]> Vigil Security, LLC

Herndon VA United States of America housley@vigilsec.com

Security Internet-Draft This document describes the conventions for using the one-way hash functions in the SHA3 family with the Cryptographic Message Syntax (CMS). The SHA3 family can be used as a message digest algorithm, as part of a signature algorithm, as part of a message authentication code, or part of a key derivation function.

Introduction The Cryptographic Message Syntax (CMS) is used to digitally sign, digest, authenticate, or encrypt arbitrary message contents. This specification describes the use of the four one-way hash functions in the SHA3 family (SHA3-224, SHA3-256, SHA3-384, and SHA3-512) with the CMS. In addition, this specification describes the use of these four one-way hash functions with the RSASSA PKCS#1 version 1.5 signature algorithm and the Elliptic Curve Digital Signature Algorithm (ECDSA) with the CMS signed-data content type. This document should not be confused with RFC 8702 , which defines conventions for using the the SHAKE family of SHA3-based extensible output functions with the CMS.

ASN.1 CMS values are generated using ASN.1 , using the Basic Encoding Rules (BER) and the Distinguished Encoding Rules (DER) .

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.

Message Digest Algorithms One-way hash functions are also referred to as message digest algorithms.
This section specifies the conventions employed by CMS implementations that support SHA3-224, SHA3-256, SHA3-384, and SHA3-512 . Digest algorithm identifiers are located in the SignedData digestAlgorithms field, the SignerInfo digestAlgorithm field, the DigestedData digestAlgorithm field, and the AuthenticatedData digestAlgorithm field. Digest values are located in the DigestedData digest field and the Message Digest authenticated attribute. In addition, digest values are input to signature algorithms. SHA3-224, SHA3-256, SHA3-384, and SHA3-512 produce output values with 224, 256, 384, and 512 bits, respectively. The object identifiers for these four one-way hash functions are as follows: When using the id-sha3-224, id-sha3-s256, id-sha3-384, or id-sha3-512 algorithm identifiers, the parameters field MUST be absent; not NULL but absent.

Signature Algorithms This section specifies the conventions employed by CMS implementations that support the four SHA3 one-way hash functions with the RSASSA PKCS#1 version 1.5 signature algorithm and the Elliptic Curve Digital Signature Algorithm (ECDSA) with the CMS signed-data content type. Signature algorithm identifiers are located in the SignerInfo signatureAlgorithm field of SignedData. Also, signature algorithm identifiers are located in the SignerInfo signatureAlgorithm field of countersignature attributes. Signature values are located in the SignerInfo signature field of SignedData. Also, signature values are located in the SignerInfo signature field of countersignature attributes.

RSASSA PKCS#1 v1.5 with SHA3 The RSASSA PKCS#1 v1.5 is defined in . When RSASSA PKCS#1 v1.5 is used in conjunction with one of the SHA3 one-way hash functions, the object identifiers are: The algorithm identifier for RSASSA PKCS#1 v1.5 subject public keys in certificates is specified in , and it is repeated here for convenience: When the rsaEncryption, id-rsassa-pkcs1-v1-5-with-sha3-224, id-rsassa-pkcs1-v1-5-with-sha3-256, id-rsassa-pkcs1-v1-5-with-sha3-384, and id-rsassa-pkcs1-v1-5-with-sha3-512 algorithm identifier is used, AlgorithmIdentifier parameters field MUST contain NULL. When the rsaEncryption algorithm identifier is used, the RSA public key, which is composed of a modulus and a public exponent, MUST be encoded using the RSAPublicKey type as specified in . The output of this encoding is carried in the certificate subject public key. The definition of RSAPublicKey is repeated here for convenience: When signing, the RSASSA PKCS#1 v1.5 signature algorithm generates a single value, and that value is used directly as the signature value.

ECDSA with SHA3 The Elliptic Curve Digital Signature Algorithm (ECDSA) is defined in . When ECDSA is used in conjunction with one of the SHA3 one-way hash functions, the object identifiers are: When using the id-ecdsa-with-sha3-224, id-ecdsa-with-sha3-256, id-ecdsa-with-sha3-384, and id-ecdsa-with-sha3-512 algorithm identifiers, the parameters field MUST be absent; not NULL but absent. The conventions for ECDSA public keys is as specified in . The ECParameters associated with the ECDSA public key in the signers certificate SHALL apply to the verification of the signature. When signing, the ECDSA algorithm generates two values. These values are commonly referred to as r and s. To easily transfer these two values as one signature, they MUST be ASN.1 encoded using the ECDSA-Sig-Value defined in and repeated here for convenience:

Message Authentication Codes using HMAC and SHA3 This section specifies the conventions employed by CMS implementations that support the HMAC with SHA3 message authentication code (MAC). MAC algorithm identifiers are located in the AuthenticatedData macAlgorithm field. MAC values are located in the AuthenticatedData mac field. When HMAC is used in conjunction with one of the SHA3 one-way hash functions, the object identifiers are: When the id-hmacWithSHA3-224, id-hmacWithSHA3-256, id-hmacWithSHA3-384, and id-hmacWithSHA3-512 algorithm identifier is used, the parameters field MUST be absent; not NULL but absent.

Key Derivation Functions The CMS KEMRecipientInfo structure is one place where algorithm identifiers for key-derivation functions are needed.

HKDF with SHA3 This section assigns four algorithm identifiers that can be employed by CMS implementations that support the HMAC-based Extract-and-Expand Key Derivation Function (HKDF) with the SHA3 family of hash functions. When HKDF is used in conjunction with one of the SHA3 one-way hash functions, the object identifiers are: When id-alg-hkdf-with-sha3-224, id-alg-hkdf-with-sha3-256, id-alg-hkdf-with-sha3-384, or id-alg-hkdf-with-sha3-512 is used in an algorithm identifier, the parameters field MUST be absent; not NULL but absent.

KMAC128-KDF and KMAC256-KDF This section specifies the conventions employed by CMS implementations that employ either the KMAC128 or KMAC256 as a key derivation function as defined in Section 4.4 of . KMAC128 and KMAC256 are specified in . The use of KMAC128 and KMAC256 as a key derivation function are defined as:

• KMAC128-KDF is KMAC128(K, X, L, S).

• KMAC256-KDF is KMAC256(K, X, L, S).

The parameters are:

• K

  the input key-derivation key. The length of K MUST be less than 2^2040.

• X

  the context, which contains the ASN.1 DER encoding of CMSORIforKEMOtherInfo when the KDF is used with .

• L

  the output length, in bits. L MUST be greater than or equal to 0, and L MUST be less than 2^2040.

• S

  the optional customization label, such as "KDF" (0x4B4446). The length of S MUST be less than 2^2040.

When KMAC128-KDF or KMAC256-KDF is used, the object identifiers are: When the id-kmac128 or id-kmac256 is used as part of an algorithm identifier, the parameters field MUST be absent if no customization label is used for S. If any other value is used for S, then parameters field MUST be present and contain the value of S, encoded as Customization.

KDF2 and KDF3 with SHA3 This section specifies the conventions employed by CMS implementations that employ either the KDF2 or KDF3 functions defined in . The CMS KEMRecipientInfo structure is one place where algorithm identifiers for key-derivation functions are needed. When KDF2 and KDF3 are used, they are identified by the id-kdf-kdf2 and id-kdf-kdf3 object identifiers, respectively. The algorithm identifier parameters carries an algorithm identifier to indicate which hash function is being employed. To support SHA3, an algorithm identifier from is carried in the parameter.

Security Considerations Implementations must protect the signer's private key. Compromise of the signer's private key permits masquerade. When more than two parties share the same message-authentication key, data origin authentication is not provided. Any party that knows the message-authentication key can compute a valid MAC, therefore the content could originate from any one of the parties. Implementations must randomly generate message-authentication keys and one-time values, such as the k value when generating a ECDSA signature. In addition, the generation of public/private key pairs relies on a random numbers. The use of inadequate pseudo-random number generators (PRNGs) to generate cryptographic values can result in little or no security. An attacker may find it much easier to reproduce the PRNG environment that produced the keys, searching the resulting small set of possibilities, rather than brute force searching the whole key space. The generation of quality random numbers is difficult. RFC 4086 offers important guidance in this area, and Appendix 3 of FIPS Pub 186-4 provides some PRNG techniques. Implementers should be aware that cryptographic algorithms become weaker with time. As new cryptanalysis techniques are developed and computing performance improves, the work factor to break a particular cryptographic algorithm will reduce. Therefore, cryptographic algorithm implementations should be modular allowing new algorithms to be readily inserted. That is, implementers should be prepared to regularly update the set of algorithms in their implementations.

IANA Considerations IANA is asked to assign one object identifier for the ASN.1 module in in the "SMI Security for S/MIME Module Identifiers (1.2.840.113549.1.9.16.0)" registry : IANA is asked to assign four object identifiers for the HKDF using SHA3 algorithm identifiers in the "SMI Security for S/MIME Algorithms (1.2.840.113549.1.9.16.3)" registry :

Acknowledgements Thanks to Daniel Van Geest and Sean Turner for their careful review and thoughtful comments. Thanks to Sara Kerman, Quynh Dang, and David Cooper for getting the object identifiers assigned for KMAC128 and KMAC256.

References Normative References American National Standards Institute National Institute of Standards and Technology National Institute of Standards and Technology This document describes HMAC, a mechanism for message authentication using cryptographic hash functions. HMAC can be used with any iterative cryptographic hash function, e.g., MD5, SHA-1, in combination with a secret shared key. The cryptographic strength of HMAC depends on the properties of the underlying hash function. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind 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 the Cryptographic Message Syntax (CMS). This syntax is used to digitally sign, digest, authenticate, or encrypt arbitrary message content. [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 document specifies a simple Hashed Message Authentication Code (HMAC)-based key derivation function (HKDF), which can be used as a building block in various protocols and applications. The key derivation function (KDF) is intended to support a wide range of applications and requirements, and is conservative in its use of cryptographic hash functions. This document is not an Internet Standards Track specification; it is published for informational purposes. The Public Key Infrastructure using X.509 (PKIX) certificate format, and many associated formats, are expressed using ASN.1. The current ASN.1 modules conform to the 1988 version of ASN.1. This document updates those ASN.1 modules to conform to the 2002 version of ASN.1. There are no bits-on-the-wire changes to any of the formats; this is simply a change to the syntax. This document is not an Internet Standards Track specification; it is published for informational purposes. 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. National Institute of Standards and Technology National Institute of Standards and Technology ITU-T ITU-T In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References IANA n.d. IANA n.d. Vigil Security, LLC Entrust DigiCert, Inc. The Cryptographic Message Syntax (CMS) supports key transport and key agreement algorithms. In recent years, cryptographers have been specifying Key Encapsulation Mechanism (KEM) algorithms, including quantum-secure KEM algorithms. This document defines conventions for the use of KEM algorithms by the originator and recipients to encrypt and decrypt CMS content. This document updates RFC 5652. Security systems are built on strong cryptographic algorithms that foil pattern analysis attempts. However, the security of these systems is dependent on generating secret quantities for passwords, cryptographic keys, and similar quantities. The use of pseudo-random processes to generate secret quantities can result in pseudo-security. A sophisticated attacker may find it easier to reproduce the environment that produced the secret quantities and to search the resulting small set of possibilities than to locate the quantities in the whole of the potential number space. Choosing random quantities to foil a resourceful and motivated adversary is surprisingly difficult. This document points out many pitfalls in using poor entropy sources or traditional pseudo-random number generation techniques for generating such quantities. It recommends the use of truly random hardware techniques and shows that the existing hardware on many systems can be used for this purpose. It provides suggestions to ameliorate the problem when a hardware solution is not available, and it gives examples of how large such quantities need to be for some applications. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document updates the "Cryptographic Message Syntax (CMS) Algorithms" (RFC 3370) and describes the conventions for using the SHAKE family of hash functions in the Cryptographic Message Syntax as one-way hash functions with the RSA Probabilistic Signature Scheme (RSASSA-PSS) and Elliptic Curve Digital Signature Algorithm (ECDSA). The conventions for the associated signer public keys in CMS are also described.

Appendix. ASN.1 Module This section contains the ASN.1 module for the algorithm identifiers using SHA3 family of hash functions . This module imports types from other ASN.1 modules that are defined in .