Internet DRAFT - draft-moran-suit-mud
draft-moran-suit-mud
SUIT B. Moran
Internet-Draft H. Tschofenig
Intended status: Standards Track Arm Limited
Expires: November 26, 2021 May 25, 2021
Strong Assertions of IoT Network Access Requirements
draft-moran-suit-mud-02
Abstract
The Manufacturer Usage Description (MUD) specification describes the
access and network functionality required a device to properly
function. The MUD description has to reflect the software running on
the device and its configuration. Because of this, the most
appropriate entity for describing device network access requirements
is the same as the entity developing the software and its
configuration.
A network presented with a MUD file by a device allows detection of
misbehavior by the device software and configuration of access
control.
This document defines a way to link a SUIT manifest to a MUD file
offering a stronger binding between the two.
Status of This Memo
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This Internet-Draft will expire on November 26, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Extensions to SUIT . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Under [RFC8520], devices report a URL to a MUD manager in the
network. RFC 8520 envisions different approaches for conveying the
information from the device to the network such as:
- DHCP,
- IEEE802.1AB Link Layer Discovery Protocol (LLDP), and
- IEEE 802.1X whereby the URL to the MUD file would be contained in
the certificate used in an EAP method.
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The MUD manager then uses the the URL to fetch the MUD file, which
contains access and network functionality required a device to
properly function.
The MUD manager must trust the service from which the URL is fetched
and to return an authentic copy of the MUD file. This concern may be
mitigated using the optional signature reference in the MUD file.
The MUD manager must also trust the device to report a correct URL.
In case of DHCP and LLDP the URL is unprotected. When the URL to the
MUD file is included in a certificate then it is authenticated and
integrity protected. A certificate created for use with network
access authentication is typically not signed by the entity that
wrote the software and configured the device, which leads to
conflation of local network access rights with rights to assert all
network access requirements.
There is a need to bind the entity that creates the software and
configuration to the MUD file because only that entity can attest the
network access requirements of the device. This specification
defines an extension to the SUIT manifest to include a MUD file (per
reference or by value). When combining a manufacturer usage
description with a manifest used for software/firmware updates
(potentially augmented with attestation) then a network operator can
get more confidence in the description of the access and network
functionality required a device to properly function.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Architecture
The intended workflow is as follows:
- At the time of onboarding, devices report their manifest in use to
the MUD manager.
- If the SUIT_MUD_container has been severed, the suit-reference-uri
can be used to retrieve the complete manifest.
- The manifest authenticity is verified by the MUD manager, which
enforces that the MUD file presented is also authentic and as
intended by the device software vendor.
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- Each time a device is updated, rebooted, or otherwise
substantially changed, it will execute an attestation.
o Among other claims in the Entity Attestation Token (EAT)
[I-D.ietf-rats-eat], the device will report its software
digest(s), configuration digest(s), primary manifest URI, and
primary manifest digest to the MUD manager.
o The MUD manager can then validate these attestation reports in
order to check that the device is operating with the expected
version of software and configuration.
o Since the manifest digest is reported, the MUD manager can look
up the corresponding manifest.
- If the MUD manager does not already have a full copy of the
manifest, it can be acquired using the reference URI.
- Once a full copy of the manifest is provided, the MUD manager can
verify the device attestation report and apply any appropriate
policy as described by the MUD file.
4. Extensions to SUIT
To enable strong assertions about the network access requirements
that a device should have for a particular software/configuration
pair, we include the ability to add MUD files to the SUIT manifest.
However, there are also circumstances in which a device should allow
the MUD to be changed without a firmware update. To enable this, we
add a MUD url to SUIT along with a subject-key identifier, according
to [RFC7093], mechanism 4 (the keyIdentifier is composed of the hash
of the DER encoding of the SubjectPublicKeyInfo value).
The following CDDL describes the extension to the SUIT_Manifest
structure:
? suit-manifest-mud => SUIT_Digest
The SUIT_Envelope is also amended:
? suit-manifest-mud => bstr .cbor SUIT_MUD_container
SUIT_MUD_container = {
? suit-mud-url => #6.32(tstr),
? suit-mud-ski => SUIT_Digest,
? suit-mud-file => bstr
}
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The MUD file is included verbatim within the bstr. No limits are
placed on the MUD file: it may be any RFC8520-compliant file.
5. Security Considerations
This specification links MUD files to other IETF technologies,
particularly to SUIT manifests, for improving security protection and
ease of use. By including MUD files (per reference or by value) in
SUIT manifests an extra layer of protection has been created and
synchronization risks can be minimized. If the MUD file and the
software/firmware loaded onto the device gets out-of-sync a device
may be firewalled and, with firewalling by networks in place, the
device may stop functioning.
6. IANA Considerations
suit-manifest-mud must be added as an extension point to the SUIT
manifest registry.
7. Normative References
[I-D.ietf-rats-eat]
Mandyam, G., Lundblade, L., Ballesteros, M., and J.
O'Donoghue, "The Entity Attestation Token (EAT)", draft-
ietf-rats-eat-09 (work in progress), March 2021.
[I-D.ietf-suit-manifest]
Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg,
"A Concise Binary Object Representation (CBOR)-based
Serialization Format for the Software Updates for Internet
of Things (SUIT) Manifest", draft-ietf-suit-manifest-12
(work in progress), February 2021.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7093] Turner, S., Kent, S., and J. Manger, "Additional Methods
for Generating Key Identifiers Values", RFC 7093,
DOI 10.17487/RFC7093, December 2013,
<https://www.rfc-editor.org/info/rfc7093>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[RFC8520] Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
Description Specification", RFC 8520,
DOI 10.17487/RFC8520, March 2019,
<https://www.rfc-editor.org/info/rfc8520>.
Authors' Addresses
Brendan Moran
Arm Limited
EMail: Brendan.Moran@arm.com
Hannes Tschofenig
Arm Limited
EMail: hannes.tschofenig@arm.com
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