Ed25519 and Ed448 Public Key Algorithms for the Secure Shell (SSH) Protocol
RFC 8709

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Internet Engineering Task Force (IETF)                         B. Harris
Request for Comments: 8709                                              
Updates: 4253                                              L. Velvindron
Category: Standards Track                                  cyberstorm.mu
ISSN: 2070-1721                                            February 2020

   Ed25519 and Ed448 Public Key Algorithms for the Secure Shell (SSH)
                                Protocol

Abstract

   This document describes the use of the Ed25519 and Ed448 digital
   signature algorithms in the Secure Shell (SSH) protocol.
   Accordingly, this RFC updates RFC 4253.

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
   https://www.rfc-editor.org/info/rfc8709.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Conventions Used in This Document
     2.1.  Requirements Language
   3.  Public Key Algorithm
   4.  Public Key Format
   5.  Signature Algorithm
   6.  Signature Format
   7.  Verification Algorithm
   8.  SSHFP DNS Resource Records
   9.  IANA Considerations
   10. Security Considerations
   11. References
     11.1.  Normative References
     11.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   Secure Shell (SSH) [RFC4251] 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 [RFC8032] is a
   digital signature system.  OpenSSH 6.5 [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 the use of the name "ssh-ed25519".  Additionally, this
   document describes the use of Ed448 and formalizes the use of the
   name "ssh-ed448".

2.  Conventions Used in This Document

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

2.1.  Requirements Language

   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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Public Key Algorithm

   This document describes a public key algorithm for use with SSH, as
   per [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.

   Standard implementations of SSH SHOULD implement these signature
   algorithms.

4.  Public Key Format

   The "ssh-ed25519" key format has the following encoding:

   string  "ssh-ed25519"

   string  key

   Here, 'key' is the 32-octet public key described in [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 in [RFC8032],
   Section 5.2.5.

5.  Signature Algorithm

   Signatures are generated according to the procedure in Sections 5.1.6
   and 5.2.6 of [RFC8032].

6.  Signature Format

   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 114-octet signature produced in accordance