Use of RSA Keys with SHA-256 and SHA-512 in the Secure Shell (SSH) Protocol
RFC 8332

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Internet Engineering Task Force (IETF)                          D. Bider
Request for Comments: 8332                               Bitvise Limited
Updates: 4252, 4253                                           March 2018
Category: Standards Track
ISSN: 2070-1721

                Use of RSA Keys with SHA-256 and SHA-512
                   in the Secure Shell (SSH) Protocol

Abstract

   This memo updates RFCs 4252 and 4253 to define new public key
   algorithms for use of RSA keys with SHA-256 and SHA-512 for server
   and client authentication in SSH connections.

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/rfc8332.

Bider                        Standards Track                    [Page 1]
RFC 8332        Use of RSA Keys with SHA-256 and SHA-512      March 2018

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   than English.

Table of Contents

   1.  Overview and Rationale  . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   3
     1.2.  Wire Encoding Terminology . . . . . . . . . . . . . . . .   3
   2.  Public Key Format vs. Public Key Algorithm  . . . . . . . . .   3
   3.  New RSA Public Key Algorithms . . . . . . . . . . . . . . . .   4
     3.1.  Use for Server Authentication . . . . . . . . . . . . . .   5
     3.2.  Use for Client Authentication . . . . . . . . . . . . . .   5
     3.3.  Discovery of Public Key Algorithms Supported by Servers .   6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
     5.1.  Key Size and Signature Hash . . . . . . . . . . . . . . .   7
     5.2.  Transition  . . . . . . . . . . . . . . . . . . . . . . .   7
     5.3.  PKCS #1 v1.5 Padding and Signature Verification . . . . .   7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

Bider                        Standards Track                    [Page 2]
RFC 8332        Use of RSA Keys with SHA-256 and SHA-512      March 2018

1.  Overview and Rationale

   Secure Shell (SSH) is a common protocol for secure communication on
   the Internet.  In [RFC4253], SSH originally defined the public key
   algorithms "ssh-rsa" for server and client authentication using RSA
   with SHA-1, and "ssh-dss" using 1024-bit DSA and SHA-1.  These
   algorithms are now considered deficient.  For US government use, NIST
   has disallowed 1024-bit RSA and DSA, and use of SHA-1 for signing
   [NIST.800-131A].

   This memo updates RFCs 4252 and 4253 to define new public key
   algorithms allowing for interoperable use of existing and new RSA
   keys with SHA-256 and SHA-512.

1.1.  Requirements Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and