]> Entrust Limited

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Entrust Limited

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OpenCA Labs

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Cisco Systems

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Security LAMPS Internet-Draft This document defines combinations of ML-DSA in hybrid with traditional algorithms RSA-PKCS#1v1.5, RSA-PSS, ECDSA, Ed25519, and Ed448. These combinations are tailored to meet security best practices and regulatory requirements. Composite ML-DSA is applicable in any application that uses X.509, PKIX, and CMS data structures and protocols that accept ML-DSA, but where the operator wants extra protection against breaks or catastrophic bugs in ML-DSA. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the LAMPS Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Changes in -03 Interop-affecting changes:

• Compacted CompositeSignaturePrivateKey to SEQUENCE SIZE (2) OF OCTET STRING instead of OneAsymmetricKey to remove redundancy
• Added support for the ML-DSA context String, and use the Composite Domain as the context for the underlying ML-DSA component algorithm.
• Added Pre-Hash and Pure modes and changed the Message format to align with FIPS-204. This breaks backwards compatibility with all previous versions.
• Updated the OID table for new Pre-Hash OIDs and added them to the IANA section.
• Updated Use in CMS section to reflect content is hashed and pure Composite ML-DSA should be used.

Editorial changes:

• Added the ASN.1 encodings for the component public keys and signature algorithm identifiers
• ASN.1 Module changes:
  • Renamed the module from Composite-Signatures-2023 -> Composite-MLDSA-2024
  • Simplified the ASN.1 module to make it more compiler-friendly (thanks Carl!) -- should not affect wire encodings.
• Updated Security Considerations about Non-separability, EUF-CMA and key reuse.

Introduction The advent of quantum computing poses a significant threat to current cryptographic systems. Traditional cryptographic algorithms such as RSA, Diffie-Hellman, DSA, and their elliptic curve variants are vulnerable to quantum attacks. During the transition to post-quantum cryptography (PQC), there is considerable uncertainty regarding the robustness of both existing and new cryptographic algorithms. While we can no longer fully trust traditional cryptography, we also cannot immediately place complete trust in post-quantum replacements until they have undergone extensive scrutiny and real-world testing to uncover and rectify potential implementation flaws. Unlike previous migrations between cryptographic algorithms, the decision of when to migrate and which algorithms to adopt is far from straightforward. Even after the migration period, it may be advantageous for an entity's cryptographic identity to incorporate multiple public-key algorithms to enhance security. Cautious implementers may opt to combine cryptographic algorithms in such a way that an attacker would need to break all of them simultaneously to compromise the protected data. These mechanisms are referred to as Post-Quantum/Traditional (PQ/T) Hybrids . Certain jurisdictions are already recommending or mandating that PQC lattice schemes be used exclusively within a PQ/T hybrid framework. The use of Composite scheme provides a straightforward implementation of hybrid solutions compatible with (and advocated by) some governments and cybersecurity agencies . Composite ML-DSA is applicable in any application that would otherwise use ML-DSA, but wants the protection against breaks or catastrophic bugs in ML-DSA.

Conventions and 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 when, and only when, they appear in all capitals, as shown here. These words may also appear in this document in lower case as plain English words, absent their normative meanings. This document is consistent with the terminology defined in . In addition, the following terminology is used throughout this document: ALGORITHM: The usage of the term "algorithm" within this document generally refers to any function which has a registered Object Identifier (OID) for use within an ASN.1 AlgorithmIdentifier. This loosely, but not precisely, aligns with the definitions of "cryptographic algorithm" and "cryptographic scheme" given in . BER: Basic Encoding Rules (BER) as defined in . CLIENT: Any software that is making use of a cryptographic key. This includes a signer, verifier, encrypter, decrypter. This is not meant to imply any sort of client-server relationship between the communicating parties. DER: Distinguished Encoding Rules as defined in . PKI: Public Key Infrastructure, as defined in . PUBLIC / PRIVATE KEY: The public and private portion of an asymmetric cryptographic key, making no assumptions about which algorithm. SIGNATURE: A digital cryptographic signature, making no assumptions about which algorithm.

Composite Design Philosophy defines composites as:

• Composite Cryptographic Element: A cryptographic element that incorporates multiple component cryptographic elements of the same type in a multi-algorithm scheme.

Composite keys, as defined here, follow this definition and should be regarded as a single key that performs a single cryptographic operation such as key generation, signing, verifying, encapsulating, or decapsulating -- using its internal sequence of component keys as if they form a single key. This generally means that the complexity of combining algorithms can and should be handled by the cryptographic library or cryptographic module, and the single composite public key, private key, ciphertext and signature can be carried in existing fields in protocols such as PKCS#10 , CMP , X.509 , CMS , and the Trust Anchor Format . In this way, composites achieve "protocol backwards-compatibility" in that they will drop cleanly into any protocol that accepts an analogous single-algorithm cryptographic scheme without requiring any modification of the protocol to handle multiple algorithms.

Overview of the Composite ML-DSA Signature Scheme Composite schemes are defined as cryptographic primitives that consist of three algorithms:

• KeyGen() -> (pk, sk): A probabilistic key generation algorithm, which generates a public key pk and a secret key sk.
• Sign(sk, Message) -> (signature): A signing algorithm which takes as input a secret key sk and a Message, and outputs a signature
• Verify(pk, Message, signature) -> true or false: A verification algorithm which takes as input a public key, a Message, and a signature and outputs true if the signature verifies correctly. Thus it proves the Message was signed with the secret key associated with the public key and verifies the integrity of the Message. If the signature and public key cannot verify the Message, it returns false.

A composite signature allows the security properties of the two underlying algorithms to be combined via standard signature operations Sign() and Verify(). This specification uses the Post-Quantum signature scheme ML-DSA as specified in and . For Traditional signature schemes, this document uses the RSA PKCS#1v1.5 and RSA-PSS algorithms defined in , the Elliptic Curve Digital Signature Algorithm ECDSA scheme defined in section 6 of , and Ed25519 / Ed448 which are defined in . A simple "signature combiner"function which prepends a domain separator value specific to the composite algorithm is used to bind the two component signatures to the composite algorithm and achieve weak non-separablity.

Pure vs Pre-hashed modes In NIST defined ML-DSA to have both pure and pre-hashed signing modes, referred to as "ML-DSA" and "HashML-DSA" respectively. Following this, this document defines "Composite-ML-DSA" and "HashComposite-ML-DSA" which mirror the external functions defined in .

Composite ML-DSA Functions

Key Generation To generate a new keypair for Composite schemes, the KeyGen() -> (pk, sk) function is used. The KeyGen() function calls the two key generation functions of the component algorithms for the Composite keypair in no particular order. Multi-process or multi-threaded applications might choose to execute the key generation functions in parallel for better key generation performance. The following process is used to generate composite keypair values:

Composite KeyGen(pk, sk) (pk, sk) Explicit inputs: None Implicit inputs: ML-DSA A placeholder for the specific ML-DSA algorithm and parameter set to use, for example, could be "ML-DSA-65". Trad A placeholder for the specific traditional algorithm and parameter set to use, for example "RSASA-PSS" or "Ed25519". Output: (pk, sk) The composite keypair. Key Generation Process: 1. Generate component keys (mldsaPK, mldsaSK) = ML-DSA.KeyGen() (tradPK, tradSK) = Trad.KeyGen() 2. Check for component key gen failure if NOT (mldsaPK, mldsaSK) or NOT (tradPK, tradSK): output "Key generation error" 3. Encode the component keys into composite structures pk = CompositeSignaturePublicKey(mldsaPK, tradPK) sk = CompositeSignaturePrivateKey(mldsaSK, tradSK) 4. Output the composite keys return (pk, sk) ]]>

The structures CompositeSignaturePublicKey and CompositeSignaturePrivateKey are described in and respectively and are used here as placeholders since implementations MAY use their own internal key representations in cases where interoperability is not required. In order to ensure fresh keys, the key generation functions MUST be executed for both component algorithms. Compliant parties MUST NOT use or import component keys that are used in other contexts, combinations, or by themselves as keys for standalone algorithm use. For more details on the security considerations around key reuse, see section . Note that in step 2 above, both component key generation processes are invoked, and no indication is given about which one failed. This SHOULD be done in a timing-invariant way to prevent side-channel attackers from learning which component algorithm failed.

Pure Signature Mode This mode mirrors HashML-DSA defined in Sections 5.2 and 5.3 of . In the pure mode the Domain separator value is concatenated with the length of the context in bytes, the context, and the message to be signed. After that, the signature process for each component algorithm is invoked and the values are then placed in the CompositeSignatureValue structure defined in . A composite signature's value MUST include two signature components and MUST be in the same order as the components from the corresponding signing key.

Composite-ML-DSA.Sign This mode mirrors ML-DSA.Sign(sk, M, ctx) defined in Algorithm 2 in Section 5.2 of .

Composite-ML-DSA.Sign(sk, M, ctx) (signature) Explicit inputs: sk Composite private key consisting of signing private keys for each component. M The Message to be signed, an octet string. ctx The Message context string, which defaults to the empty string. Implicit inputs: ML-DSA A placeholder for the specific ML-DSA algorithm and parameter set to use, for example, could be "ML-DSA-65". Trad A placeholder for the specific ML-DSA algorithm and parameter set to use, for example "RSASA-PSS with id-sha256" or "Ed25519". Domain Domain separator value for binding the signature to the Composite OID. See section on Domain Separators below. Output: signature The composite signature, a CompositeSignatureValue. Signature Generation Process: 1. If |ctx| > 255: return error 2. Compute the Message M'. M' = Domain || len(ctx) || ctx || M 3. Separate the private key into component keys. (mldsaSK, tradSK) = sk 4. Generate the 2 component signatures independently, by calculating the signature over M' according to their algorithm specifications. mldsaSig = ML-DSA.Sign( mldsaSK, M', ctx=Domain ) tradSig = Trad.Sign( tradSK, M' ) 5. If either ML-DSA.Sign() or Trad.Sign() return an error, then this process must return an error. if NOT mldsaSig or NOT tradSig: output "Signature generation error" 6. Encode each component signature into a CompositeSignatureValue. signature := CompositeSignatureValue(mldsaSig, tradSig) 7. Output signature return signature ]]>

It is possible to use component private keys stored in separate software or hardware keystores. Variations in the process to accommodate particular private key storage mechanisms are considered to be conformant to this document so long as it produces the same output and error handling as the process sketched above. Note that in step 5 above, both component signature processes are invoked, and no indication is given about which one failed. This SHOULD be done in a timing-invariant way to prevent side-channel attackers from learning which component algorithm failed.

Composite-ML-DSA.Verify This mode mirrors ML-DSA.Verify(pk, M, signature, ctx) defined in Algorithm 3 in Section 5.3 of . Compliant applications MUST output "Valid signature" (true) if and only if all component signatures were successfully validated, and "Invalid signature" (false) otherwise.

Composite-ML-DSA.Verify(pk, Message, signature, Context) 255 return error 2. Separate the keys and signatures (pk1, pk2) = pk (s1, s2) = signature If Error during Desequencing, or if any of the component keys or signature values are not of the correct key type or length for the given component algorithm then output "Invalid signature" and stop. 3. Compute the Message M'. M' = Domain || len(ctx) || ctx || M 4. Check each component signature individually, according to its algorithm specification. If any fail, then the entire signature validation fails. if not ML-DSA.Verify( pk1, M', s1, ctx=Domain) then output "Invalid signature" if not Trad.Verify( pk2, M', s2) then output "Invalid signature" if all succeeded, then output "Valid signature" ]]>

Note that in step 4 above, the function fails early if the first component fails to verify. Since no private keys are involved in a signature verification, there are no timing attacks to consider, so this is ok.

PreHash-Signature Mode This mode mirrors HashML-DSA defined in Section 5.4 of . In the pre-hash mode the Domain separator is concatenated with the length of the context in bytes, the context, an additional DER encoded value that represents the OID of the Hash function and finally the hash of the message to be signed. After that, the signature process for each component algorithm is invoked and the values are then placed in the CompositeSignatureValue structure defined in . A composite signature's value MUST include two signature components and MUST be in the same order as the components from the corresponding signing key.

HashComposite-ML-DSA-Sign signature mode This mode mirrors HashML-DSA.Sign(sk, M, ctx, PH) defined in Section 5.4.1 of . In the pre-hash mode the Domain separator is concatenated with the length of the context in bytes, the context, an additional DER encoded value that indicates which Hash function was used for the pre-hash and finally the pre-hashed message PH(M).

HashComposite-ML-DSA.Sign(sk, M, ctx, PH) (signature) Explicit inputs: sk Composite private key consisting of signing private keys for each component. M The Message to be signed, an octet string. ctx The Message context string, which defaults to the empty string PH The Message Digest Algorithm for pre-hashing. See section on pre-hashing the message below. Implicit inputs: ML-DSA A placeholder for the specific ML-DSA algorithm and parameter set to use, for example, could be "ML-DSA-65". Trad A placeholder for the specific ML-DSA algorithm and parameter set to use, for example "RSASA-PSS with id-sha256" or "Ed25519". Domain Domain separator value for binding the signature to the Composite OID. See section on Domain Separators below. HashOID The DER Encoding of the Object Identifier of the PreHash algorithm (PH) which is passed into the function. Output: signature The composite signature, a CompositeSignatureValue. Signature Generation Process: 1. If |ctx| > 255: return error 2. Compute the Message format M'. M' := Domain || len(ctx) || ctx || HashOID || PH(M) 3. Separate the private key into component keys. (mldsaSK, tradSK) = sk 4. Generate the 2 component signatures independently, by calculating the signature over M' according to their algorithm specifications. mldsaSig = ML-DSA.Sign( mldsaSK, M', ctx=Domain ) tradSig = Trad.Sign( tradSK, M' ) 5. If either ML-DSA.Sign() or Trad.Sign() return an error, then this process must return an error. if NOT mldsaSig or NOT tradSig: output "Signature generation error" 6. Encode each component signature into a CompositeSignatureValue. signature := CompositeSignatureValue(mldsaSig, tradSig) 7. Output signature return signature ]]>

It is possible to use component private keys stored in separate software or hardware keystores. Variations in the process to accommodate particular private key storage mechanisms are considered to be conformant to this document so long as it produces the same output and error handling as the process sketched above. Note that in step 5 above, both component signature processes are invoked, and no indication is given about which one failed. This SHOULD be done in a timing-invariant way to prevent side-channel attackers from learning which component algorithm failed.

HashComposite-ML-DSA-Verify This mode mirrors HashML-DSA.Verify(pk, M, signature, ctx, PH) defined in Section 5.4.1 of . Compliant applications MUST output "Valid signature" (true) if and only if all component signatures were successfully validated, and "Invalid signature" (false) otherwise.

HashComposite-ML-DSA.Verify(pk, M, signature, ctx, PH) 255 return error 2. Separate the keys and signatures (pk1, pk2) = pk (s1, s2) = signature If Error during Desequencing, or if any of the component keys or signature values are not of the correct key type or length for the given component algorithm then output "Invalid signature" and stop. 3. Compute a Hash of the Message. M' = Domain || len(ctx) || ctx || HashOID || PH(M) 4. Check each component signature individually, according to its algorithm specification. If any fail, then the entire signature validation fails. if not ML-DSA.Verify( pk1, M', s1, ctx=Domain ) then output "Invalid signature" if not Trad.Verify( pk2, M', s2 ) then output "Invalid signature" if all succeeded, then output "Valid signature" ]]>

Note that in step 4 above, the function fails early if the first component fails to verify. Since no private keys are involved in a signature verification, there are no timing attacks to consider, so this is ok.

Composite Key Structures In order to form composite public keys and signature values, we define ASN.1-based composite encodings such that these structures can be used as a drop-in replacement for existing public key and signature fields such as those found in PKCS#10 , CMP , X.509 , CMS .

CompositeSignaturePublicKey The wire encoding of a Composite ML-DSA public key is: Since RSA and ECDSA component public keys are themselves in a DER encoding, the following ASN.1 structures show the internal structure of the various public key types used in this specification: id-raw-key is defined by this document. It signifies that the public key has no ASN.1 wrapping and the raw bits are placed here according to the encoding of the underlying algorithm specification. In some situations and protocols, the key might be wrapped in ASN.1 or may have some other additional decoration or encoding. If so, such wrapping MUST be removed prior to encoding the key itself as a BIT STRING. For use with this document, ML-DSA keys MUST be be the raw BIT STRING representation as specified in and Edwards Curve keys MUST be the raw BIT STRING representation as specified in . Some applications may need to reconstruct the SubjectPublicKeyInfo objects corresponding to each component public key. or in provides the necessary mapping between composite and their component algorithms for doing this reconstruction. This also motivates the design choice of SEQUENCE OF BIT STRING instead of SEQUENCE OF OCTET STRING; using BIT STRING allows for easier transcription between CompositeSignaturePublicKey and SubjectPublicKeyInfo. When the CompositeSignaturePublicKey must be provided in octet string or bit string format, the data structure is encoded as specified in . Component keys of a CompositeSignaturePublicKey MUST NOT be used in any other type of key or as a standalone key. For more details on the security considerations around key reuse, see section . The following ASN.1 Information Object Class is defined to allow for compact definitions of each composite algorithm, leading to a smaller overall ASN.1 module. As an example, the public key type id-MLDSA44-ECDSA-P256 is defined as: The full set of key types defined by this specification can be found in the ASN.1 Module in .

CompositeSignaturePrivateKey When a Composite ML-DSA private key is to be exported from a cryptographic module, it uses an analogous definition to the public keys: Each element of the CompositeSignaturePrivateKey Sequence is an OCTET STRING according to the encoding of the underlying algorithm specification and will decode into the respective private key structures in an analogous way to the public key structures defined in . This document does not provide helper classes for private keys. The PrivateKey for each component algorithm MUST be in the same order as defined in . Use cases that require an interoperable encoding for composite private keys will often need to place a CompositeSignaturePrivateKey inside a OneAsymmetricKey structure defined in , such as when private keys are carried in PKCS #12 , CMP or CRMF . The definition of OneAsymmetricKey is copied here for convenience: When a CompositeSignaturePrivateKey is conveyed inside a OneAsymmetricKey structure (version 1 of which is also known as PrivateKeyInfo) , the privateKeyAlgorithm field SHALL be set to the corresponding composite algorithm identifier defined according to and its parameters field MUST be absent. The privateKey field SHALL contain the CompositeSignaturePrivateKey, and the publicKey field remains OPTIONAL. If the publicKey field is present, it MUST be a CompositeSignaturePublicKey. Some applications may need to reconstruct the OneAsymmetricKey objects corresponding to each component private key. provides the necessary mapping between composite and their component algorithms for doing this reconstruction. Component keys of a CompositeSignaturePrivateKey MUST NOT be used in any other type of key or as a standalone key. For more details on the security considerations around key reuse, see section .

Encoding Rules Many protocol specifications will require that the composite public key and composite private key data structures be represented by an octet string or bit string. When an octet string is required, the DER encoding of the composite data structure SHALL be used directly. When a bit string is required, the octets of the DER encoded composite data structure SHALL be used as the bits of the bit string, with the most significant bit of the first octet becoming the first bit, and so on, ending with the least significant bit of the last octet becoming the last bit of the bit string. In the interests of simplicity and avoiding compatibility issues, implementations that parse these structures MAY accept both BER and DER.

Key Usage Bits When any of the Composite ML-DSA AlgorithmIdentifier appears in the SubjectPublicKeyInfo field of an X.509 certificate , the key usage certificate extension MUST only contain only signing-type key usages. The normal keyUsage rules for signing-type keys from apply, and are reproduced here for completeness. For Certification Authority (CA) certificates that carry a composite public key, any combination of the following values MAY be present and any other values MUST NOT be present: For End Entity certificates, any combination of the following values MAY be present and any other values MUST NOT be present: Composite ML-DSA keys MUST NOT be used in a "dual usage" mode because even if the traditional component key supports both signing and encryption, the post-quantum algorithms do not and therefore the overall composite algorithm does not.

Composite Signature Structures

sa-CompositeSignature The ASN.1 algorithm object for a composite signature is:

CompositeSignatureValue The output of a Composite ML-DSA algorithm is the DER encoding of the following structure: The CompositeSignatureValue is the DER encoing of a SEQUENCE of the signature values from the underlying component algorithms. It is represented in ASN.1 as follows: The order of the component signature values is the same as the order defined in .

Algorithm Identifiers This table summarizes the list of Composite ML-DSA algorithms and lists the OID and the two component algorithms. Domain separator values are defined below in . EDNOTE: these are prototyping OIDs to be replaced by IANA. <CompSig>.1 is equal to 2.16.840.1.114027.80.8.1.1

Composite-ML-DSA Algorithm Identifiers Pure Composite-ML-DSA Signature public key types: Pure ML-DSA Composite Signature Algorithms

Composite Signature AlgorithmID	OID	First AlgorithmID	Second AlgorithmID
id-MLDSA44-RSA2048-PSS	<CompSig>.21	id-ML-DSA-44	id-RSASA-PSS with id-sha256
id-MLDSA44-RSA2048-PKCS15	<CompSig>.22	id-ML-DSA-44	sha256WithRSAEncryption
id-MLDSA44-Ed25519	<CompSig>.23	id-ML-DSA-44	id-Ed25519
id-MLDSA44-ECDSA-P256	<CompSig>.24	id-ML-DSA-44	ecdsa-with-SHA256 with secp256r1
id-MLDSA65-RSA3072-PSS	<CompSig>.26	id-ML-DSA-65	id-RSASA-PSS with id-sha256
id-MLDSA65-RSA3072-PKCS15	<CompSig>.27	id-ML-DSA-65	sha256WithRSAEncryption
id-MLDSA65-RSA4096-PSS	<CompSig>.34	id-ML-DSA-65	id-RSASA-PSS with id-sha384
id-MLDSA65-RSA4096-PKCS15	<CompSig>.35	id-ML-DSA-65	sha384WithRSAEncryption
id-MLDSA65-ECDSA-P384	<CompSig>.28	id-ML-DSA-65	ecdsa-with-SHA384 with secp384r1
id-MLDSA65-ECDSA-brainpoolP256r1	<CompSig>.29	id-ML-DSA-65	ecdsa-with-SHA256 with brainpoolP256r1
id-MLDSA65-Ed25519	<CompSig>.30	id-ML-DSA-65	id-Ed25519
id-MLDSA87-ECDSA-P384	<CompSig>.31	id-ML-DSA-87	ecdsa-with-SHA384 with secp384r1
id-MLDSA87-ECDSA-brainpoolP384r1	<CompSig>.32	id-ML-DSA-87	ecdsa-with-SHA384 with brainpoolP384r1
id-MLDSA87-Ed448	<CompSig>.33	id-ML-DSA-87	id-Ed448

See the ASN.1 module in section for the explicit definitions of the above Composite ML-DSA algorithms. Full specifications for the referenced algorithms can be found in .

HashComposite-ML-DSA Algorithm Identifiers HashComposite-ML-DSA Signature public key types: Hash ML-DSA Composite Signature Algorithms

Composite Signature AlgorithmID	OID	First AlgorithmID	Second AlgorithmID	Pre-Hash
id-HashMLDSA44-RSA2048-PSS-SHA256	<CompSig>.40	id-ML-DSA-44	id-RSASA-PSS with id-sha256	id-sha256
id-HashMLDSA44-RSA2048-PKCS15-SHA256	<CompSig>.41	id-ML-DSA-44	sha256WithRSAEncryption	id-sha256
id-HashMLDSA44-Ed25519-SHA512	<CompSig>.42	id-ML-DSA-44	id-Ed25519	id-sha512
id-HashMLDSA44-ECDSA-P256-SHA256	<CompSig>.43	id-ML-DSA-44	ecdsa-with-SHA256 with secp256r1	id-sha256
id-HashMLDSA65-RSA3072-PSS-SHA512	<CompSig>.44	id-ML-DSA-65	id-RSASA-PSS with id-sha256	id-sha512
id-HashMLDSA65-RSA3072-PKCS15-SHA512	<CompSig>.45	id-ML-DSA-65	sha256WithRSAEncryption	id-sha512
id-HashMLDSA65-RSA4096-PSS-SHA512	<CompSig>.46	id-ML-DSA-65	id-RSASA-PSS with id-sha384	id-sha512
id-HashMLDSA65-RSA4096-PKCS15-SHA512	<CompSig>.47	id-ML-DSA-65	sha384WithRSAEncryption	id-sha512
id-HashMLDSA65-ECDSA-P384-SHA512	<CompSig>.48	id-ML-DSA-65	ecdsa-with-SHA384 with secp384r1	id-sha512
id-HashMLDSA65-ECDSA-brainpoolP256r1-SHA512	<CompSig>.49	id-ML-DSA-65	ecdsa-with-SHA256 with brainpoolP256r1	id-sha512
id-HashMLDSA65-Ed25519-SHA512	<CompSig>.50	id-ML-DSA-65	id-Ed25519	id-sha512
id-HashMLDSA87-ECDSA-P384-SHA512	<CompSig>.51	id-ML-DSA-87	ecdsa-with-SHA384 with secp384r1	id-sha512
id-HashMLDSA87-ECDSA-brainpoolP384r1-SHA512	<CompSig>.52	id-ML-DSA-87	ecdsa-with-SHA384 with brainpoolP384r1	id-sha512
id-HashMLDSA87-Ed448-SHA512	<CompSig>.53	id-ML-DSA-87	id-Ed448	id-sha512

See the ASN.1 module in for the explicit definitions of the above Composite ML-DSA algorithms. The Pre-Hash algorithm is used as the PH algorithm in and the DER Encoded OID value of this Hash is used as HashOID for the Message format in step 2 of HashComposite-ML-DSA.Sign in section and HashComposite-ML-DSA.Verify in . Full specifications for the referenced algorithms can be found in .

Domain Separators As mentioned above, the OID input value is used as a domain separator for the Composite Signature Generation and verification process and is the DER encoding of the OID. The following table shows the HEX encoding for each Signature AlgorithmID. Pure ML-DSA Composite Signature Domain Separators

Composite Signature AlgorithmID	Domain Separator (in Hex encoding)
id-MLDSA44-RSA2048-PSS	060B6086480186FA6B50080115
id-MLDSA44-RSA2048-PKCS15	060B6086480186FA6B50080116
id-MLDSA44-Ed25519	060B6086480186FA6B50080117
id-MLDSA44-ECDSA-P256	060B6086480186FA6B50080118
id-MLDSA65-RSA3072-PSS	060B6086480186FA6B5008011A
id-MLDSA65-RSA3072-PKCS15	060B6086480186FA6B5008011B
id-MLDSA65-RSA4096-PSS	060B6086480186FA6B50080122
id-MLDSA65-RSA4096-PKCS15	060B6086480186FA6B50080123
id-MLDSA65-ECDSA-P384	060B6086480186FA6B5008011C
id-MLDSA65-ECDSA-brainpoolP256r1	060B6086480186FA6B5008011D
id-MLDSA65-Ed25519	060B6086480186FA6B5008011E
id-MLDSA87-ECDSA-P384	060B6086480186FA6B5008011F
id-MLDSA87-ECDSA-brainpoolP384r1	060B6086480186FA6B50080120
id-MLDSA87-Ed448	060B6086480186FA6B50080121

Hash ML-DSA Composite Signature Domain Separators

Composite Signature AlgorithmID	Domain Separator (in Hex encoding)
id-HashMLDSA44-RSA2048-PSS-SHA256	060B6086480186FA6B50080128
id-HashMLDSA44-RSA2048-PKCS15-SHA256	060B6086480186FA6B50080129
id-HashMLDSA44-Ed25519-SHA512	060B6086480186FA6B5008012A
id-HashMLDSA44-ECDSA-P256-SHA256	060B6086480186FA6B5008012B
id-HashMLDSA65-RSA3072-PSS-SHA512	060B6086480186FA6B5008012C
id-HashMLDSA65-RSA3072-PKCS15-SHA512	060B6086480186FA6B5008012D
id-HashMLDSA65-RSA4096-PSS-SHA512	060B6086480186FA6B5008012E
id-HashMLDSA65-RSA4096-PKCS15-SHA512	060B6086480186FA6B5008012F
id-HashMLDSA65-ECDSA-P384-SHA512	060B6086480186FA6B50080130
id-HashMLDSA65-ECDSA-brainpoolP256r1-SHA512	060B6086480186FA6B50080131
id-HashMLDSA65-Ed25519-SHA512	060B6086480186FA6B50080132
id-HashMLDSA87-ECDSA-P384-SHA512	060B6086480186FA6B50080133
id-HashMLDSA87-ECDSA-brainpoolP384r1-SHA512	060B6086480186FA6B50080134
id-HashMLDSA87-Ed448-SHA512	060B6086480186FA6B50080135

Rationale for choices

• Pair equivalent levels.
• NIST-P-384 is CNSA approved [CNSA2.0] for all classification levels.
• 521 bit curve not widely used.

SHA2 is used throughout in order to facilitate implementations that do not have easy access to SHA3 outside of the ML-DSA function. At the higher security levels of pre-hashed Composite ML-DSA, for example id-HashMLDSA87-ECDSA-brainpoolP384r1-SHA512, the 384-bit elliptic curve component is used with SHA2-384 is its pre-hash (ie the pre-hash that is considered to be internal to the ECDSA component), yet SHA2-512 is used as the pre-hash for the overall composite because in this case the pre-hash must not weaken the ML-DSA-87 component against a collision attack.

RSA-PSS Parameters Use of RSA-PSS requires extra parameters to be specified, which differ for each security level.

RSA2048-PSS The RSA component keys MUST be generated at the 2048-bit security level in order to compliment ML-DSA-44 As with the other composite signature algorithms, when id-MLDSA44-RSA2048-PSS and id-HashMLDSA44-RSA2048-PSS-SHA256 is used in an AlgorithmIdentifier, the parameters MUST be absent. id-MLDSA44-RSA2048-PSS and id-HashMLDSA44-RSA2048-PSS-SHA256 SHALL instantiate RSA-PSS with the following parameters: RSA-PSS 2048 Parameters

RSA-PSS Parameter	Value
Mask Generation Function	mgf1
Mask Generation params	SHA-256
Message Digest Algorithm	SHA-256
Salt Length in bits	256

where:

• Mask Generation Function (mgf1) is defined in
• SHA-256 is defined in .

RSA3072-PSS The RSA component keys MUST be generated at the 3072-bit security level in order to compliment ML-DSA-65. As with the other composite signature algorithms, when id-MLDSA65-RSA3072-PSS or id-HashMLDSA65-RSA3072-PSS-SHA512 is used in an AlgorithmIdentifier, the parameters MUST be absent. id-MLDSA65-RSA3072-PSS or id-HashMLDSA65-RSA3072-PSS-SHA512 SHALL instantiate RSA-PSS with the following parameters: RSA-PSS 3072 Parameters

RSA-PSS Parameter	Value
Mask Generation Function	mgf1
Mask Generation params	SHA-256
Message Digest Algorithm	SHA-256
Salt Length in bits	256

where:

• Mask Generation Function (mgf1) is defined in
• SHA-256 is defined in .

RSA4096-PSS The RSA component keys MUST be generated at the 4096-bit security level in order to match with ML-DSA-65. As with the other composite signature algorithms, when id-MLDSA65-RSA4096-PSS or id-HashMLDSA65-RSA4096-PSS-SHA384 is used in an AlgorithmIdentifier, the parameters MUST be absent. id-MLDSA65-RSA4096-PSS or id-HashMLDSA65-RSA4096-PSS-SHA384 SHALL instantiate RSA-PSS with the following parameters: RSA-PSS 4096 Parameters

RSA-PSS Parameter	Value
Mask Generation Function	mgf1
Mask Generation params	SHA-384
Message Digest Algorithm	SHA-384
Salt Length in bits	384

where:

• Mask Generation Function (mgf1) is defined in
• SHA-384 is defined in .

Use in CMS [EDNOTE: The convention in LAMPS is to specify algorithms and their CMS conventions in separate documents. Here we have presented them in the same document, but this section has been written so that it can easily be moved to a standalone document.] Composite Signature algorithms MAY be employed for one or more recipients in the CMS signed-data content type . All recommendations for using Composite ML-DSA in CMS are fully aligned with the use of ML-DSA in CMS . [EDNOTE: at time of writing, this draft is not aligned with because it uses SHAKE for the digest algorithm. We believe that it should use SHA2, and we are sorting this out between authors. See: https://mailarchive.ietf.org/arch/msg/spasm/yM8kS1kCoizWCMjS8pdcV3IFaDg/]

Underlying Components A compliant implementation MUST support the following algorithms for the SignerInfo digestAlgorithm field when the corresponding Composite ML-DSA algorithm is listed in the SignerInfo signatureAlgorithm field. Implementations MAY also support other algorithms for the SignerInfo digestAlgorithm and SHOULD use algorithms of equivalent strength or greater. Recommended Composite Signature Digest Algorithms

Composite Signature AlgorithmID	digestAlgorithm
id-MLDSA44-RSA2048-PSS	SHA256
id-MLDSA44-RSA2048-PKCS15	SHA256
id-MLDSA44-Ed25519	SHA512
id-MLDSA44-ECDSA-P256	SHA256
id-MLDSA65-RSA3072-PSS	SHA512
id-MLDSA65-RSA3072-PKCS15	SHA512
id-MLDSA65-RSA4096-PSS	SHA512
id-MLDSA65-RSA4096-PKCS15	SHA512
id-MLDSA65-ECDSA-P384	SHA512
id-MLDSA65-ECDSA-brainpoolP256r1	SHA512
id-MLDSA65-Ed25519	SHA512
id-MLDSA87-ECDSA-P384	SHA512
id-MLDSA87-ECDSA-brainpoolP384r1	SHA512
id-MLDSA87-Ed448	SHA512

where:

• SHA2 instantiations are defined in [FIPS180].

Note: The Hash ML-DSA Composite identifiers are not included in this list because the message content is already digested before being passed to the Composite-ML-DSA.Sign() function.

SignedData Conventions As specified in CMS , the digital signature is produced from the message digest and the signer's private key. The signature is computed over different values depending on whether signed attributes are absent or present. When signed attributes are absent, the composite signature is computed over the message digest of the content. When signed attributes are present, a hash is computed over the content using the hash function specified in , and then a message-digest attribute is constructed to contain the resulting hash value, and then the result of DER encoding the set of signed attributes, which MUST include a content-type attribute and a message-digest attribute, and then the composite signature is computed over the DER-encoded output. In summary: When using Composite Signatures, the fields in the SignerInfo are used as follows: digestAlgorithm: Per Section 5.3 of , the digestAlgorithm contains the one-way hash function used by the CMS signer. To ensure collision resistance, the identified message digest algorithm SHOULD produce a hash value of a size that is at least twice the collision strength of the internal commitment hash used by ML-DSA component algorithm of the Composite Signature. signatureAlgorithm: The signatureAlgorithm MUST contain one of the the Composite Signature algorithm identifiers as specified in signature: The signature field contains the signature value resulting from the composite signing operation of the specified signatureAlgorithm.

Certificate Conventions The conventions specified in this section augment RFC 5280 . The willingness to accept a composite Signature Algorithm MAY be signaled by the use of the SMIMECapabilities Attribute as specified in Section 2.5.2. of or the SMIMECapabilities certificate extension as specified in [RFC4262]. The intended application for the public key MAY be indicated in the key usage certificate extension as specified in Section 4.2.1.3 of . If the keyUsage extension is present in a certificate that conveys a composite Signature public key, then the key usage extension MUST contain only the following value: The keyEncipherment and dataEncipherment values MUST NOT be present. That is, a public key intended to be employed only with a composite signature algorithm MUST NOT also be employed for data encryption. This requirement does not carry any particular security consideration; only the convention that signature keys be identified with 'digitalSignature','nonRepudiation','keyCertSign' or 'cRLSign' key usages.

SMIMECapabilities Attribute Conventions Section 2.5.2 of defines the SMIMECapabilities attribute to announce a partial list of algorithms that an S/MIME implementation can support. When constructing a CMS signed-data content type , a compliant implementation MAY include the SMIMECapabilities attribute. The SMIMECapability SEQUENCE representing a composite signature Algorithm MUST include the appropriate object identifier as per in the capabilityID field.

ASN.1 Module Composite-MLDSA-2024 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-composite-mldsa(TBDMOD) } DEFINITIONS IMPLICIT TAGS ::= BEGIN EXPORTS ALL; IMPORTS PUBLIC-KEY, SIGNATURE-ALGORITHM, SMIME-CAPS, AlgorithmIdentifier{} FROM AlgorithmInformation-2009 -- RFC 5912 [X509ASN1] { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-algorithmInformation-02(58) } SubjectPublicKeyInfo FROM PKIX1Explicit-2009 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51) } OneAsymmetricKey FROM AsymmetricKeyPackageModuleV1 { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-asymmetricKeyPkgV1(50) } RSAPublicKey, ECPoint FROM PKIXAlgs-2009 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-algorithms2008-02(56) } sa-rsaSSA-PSS FROM PKIX1-PSS-OAEP-Algorithms-2009 {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-rsa-pkalgs-02(54)} ; -- -- Object Identifiers -- -- Defined in ITU-T X.690 der OBJECT IDENTIFIER ::= {joint-iso-itu-t asn1(1) ber-derived(2) distinguished-encoding(1)} -- Just for testing, to be assigned by IANA id-raw-key OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) raw(999) 1 } -- -- Signature Algorithm -- -- -- Composite Signature basic structures -- CompositeSignaturePublicKey ::= SEQUENCE SIZE (2) OF BIT STRING CompositeSignaturePublicKeyOs ::= OCTET STRING (CONTAINING CompositeSignaturePublicKey ENCODED BY der) CompositeSignaturePublicKeyBs ::= BIT STRING (CONTAINING CompositeSignaturePublicKey ENCODED BY der) CompositeSignaturePrivateKey ::= SEQUENCE SIZE (2) OF OCTET STRING CompositeSignatureValue ::= SEQUENCE SIZE (2) OF BIT STRING RsaCompositeSignaturePublicKey ::= SEQUENCE { firstPublicKey BIT STRING (ENCODED BY id-raw-key), secondPublicKey BIT STRING (CONTAINING RSAPublicKey) } EcCompositeSignaturePublicKey ::= SEQUENCE { firstPublicKey BIT STRING (ENCODED BY id-raw-key), secondPublicKey BIT STRING (CONTAINING ECPoint) } EdCompositeSignaturePublicKey ::= SEQUENCE { firstPublicKey BIT STRING (ENCODED BY id-raw-key), secondPublicKey BIT STRING (ENCODED BY id-raw-key) } -- Composite Signature Value is just a sequence of OCTET STRINGS -- CompositeSignaturePair{FirstSignatureValue, SecondSignatureValue} ::= -- SEQUENCE { -- signaturevalue1 FirstSignatureValue, -- signaturevalue2 SecondSignatureValue } -- An Explicit Compsite Signature is a set of Signatures which -- are composed of OCTET STRINGS -- ExplicitCompositeSignatureValue ::= CompositeSignaturePair { -- OCTET STRING,OCTET STRING} -- -- Information Object Classes -- pk-CompositeSignature {OBJECT IDENTIFIER:id, PublicKeyType} PUBLIC-KEY ::= { IDENTIFIER id KEY PublicKeyType PARAMS ARE absent CERT-KEY-USAGE { digitalSignature, nonRepudiation, keyCertSign, cRLSign} } sa-CompositeSignature{OBJECT IDENTIFIER:id, PUBLIC-KEY:publicKeyType } SIGNATURE-ALGORITHM ::= { IDENTIFIER id VALUE CompositeSignatureValue PARAMS ARE absent PUBLIC-KEYS {publicKeyType} } -- PURE Version of OIDS -- TODO: OID to be replaced by IANA id-MLDSA44-RSA2048-PSS OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 21 } pk-MLDSA44-RSA2048-PSS PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA44-RSA2048-PSS, RsaCompositeSignaturePublicKey} sa-MLDSA44-RSA2048-PSS SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA44-RSA2048-PSS, pk-MLDSA44-RSA2048-PSS } -- TODO: OID to be replaced by IANA id-MLDSA44-RSA2048-PKCS15 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 22 } pk-MLDSA44-RSA2048-PKCS15 PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA44-RSA2048-PKCS15, RsaCompositeSignaturePublicKey} sa-MLDSA44-RSA2048-PKCS15 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA44-RSA2048-PKCS15, pk-MLDSA44-RSA2048-PKCS15 } -- TODO: OID to be replaced by IANA id-MLDSA44-Ed25519 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 23 } pk-MLDSA44-Ed25519 PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA44-Ed25519, EdCompositeSignaturePublicKey} sa-MLDSA44-Ed25519 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA44-Ed25519, pk-MLDSA44-Ed25519 } -- TODO: OID to be replaced by IANA id-MLDSA44-ECDSA-P256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 24 } pk-MLDSA44-ECDSA-P256 PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA44-ECDSA-P256, EcCompositeSignaturePublicKey} sa-MLDSA44-ECDSA-P256 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA44-ECDSA-P256, pk-MLDSA44-ECDSA-P256 } -- TODO: OID to be replaced by IANA id-MLDSA65-RSA3072-PSS OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 26 } pk-MLDSA65-RSA3072-PSS PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA65-RSA3072-PSS, RsaCompositeSignaturePublicKey} sa-MLDSA65-RSA3072-PSS SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA65-RSA3072-PSS, pk-MLDSA65-RSA3072-PSS } -- TODO: OID to be replaced by IANA id-MLDSA65-RSA3072-PKCS15 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 27 } pk-MLDSA65-RSA3072-PKCS15 PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA65-RSA3072-PKCS15, RsaCompositeSignaturePublicKey} sa-MLDSA65-RSA3072-PKCS15 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA65-RSA3072-PKCS15, pk-MLDSA65-RSA3072-PKCS15 } -- TODO: OID to be replaced by IANA id-MLDSA65-RSA4096-PSS OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 34 } pk-MLDSA65-RSA4096-PSS PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA65-RSA4096-PSS, RsaCompositeSignaturePublicKey} sa-MLDSA65-RSA4096-PSS SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA65-RSA4096-PSS, pk-MLDSA65-RSA4096-PSS } -- TODO: OID to be replaced by IANA id-MLDSA65-RSA4096-PKCS15 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 35 } pk-MLDSA65-RSA4096-PKCS15 PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA65-RSA4096-PKCS15, RsaCompositeSignaturePublicKey} sa-MLDSA65-RSA4096-PKCS15 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA65-RSA4096-SHA512, pk-MLDSA65-RSA4096-SHA512 } -- TODO: OID to be replaced by IANA id-MLDSA65-ECDSA-P384 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 28 } pk-MLDSA65-ECDSA-P384 PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA65-ECDSA-P384, EcCompositeSignaturePublicKey} sa-MLDSA65-ECDSA-P256 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA65-ECDSA-P384, pk-MLDSA65-ECDSA-P384 } -- TODO: OID to be replaced by IANA id-MLDSA65-ECDSA-brainpoolP256r1 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 29 } pk-MLDSA65-ECDSA-brainpoolP256r1 PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA65-ECDSA-brainpoolP256r1, EcCompositeSignaturePublicKey} sa-MLDSA65-ECDSA-brainpoolP256r1 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA65-ECDSA-brainpoolP256r1, pk-MLDSA65-ECDSA-brainpoolP256r1 } -- TODO: OID to be replaced by IANA id-MLDSA65-Ed25519 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 30 } pk-MLDSA65-Ed25519 PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA65-Ed25519, EdCompositeSignaturePublicKey} sa-MLDSA65-Ed25519 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA65-Ed25519, pk-MLDSA65-Ed25519 } -- TODO: OID to be replaced by IANA id-MLDSA87-ECDSA-P384 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 31 } pk-MLDSA87-ECDSA-P384 PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA87-ECDSA-P384, EcCompositeSignaturePublicKey} sa-MLDSA87-ECDSA-P384 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA87-ECDSA-P384, pk-MLDSA87-ECDSA-P384 } -- TODO: OID to be replaced by IANA id-MLDSA87-ECDSA-brainpoolP384r1 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 32 } pk-MLDSA87-ECDSA-brainpoolP384r1 PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA87-ECDSA-brainpoolP384r1, EcCompositeSignaturePublicKey} sa-MLDSA87-ECDSA-brainpoolP384r1 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA87-ECDSA-brainpoolP384r1, pk-MLDSA87-ECDSA-brainpoolP384r1 } -- TODO: OID to be replaced by IANA id-MLDSA87-Ed448 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 33 } pk-MLDSA87-Ed448 PUBLIC-KEY ::= pk-CompositeSignature{ id-MLDSA87-Ed448, EdCompositeSignaturePublicKey} sa-MLDSA87-Ed448 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-MLDSA87-Ed448, pk-MLDSA87-Ed448 } -- PreHash Version of the OIDs -- TODO: OID to be replaced by IANA id-HashMLDSA44-RSA2048-PSS-SHA256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 40 } pk-HashMLDSA44-RSA2048-PSS-SHA256 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA44-RSA2048-PSS-SHA256, RsaCompositeSignaturePublicKey} sa-HashMLDSA44-RSA2048-PSS-SHA256 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA44-RSA2048-PSS-SHA256, pk-HashMLDSA44-RSA2048-PSS-SHA256 } -- TODO: OID to be replaced by IANA id-HashMLDSA44-RSA2048-PKCS15-SHA256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 41 } pk-HashMLDSA44-RSA2048-PKCS15-SHA256 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA44-RSA2048-PKCS15-SHA256, RsaCompositeSignaturePublicKey} sa-HashMLDSA44-RSA2048-PKCS15-SHA256 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA44-RSA2048-PKCS15-SHA256, pk-HashMLDSA44-RSA2048-PKCS15-SHA256 } -- TODO: OID to be replaced by IANA id-HashMLDSA44-Ed25519-SHA512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 42 } pk-HashMLDSA44-Ed25519-SHA512 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA44-Ed25519-SHA512, EdCompositeSignaturePublicKey} sa-HashMLDSA44-Ed25519-SHA512 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA44-Ed25519-SHA512, pk-HashMLDSA44-Ed25519-SHA512 } -- TODO: OID to be replaced by IANA id-HashMLDSA44-ECDSA-P256-SHA256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 43 } pk-HashMLDSA44-ECDSA-P256-SHA256 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA44-ECDSA-P256-SHA256, EcCompositeSignaturePublicKey} sa-HashMLDSA44-ECDSA-P256-SHA256 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA44-ECDSA-P256-SHA256, pk-HashMLDSA44-ECDSA-P256-SHA256 } -- TODO: OID to be replaced by IANA id-HashMLDSA65-RSA3072-PSS-SHA512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 44 } pk-HashMLDSA65-RSA3072-PSS-SHA512 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA65-RSA3072-PSS-SHA512, RsaCompositeSignaturePublicKey} sa-HashMLDSA65-RSA3072-PSS-SHA512 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA65-RSA3072-PSS-SHA512, pk-HashMLDSA65-RSA3072-PSS-SHA512 } -- TODO: OID to be replaced by IANA id-HashMLDSA65-RSA3072-PKCS15-SHA512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 45 } pk-HashMLDSA65-RSA3072-PKCS15-SHA512 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA65-RSA3072-PKCS15-SHA512, RsaCompositeSignaturePublicKey} sa-HashMLDSA65-RSA3072-PKCS15-SHA512 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA65-RSA3072-PKCS15-SHA512, pk-HashMLDSA65-RSA3072-PKCS15-SHA512 } -- TODO: OID to be replaced by IANA id-HashMLDSA65-RSA4096-PSS-SHA512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 46 } pk-HashMLDSA65-RSA4096-PSS-SHA512 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA65-RSA4096-PSS-SHA512, RsaCompositeSignaturePublicKey} sa-HashMLDSA65-RSA4096-PSS-SHA512 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA65-RSA4096-PSS-SHA512, pk-HashMLDSA65-RSA4096-PSS-SHA512 } -- TODO: OID to be replaced by IANA id-HashMLDSA65-RSA4096-PKCS15-SHA512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 47 } pk-HashMLDSA65-RSA4096-PKCS15-SHA512 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA65-RSA4096-PKCS15-SHA512, RsaCompositeSignaturePublicKey} sa-HashMLDSA65-RSA4096-PKCS15-SHA512 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA65-RSA4096-PKCS15-SHA512, pk-HashMLDSA65-RSA4096-PKCS15-SHA512 } -- TODO: OID to be replaced by IANA id-HashMLDSA65-ECDSA-P384-SHA512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 48 } pk-HashMLDSA65-ECDSA-P384-SHA512 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA65-ECDSA-P384-SHA512, EcCompositeSignaturePublicKey} sa-HashMLDSA65-ECDSA-P256-SHA512 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA65-ECDSA-P384-SHA512, pk-HashMLDSA65-ECDSA-P384-SHA512 } -- TODO: OID to be replaced by IANA id-HashMLDSA65-ECDSA-brainpoolP256r1-SHA512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 49 } pk-HashMLDSA65-ECDSA-brainpoolP256r1-SHA512 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA65-ECDSA-brainpoolP256r1-SHA512, EcCompositeSignaturePublicKey} sa-HashMLDSA65-ECDSA-brainpoolP256r1-SHA512 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA65-ECDSA-brainpoolP256r1-SHA512, pk-HashMLDSA65-ECDSA-brainpoolP256r1-SHA512 } -- TODO: OID to be replaced by IANA id-HashMLDSA65-Ed25519-SHA512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 50 } pk-HashMLDSA65-Ed25519-SHA512 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA65-Ed25519-SHA512, EdCompositeSignaturePublicKey} sa-HashMLDSA65-Ed25519-SHA512 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA65-Ed25519-SHA512, pk-HashMLDSA65-Ed25519-SHA512 } -- TODO: OID to be replaced by IANA id-HashMLDSA87-ECDSA-P384-SHA512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 51 } pk-HashMLDSA87-ECDSA-P384-SHA512 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA87-ECDSA-P384-SHA512, EcCompositeSignaturePublicKey} sa-HashMLDSA87-ECDSA-P384-SHA512 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA87-ECDSA-P384-SHA512, pk-HashMLDSA87-ECDSA-P384-SHA512 } -- TODO: OID to be replaced by IANA id-HashMLDSA87-ECDSA-brainpoolP384r1-SHA512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 52 } pk-HashMLDSA87-ECDSA-brainpoolP384r1-SHA512 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA87-ECDSA-brainpoolP384r1-SHA512, EcCompositeSignaturePublicKey} sa-HashMLDSA87-ECDSA-brainpoolP384r1-SHA512 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA87-ECDSA-brainpoolP384r1-SHA512, pk-HashMLDSA87-ECDSA-brainpoolP384r1-SHA512 } -- TODO: OID to be replaced by IANA id-HashMLDSA87-Ed448-SHA512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) algorithm(80) composite(8) signature(1) 53 } pk-HashMLDSA87-Ed448-SHA512 PUBLIC-KEY ::= pk-CompositeSignature{ id-HashMLDSA87-Ed448-SHA512, EdCompositeSignaturePublicKey} sa-HashMLDSA87-Ed448-SHA512 SIGNATURE-ALGORITHM ::= sa-CompositeSignature{ id-HashMLDSA87-Ed448-SHA512, pk-HashMLDSA87-Ed448-SHA512 } SignatureAlgorithmSet SIGNATURE-ALGORITHM ::= { sa-MLDSA44-RSA2048-PSS | sa-MLDSA44-RSA2048-PKCS15 | sa-MLDSA44-Ed25519 | sa-MLDSA44-ECDSA-P256 | sa-MLDSA65-RSA3072-PSS | sa-MLDSA65-RSA3072-PKCS15 | sa-MLDSA65-RSA4096-PSS | sa-MLDSA65-RSA4096-PKCS15 | sa-MLDSA65-ECDSA-P256 | sa-MLDSA65-ECDSA-brainpoolP256r1 | sa-MLDSA65-Ed25519 | sa-MLDSA87-ECDSA-P384 | sa-MLDSA87-ECDSA-brainpoolP384r1 | sa-MLDSA87-Ed448, ... } -- -- Expand the S/MIME capabilities set used by CMS [RFC5911] -- -- TODO: this doesn't compile, error: -- "The referenced object in the 'ValueFromObject' -- syntax with the field '&smimeCaps' is invalid or does not exist." -- We need help from an SMIME expert SMimeCaps SMIME-CAPS ::= { sa-MLDSA44-RSA2048-PSS.&smimeCaps | sa-MLDSA44-RSA2048-PKCS15.&smimeCaps | sa-MLDSA44-Ed25519.&smimeCaps | sa-MLDSA44-ECDSA-P256.&smimeCaps | sa-MLDSA65-RSA3072-PSS.&smimeCaps | sa-MLDSA65-RSA3072-PKCS15.&smimeCaps | sa-MLDSA65-RSA4096-PSS.&smimeCaps | sa-MLDSA65-RSA4096-PKCS15.&smimeCaps | sa-MLDSA65-ECDSA-P256.&smimeCaps | sa-MLDSA65-ECDSA-brainpoolP256r1.&smimeCaps | sa-MLDSA65-Ed25519.&smimeCaps | sa-MLDSA87-ECDSA-P384.&smimeCaps | sa-MLDSA87-ECDSA-brainpoolP384r1.&smimeCaps | sa-MLDSA87-Ed448.&smimeCaps, ... } END ]]>

IANA Considerations IANA is requested to allocate a value from the "SMI Security for PKIX Module Identifier" registry for the included ASN.1 module, and allocate values from "SMI Security for PKIX Algorithms" to identify the fourteen Algorithms defined within.

Object Identifier Allocations EDNOTE to IANA: OIDs will need to be replaced in both the ASN.1 module and in and .

Module Registration - SMI Security for PKIX Module Identifier

• Decimal: IANA Assigned - Replace TBDMOD
• Description: Composite-Signatures-2023 - id-mod-composite-signatures
• References: This Document

Object Identifier Registrations - SMI Security for PKIX Algorithms

• id-raw-key
• Decimal: IANA Assigned
• Description: Designates a public key BIT STRING with no ASN.1 structure.
• References: This Document
• id-MLDSA44-RSA2048-PSS-SHA256
• Decimal: IANA Assigned
• Description: id-MLDSA44-RSA2048-PSS-SHA256
• References: This Document
• id-MLDSA44-RSA2048-PKCS15-SHA256
• Decimal: IANA Assigned
• Description: id-MLDSA44-RSA2048-PKCS15-SHA256
• References: This Document
• id-MLDSA44-Ed25519
• Decimal: IANA Assigned
• Description: id-MLDSA44-Ed25519
• References: This Document
• id-MLDSA44-ECDSA-P256-SHA256
• Decimal: IANA Assigned
• Description: id-MLDSA44-ECDSA-P256-SHA256
• References: This Document
• id-MLDSA65-RSA3072-PSS-SHA512
• Decimal: IANA Assigned
• Description: id-MLDSA65-RSA3072-PSS-SHA512
• References: This Document
• id-MLDSA65-RSA3072-PKCS15-SHA512
• Decimal: IANA Assigned
• Description: id-MLDSA65-RSA3072-PKCS15-SHA512
• References: This Document
• id-MLDSA65-RSA4096-PSS-SHA512
• Decimal: IANA Assigned
• Description: id-MLDSA65-RSA4096-PSS-SHA512
• References: This Document
• id-MLDSA65-RSA4096-PKCS15-SHA512
• Decimal: IANA Assigned
• Description: id-MLDSA65-RSA4096-PKCS15-SHA512
• References: This Document
• id-MLDSA65-ECDSA-P384-SHA512
• Decimal: IANA Assigned
• Description: id-MLDSA65-ECDSA-P384-SHA512
• References: This Document
• id-MLDSA65-ECDSA-brainpoolP256r1-SHA512
• Decimal: IANA Assigned
• Description: id-MLDSA65-ECDSA-brainpoolP256r1-SHA512
• References: This Document
• id-MLDSA65-Ed25519
• Decimal: IANA Assigned
• Description: id-MLDSA65-Ed25519
• References: This Document
• id-MLDSA87-ECDSA-P384-SHA512
• Decimal: IANA Assigned
• Description: id-MLDSA87-ECDSA-P384-SHA512
• References: This Document
• id-MLDSA87-ECDSA-brainpoolP384r1-SHA512
• Decimal: IANA Assigned
• Description: id-MLDSA87-ECDSA-brainpoolP384r1-SHA512
• References: This Document
• id-MLDSA87-Ed448
• Decimal: IANA Assigned
• Description: id-MLDSA87-Ed448
• References: This Document
• id-HashMLDSA44-RSA2048-PSS-SHA256
• Decimal: IANA Assigned
• Description: id-HashMLDSA44-RSA2048-PSS-SHA256
• References: This Document
• id-HashMLDSA44-RSA2048-PKCS15-SHA256
• Decimal: IANA Assigned
• Description: id-HashMLDSA44-RSA2048-PKCS15-SHA256
• References: This Document
• id-HashMLDSA44-Ed25519-SHA512
• Decimal: IANA Assigned
• Description: id-HashMLDSA44-Ed25519-SHA512
• References: This Document
• id-HashMLDSA44-ECDSA-P256-SHA256
• Decimal: IANA Assigned
• Description: id-HashMLDSA44-ECDSA-P256-SHA256
• References: This Document
• id-HashMLDSA65-RSA3072-PSS-SHA512
• Decimal: IANA Assigned
• Description: id-HashMLDSA65-RSA3072-PSS-SHA512
• References: This Document
• id-HashMLDSA65-RSA3072-PKCS15-SHA512
• Decimal: IANA Assigned
• Description: id-HashMLDSA65-RSA3072-PKCS15-SHA512
• References: This Document
• id-HashMLDSA65-RSA4096-PSS-SHA512
• Decimal: IANA Assigned
• Description: id-HashMLDSA65-RSA4096-PSS-SHA512
• References: This Document
• id-HashMLDSA65-RSA4096-PKCS15-SHA512
• Decimal: IANA Assigned
• Description: id-HashMLDSA65-RSA4096-PKCS15-SHA512
• References: This Document
• id-HashMLDSA65-ECDSA-P384-SHA512
• Decimal: IANA Assigned
• Description: id-HashMLDSA65-ECDSA-P384-SHA512
• References: This Document
• id-HashMLDSA65-ECDSA-brainpoolP256r1-SHA512
• Decimal: IANA Assigned
• Description: id-HashMLDSA65-ECDSA-brainpoolP256r1-SHA512
• References: This Document
• id-HashMLDSA65-Ed25519-SHA512
• Decimal: IANA Assigned
• Description: id-HashMLDSA65-Ed25519-SHA512
• References: This Document
• id-HashMLDSA87-ECDSA-P384-SHA512
• Decimal: IANA Assigned
• Description: id-HashMLDSA87-ECDSA-P384-SHA512
• References: This Document
• id-HashMLDSA87-ECDSA-brainpoolP384r1-SHA512
• Decimal: IANA Assigned
• Description: id-HashMLDSA87-ECDSA-brainpoolP384r1-SHA512
• References: This Document
• id-HashMLDSA87-Ed448-SHA512
• Decimal: IANA Assigned
• Description: id-HashMLDSA87-Ed448-SHA512
• References: This Document

Security Considerations

Non-separability and EUF-CMA The signature combiner defined in this document is Weakly Non-Separable (WNS), as defined in , since the forged message M’ will include the composite domain separator as evidence. The prohibition on key reuse between composite and single-algorithm contexts discussed in further strengthens the non-separability in practice, but does not achieve Strong Non-Separability (SNS) since policy mechanisms such as this are outside the definition of SNS. Unforgeability properties are somewhat more nuanced. The classic EUF-CMA game is in reference to a pair of algorithms ( Sign(), Verify() ) where the attacker has access to a signing oracle using the Sign() and must produce a signature-message pair (s, m) that is accepted by the verifier using Verify() and where m was never signed by the oracle. The pair ( CompositeML-DSA.Sign(), CompositeML-DSA.Verify() ) is EUF-CMA secure so long as at least one component algorithm is EUF-CMA secure. There is a stronger notion of Strong Existential Unforgeability (SUF) in which an attacker is required to produce a new signature to an already-signed message. CompositeML-DSA only achieves SUF security if both components are SUF secure, which is not a useful property; the argument is that if the first component algorithm is not SUF secure then by definition it admits at least one (s1*, m) pair where s1* was not produced by the honest signer and it then can be combined with an honestly-signed (s2, m) signature over the same message m to create ( (s1*, s2), m) which violates SUF for the composite algorithm. In addition to the classic EUF-CMA game, we should also consider a “cross-protocol” version of the EUF-CMA game that is relevant to hybrids. Specifically, we want to consider a modified version of the EUF-CMA game where the attacker has access to either a signing oracle over the two component algorithms in isolation, Trad.Sign() and ML-DSA.Sign(), and attempts to fraudulently present them as a composite, or where the attacker has access to a composite oracle for signing and then attempts to split the signature back into components and present them to either ML-DSA.Verify() or Trad.Verify(). The latter version bears a resemblance to a stripping attack, which parallel signatures are subject to, but is slightly different in that the cross-protocol EUF-CMA game also considers modification message definition as signed differs from the message the verifier accepts. In contrast stripping attacks consider only removing one component signature and attempting verification under the remaining and the same original message. In the case of CompositeML-DSA, a specific message forgery exists for a cross-protocol EUF-CMA attack, namely introduced by the prefix construction addition to M. This applies to use of individual component signing oracles with fraudulent presentation of the signature to a composite verification oracle, and use of a composite signing oracle with fraudulent splitting of the signature for presentation to component verification oracle(s) of either ML-DSA.Verify() or Trad.Verify(). In the first case, an attacker with access to signing oracles for the two component algorithms can sign M’ and then trivially assemble a composite. In the second case, the message M’ (containing the composite domain separator) can be presented as having been signed by a standalone component algorithm. However, use of the context string for domain separation enables Weak Non-Separability and auditable checks on hybrid use, which is deemed a reasonable trade-off. Moreover and very importantly, the cross-protocol EUF-CMA attack in either direction is foiled if implementors strictly follow the prohibition on key reuse presented in since then there cannot exist simultaneously composite and non-composite signers and verifiers for the same keys. Consequently, following the specification and verification of the policy mechanism, such as a composite X.509 certificate which defines the bound keys, is essential when using keys intended for use with a CompositeML-DSA signing algorithm.

Key Reuse When using single-algorithm cryptography, the best practice is to always generate fresh key material for each purpose, for example when renewing a certificate, or obtaining both a TLS and S/MIME certificate for the same device, however in practice key reuse in such scenarios is not always catastrophic to security and therefore often tolerated, despite cross-protocol attacks having been shown. (citation needed here) Within the broader context of PQ / Traditional hybrids, we need to consider new attack surfaces that arise due to the hybrid constructions and did not exist in single-algorithm contexts. One of these is key reuse where the component keys within a hybrid are also used by themselves within a single-algorithm context. For example, it might be tempting for an operator to take an already-deployed RSA key pair and combine it with an ML-DSA key pair to form a hybrid key pair for use in a hybrid algorithm. Within a hybrid signature context this leads to a class of attacks referred to as "stripping attacks" discussed in and may also open up risks from further cross-protocol attacks. Despite the weak non-separability property offered by the composite signature combiner, it is still RECOMMENDED to avoid key reuse as key reuse in single-algorithm use cases could introduce EUF-CMA vulnerabilities. In addition, there is a further implication to key reuse regarding certificate revocation. Upon receiving a new certificate enrollment request, many certification authorities will check if the requested public key has been previously revoked due to key compromise. Often a CA will perform this check by using the public key hash. Therefore, even if both components of a composite have been previously revoked, the CA may only check the hash of the combined composite key and not find the revocations. Therefore, it is RECOMMENDED to avoid key reuse and always generate fresh component keys for a new composite. It is also RECOMMENDED that CAs performing revocation checks on a composite key should also check both component keys independently.

Policy for Deprecated and Acceptable Algorithms Traditionally, a public key, certificate, or signature contains a single cryptographic algorithm. If and when an algorithm becomes deprecated (for example, RSA-512, or SHA1), then clients performing signatures or verifications should be updated to adhere to appropriate policies. In the composite model this is less obvious since implementers may decide that certain cryptographic algorithms have complementary security properties and are acceptable in combination even though one or both algorithms are deprecated for individual use. As such, a single composite public key or certificate may contain a mixture of deprecated and non-deprecated algorithms. Since composite algorithms are registered independently of their component algorithms, their deprecation can be handled independently from that of their component algorithms. For example a cryptographic policy might continue to allow id-MLDSA65-ECDSA-P256-SHA512 even after ECDSA-P256 is deprecated. When considering stripping attacks, one need consider the case where an attacker has fully compromised one of the component algorithms to the point that they can produce forged signatures that appear valid under one of the component public keys, and thus fool a victim verifier into accepting a forged signature. The protection against this attack relies on the victim verifier trusting the pair of public keys as a single composite key, and not trusting the individual component keys by themselves. Specifically, in order to achieve this non-separability property, this specification makes two assumptions about how the verifier will establish trust in a composite public key:

1. This specification assumes that all of the component keys within a composite key are freshly generated for the composite; ie a given public key MUST NOT appear as a component within a composite key and also within single-algorithm constructions.
2. This specification assumes that composite public keys will be bound in a structure that contains a signature over the public key (for example, an X.509 Certificate ), which is chained back to a trust anchor, and where that signature algorithm is at least as strong as the composite public key that it is protecting.

There are mechanisms within Internet PKI where trusted public keys do not appear within signed structures -- such as the Trust Anchor format defined in . In such cases, it is the responsibility of implementers to ensure that trusted composite keys are distributed in a way that is tamper-resistant and does not allow the component keys to be trusted independently.

References Normative References 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. This memo represents a republication of PKCS #10 v1.7 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series, and change control is retained within the PKCS process. The body of this document, except for the security considerations section, is taken directly from the PKCS #9 v2.0 or the PKCS #10 v1.7 document. This memo provides information for the Internet community. This document describes the Internet X.509 Public Key Infrastructure (PKI) Certificate Management Protocol (CMP). Protocol messages are defined for X.509v3 certificate creation and management. CMP provides on-line interactions between PKI components, including an exchange between a Certification Authority (CA) and a client system. [STANDARDS-TRACK] This document describes the Certificate Request Message Format (CRMF) syntax and semantics. This syntax is used to convey a request for a certificate to a Certification Authority (CA), possibly via a Registration Authority (RA), for the purposes of X.509 certificate production. The request will typically include a public key and the associated registration information. This document does not define a certificate request protocol. [STANDARDS-TRACK] This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK] This document specifies the syntax and semantics for the Subject Public Key Information field in certificates that support Elliptic Curve Cryptography. This document updates Sections 2.3.5 and 5, and the ASN.1 module of "Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3279. [STANDARDS-TRACK] This memo proposes several elliptic curve domain parameters over finite prime fields for use in cryptographic applications. The domain parameters are consistent with the relevant international standards, and can be used in X.509 certificates and certificate revocation lists (CRLs), for Internet Key Exchange (IKE), Transport Layer Security (TLS), XML signatures, and all applications or protocols based on the cryptographic message syntax (CMS). This document is not an Internet Standards Track specification; it is published for informational purposes. This document describes the Cryptographic Message Syntax (CMS). This syntax is used to digitally sign, digest, authenticate, or encrypt arbitrary message content. [STANDARDS-TRACK] This document updates RFC 3279 to specify algorithm identifiers and ASN.1 encoding rules for the Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA) digital signatures when using SHA-224, SHA-256, SHA-384, or SHA-512 as the hashing algorithm. This specification applies to the Internet X.509 Public Key infrastructure (PKI) when digital signatures are used to sign certificates and certificate revocation lists (CRLs). This document also identifies all four SHA2 hash algorithms for use in the Internet X.509 PKI. [STANDARDS-TRACK] This document defines the syntax for private-key information and a content type for it. Private-key information includes a private key for a specified public-key algorithm and a set of attributes. The Cryptographic Message Syntax (CMS), as defined in RFC 5652, can be used to digitally sign, digest, authenticate, or encrypt the asymmetric key format content type. This document obsoletes RFC 5208. [STANDARDS-TRACK] This note describes the fundamental algorithms of Elliptic Curve Cryptography (ECC) as they were defined in some seminal references from 1994 and earlier. These descriptions may be useful for implementing the fundamental algorithms without using any of the specialized methods that were developed in following years. Only elliptic curves defined over fields of characteristic greater than three are in scope; these curves are those used in Suite B. This document is not an Internet Standards Track specification; it is published for informational purposes. Federal Information Processing Standard, FIPS This memo specifies two elliptic curves over prime fields that offer a high level of practical security in cryptographic applications, including Transport Layer Security (TLS). These curves are intended to operate at the ~128-bit and ~224-bit security level, respectively, and are generated deterministically based on a list of required properties. This document describes elliptic curve signature scheme Edwards-curve Digital Signature Algorithm (EdDSA). The algorithm is instantiated with recommended parameters for the edwards25519 and edwards448 curves. An example implementation and test vectors are provided. 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. This document specifies algorithm identifiers and ASN.1 encoding formats for elliptic curve constructs using the curve25519 and curve448 curves. The signature algorithms covered are Ed25519 and Ed448. The key agreement algorithms covered are X25519 and X448. The encoding for public key, private key, and Edwards-curve Digital Signature Algorithm (EdDSA) structures is provided. When the Curdle Security Working Group was chartered, a range of object identifiers was donated by DigiCert, Inc. for the purpose of registering the Edwards Elliptic Curve key agreement and signature algorithms. This donated set of OIDs allowed for shorter values than would be possible using the existing S/MIME or PKIX arcs. This document describes the donated range and the identifiers that were assigned from that range, transfers control of that range to IANA, and establishes IANA allocation policies for any future assignments within that range. ITU-T National Institute of Standards and Technology (NIST) National Institute of Standards and Technology (NIST) Informative References This document specifies algorithm identifiers and ASN.1 encoding formats for digital signatures and subject public keys used in the Internet X.509 Public Key Infrastructure (PKI). Digital signatures are used to sign certificates and certificate revocation list (CRLs). Certificates include the public key of the named subject. [STANDARDS-TRACK] This document describes a structure for representing trust anchor information. A trust anchor is an authoritative entity represented by a public key and associated data. The public key is used to verify digital signatures, and the associated data is used to constrain the types of information or actions for which the trust anchor is authoritative. The structures defined in this document are intended to satisfy the format-related requirements defined in Trust Anchor Management Requirements. [STANDARDS-TRACK] PKCS #12 v1.1 describes a transfer syntax for personal identity information, including private keys, certificates, miscellaneous secrets, and extensions. Machines, applications, browsers, Internet kiosks, and so on, that support this standard will allow a user to import, export, and exercise a single set of personal identity information. This standard supports direct transfer of personal information under several privacy and integrity modes. This document represents a republication of PKCS #12 v1.1 from RSA Laboratories' Public Key Cryptography Standard (PKCS) series. By publishing this RFC, change control is transferred to the IETF. This document describes version 2 of the Internet Key Exchange (IKE) protocol. IKE is a component of IPsec used for performing mutual authentication and establishing and maintaining Security Associations (SAs). This document obsoletes RFC 5996, and includes all of the errata for it. It advances IKEv2 to be an Internet Standard. When the Public-Key Infrastructure using X.509 (PKIX) Working Group was chartered, an object identifier arc was allocated by IANA for use by that working group. This document describes the object identifiers that were assigned in that arc, returns control of that arc to IANA, and establishes IANA allocation policies for any future assignments within that arc. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. This document defines Secure/Multipurpose Internet Mail Extensions (S/MIME) version 4.0. S/MIME provides a consistent way to send and receive secure MIME data. Digital signatures provide authentication, message integrity, and non-repudiation with proof of origin. Encryption provides data confidentiality. Compression can be used to reduce data size. This document obsoletes RFC 5751. This document provides recommendations for the implementation of public-key cryptography based on the RSA algorithm, covering cryptographic primitives, encryption schemes, signature schemes with appendix, and ASN.1 syntax for representing keys and for identifying the schemes. This document represents a republication of PKCS #1 v2.2 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series. By publishing this RFC, change control is transferred to the IETF. This document also obsoletes RFC 3447. SandboxAQ Naval Postgraduate School SandboxAQ UK National Cyber Security Centre This document describes classification of design goals and security considerations for hybrid digital signature schemes, including proof composability, non-separability of the component signatures given a hybrid signature, backwards/forwards compatiblity, hybrid generality, and simultaneous verification. Discussion of this work is encouraged to happen on the IETF PQUIP mailing list pqc@ietf.org or on the GitHub repository which contains the draft: https://github.com/dconnolly/draft-ietf-pquip-hybrid- signature-spectrums CableLabs Inc. D-Trust GmbH With the need to evolve the cryptography used in today applications, devices, and networks, there might be many scenarios where the use of a single-key certificate is not sufficient. For example, there might be the need for migrating between two existing algorithms (e.g., from classic to post-quantum) or there might be the need to test the capabilities of devices via test drivers and/or non-standard algorithms. Differently from the situation where algorithms are not yet (or no more) trusted to be used by themselves, this document addresses the use of multiple keys and signatures that can be individually trusted to implement a generic 1-threshold and K-threshold signature validation procedures. This document provides the definition of a new type of multi- algorithm public key and relies on the definition of CompositePrivateKey, and CompositeSignature which are sequences of the respective structure for each component algorithm as defined in [I-D.ounsworth-pq-composite-sigs] and [I-D.ounsworth-pq-composite-sigs]. UK National Cyber Security Centre UK National Cyber Security Centre Naval Postgraduate School One aspect of the transition to post-quantum algorithms in cryptographic protocols is the development of hybrid schemes that incorporate both post-quantum and traditional asymmetric algorithms. This document defines terminology for such schemes. It is intended to be used as a reference and, hopefully, to ensure consistency and clarity across different protocols, standards, and organisations. AWS AWS sn3rd Cloudflare Digital signatures are used within X.509 certificates, Certificate Revocation Lists (CRLs), and to sign messages. This document describes the conventions for using the Module-Lattice-Based Digital Signature Algorithm (ML-DSA) in Internet X.509 certificates and certificate revocation lists. The conventions for the associated signatures, subject public keys, and private key are also described. UK National Cyber Security Centre UK National Cyber Security Centre CryptoNext Security The Module-Lattice-Based Digital Signature Algorithm (ML-DSA), as defined in FIPS 204, is a post-quantum digital signature scheme that aims to be secure against an adversary in posession of a Cryptographically Relevant Quantum Computer (CRQC). This document specifies the conventions for using the ML-DSA signature algorithm with the Cryptographic Message Syntax (CMS). In addition, the algorithm identifier and public key syntax are provided. Federal Office for Information Security (BSI) French Cybersecurity Agency (ANSSI) Federal Office for Information Security (BSI) Netherlands National Communications Security Agency (NLNCSA) Swedish National Communications Security Authority, Swedish Armed Forces n.d.

Samples

Explicit Composite Signature Examples TODO - Need Samples

Component Algorithm Reference This section provides references to the full specification of the algorithms used in the composite constructions. Component Signature Algorithms used in Composite Constructions

Component Signature Algorithm ID	OID	Specification
id-ML-DSA-44	2.16.840.1.101.3.4.3.17
id-ML-DSA-65	2.16.840.1.101.3.4.3.18
id-ML-DSA-87	2.16.840.1.101.3.4.3.19
id-Ed25519	1.3.101.112
id-Ed448	1.3.101.113
ecdsa-with-SHA256	1.2.840.10045.4.3.2
ecdsa-with-SHA512	1.2.840.10045.4.3.4
sha256WithRSAEncryption	1.2.840.113549.1.1.11
sha512WithRSAEncryption	1.2.840.113549.1.1.13
id-RSASA-PSS	1.2.840.113549.1.1.10

Elliptic Curves used in Composite Constructions

Elliptic CurveID	OID	Specification
secp256r1	1.2.840.10045.3.1.7
secp384r1	1.3.132.0.34
brainpoolP256r1	1.3.36.3.3.2.8.1.1.7
brainpoolP384r1	1.3.36.3.3.2.8.1.1.11

Hash algorithms used in Composite Constructions

HashID	OID	Specification
id-sha256	2.16.840.1.101.3.4.2.1
id-sha512	2.16.840.1..101.3.4.2.3

Component AlgorithmIdentifiers for Public Keys and Signatures To ease implementing Composite Signatures this section specifies the Algorithms Identifiers for each component algorithm. They are provided as ASN.1 value notation and copy and paste DER encoding to avoid any ambiguity. Developers may use this information to reconstruct non hybrid public keys and signatures from each component that can be fed to crypto APIs to create or verify a single component signature. For newer Algorithms like Ed25519 or ML-DSA the AlgorithmIdentifiers are the same for Public Key and Signature. Older Algorithms have different AlgorithmIdentifiers for keys and signatures and are specified separately here for each component. ML-DSA-44 -- AlgorithmIdentifier of Public Key and Signature ML-DSA-65 -- AlgorithmIdentifier of Public Key and Signature ML-DSA-87 -- AlgorithmIdentifier of Public Key and Signature RSA PSS 2048 -- AlgorithmIdentifier of Public Key RSA PSS 2048 -- AlgorithmIdentifier of Signature RSA PSS 3072 & 4096 -- AlgorithmIdentifier of Public Key RSA PSS 3072 & 4096 -- AlgorithmIdentifier of Signature RSA PKCS 1.5 2048 -- AlgorithmIdentifier of Public Key RSA PKCS 1.5 2048 -- AlgorithmIdentifier of Signature RSA PKCS 1.5 3072 & 4096 -- AlgorithmIdentifier of Public Key RSA PKCS 1.5 3072 & 4096 -- AlgorithmIdentifier of Signature ECDSA NIST 256 -- AlgorithmIdentifier of Public Key ECDSA NIST 256 -- AlgorithmIdentifier of Signature ECDSA NIST-384 -- AlgorithmIdentifier of Public Key ECDSA NIST-384 -- AlgorithmIdentifier of Signature ECDSA Brainpool-256 -- AlgorithmIdentifier of Public Key ECDSA Brainpool-256 -- AlgorithmIdentifier of Signature ECDSA Brainpool-384 -- AlgorithmIdentifier of Public Key ECDSA Brainpool-384 -- AlgorithmIdentifier of Signature Ed25519 -- AlgorithmIdentifier of Public Key and Signature Ed448 -- AlgorithmIdentifier of Public Key and Signature

Implementation Considerations

FIPS certification One of the primary design goals of this specification is for the overall composite algorithm to be able to be considered FIPS-approved even when one of the component algorithms is not. Implementors seeking FIPS certification of a composite Signature algorithm where only one of the component algorithms has been FIPS-validated or FIPS-approved should credit the FIPS-validated component algorithm with full security strength, the non-FIPS-validated component algorithm with zero security, and the overall composite should be considered at least as strong and thus FIPS-approved. The authors wish to note that this gives composite algorithms great future utility both for future cryptographic migrations as well as bridging across jurisdictions, for example defining composite algorithms which combine FIPS cryptography with cryptography from a different national standards body.

Backwards Compatibility The term "backwards compatibility" is used here to mean something more specific; that existing systems as they are deployed today can interoperate with the upgraded systems of the future. This draft explicitly does not provide backwards compatibility, only upgraded systems will understand the OIDs defined in this document. If backwards compatibility is required, then additional mechanisms will be needed. Migration and interoperability concerns need to be thought about in the context of various types of protocols that make use of X.509 and PKIX with relation to digital signature objects, from online negotiated protocols such as TLS 1.3 and IKEv2 , to non-negotiated asynchronous protocols such as S/MIME signed email , document signing such as in the context of the European eIDAS regulations [eIDAS2014], and publicly trusted code signing [codeSigningBRsv2.8], as well as myriad other standardized and proprietary protocols and applications that leverage CMS signed structures. Composite simplifies the protocol design work because it can be implemented as a signature algorithm that fits into existing systems.

Hybrid Extensions (Keys and Signatures) The use of Composite Crypto provides the possibility to process multiple algorithms without changing the logic of applications but updating the cryptographic libraries: one-time change across the whole system. However, when it is not possible to upgrade the crypto engines/libraries, it is possible to leverage X.509 extensions to encode the additional keys and signatures. When the custom extensions are not marked critical, although this approach provides the most backward-compatible approach where clients can simply ignore the post-quantum (or extra) keys and signatures, it also requires all applications to be updated for correctly processing multiple algorithms together.

Intellectual Property Considerations The following IPR Disclosure relates to this draft: https://datatracker.ietf.org/ipr/3588/

Contributors and Acknowledgements This document incorporates contributions and comments from a large group of experts. The Editors would especially like to acknowledge the expertise and tireless dedication of the following people, who attended many long meetings and generated millions of bytes of electronic mail and VOIP traffic over the past few years in pursuit of this document: Daniel Van Geest (CryptoNext), Dr. Britta Hale (Naval Postgraduade School), Tim Hollebeek (Digicert), Panos Kampanakis (Cisco Systems), Richard Kisley (IBM), Serge Mister (Entrust), Piotr Popis, François Rousseau, Falko Strenzke, Felipe Ventura (Entrust), Alexander Ralien (Siemens), José Ignacio Escribano, Jan Oupický, 陳志華 (Abel C. H. Chen, Chunghwa Telecom), 林邦曄 (Austin Lin, Chunghwa Telecom) and Mojtaba Bisheh-Niasar We especially want to recognize the contributions of Dr. Britta Hale who has helped immensely with strengthening the signature combiner construction, and with analyzing the scheme with respect to EUF-CMA and Non-Separability properties. We are grateful to all who have given feedback over the years, formally or informally, on mailing lists or in person, including any contributors who may have been inadvertently omitted from this list. This document borrows text from similar documents, including those referenced below. Thanks go to the authors of those documents. "Copying always makes things easier and less error prone" - .

Making contributions Additional contributions to this draft are welcome. Please see the working copy of this draft at, as well as open issues at: https://github.com/lamps-wg/draft-composite-sigs