Chacha derived AEAD algorithms in JSON Object Signing and Encryption (JOSE)
draft-amringer-jose-chacha-01

Abstract

This document defines how to use the AEAD algorithms "AEAD_XCHACHA20_POLY1305" and "AEAD_CHACHA20_POLY1305" from [RFC8439] and [I-D.irtf-cfrg-xchacha] in JSON Object Signing and Encryption (JOSE).

Status of This Memo

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This Internet-Draft will expire on January 24, 2020.

Copyright Notice

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Table of Contents

• 1. Introduction
• 1.1. Notation and Conventions
• 2. Key Encryption
• 2.1. Algorithms
• 2.2. Header Parameters Used for Key Encryption
• 2.2.1. "iv" (Initialization Vector) Header Parameter
• 2.2.2. "tag" (Authentication Tag) Header Parameter
• 3. Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static
• 4. Content Encryption
• 4.1. Algorithms
• 5. IANA Considerations
• 6. Normative References
• Author's Address

1. Introduction

The Internet Research Task Force (IRTF) Crypto Forum Research Group (CFRG) defined the ChaCha20 and Poly1305 algorithms to be used in IETF protocols both independantly and as an AEAD construction ([RFC8439]). It has also been presented with a definition of an eXtended-nonce variant ([I-D.irtf-cfrg-xchacha]) for use in stateless contexts. This document defines how to use those algorithms in JOSE in an interoperable manner.

This document defines the conventions to use in the context of [RFC7516], and [RFC7517].

1.1. Notation and Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

The JOSE key format ("JSON Web Key (JWK)") is defined by [RFC7517] and thumbprints for it ("JSON Web Key (JWK) Thumbprint") in [RFC7638].

2. Key Encryption

2.1. Algorithms

This section defines the specifics of encrypting a JWE Content Encryption Key (CEK) with AEAD_CHACHA20_POLY1305 [RFC8439] and AEAD_XCHACHA20_POLY1305 [I-D.irtf-cfrg-xchacha].

Use of an Initialization Vector (IV) is REQUIRED with this algorithm. The IV is represented in base64url-encoded form as the "iv" (initialization vector) Header Parameter value.

The Additional Authenticated Data value used is the empty octet string.

The JWE Encrypted Key value is the ciphertext output.

The Authentication Tag output is represented in base64url-encoded form as the "tag" (authentication tag) Header Parameter value.

The following "alg" (algorithm) Header Parameter values are used to indicate that the JWE Encrypted Key is the result of encrypting the CEK using the corresponding algorithm and IV size:

2.2. Header Parameters Used for Key Encryption

The following Header Parameters are used for both algorithms defined for key encryption.

2.2.1. "iv" (Initialization Vector) Header Parameter

The "iv" (initialization vector) Header Parameter value is the base64url-encoded representation of the 96-bit or 192-bit IV value used for the key encryption operation. This Header Parameter MUST be present and MUST be understood and processed by implementations when these algorithms are used.

2.2.2. "tag" (Authentication Tag) Header Parameter

The "tag" (authentication tag) Header Parameter value is the base64url-encoded representation of the 128-bit Authentication Tag value resulting from the key encryption operation. This Header Parameter MUST be present and MUST be understood and processed by implementations when these algorithms are used.

3. Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static

This section defines the specifics of key agreement with Elliptic Curve Diffie-Hellman Ephemeral Static [RFC6090], in combination with the Concat KDF, as defined in Section 5.8.2.1 of NIST.800-56A for use as a symmetric key to wrap the CEK with the "C20PKW", or "XC20PKW" algorithms, in the Key Agreement with Key Wrapping mode.

This mode is used exactly as defined in Section 4.6 of RFC7518, except that the combined key wrapping algorithms are the ones indicated in this document. All headers pertaining to both the ECDH-ES and key wrapping components ("iv",' "tag", "epk", "apu", "apv") have the same meaning and requirement as in their original definitions.

The following "alg" (algorithm) Header Parameter values are used to indicate that the JWE Encrypted Key is the result of encrypting the CEK using the corresponding algorithm:

4. Content Encryption

4.1. Algorithms

This section defines the specifics of performing authenticated encryption with ChaCha20-Poly1305.

The CEK is used as the encryption key.

Use of an IV is REQUIRED with this algorithm.

The following "enc" (encryption algorithm) Header Parameter values are used to indicate that the JWE Ciphertext and JWE Authentication Tag values have been computed using the corresponding algorithm and IV size:

5. IANA Considerations

The following is added to the "JSON Web Signature and Encryption Algorithms" registry:

o Algorithm Name: "C20PKW" o Algorithm Description: Key wrapping with ChaCha20-Poly1305 o Algorithm Usage Location(s): "alg" o JOSE Implementation Requirements: Recommended o Change Controller: IESG o Specification Document(s): Section 2 of [RFC-THIS] o Algorithm Analysis Documents(s): [RFC8439]

o Algorithm Name: "XC20PKW" o Algorithm Description: Key wrapping with XChaCha20-Poly1305 o Algorithm Usage Location(s): "alg" o JOSE Implementation Requirements: Recommended o Change Controller: IESG o Specification Document(s): Section 2 of [RFC-THIS] o Algorithm Analysis Documents(s): [I-D.irtf-cfrg-xchacha]

o Algorithm Name: "C20P" o Algorithm Description: ChaCha20-Poly1305 o Algorithm Usage Location(s): "enc" o JOSE Implementation Requirements: Recommended o Change Controller: IESG o Specification Document(s): Section 3 of [RFC-THIS] o Algorithm Analysis Documents(s): [RFC8439]

o Algorithm Name: "XC20P" o Algorithm Description: ChaCha20-Poly1305 o Algorithm Usage Location(s): "enc" o JOSE Implementation Requirements: Recommended o Change Controller: IESG o Specification Document(s): Section 3 of [RFC-THIS] o Algorithm Analysis Documents(s): [I-D.irtf-cfrg-xchacha]

6. Normative References

Author's Address