Use of RSA Keys with SHA-2 256 and 512 in Secure Shell (SSH)
draft-ietf-curdle-rsa-sha2-03

Document Type Active Internet-Draft (curdle WG)
Last updated 2017-03-27 (latest revision 2017-02-27)
Replaces draft-rsa-dsa-sha2-256
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Internet-Draft                                                  D. Bider
Updates: 4252, 4253 (if approved)                        Bitvise Limited
Intended status: Standards Track                       February 27, 2017
Expires: August 27, 2017

      Use of RSA Keys with SHA-2 256 and 512 in Secure Shell (SSH)
                   draft-ietf-curdle-rsa-sha2-03.txt

Abstract

  This memo defines an algorithm name, public key format, and signature
  format for use of RSA keys with SHA-2 512 for server and client
  authentication in SSH connections.

Status

  This Internet-Draft is submitted in full conformance with the
  provisions of BCP 78 and BCP 79.

  Internet-Drafts are working documents of the Internet Engineering Task
  Force (IETF), its areas, and its working groups.  Note that other
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Copyright

  Copyright (c) 2017 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
  (http://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
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  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.

Bider                                                           [Page 1]
Internet-Draft         RSA Keys with SHA-2 in SSH          February 2017

1.  Overview and Rationale

  Secure Shell (SSH) is a common protocol for secure communication on
  the Internet. In [RFC4253], SSH originally defined the signature
  methods "ssh-rsa" for server and client authentication using RSA with
  SHA-1, and "ssh-dss" using 1024-bit DSA and SHA-1.
   
  A decade later, these signature methods are considered deficient.
  For US government use, NIST has disallowed 1024-bit RSA and DSA, and
  use of SHA-1 for signing [800-131A].
   
  This memo defines a new algorithm name allowing for interoperable use
  of RSA keys with SHA-2 256 and SHA-2 512, and a mechanism for servers
  to inform SSH clients of signature algorithms they support and accept.

1.1.  Requirements Terminology

  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].

2.  Public Key Algorithms

  This memo adopts the style and conventions of [RFC4253] in specifying
  how use of a signature algorithm is indicated in SSH.

  The following new signature algorithms are defined:
   
    rsa-sha2-256    RECOMMENDED    sign    Raw RSA key
    rsa-sha2-512    OPTIONAL       sign    Raw RSA key

  These signature algorithms are suitable for use both in the SSH transport
  layer [RFC4253] for server authentication, and in the authentication
  layer [RFC4252] for client authentication.

  Since RSA keys are not dependent on the choice of hash function, both
  new algorithms reuse the public key format of the existing "ssh-rsa"
  algorithm as defined in [RFC4253]:

    string    "ssh-rsa"
    mpint     e
    mpint     n
      
  All aspects of the "ssh-rsa" format are kept, including the encoded
  string "ssh-rsa", in order to allow users' existing RSA keys to be
  used with the new signature formats, without requiring re-encoding,
  or affecting already trusted key fingerprints.
   
  Signing and verifying using these algorithms is performed according to
  the RSASSA-PKCS1-v1_5 scheme in [RFC3447] using SHA-2 [FIPS-180-4] as
  hash; MGF1 as mask function; and salt length equal to hash size.

Bider                                                           [Page 2]
Internet-Draft         RSA Keys with SHA-2 in SSH          February 2017
   
  
  For the algorithm "rsa-sha2-256", the hash used is SHA-2 256.
  For the algorithm "rsa-sha2-512", the hash used is SHA-2 512.
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