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
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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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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