Use of Static-Static ECDH in JSON Object Signing and Encryption (JOSE)
draft-amringer-jose-ecdh-ss-00

Abstract

This document defines how to use the Static-Static mode of ECDH in JSON Object Signing and Encryption (JOSE).

Status of This Memo

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This Internet-Draft will expire on July 15, 2020.

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Table of Contents

• 1. Introduction
• 1.1. Notation and Conventions
• 2. Key Agreement with Elliptic Curve Diffie-Hellman Static-Static
• 2.1. Header Parameters Used for ECDH Key Agreement
• 2.1.1. "spk" (Sender Public Key) Header Parameter
• 2.1.2. "apu" (Agreement PartyUInfo) Header Parameter
• 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. IANA Considerations
• 4. References
• 4.1. Normative References
• 4.2. Informative References
• Author's Address

1. Introduction

The Internet Research Task Force (IRTF) JOSE Working Group defined the ECDH-ES as a key agreement mechanism in the JOSE context. This document defines how to use the ECDH key agreement mechanism in Static-Static mode in JOSE in an interoperable manner.

This document defines the conventions to use in the context of [RFC7516]

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 Agreement with Elliptic Curve Diffie-Hellman Static-Static

This section defines the specifics of key agreement with Elliptic Curve Diffie-Hellman Static-Static, 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", "XC20PKW", "A128KW", "A192KW", "A256KW" algorithms, in the Key Agreement with Key Wrapping mode.

This mode is used as defined as the atlernate way for ECDH-ES in Section 4.6.2 of RFC7518 where the "apu" parameter MUST represent a random 512-bit value (analogous to PartyAInfo in Ephemeral-Static mode in [RFC2631]).

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:

2.1. Header Parameters Used for ECDH Key Agreement

The following Header Parameters are used.

2.1.1. "spk" (Sender Public Key) Header Parameter

The "spk" (sender public key) value created by the originator for the use in key agreement algorithms. This key is represented either directly as a JSON Web Key [JWK] public key value, or encapsulated inside a JWE encoded using the compact serialization. The JWK MUST contain only public key parameters and SHOULD contain only the minimum JWK parameters necessary to represent the key; other JWK parameters included can be checked for consistency and honored, or they can be ignored. This Header Parameter MUST be present and MUST be understood and processed by implementations when an algorithm from this document is used.

2.1.2. "apu" (Agreement PartyUInfo) Header Parameter

The "apu" (agreement PartyUInfo) value for key agreement, represented as a base64url-encoded string. Its value contains a random 512-bit value. Use of this Header Parameter is REQUIRED. This Header Parameter MUST be understood and processed by implementations when an algorithm from this document is used.

2.2. Header Parameters Used for Key Encryption

The following Header Parameters are used when the chosen "alg" algorithm includes a key encryption step.

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 nonce value used for the key encryption operation. This Header Parameter MUST be present and MUST be understood and processed by implementations when an algorithm from this document is 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. IANA Considerations

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

o Algorithm Name: "ECDH-SS" o Algorithm Description: ECDH-SS using Concat KDF o Algorithm Usage Location(s): "alg" o JOSE Implementation Requirements: Optional o Change Controller: IESG o Specification Document(s): Section 2 of [RFC-THIS] o Algorithm Analysis Documents(s): [RFC8439]

o Algorithm Name: "ECDH-SS+C20PKW" o Algorithm Description: ECDH-SS using Concat KDF and "C20PKW" o Algorithm Usage Location(s): "alg" o JOSE Implementation Requirements: Optional 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: "ECDH-SS+XC20PKW" o Algorithm Description: ECDH-SS using Concat KDF and "XC20PKW" o Algorithm Usage Location(s): "alg" o JOSE Implementation Requirements: Optional 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: "ECDH-SS+A128KW" o Algorithm Description: ECDH-SS using Concat KDF and "A128KW" o Algorithm Usage Location(s): "alg" o JOSE Implementation Requirements: Optional 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: "ECDH-SS+A192KW" o Algorithm Description: ECDH-SS using Concat KDF and "A192KW" o Algorithm Usage Location(s): "alg" o JOSE Implementation Requirements: Optional 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: "ECDH-SS+A256KW" o Algorithm Description: ECDH-SS using Concat KDF and "A256KW" o Algorithm Usage Location(s): "alg" o JOSE Implementation Requirements: Optional o Change Controller: IESG o Specification Document(s): Section 2 of [RFC-THIS] o Algorithm Analysis Documents(s): [I-D.irtf-cfrg-xchacha]

4. References

4.1. Normative References

4.2. Informative References

Author's Address