(No Working Group) G. Amringer
Internet-Draft January 12, 2020
Intended status: Informational
Expires: July 15, 2020

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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Table of Contents

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:

"alg" value Key Management Algorithm
ECDH-SS ECDH-SS using Concat KDF for use directly as a symmetric key
ECDH-SS+C20PKW ECDH-SS using Concat KDF and CEK wrapped with C20PKW
ECDH-SS+XC20PKW ECDH-SS using Concat KDF and CEK wrapped with XC20PKW
ECDH-SS+A128KW ECDH-SS using Concat KDF and CEK wrapped with A128KW
ECDH-SS+A192KW ECDH-SS using Concat KDF and CEK wrapped with A192KW
ECDH-SS+A256KW ECDH-SS using Concat KDF and CEK wrapped with A256KW

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

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2631] Rescorla, E., "Diffie-Hellman Key Agreement Method", RFC 2631, DOI 10.17487/RFC2631, June 1999.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", RFC 7516, DOI 10.17487/RFC7516, May 2015.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, DOI 10.17487/RFC7517, May 2015.
[RFC7638] Jones, M. and N. Sakimura, "JSON Web Key (JWK) Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September 2015.
[RFC8439] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF Protocols", RFC 8439, DOI 10.17487/RFC8439, June 2018.

4.2. Informative References

[I-D.irtf-cfrg-xchacha] Arciszewski, S., "XChaCha: eXtended-nonce ChaCha and AEAD_XChaCha20_Poly1305", Internet-Draft draft-irtf-cfrg-xchacha-01, July 2019.

Author's Address

Guillaume Amringer Canada EMail: g.amringer@gmail.com