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.¶
-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 /
- ]
-)
-¶
-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 /
- ]
-)
-¶
-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.¶
-
-18( / COSE Sign 1 /
- [
- h'a4013822...3a616263', / Protected /
- {} / Unprotected /
- h'935b5a91...e18a588a', / Payload /
- h'15280897...93ef39e5' / Signature /
- ]
-)
-¶
-When producing COSE_sign1 with remote signing services, such as a signing api exposed over HTTPS and backed by an HSM, the "ToBeSigned" bytes as described in Section 4.4 of [RFC9052] need to be transmitted to the HSM in order to be signed.¶
+Some signature algorithms such as ES256 or ES384 allow the "ToBeSigned" to be hashed on the client and sent to the server along with metadata in order to produce a signature.¶
+Other signature algorithms such as EdDSA with Ed25519, or ML-DSA do not expose such a capability.¶
+By producing the "ToBeSigned" on the client, and ensuring that the payload is always a hashed value, the total size of the message to be sent to the servce for signing is constrained.¶
+It is still possible for the protected header to be large, but the payload will always be of a fixed size, associated with the hash function chosen.¶
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.¶
+The terms COSE, CDDL, and EDN are defined in [RFC9052], [RFC8610], [I-D.draft-ietf-cbor-edn-literals] respectively.¶
To represent a hash of a payload, the following headers are defined:¶
-the hash algorithm used to generate the hash of the payload¶
+To represent a hash of a payload, the following headers are defined:¶
+the hash algorithm used to produce the payload.¶
the content type of the payload the hash represents¶
+the content type of the bytes that were hashed to produce the payload.¶
an identifier enabling a verifier to retrieve the full payload preimage.¶
+an identifier enabling a verifier to retrieve the bytes which were hashed to produce the payload.¶
Hash_Envelope_Protected_Header = {
; Cryptographic algorithm to use
@@ -1326,11 +1302,11 @@
; storage.example/244f...9c19
? &(payload_location: TBD_3) => tstr
- * int => any
+ * int / tstr => any
}
Hash_Envelope_Unprotected_Header = {
- * int => any
+ * int / tstr => any
}
Hash_Envelope_as_COSE_Sign1 = [
@@ -1341,172 +1317,300 @@
]
Hash_Envelope = #6.18(Hash_Envelope_as_COSE_Sign1)
-
¶
+¶
Label 16 (typ) MAY be used to assign a content format or media type to the entire hash envelope.¶
Label TBD_1 (payload hash alg) MUST be present in the protected header and MUST NOT be present in the unprotected header.¶
Label TBD_2 (content type of the preimage of the payload) MAY be present in the protected header or unprotected header.¶
Label TBD_3 (payload_location) MAY be added to the protected header and MUST NOT be presented in the unprotected header.¶
Label 3 (content_type) MUST NOT be present in the protected or unprotected headers.¶
Label 3 is easily confused with label TBD_2 payload_preimage_content_type.
+The difference between content_type (3) and payload_preimage_content_type (TBD2) is content_type is used to identify the content format associated with payload, whereas payload_preimage_content_type is used to identify the content format of the bytes which are hashed to produce the payload.¶
Label 16 (typ), label TBD_1 (payload hash alg) and label 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.¶
Label TBD_3 (payload_location) MAY be added to the protected header and MUST NOT be presented in the unprotected header.¶
Label 3 (content_type) MUST NOT be used as it is easily confused with label TBD_2 payload_preimage_content_type).¶
For example:¶
-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.¶
+
-{
- / 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
-}
-¶
-In this example, the sha256 hash algorithm (-16) is used to hash the payload, which is of content type "application/example+json". +The full payload is located at "https://storage.example/244f...9c19". +The COSE_sign1 is of type "application/example+cose". +The sha256 hash is signed with ES384 which starts by taking the sha384 hash of the payload (which is a sha256 hash).¶
The cose headers defined in this document SHOULD NOT be used in unprotected or protected headers associated with COSE_Encrypt.¶
+When present in COSE_Encrypt, the header parameters registered in this document leak information about the ciphertext. +These parameters SHOULD NOT be present in COSE_Encrypt headers unless this disclosure is acceptable.¶
TODO Security¶
+TODO Security¶
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.¶
+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.¶
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.¶
-IANA is requested to add the following entries to the COSE Header Algorithm Parameters Registry.¶
+Name: payload hash algorithm¶
+Name: payload_hash_alg¶
Label: TBD_1¶
+Label: TBD_1¶
Value type: int¶
+Value type: int¶
Value registry: https://www.iana.org/assignments/named-information/named-information.xhtml¶
+Value registry: https://www.iana.org/assignments/cose/cose.xhtml#algorithms¶
Description: Hash algorithm used to produce the payload.¶
+Description: Hash algorithm used to produce the payload.¶
Name: SHAKE256¶
+Name: payload_preimage_content_type¶
Label: TBD_2¶
+Label: TBD_2¶
Value type: int¶
+Value type: int¶
Value registry: https://www.iana.org/assignments/named-information/named-information.xhtml¶
+Value registry: https://www.iana.org/assignments/core-parameters/core-parameters.xhtml#content-formats¶
Description: SHAKE256 a described in https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.202.pdf¶
+Description: The content format associated with the bytes that were hashed to produce the payload.¶
Name: ASCON128¶
+Name: payload_location¶
Label: TBD_3¶
+Label: TBD_3¶
Value type: int¶
+Value type: tstr¶
Value registry: https://www.iana.org/assignments/named-information/named-information.xhtml¶
+Value registry: none¶
Description: ASCON128 a described in https://csrc.nist.gov/CSRC/media/Projects/lightweight-cryptography/documents/round-2/spec-doc-rnd2/ascon-spec-round2.pdf¶
+Description: A string or URI as a hint for the location of the payload¶
Note to RFC Editor: Please remove this section as well as references to [BCP205] before AUTH48.¶
+This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [BCP205]. +The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. +Please note that the listing of any individual implementation here does not imply endorsement by the IETF. +Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. +This is not intended as, and must not be construed to be, a catalog of available implementations or their features. +Readers are advised to note that other implementations may exist.¶
+According to [BCP205], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. +It is up to the individual working groups to use this information as they see fit".¶
+Organization: Transmute Industries Inc¶
+Name: https://github.com/transmute-industries/transmute¶
+Description: A command line tool and GitHub action for securing software artifacts in GitHub workflows.¶
+Maturity: Prototype¶
+Coverage: The current version ('main') implements this specification and demonstrates hash envelope signing with Azure Key Vault and Google Cloud KMS in addition to supporting local keys.¶
+License: Apache-2.0¶
+Implementation Experience: No interop testing has been done yet. The code works as proof of concept, but is not yet production ready.¶
+Contact: Orie Steele (orie@transmute.industries)¶
+Organization: DataTrails¶
+Name: https://github.com/datatrails/scitt-action¶
+Description: A GitHub Action for registering statements about artifacts on a transparency service.¶
+Maturity: Preview¶
+Coverage: The current version ('main') implements this specification and demonstrates hash envelope signing with DataTrails implementation of SCITT.¶
+License: MIT¶
+Implementation Experience: Interop testing has been performed between DigiCert and DataTrails. The code works as proof of concept, but is not yet production ready.¶
+Contact: Steve Lasker (steve.lasker@datatrails.ai)¶
+Organization: DigiCert¶
+Name: https://github.com/digicert/scitt-action¶
+Description: A GitHub Action for remote signing and registering statements about artifacts on a transparency service.¶
+Maturity: Preview¶
+Coverage: The current version ('main') implements this specification and demonstrates hash envelope signing with DigiCert Software Trust Manager.¶
+License: MIT¶
+Implementation Experience: Interop testing has been performed between DigiCert and DataTrails. The code works as proof of concept, but is not yet production ready.¶
+Contact: Corey Bonnell (Corey.Bonnell@digicert.com>)¶
+The following individuals provided input into the final form of the document: Carsten Bormann, Henk Birkholz, Antoine Delignat-Lavaud, Cedric Fournet.¶
+The following individuals provided input into the final form of the document: Carsten Bormann, Henk Birkholz, Antoine Delignat-Lavaud, Cedric Fournet.¶