Network Working Group O. Steele Internet-Draft Transmute Intended status: Standards Track S. Lasker Expires: 9 January 2025 DataTrails H. Birkholz Fraunhofer SIT 8 July 2024 COSE Hash Envelope draft-steele-cose-hash-envelope-01 Abstract This document defines new COSE header parameters for signaling a payload as an output of a hash function. This mechanism enables faster validation as access to the original payload is not required for signature validation. Additionally, hints of the detached payload's content format and availability are defined providing references to optional discovery mechanisms that can help to find original payload content. About This Document This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://OR13.github.io/draft-steele-cose-hash-envelope/draft-steele- cose-hash-envelope.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-steele-cose-hash- envelope/. Discussion of this document takes place on the CBOR Object Signing and Encryption Working Group mailing list (mailto:cose@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/cose/. Subscribe at https://www.ietf.org/mailman/listinfo/cose/. Source for this draft and an issue tracker can be found at https://github.com/OR13/draft-steele-cose-hash-envelope. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Steele, et al. Expires 9 January 2025 [Page 1] Internet-Draft COSE Hash Envelope July 2024 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 https://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 9 January 2025. Copyright Notice Copyright (c) 2024 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 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 extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Attached Payload . . . . . . . . . . . . . . . . . . . . 3 1.2. Detached Payload . . . . . . . . . . . . . . . . . . . . 3 1.3. Hashed Payload . . . . . . . . . . . . . . . . . . . . . 3 2. Header Parameters . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Signed Hash Envelopes Example . . . . . . . . . . . . . . 4 2.2. Protected Header . . . . . . . . . . . . . . . . . . . . 5 3. Encrypted Hashes . . . . . . . . . . . . . . . . . . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6 4.1. Choice of Hash Function . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5.1. Requirements Notation . . . . . . . . . . . . . . . . . . 6 5.2. COSE Header Algorithm Parameters . . . . . . . . . . . . 6 5.3. Named Information Hash Algorithm Registry . . . . . . . . 7 6. Normative References . . . . . . . . . . . . . . . . . . . . 7 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Steele, et al. Expires 9 January 2025 [Page 2] Internet-Draft COSE Hash Envelope July 2024 1. Introduction COSE defined detached payloads in Section 2 of [RFC9052], using nil as the payload. In order to verify a signature over a detached payload, the verifier must have access to the payload content. Storing a hash of the content allows for small signature envelopes, that are easy to transport and verify independently. Additional hints in the protected header ensure cryptographic agility for the hashing & signing algorithms, and discoverability for the original content which could be prohibitively large to move over a network. 1.1. Attached Payload COSE_sign1 envelope with an attached payload, providing for signature validation. 18( / COSE Sign 1 / [ h'a4013822...3a616263', / Protected / {} / Unprotected / h'317cedc7...c494e772', / Payload / h'15280897...93ef39e5' / Signature / ] ) 1.2. Detached Payload COSE_sign1 envelope with a detached payload (nil), which is compact but the payload must be distributed out of band to validate the signature 18( / COSE Sign 1 / [ h'a4013822...3a616263', / Protected / {} / Unprotected / nil, / Detached Payload / h'15280897...93ef39e5' / Signature / ] ) 1.3. Hashed Payload A hashed payload functions equivalently to an attached payload, with the benefits of being compact in size and providing the ability to validate the signature. Steele, et al. Expires 9 January 2025 [Page 3] Internet-Draft COSE Hash Envelope July 2024 18( / COSE Sign 1 / [ h'a4013822...3a616263', / Protected / {} / Unprotected / h'935b5a91...e18a588a', / Payload / h'15280897...93ef39e5' / Signature / ] ) 2. Header Parameters To represent a hash of a payload, the following headers are defined: TBD_1: the hash algorithm used to generate the hash of the payload TBD_2: the content type of the payload the hash represents TBD_3: an identifier enabling a verifier to retrieve the full payload preimage. 2.1. Signed Hash Envelopes Example Steele, et al. Expires 9 January 2025 [Page 4] Internet-Draft COSE Hash Envelope July 2024 Hash_Envelope_Protected_Header = { ; Cryptographic algorithm to use ? &(alg: 1) => int, ; Type of the envelope ? &(typ: 16) => int / tstr ; Hash algorithm used to produce the payload from content ; -16 for SHA-256, ; See https://www.iana.org/assignments/cose/cose.xhtml &(payload_hash_alg: TBD_1) => int ; Content type of the preimage ; (content to be hashed) of the payload ; 50 for application/json, ; See https://datatracker.ietf.org/doc/html/rfc7252#section-12.3 &(payload_preimage_content_type: TBD_2) => int ; Location the content of the hashed payload is stored ; For example: ; storage.example/244f...9c19 ? &(payload_location: TBD_3) => tstr * int => any } Hash_Envelope_Unprotected_Header = { * int => any } Hash_Envelope_as_COSE_Sign1 = [ protected : bstr .cbor Hash_Envelope_Protected_Header, unprotected : Hash_Envelope_Unprotected_Header, payload: bstr / nil, signature : bstr ] Hash_Envelope = #6.18(Hash_Envelope_as_COSE_Sign1) 2.2. Protected Header 16 (typ), TBD_1 (payload hash alg) and TBD_2 (content type of the preimage of the payload) MUST be present in the protected header and MUST NOT be present in the unprotected header. TBD_3 (payload_location) MAY be added to the protected header and MUST NOT be presented in the unprotected header. For example: Steele, et al. Expires 9 January 2025 [Page 5] Internet-Draft COSE Hash Envelope July 2024 { / alg : ES384 / 1: -35, / kid / 4: h'75726e3a...32636573', / typ / 16: application/hashed+cose / payload_hash_alg sha-256 / TBD_1: 1 / payload_preimage_content_type / TBD_2: application/jwk+json / payload_location / TBD_3 : storage.example/244f...9c19 } 3. Encrypted Hashes Should we define this? 4. Security Considerations TODO Security 4.1. Choice of Hash Function It is RECOMMENDED to align the strength of the chosen hash function to the strength of the chosen signature algorithm. For example, when signing with ECDSA using P-256 and SHA-256, use SHA-256 to hash the payload. 5. IANA Considerations 5.1. Requirements Notation 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. 5.2. COSE Header Algorithm Parameters * Name: payload hash algorithm * Label: TBD_1 * Value type: int * Value registry: https://www.iana.org/assignments/named- information/named-information.xhtml * Description: Hash algorithm used to produce the payload. Steele, et al. Expires 9 January 2025 [Page 6] Internet-Draft COSE Hash Envelope July 2024 5.3. Named Information Hash Algorithm Registry * Name: SHAKE256 * Label: TBD_2 * Value type: int * Value registry: https://www.iana.org/assignments/named- information/named-information.xhtml * Description: SHAKE256 a described in https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.202.pdf * Name: ASCON128 * Label: TBD_3 * Value type: int * Value registry: https://www.iana.org/assignments/named- information/named-information.xhtml * Description: ASCON128 a described in https://csrc.nist.gov/CSRC/media/Projects/lightweight- cryptography/documents/round-2/spec-doc-rnd2/ascon-spec-round2.pdf 6. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE): Structures and Process", STD 96, RFC 9052, DOI 10.17487/RFC9052, August 2022, . Acknowledgments The following individuals provided input into the final form of the document: Carsten Bormann, Henk Birkholz, Antoine Delignat-Lavaud, Cedric Fournet. Steele, et al. Expires 9 January 2025 [Page 7] Internet-Draft COSE Hash Envelope July 2024 Authors' Addresses Orie Steele Transmute Email: orie@transmute.industries Steve Lasker DataTrails Email: steve.lasker@datatrails.ai Henk Birkholz Fraunhofer SIT Rheinstrasse 75 64295 Darmstadt Germany Email: henk.birkholz@ietf.contact Steele, et al. Expires 9 January 2025 [Page 8]