Ed25519 and Ed448 public key algorithms for the Secure Shell (SSH) protocol

Secure Shell (SSH) is a secure remote-login protocol. It provides for an extensible variety of public key algorithms for identifying servers and users to one another. Ed25519 is a digital signature system. OpenSSH 6.5 introduced support for using Ed25519 for server and user authentication and was then followed by other SSH implementations. This document describes the method implemented by OpenSSH and others, and formalizes its use of the name "ssh-ed25519". Additionally, it also describes the use of Ed448 and formalizes its use of the name "ssh-ed448". [TO BE REMOVED: Please send comments on this draft to curdle@ietf.org.]

The descriptions of key and signature formats use the notation introduced in [RFC4251], Section 3 and the string data type from [RFC4251], Section 5.

This document describes a public key algorithm for use with SSH in accordance with [RFC4253], Section 6.6. The name of the algorithm is "ssh-ed25519". This algorithm only supports signing and not encryption. Additionally, this document describes another public key algorithm. The name of the algorithm is "ssh-ed448". This algorithm only supports signing and not encryption.

The "ssh-ed25519" key format has the following encoding: string "ssh-ed25519" string key Here 'key' is the 32-octet public key described by [RFC8032], Section 5.1.5.

The "ssh-ed448" key format has the following encoding: string "ssh-ed448" string key Here 'key' is the 57-octet public key described by [RFC8032], Section 5.2.5.

Signatures are generated according to the procedure in [RFC8032], Section 5.2.6.

The "ssh-ed25519" key format has the following encoding: string "ssh-ed25519" string signature Here 'signature' is the 64-octet signature produced in accordance with [RFC8032], Section 5.1.6.

The "ssh-ed448" key format has the following encoding: string "ssh-ed448" string signature Here 'signature' is the 57-octet signature produced in accordance with [RFC8032], Section 5.2.6.

ED25519 signatures are verified according to the procedure in [RFC8032], Section 5.1.7. ED448 signatures are verified according to the procedure in [RFC8032], Section 5.2.7.

Usage and generation of SSHFP DNS resource record is described in . The generation of SSHFP resource records for "ssh-ed25519" keys is described in . This section illustrates the generation of SSHFP resource records for "ssh-ed448" keys and the document specifies the corresponding Ed448 code point to the "SSHFP RR Types for public key algorithms" IANA registry. The generation of SSHFP resource records for "ssh-ed25519" keys is described in . The generation of SSHFP resource records for "ssh-ed448" keys is described as follows. the SSHFP Resource Record for the Ed448 public key with SHA-256 fingerprint would be example be: example.com. IN SSHFP TBD 2 ( a87f1b687ac0e57d2a081a2f2826723 34d90ed316d2b818ca9580ea384d924 01 ) The 2 here indicates SHA-256 .

This document augments the Public Key Algorithm Names in [RFC4250], Section 4.6.2. IANA is requested to add to the Public Key Algorithm Names registry with the following entry: Public Key Algorithm NameReference ssh-ed25519This Draft ssh-ed448This Draft IANA is requested to add the following entry to the "SSHFP RR Types for public key algorithms" registry : +--------+-------------+------------+ | Value | Description | Reference | +--------+-------------+------------+ | TBD | Ed448 | [this-draft] | +--------+-------------+------------+ We suggest 6 as value. [TO BE REMOVED: This registration should take place at the following location: <http://www.iana.org/assignments/ssh-parameters/ssh-parameters.xhtml#ssh-parameters-19>]

The security considerations in [RFC4251], Section 9 apply to all SSH implementations, including those using Ed25519 and Ed448. The security considerations in [RFC8032], Section 8 and apply to all uses of Ed25519 and Ed448 including those in SSH.

The OpenSSH implementation of Ed25519 in SSH was written by Markus Friedl. We are also grateful to Mark Baushke and Daniel Migault for their comments.