Clarifications for Ed25519, Ed448, X25519, and X448 Algorithm Identifiers

Clarifications for Ed25519, Ed448, X25519, and X448 Algorithm Identifiers sn3rd

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sec lamps PKIX X.509 keyUsage Elliptic Curve Cryptography This document updates RFC 8410 to clarify existing semantics, and specify missing semantics, for key usage bits when used in certificates that support the Ed25519, Ed448, X25519, and X448 Elliptic Curve Cryptography algorithms.

Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

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Table of Contents

. Introduction
. Terminology
. New Section 5 for RFC 8410
. Security Considerations
. IANA Considerations
. References
- . Normative References
- . Informative References
Acknowledgments
Authors' Addresses

Introduction specifies the syntax and semantics for the Subject Public Key Information field in certificates that support Ed25519, Ed448, X25519, and X448 Elliptic Curve Cryptography (ECC) algorithms. As part of these semantics, it defines what combinations are permissible for the values of the keyUsage extension . did not define what values are not permissible, nor did it refer to keyEncipherment or dataEncipherment. has also been submitted to clarify that keyCertSign is always set in certification authority certificates. To address these changes, this document replaces with .

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.

New Section 5 for RFC 8410 The intended application for the key is indicated in the keyUsage certificate extension. If the keyUsage extension is present in a certificate that indicates id-X25519 or id-X448 in SubjectPublicKeyInfo, then the following MUST be present: keyAgreement One of the following MAY also be present: encipherOnly decipherOnly and any of the following MUST NOT be present: digitalSignature nonRepudiation keyEncipherment dataEncipherment keyCertSign cRLSign If the keyUsage extension is present in an end-entity certificate that indicates id-Ed25519 or id-Ed448 in SubjectPublicKeyInfo, then the keyUsage extension MUST contain at least one of the following: nonRepudiation digitalSignature cRLSign and any of the following MUST NOT be present: keyEncipherment dataEncipherment keyAgreement keyCertSign encipherOnly decipherOnly If the keyUsage extension is present in a CRL issuer certificate that indicates id-Ed25519 or id-Ed448 in SubjectPublicKeyInfo, then the keyUsage extension MUST contain: cRLSign and zero or more of the following: nonRepudiation digitalSignature and any of the following MUST NOT be present: keyEncipherment dataEncipherment keyAgreement encipherOnly decipherOnly and if the CRL issuer is also a certification authority, then the keyUsage extension MUST also contain: keyCertSign If the keyUsage extension is present in a certification authority certificate that indicates id-Ed25519 or id-Ed448 in SubjectPublicKeyInfo, then the keyUsage extension MUST contain: keyCertSign and zero or more of the following: nonRepudiation digitalSignature cRLSign and any of the following MUST NOT be present: keyEncipherment dataEncipherment keyAgreement encipherOnly decipherOnly

Security Considerations This document introduces no new security considerations beyond those found in .

IANA Considerations This document has no IANA actions.

References Normative References Key words for use in RFCs to Indicate Requirement Levels 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. Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile 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] Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words 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. Algorithm Identifiers for Ed25519, Ed448, X25519, and X448 for Use in the Internet X.509 Public Key Infrastructure 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. Informative References Erratum ID 5696 RFC Errata RFC 8410

Acknowledgments We would like to thank , , and for their comments.