Device architecture

   Firmware update MAY be handled by a firmware loader (FLD) entity,
   and/or by other physical protocol (PHYP), for example Serial
   Programming (SP) or Parallel Programming (PP).

   When OTP memory is available, it MAY stores a permanent part of the
   update procedure (named firmware loader in this draft).

   Non volatile memory such as FLASH MAY be fully erased. When no OTP
   is available the main processor MAY be totally reprogrammed through
   physical protocols; i.e. physical access to the device MAY lead to
   its full control.

   A firmware loader enables the remote update of the NVR of the main
   processor. It MAY be secure (FLD-SEC) or not. If it is secure, a

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   symmetric or asymmetric procedure (and associated keys) is used in
   order to check the firmware authenticity. The two main classes of
   security procedures deal with symmetric algorithms (for example AES-
   CCM) or asymmetric signatures (for example ECDSA). It MAY support
   post quantum cryptographic algorithms.

   Even if the firmware loader is secure, cryptographic keys MAY be
   recovered by side-channel attacks [SIDECHANNEL][DIVKEY]. Therefore
   Tamper Resistant key (TRT-KEY) is a very important attribute. The
   impact of a side channel attack may be limited to a single object if
   the keys are diversified (DIV-KEY).

   We propose to characterize a device by a set (SecAtt) of five
   Boolean attributes (0/1):

   SecAtt = {FML, OTP, FLD-SEC, TRT-KEY, DIV-KEY}

   This leads to the definition of 2 + 16 = 18 classes of objects.
   - {0,0,0,0,0}, no firmware loader, no OTP.
   - {0,1,0,0,0}, no firmware loader, OTP available.
   - {1,1/0,1/0,1/0,1/0}, firmware loader available.

   For example some objects firmware (class = {0,0,0,0,0}) are just
   updated via HTTPS requests.

   Some highly secure devices similar to banking cards, SHOULD have all
   the security attributes (class = {1,1,1,1,1});

2 Security Considerations for Firmware Update

2.1 Firmware Loader, FLD

   A firmware loader is mainly a command interpreter that enables a
   logical/remote firmware update. It avoids the use of physical
   procedures such as Serial Programming a Parallel Programming. It is
   store either in non erasable or erasable non volatile memory.

2.2 One Time Programmable Memory, OTP

   The OTP attribute means that the main processor stores permanent
   software typically a firmware loader or a subset of this entity.

   If no OTP is available the full memory content of the main processor
   can be erased and fully updated. No minimum device behavior is
   guaranteed in this case.

2.3 Secure Firmware Loader, FLD-SEC

   A secure bootloader checks the authenticity and integrity of the
   firmware update by cryptographic means. This implies the use of
   symmetric secret keys, asymmetric private keys, or asymmetric public

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   keys associated to certificates. Most of cryptographic algorithms
   MAY be broken by side-channel attacks. If a long term vision is
   required it MAY support post quantum cryptographic algorithms.

2.4 Tamper Resistant Key, TRT-KEY

   Cryptographic keys may be recovered by side-channel attack. A Tamper
   Resistant computing environment SHOULD avoid these attacks.

2.5 Diversified Key, DIV-KEY

   The use of diversified secrets keys limits the side channel attack
   scope to a single object. The lack of tamper resistant computing and
   the use of single secret shared by multiple nodes MAY create major
   security threats.

3 IANA Considerations

   TODO

4 Security Considerations

   TODO

5 References

5.1 Normative References

   [SUIT], Moran, B., Meriac, M., Tschofenig, H., and D. Brown, "A
   Firmware Update Architecture for Internet of Things Devices", draft-
   ietf-suit-architecture-01 (work in progress), July 2018.

5.2 Informative References

   [SIDECHANNEL] David Oswald, "IMPLEMENTATION ATTACKS: FROM THEORY TO
   PRACTICE DISSERTATION", zur Erlangung des Grades eines Doktor
   ingenieurs der Fakultat fur Elektrotechnik und Informationstechnik
   an der Ruhr-Universitat Bochum, Bochum, September 2013

   [DIVKEY] Eyal Ronen, Adi Shamir, "Extended Functionality Attacks on
   IoT Devices: The Case of Smart Lights", 2016 IEEE European Symposium
   on Security and Privacy (EuroS&P)

6 Authors' Addresses

   Pascal Urien
   Telecom ParisTech
   23 avenue d'Italie
   75013 Paris               Phone: NA
   France                    Email: Pascal.Urien@telecom-paristech.fr


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