SUIT B. Moran
Internet-Draft Arm Limited
Intended status: Standards Track Ø. Rønningstad
Expires: 18 September 2025 Nordic Semiconductor
A. Tsukamoto
Openchip & Software Technologies, S.L.
17 March 2025
Mandatory-to-Implement Algorithms for Authors and Recipients of Software
Update for the Internet of Things manifests
draft-ietf-suit-mti-13
Abstract
This document specifies cryptographic algorithm profiles to be used
with the SUIT manifest (see draft-ietf-suit-manifest). These are the
mandatory-to-implement algorithms to ensure interoperability.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 18 September 2025.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Symmetric MTI profile:
suit-sha256-hmac-a128kw-a128ctr . . . . . . . . . . . . . 4
3.2. Current Constrained Asymmetric MTI Profile 1:
suit-sha256-es256-ecdh-a128ctr . . . . . . . . . . . . . 4
3.3. Current Constrained Asymmetric MTI Profile 2:
suit-sha256-eddsa-ecdh-a128ctr . . . . . . . . . . . . . 4
3.4. Current AEAD Asymmetric MTI Profile 1:
suit-sha256-es256-ecdh-a128gcm . . . . . . . . . . . . . 5
3.5. Current AEAD Asymmetric MTI Profile 2:
suit-sha256-eddsa-ecdh-chacha-poly . . . . . . . . . . . 5
3.6. Future Constrained Asymmetric MTI Profile 1:
suit-sha256-hsslms-a256kw-a256ctr . . . . . . . . . . . . 6
4. Reporting Profiles . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5.1. Payload encryption as a cybersecurity defense . . . . . . 6
5.2. Use of AES-CTR in payload encryption . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. A. Full CDDL . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
This document specifies algorithm profiles for SUIT manifest parsers
and authors to ensure better interoperability. These profiles apply
specifically to a constrained node software update use case.
Mandatory algorithms may change over time due to an evolving threat
landscape. Algorithms are grouped into algorithm profiles to account
for this. Profiles may be deprecated over time. SUIT will define
five choices of Mandatory To Implement (MTI) profile specifically for
constrained node software update. These profiles are:
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* One Symmetric MTI profile
* Two "Current" Constrained Asymmetric MTI profiles
* Two "Current" AEAD Asymmetric MTI profiles
* One "Future" Constrained Asymmetric MTI profile
At least one MTI algorithm in each category MUST be FIPS qualified.
Because SUIT presents an asymmetric communication profile, where
manifest authors have unlimited resources and manifest recipients
have constrained resources, the requirements for Recipients and
Authors are different.
Recipients MAY choose which MTI profile they wish to implement. It
is RECOMMENDED that they implement the "Future" Asymmetric MTI
profile. Recipients MAY implement any number of other profiles.
Recipients MAY choose not to implement an encryption algorithm if
encrypted payloads will never be used.
Authors MUST implement all MTI profiles. Authors MAY implement any
number of other profiles.
This draft makes use of AES-CTR in COSE ([RFC9459]), which is
Deprecated. AES-CTR is used because it enables out-of-order
reception and decryption of blocks, which is necessary for some
constrained node use cases. Out-of-order reception with on-the-fly
decryption is not available in the prefered encryption algorithms.
Authenticated Encryption with Additional Data (AEAD) is preferred
over un-authenticated encryption and an AEAD profile SHOULD be
selected wherever possible. See Security Considerations in this
draft (Section 5.2) and in [RFC9459] (Section 8) for additional
details on the considerations for the use of AES-CTR.
Other use-cases of the SUIT Manifest ([I-D.ietf-suit-manifest]) MAY
define their own MTI algorithms.
2. Algorithms
The algorithms that form a part of the profiles defined in this
document are grouped into:
* Digest Algorithms
* Authentication Algorithms
* Key Exchange Algorithms (OPTIONAL)
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* Encryption Algorithms (OPTIONAL)
3. Profiles
Recognized profiles are defined below.
3.1. Symmetric MTI profile: suit-sha256-hmac-a128kw-a128ctr
+================+=================+==========+
| Algorithm Type | Algorithm | COSE Key |
+================+=================+==========+
| Digest | SHA-256 | -16 |
+----------------+-----------------+----------+
| Authentication | HMAC-256 | 5 |
+----------------+-----------------+----------+
| Key Exchange | A128KW Key Wrap | -3 |
+----------------+-----------------+----------+
| Encryption | A128CTR | -65534 |
+----------------+-----------------+----------+
Table 1
3.2. Current Constrained Asymmetric MTI Profile 1: suit-sha256-es256-
ecdh-a128ctr
+================+==================+==========+
| Algorithm Type | Algorithm | COSE Key |
+================+==================+==========+
| Digest | SHA-256 | -16 |
+----------------+------------------+----------+
| Authentication | ES256 | -7 |
+----------------+------------------+----------+
| Key Exchange | ECDH-ES + A128KW | -29 |
+----------------+------------------+----------+
| Encryption | A128CTR | -65534 |
+----------------+------------------+----------+
Table 2
3.3. Current Constrained Asymmetric MTI Profile 2: suit-sha256-eddsa-
ecdh-a128ctr
+================+==================+==========+
| Algorithm Type | Algorithm | COSE Key |
+================+==================+==========+
| Digest | SHA-256 | -16 |
+----------------+------------------+----------+
| Authentication | EDDSA | -8 |
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+----------------+------------------+----------+
| Key Exchange | ECDH-ES + A128KW | -29 |
+----------------+------------------+----------+
| Encryption | A128CTR | -65534 |
+----------------+------------------+----------+
Table 3
3.4. Current AEAD Asymmetric MTI Profile 1: suit-sha256-es256-ecdh-
a128gcm
+================+==================+==========+
| Algorithm Type | Algorithm | COSE Key |
+================+==================+==========+
| Digest | SHA-256 | -16 |
+----------------+------------------+----------+
| Authentication | ES256 | -7 |
+----------------+------------------+----------+
| Key Exchange | ECDH-ES + A128KW | -29 |
+----------------+------------------+----------+
| Encryption | A128GCM | 1 |
+----------------+------------------+----------+
Table 4
3.5. Current AEAD Asymmetric MTI Profile 2: suit-sha256-eddsa-ecdh-
chacha-poly
+================+===================+==========+
| Algorithm Type | Algorithm | COSE Key |
+================+===================+==========+
| Digest | SHA-256 | -16 |
+----------------+-------------------+----------+
| Authentication | EDDSA | -8 |
+----------------+-------------------+----------+
| Key Exchange | ECDH-ES + A128KW | -29 |
+----------------+-------------------+----------+
| Encryption | ChaCha20/Poly1305 | 24 |
+----------------+-------------------+----------+
Table 5
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3.6. Future Constrained Asymmetric MTI Profile 1: suit-sha256-hsslms-
a256kw-a256ctr
+================+===========+==========+
| Algorithm Type | Algorithm | COSE Key |
+================+===========+==========+
| Digest | SHA-256 | -16 |
+----------------+-----------+----------+
| Authentication | HSS-LMS | -46 |
+----------------+-----------+----------+
| Key Exchange | A256KW | -5 |
+----------------+-----------+----------+
| Encryption | A256CTR | -65532 |
+----------------+-----------+----------+
Table 6
This draft does not specify a particular set of HSS-LMS parameters.
Deep trees are RECOMMENDED due to key lifetimes in IoT devices.
4. Reporting Profiles
When using Manifest Recipients Response communication, particularly
data structures that are designed for reporting of update
capabilities, status, progress, or success, the same profile as the
is used on the SUIT manifest SHOULD be used. There are cases where
this is not possible, such as suit-sha256-hsslms-a256kw-a256ctr. In
this case, the closest equivalent profile SHOULD be used, for example
suit-sha256-es256-ecdh-a128ctr.
5. Security Considerations
Payload encryption is predominantly to protect user data, such as
personalisation data, in transit ([RFC8890]). It can also serve to
protect Intellectual Property in transit.
5.1. Payload encryption as a cybersecurity defense
To define the purpose of payload encryption as a defensive
cybersecurity tool, it is important to define the capabilities of
modern threat actors. A variety of capabilities are possible:
* find bugs by binary code inspection
* send unexpected data to communication interfaces, looking for
unexpected behavior
* use fault injection to bypass or manipulate code
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* use communication attacks or fault injection along with gadgets
found in the code
Given this range of capabilities, it is important to understand which
capabilities are impacted by firmware encryption. Threat actors who
find bugs by manual inspection or use gadgets found in the code will
need to first extract the code from the target. In the IoT context,
it is expected that most threat actors will start with sample devices
and physical access to test attacks.
Due to these factors, payload encryption serves to limit the pool of
attackers to those who have the technical capability to extract code
from physical devices and those who perform code-free attacks.
5.2. Use of AES-CTR in payload encryption
AES-CTR mode with a digest is specified, see [RFC9459]. All of the
AES-CTR security considerations in [RFC9459] apply. A non-AEAD
encryption mode is specified in this draft due to the following
mitigating circumstances:
* Out-of-order decryption must be supported. Therefore, we must use
a stream cipher that supports random access.
* Chosen plaintext attacks are extremely difficult to achieve, since
the payloads are typically constructed in a relatively secure
environment--the developer's computer or build infrastructure--and
should be signed in an air-gapped or similarly protected
environment. In short, the plaintext is authenticated prior to
encryption.
* Content Encryption Keys must be used to encrypt only once. See
[I-D.ietf-suit-firmware-encryption].
As a result of these mitigating circumstances, AES-CTR is an
acceptable cipher for typical software/firmware delivery scenarios.
6. IANA Considerations
IANA is requested to create a page for COSE Algorithm Profiles within
the category for Software Update for the Internet of Things (SUIT)
IANA is also requested to create a registry for COSE Alforithm
Profiles within this page. The initial content of the registry is:
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+=============+=========+======+====+========+==========+==========+=========+
|Profile |Status |Digest|Auth|Key |Encryption|Descriptor|Reference|
| | | | |Exchange| |Array | |
+=============+=========+======+====+========+==========+==========+=========+
|suit-sha256- |MANDATORY|-16 |5 |-3 |-65534 |[-16, 5, |Section |
|hmac-a128kw- | | | | | |-3, |3.1 |
|a128ctr | | | | | |-65534] | |
+-------------+---------+------+----+--------+----------+----------+---------+
|suit- |MANDATORY|-16 |-7 |-29 |-65534 |[-16, -7, |Section |
|sha256-es256-| | | | | |-29, |3.2 |
|ecdh-a128ctr | | | | | |-65534] | |
+-------------+---------+------+----+--------+----------+----------+---------+
|suit-sha256- |MANDATORY|-16 |-8 |-29 |-65534 |[-16, -8, |Section |
|eddsa-ecdh- | | | | | |-29, |3.3 |
|a128ctr | | | | | |-65534] | |
+-------------+---------+------+----+--------+----------+----------+---------+
|suit- |MANDATORY|-16 |-7 |-29 |1 |[-16, -7, |Section |
|sha256-es256-| | | | | |-29, 1] |3.4 |
|ecdh-a128gcm | | | | | | | |
+-------------+---------+------+----+--------+----------+----------+---------+
|suit-sha256- |MANDATORY|-16 |-8 |-29 |24 |[-16, -8, |Section |
|eddsa-ecdh- | | | | | |-29, 24] |3.5 |
|chacha-poly | | | | | | | |
+-------------+---------+------+----+--------+----------+----------+---------+
|suit-sha256- |MANDATORY|-16 |-46 |-5 |-65532 |[-16, -46,|Section |
|hsslms- | | | | | |-5, |3.6 |
|a256kw- | | | | | |-65532] | |
|a256ctr | | | | | | | |
+-------------+---------+------+----+--------+----------+----------+---------+
Table 7
New entries to this registry require standards action.
7. References
7.1. Normative References
[I-D.ietf-suit-manifest]
Moran, B., Tschofenig, H., Birkholz, H., Zandberg, K., and
O. Rønningstad, "A Concise Binary Object Representation
(CBOR)-based Serialization Format for the Software Updates
for Internet of Things (SUIT) Manifest", Work in Progress,
Internet-Draft, draft-ietf-suit-manifest-33, 24 February
2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
suit-manifest-33>.
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[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/rfc/rfc8152>.
[RFC8778] Housley, R., "Use of the HSS/LMS Hash-Based Signature
Algorithm with CBOR Object Signing and Encryption (COSE)",
RFC 8778, DOI 10.17487/RFC8778, April 2020,
<https://www.rfc-editor.org/rfc/rfc8778>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/rfc/rfc9052>.
[RFC9459] Housley, R. and H. Tschofenig, "CBOR Object Signing and
Encryption (COSE): AES-CTR and AES-CBC", RFC 9459,
DOI 10.17487/RFC9459, September 2023,
<https://www.rfc-editor.org/rfc/rfc9459>.
7.2. Informative References
[I-D.ietf-suit-firmware-encryption]
Tschofenig, H., Housley, R., Moran, B., Brown, D., and K.
Takayama, "Encrypted Payloads in SUIT Manifests", Work in
Progress, Internet-Draft, draft-ietf-suit-firmware-
encryption-23, 29 January 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-suit-
firmware-encryption-23>.
[IANA-COSE]
"CBOR Object Signing and Encryption (COSE)", 2022,
<https://www.iana.org/assignments/cose/cose.xhtml>.
[RFC8890] Nottingham, M., "The Internet is for End Users", RFC 8890,
DOI 10.17487/RFC8890, August 2020,
<https://www.rfc-editor.org/rfc/rfc8890>.
Appendix A. A. Full CDDL
The following CDDL creates a subset of COSE for use with SUIT. Both
tagged and untagged messages are defined. SUIT only uses tagged COSE
messages, but untagged messages are also defined for use in protocols
that share a ciphersuite with SUIT.
To be valid, the following CDDL MUST have the COSE CDDL appended to
it. The COSE CDDL can be obtained by following the directions in
[RFC9052], Section 1.4.
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SUIT_COSE_tool_tweak /= suit-sha256-hmac-a128kw-a128ctr
SUIT_COSE_tool_tweak /= suit-sha256-es256-ecdh-a128ctr
SUIT_COSE_tool_tweak /= suit-sha256-eddsa-ecdh-a128ctr
SUIT_COSE_tool_tweak /= suit-sha256-es256-ecdh-a128gcm
SUIT_COSE_tool_tweak /= suit-sha256-eddsa-ecdh-chacha-poly
SUIT_COSE_tool_tweak /= suit-sha256-hsslms-a256kw-a256ctr
SUIT_COSE_tool_tweak /= SUIT_COSE_Profiles
SUIT_COSE_Profiles /= SUIT_COSE_Profile_HMAC_A128KW_A128CTR
SUIT_COSE_Profiles /= SUIT_COSE_Profile_ES256_ECDH_A128CTR
SUIT_COSE_Profiles /= SUIT_COSE_Profile_EDDSA_ECDH_A128CTR
SUIT_COSE_Profiles /= SUIT_COSE_Profile_ES256_ECDH_A128GCM
SUIT_COSE_Profiles /= SUIT_COSE_Profile_EDDSA_ECDH_CHACHA20_POLY1304
SUIT_COSE_Profiles /= SUIT_COSE_Profile_HSSLMS_A256KW_A256CTR
suit-sha256-hmac-a128kw-a128ctr = [-16, 5, -3, -65534]
suit-sha256-es256-ecdh-a128ctr = [-16, -7, -29, -65534]
suit-sha256-eddsa-ecdh-a128ctr = [-16, -8, -29, -65534]
suit-sha256-es256-ecdh-a128gcm = [-16, -7, -29, 1]
suit-sha256-eddsa-ecdh-chacha-poly = [-16, -8, -29, 24]
suit-sha256-hsslms-a256kw-a256ctr = [-16, -46, -5, -65532]
SUIT_COSE_Profile_HMAC_A128KW_A128CTR =
SUIT_COSE_Profile<5,-65534> .and COSE_Messages
SUIT_COSE_Profile_ES256_ECDH_A128CTR =
SUIT_COSE_Profile<-7,-65534> .and COSE_Messages
SUIT_COSE_Profile_EDDSA_ECDH_A128CTR =
SUIT_COSE_Profile<-8,-65534> .and COSE_Messages
SUIT_COSE_Profile_ES256_ECDH_A128GCM =
SUIT_COSE_Profile<-7,1> .and COSE_Messages
SUIT_COSE_Profile_EDDSA_ECDH_CHACHA20_POLY1304 =
SUIT_COSE_Profile<-8,24> .and COSE_Messages
SUIT_COSE_Profile_HSSLMS_A256KW_A256CTR =
SUIT_COSE_Profile<-46,-65532> .and COSE_Messages
SUIT_COSE_Profile<authid, encid> = SUIT_COSE_Messages<authid,encid>
SUIT_COSE_Messages<authid, encid> =
SUIT_COSE_Untagged_Message<authid, encid> /
SUIT_COSE_Tagged_Message<authid, encid>
SUIT_COSE_Untagged_Message<authid, encid> = SUIT_COSE_Sign<authid> /
SUIT_COSE_Sign1<authid> / SUIT_COSE_Encrypt<encid> /
SUIT_COSE_Encrypt0<encid> / SUIT_COSE_Mac<authid> /
SUIT_COSE_Mac0<authid>
SUIT_COSE_Tagged_Message<authid, encid> =
SUIT_COSE_Sign_Tagged<authid> / SUIT_COSE_Sign1_Tagged<authid> /
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SUIT_COSE_Encrypt_Tagged<encid> / SUIT_COSE_Encrypt0_Tagged<encid> /
SUIT_COSE_Mac_Tagged<authid> / SUIT_COSE_Mac0_Tagged<authid>
; Note: This is not the same definition as is used in COSE.
; It restricts a COSE header definition further without
; repeating the COSE definition. It should be merged
; with COSE by using the CDDL .and operator.
SUIT_COSE_Profile_Headers<algid> = (
protected : bstr .cbor SUIT_COSE_alg_map<algid>,
unprotected : SUIT_COSE_header_map
)
SUIT_COSE_alg_map<algid> = {
1 => algid,
* int => any
}
SUIT_COSE_header_map = {
* int => any
}
SUIT_COSE_Sign_Tagged<authid> = #6.98(SUIT_COSE_Sign<authid>)
SUIT_COSE_Sign<authid> = [
SUIT_COSE_Profile_Headers<authid>,
payload : bstr / nil,
signatures : [+ SUIT_COSE_Signature<authid>]
]
SUIT_COSE_Signature<authid> = [
SUIT_COSE_Profile_Headers<authid>,
signature : bstr
]
SUIT_COSE_Sign1_Tagged<authid> = #6.18(SUIT_COSE_Sign1<authid>)
SUIT_COSE_Sign1<authid> = [
SUIT_COSE_Profile_Headers<authid>,
payload : bstr / nil,
signature : bstr
]
SUIT_COSE_Encrypt_Tagged<encid> = #6.96(SUIT_COSE_Encrypt<encid>)
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SUIT_COSE_Encrypt<encid> = [
SUIT_COSE_Profile_Headers<encid>,
ciphertext : bstr / nil,
recipients : [+SUIT_COSE_recipient<encid>]
]
SUIT_COSE_recipient<encid> = [
SUIT_COSE_Profile_Headers<encid>,
ciphertext : bstr / nil,
? recipients : [+SUIT_COSE_recipient<encid>]
]
SUIT_COSE_Encrypt0_Tagged<encid> = #6.16(SUIT_COSE_Encrypt0<encid>)
SUIT_COSE_Encrypt0<encid> = [
SUIT_COSE_Profile_Headers<encid>,
ciphertext : bstr / nil,
]
SUIT_COSE_Mac_Tagged<authid> = #6.97(SUIT_COSE_Mac<authid>)
SUIT_COSE_Mac<authid> = [
SUIT_COSE_Profile_Headers<authid>,
payload : bstr / nil,
tag : bstr,
recipients :[+SUIT_COSE_recipient<authid>]
]
SUIT_COSE_Mac0_Tagged<authid> = #6.17(SUIT_COSE_Mac0<authid>)
SUIT_COSE_Mac0<authid> = [
SUIT_COSE_Profile_Headers<authid>,
payload : bstr / nil,
tag : bstr,
]
Authors' Addresses
Brendan Moran
Arm Limited
Email: brendan.moran.ietf@gmail.com
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Øyvind Rønningstad
Nordic Semiconductor
Email: oyvind.ronningstad@gmail.com
Akira Tsukamoto
Openchip & Software Technologies, S.L.
Email: akira.tsukamoto@gmail.com
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