]> Arm Limited

brendan.moran.ietf@gmail.com

Nordic Semiconductor

oyvind.ronningstad@gmail.com

Openchip & Software Technologies, S.L.

akira.tsukamoto@gmail.com

Security SUIT Internet-Draft This document defines cryptographic algorithm profiles for use with the Software Updates for Internet of Things (SUIT) manifest. These profiles specify sets of algorithms to promote interoperability across implementations. The SUIT manifest, as defined in "A Manifest Information Model for Firmware Updates in Internet of Things (IoT) Devices" (RFC 9124), provides a flexible and extensible format for describing how firmware and software updates are to be fetched, verified, decrypted, and installed on resource-constrained devices. To ensure the security of these update processes, the manifest relies on cryptographic algorithms for functions such as digital signature verification, integrity checking, and confidentiality. Given the diversity of IoT deployments and the evolving cryptographic landscape, algorithm agility is essential. This document groups algorithms into named profiles to accommodate varying levels of device capabilities and security requirements. These profiles support the use cases laid out in the SUIT architecture, published in "A Firmware Update Architecture for Internet of Things" (RFC 9019).

Introduction This document defines algorithm profiles intended for authors of Software Updates of Internet of Things (SUIT) manifests and their recipients, with the goal of promoting interoperability in software update scenarios for constrained nodes. These profiles specify sets of algorithms that are tailored to the evolving security landscape, recognizing that cryptographic requirements may change over time. The following profiles are defined: One profile designed for constrained devices that support only symmetric key cryptography Two profiles for constrained devices capable of using asymmetric key cryptography Two profiles that employ Authenticated Encryption with Associated Data (AEAD) ciphers One constrained asymmetric profile that uses a hash-based signature scheme Due to the asymmetric nature of SUIT deployments - where manifest authors typically operate in resource-rich environments while recipients are resource-constrained - the cryptographic requirements differ between these two roles. This specification uses AES-CTR in combination with a digest algorithm, as defined in , to support use cases that require out-of-order block reception and decryption-capabilities not offered by AEAD algorithms. For further discussion of these constrained use cases, refer to . Other SUIT use cases (see ) may define different profiles.

Conventions and Definitions 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 when, and only when, they appear in all capitals, as shown here. This specification uses the following abbreviations: Advanced Encryption Standard (AES) AES Counter (AES-CTR) Mode AES Key Wrap (AES-KW) Authenticated Encryption with Associated Data (AEAD) Concise Binary Object Representation (CBOR) CBOR Object Signing and Encryption (COSE) Concise Data Definition Language (CDDL) Elliptic Curve Diffie-Hellman Ephemeral-Static (ECDH-ES) Hash-based Message Authentication Code (HMAC) Hierarchical Signature System / Leighton-Micali Signature (HSS/LMS) Software Updates for Internet of Things (SUIT) SUIT specifically addresses the requirements of constrained devices and networks, as described in . The terms "Author", "Recipient", and "Manifest" are defined in .

Profiles Each profile consists of algorithms from the following categories: Digest Algorithms Authentication Algorithms Key Exchange Algorithms (optional) Encryption Algorithms (optional) Each profile references specific algorithm identifiers, as defined in . Since these algorithm identifiers are used in the context of the IETF SUIT manifest , they are represented using CBOR Object Signing and Encryption (COSE) structures as defined in and . The use of the profiles by authors and recipients is based on the following assumptions: Recipients MAY choose which profile they wish to implement. It is RECOMMENDED that they implement the suit-sha256-hsslms-a256kw-a256ctr profile (). Recipients MAY implement any number of other profiles not defined in this document. Recipients MAY choose not to implement encryption and the corresponding key exchange algorithms if they do not intend to support encrypted payloads. Authors MUST implement all profiles with a status set to 'MANDATORY' in . Authors MAY implement any number of additional profiles.

Profile suit-sha256-hmac-a128kw-a128ctr This profile only offers support for symmetric cryptographic algorithms. Algorithm Type Algorithm COSE Key Digest SHA-256 -16 Authentication HMAC-256 5 Key Exchange A128KW Key Wrap -3 Encryption A128CTR -65534

Profile suit-sha256-esp256-ecdh-a128ctr This profile supports asymmetric algorithms for use with constrained devices. Algorithm Type Algorithm COSE Key Digest SHA-256 -16 Authentication ESP256 -9 Key Exchange ECDH-ES + A128KW -29 Encryption A128CTR -65534

Profile suit-sha256-ed25519-ecdh-a128ctr This profile supports an alternative choice of asymmetric algorithms for use with constrained devices. Algorithm Type Algorithm COSE Key Digest SHA-256 -16 Authentication Ed25519 -19 Key Exchange ECDH-ES + A128KW -29 Encryption A128CTR -65534

Profile suit-sha256-esp256-ecdh-a128gcm This profile supports asymmetric algorithms in combination with AEAD algorithms. Algorithm Type Algorithm COSE Key Digest SHA-256 -16 Authentication ESP256 -9 Key Exchange ECDH-ES + A128KW -29 Encryption A128GCM 1

Profile suit-sha256-ed25519-ecdh-chacha-poly This profile also supports asymmetric algorithms with AEAD algorithms but offers an alternative to suit-sha256-esp256-ecdh-a128gcm. Algorithm Type Algorithm COSE Key Digest SHA-256 -16 Authentication Ed25519 -19 Key Exchange ECDH-ES + A128KW -29 Encryption ChaCha20/Poly1305 24

Profile suit-sha256-hsslms-a256kw-a256ctr This profile utilizes a stateful hash-based signature algorithm, namely the Hierarchical Signature System / Leighton-Micali Signature (HSS/LMS), as a unique alternative to the profiles listed above. A note regarding the use of the HSS/LMS: The decision as to how deep the tree is, is a decision that affects authoring tools only (see ). Verification is not affected by the choice of the "W" parameter, but the size of the signature is affected. To support the long lifetimes required by IoT devices, it is RECOMMENDED to use trees with greater height (see ). Algorithm Type Algorithm COSE Key Digest SHA-256 -16 Authentication HSS/LMS -46 Key Exchange A256KW -5 Encryption A256CTR -65532

Security Considerations Payload encryption is used to protect sensitive content such as machine learning models, proprietary algorithms, and personal data . In the context of SUIT, the primary purpose of payload encryption is to defend against unauthorized observation during distribution. By encrypting the payload, confidential information can be safeguarded from eavesdropping. However, encrypting firmware or software update payloads on commodity devices do not constitute an effective cybersecurity defense against targeted attacks. Once an attacker gains access to a device, they may still be able to extract the plaintext payload.

Payload Encryption as Part of a Defense-in-Depth Strategy 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 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.

Use of AES-CTR in Payload Encryption AES-CTR mode with a digest is specified, see . All of the AES-CTR security considerations in apply. See for additional background information.

Operational Considerations While this document focuses on the cryptographic aspects of manifest processing, several operational and manageability considerations are relevant when deploying these profiles in practice.

Profile Support Discovery To enable interoperability of the described profiles, it is important for a manifest author to determine which profiles are supported by a device. Furthermore, it is also important for the author and the distribution system (see ) to know whether firmware for a particular device or family of devices needs to be encrypted, and which key distribution mechanism shall be used. This information can be obtained through: Manual configuration. Device management systems, as described in , which typically maintain metadata about device capabilities and their lifecycle status. These systems may use proprietary or standardized management protocols to expose supported features. LwM2M is one such standardized protocol. The Trusted Execution Environment Provisioning (TEEP) protocol is another option. Capability reporting mechanisms, such as those described in , which define structures that allow a device to communicate supported SUIT features and cryptographic capabilities to a management or attestation entity.

Profile Selection and Control When a device supports multiple algorithm profiles, it is expected that the SUIT manifest author indicates the appropriate profile based on the intended recipient(s) and other policies. The manifest itself indicates which algorithms are used; devices are expected to validate manifests using supported algorithms. Devices do not autonomously choose which profile to apply; rather, they either accept or reject a manifest based on the algorithm profile it uses. There is no protocol-level negotiation of profiles at SUIT manifest processing time. Any dynamic profile selection or configuration is expected to occur as part of other protocols, for example, through device management.

Profile Provisioning and Constraints Provisioning for a given profile may include: Installation of trust anchors for acceptable signers. Distribution of keys used by the content key distribution mechanism (see ). Availability of specific cryptographic libraries or hardware support (e.g., for post-quantum algorithms or AEAD ciphers). Evaluation of the required storage and processing resources for the selected profile. Support for manifest processing capabilities. There may be conditions under which switching to a different algorithm profile is not feasible, such as: Lack of hardware support (e.g., no crypto acceleration). Resource limitations on memory-constrained devices (e.g., insufficient flash or RAM). Deployment policy constraints or regulatory compliance requirements. In such cases, a device management or update orchestration system should take these constraints into account when constructing and distributing manifests.

Logging and Reporting Implementations MAY log failures to process a manifest due to unsupported algorithm profiles or unavailable cryptographic functionality. When supported, such events SHOULD be reported using secure mechanisms, such as those described in , to assist operators in diagnosing update failures or misconfigurations.

IANA Considerations IANA is requested to create a page for "COSE SUIT Algorithm Profiles" within the "Software Update for the Internet of Things (SUIT)" registry group. IANA is also requested to create a registry for "COSE SUIT Algorithm Profiles" within that registry group. While most profile attributes are self-explanatory, the status field warrants a brief explanation. This field can take one of three values: MANDATORY, NOT RECOMMENDED, or OPTIONAL. MANDATORY indicates that the profile is mandatory to implement for manifest authors. NOT RECOMMENDED means that the profile should generally be avoided in new implementations. OPTIONAL suggests that support for the profile is permitted but not required. IANA is requested to add a note that mirrors these status values to the registry. Adding new profiles or updating the status of existing profiles requires Standards Action (). As time progresses, algorithm profiles may loose their MANDATORY status. Then, their status will become either OPTIONAL or NOT RECOMMENDED for new implementations. Likewise, a profile may be transitioned from OPTIONAL to NOT RECOMMENDED. Since it may be impossible to update certain parts of the IoT device firmware in the field, such as first stage bootloaders, support for all relevant algorithms will almost always be required by authoring tools. The initial content of the "COSE SUIT Algorithm Profiles" registry is:

Profile: suit-sha256-hmac-a128kw-a128ctr Profile: suit-sha256-hmac-a128kw-a128ctr Status: MANDATORY Digest: -16 Auth: 5 Key Exchange: -3 Encryption: -65534 Descriptor Array: [-16, 5, -3, -65534] Reference: Section 3.1 of THIS_DOCUMENT

Profile: suit-sha256-esp256-ecdh-a128ctr Profile: suit-sha256-esp256-ecdh-a128ctr Status: MANDATORY Digest: -16 Auth: -9 Key Exchange: -29 Encryption: -65534 Descriptor Array: [-16, -9, -29, -65534] Reference: Section 3.2 of THIS_DOCUMENT

Profile: suit-sha256-ed25519-ecdh-a128ctr Profile: suit-sha256-ed25519-ecdh-a128ctr Status: MANDATORY Digest: -16 Auth: -19 Key Exchange: -29 Encryption: -65534 Descriptor Array: [-16, -19, -29, -65534] Reference: Section 3.3 of THIS_DOCUMENT

Profile: suit-sha256-esp256-ecdh-a128gcm Profile: suit-sha256-esp256-ecdh-a128gcm Status: MANDATORY Digest: -16 Auth: -9 Key Exchange: -29 Encryption: 1 Descriptor Array: [-16, -9, -29, 1] Reference: Section 3.4 of THIS_DOCUMENT

Profile: suit-sha256-ed25519-ecdh-chacha-poly Profile: suit-sha256-ed25519-ecdh-chacha-poly Status: MANDATORY Digest: -16 Auth: -19 Key Exchange: -29 Encryption: 24 Descriptor Array: [-16, -19, -29, 24] Reference: Section 3.5 of THIS_DOCUMENT

Profile: suit-sha256-hsslms-a256kw-a256ctr Profile: suit-sha256-hsslms-a256kw-a256ctr Status: MANDATORY Digest: -16 Auth: -46 Key Exchange: -5 Encryption: -65532 Descriptor Array: [-16, -46, -5, -65532] Reference: Section 3.6 of THIS_DOCUMENT

This document specifies the conventions for using the Hierarchical Signature System (HSS) / Leighton-Micali Signature (LMS) hash-based signature algorithm with the CBOR Object Signing and Encryption (COSE) syntax. The HSS/LMS algorithm is one form of hash-based digital signature; it is described in RFC 8554. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines the CBOR Object Signing and Encryption (COSE) protocol. This specification describes how to create and process signatures, message authentication codes, and encryption using CBOR for serialization. This specification additionally describes how to represent cryptographic keys using CBOR. This document, along with RFC 9053, obsoletes RFC 8152. The Concise Binary Object Representation (CBOR) data format is designed for small code size and small message size. CBOR Object Signing and Encryption (COSE) is specified in RFC 9052 to provide basic security services using the CBOR data format. This document specifies the conventions for using AES-CTR and AES-CBC as content encryption algorithms with COSE. Arm Limited University of Applied Sciences Bonn-Rhein-Sieg Fraunhofer SIT Inria Nordic Semiconductor This specification describes the format of a manifest. A manifest is a bundle of metadata about code/data obtained by a recipient (chiefly the firmware for an Internet of Things (IoT) device), where to find the code/data, the devices to which it applies, and cryptographic information protecting the manifest. Software updates and Trusted Invocation both tend to use sequences of common operations, so the manifest encodes those sequences of operations, rather than declaring the metadata. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. This document proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or JSON. University of Applied Sciences Bonn-Rhein-Sieg Vigil Security, LLC Arm Limited Linaro SECOM CO., LTD. This document specifies techniques for encrypting software, firmware, machine learning models, and personalization data by utilizing the IETF SUIT manifest. Key agreement is provided by ephemeral-static (ES) Diffie-Hellman (DH) and AES Key Wrap (AES-KW). ES-DH uses public key cryptography while AES-KW uses a pre-shared key. Encryption of the plaintext is accomplished with conventional symmetric key cryptography. Arm Limited Fraunhofer SIT The Software Update for the Internet of Things (SUIT) manifest provides a way for many different update and boot workflows to be described by a common format. This specification describes a lightweight feedback mechanism that allows a developer in possession of a manifest to reconstruct the decisions made and actions performed by a manifest processor. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines a set of algorithms that can be used with the CBOR Object Signing and Encryption (COSE) protocol (RFC 9052). This document, along with RFC 9052, obsoletes RFC 8152. Vulnerabilities in Internet of Things (IoT) devices have raised the need for a reliable and secure firmware update mechanism suitable for devices with resource constraints. Incorporating such an update mechanism is a fundamental requirement for fixing vulnerabilities, but it also enables other important capabilities such as updating configuration settings and adding new functionality. In addition to the definition of terminology and an architecture, this document provides the motivation for the standardization of a manifest format as a transport-agnostic means for describing and protecting firmware updates. This document offers guidance for developing privacy considerations for inclusion in protocol specifications. It aims to make designers, implementers, and users of Internet protocols aware of privacy-related design choices. It suggests that whether any individual RFC warrants a specific privacy considerations section will depend on the document's content. Broadcom Amazon Microsoft Openchip & Software Technologies, S.L. This document specifies a protocol that installs, updates, and deletes Trusted Components in a device with a Trusted Execution Environment (TEE). This specification defines an interoperable protocol for managing the lifecycle of Trusted Components. Open Mobile Alliance

Full CDDL The following CDDL snippet 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 .

.and COSE_Messages SUIT_COSE_Profile_ESP256_ECDH_A128CTR = SUIT_COSE_Profile<-9,-65534> .and COSE_Messages SUIT_COSE_Profile_ED25519_ECDH_A128CTR = SUIT_COSE_Profile<-19,-65534> .and COSE_Messages SUIT_COSE_Profile_ESP256_ECDH_A128GCM = SUIT_COSE_Profile<-9,1> .and COSE_Messages SUIT_COSE_Profile_ED25519_ECDH_CHACHA20_POLY1304 = SUIT_COSE_Profile<-19,24> .and COSE_Messages SUIT_COSE_Profile_HSSLMS_A256KW_A256CTR = SUIT_COSE_Profile<-46,-65532> .and COSE_Messages SUIT_COSE_Profile = SUIT_COSE_Messages SUIT_COSE_Messages = SUIT_COSE_Untagged_Message / SUIT_COSE_Tagged_Message SUIT_COSE_Untagged_Message = SUIT_COSE_Sign / SUIT_COSE_Sign1 / SUIT_COSE_Encrypt / SUIT_COSE_Encrypt0 / SUIT_COSE_Mac / SUIT_COSE_Mac0 SUIT_COSE_Tagged_Message = SUIT_COSE_Sign_Tagged / SUIT_COSE_Sign1_Tagged / SUIT_COSE_Encrypt_Tagged / SUIT_COSE_Encrypt0_Tagged<\ encid> / SUIT_COSE_Mac_Tagged / SUIT_COSE_Mac0_Tagged ; 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 = ( protected : bstr .cbor SUIT_COSE_alg_map, unprotected : SUIT_COSE_header_map ) SUIT_COSE_alg_map = { 1 => algid, * int => any } SUIT_COSE_header_map = { * int => any } SUIT_COSE_Sign_Tagged = #6.98(SUIT_COSE_Sign) SUIT_COSE_Sign = [ SUIT_COSE_Profile_Headers, payload : bstr / nil, signatures : [+ SUIT_COSE_Signature] ] SUIT_COSE_Signature = [ SUIT_COSE_Profile_Headers, signature : bstr ] SUIT_COSE_Sign1_Tagged = #6.18(SUIT_COSE_Sign1) SUIT_COSE_Sign1 = [ SUIT_COSE_Profile_Headers, payload : bstr / nil, signature : bstr ] SUIT_COSE_Encrypt_Tagged = #6.96(SUIT_COSE_Encrypt) SUIT_COSE_Encrypt = [ SUIT_COSE_Profile_Headers, ciphertext : bstr / nil, recipients : [+SUIT_COSE_recipient] ] SUIT_COSE_recipient = [ SUIT_COSE_Profile_Headers, ciphertext : bstr / nil, ? recipients : [+SUIT_COSE_recipient] ] SUIT_COSE_Encrypt0_Tagged = #6.16(SUIT_COSE_Encrypt0) SUIT_COSE_Encrypt0 = [ SUIT_COSE_Profile_Headers, ciphertext : bstr / nil, ] SUIT_COSE_Mac_Tagged = #6.97(SUIT_COSE_Mac) SUIT_COSE_Mac = [ SUIT_COSE_Profile_Headers, payload : bstr / nil, tag : bstr, recipients :[+SUIT_COSE_recipient] ] SUIT_COSE_Mac0_Tagged = #6.17(SUIT_COSE_Mac0) SUIT_COSE_Mac0 = [ SUIT_COSE_Profile_Headers, payload : bstr / nil, tag : bstr, ] ]]>

Acknowledgments We would like to specifically thank Henk Birkholz, Mohamed Boucadair, Deb Cooley, Lorenzo Corneo, Linda Dunbar, Russ Housley, Michael B. Jones, Jouni Korhonen, Magnus Nyström, Michael Richardson, and Hannes Tschofenig for their review comments.