Use of the HSS/LMS Hash-Based Signature Algorithm in the Cryptographic Message Syntax (CMS)
RFC 8708

Document Type RFC - Proposed Standard (February 2020; No errata)
Author Russ Housley 
Last updated 2020-03-09
Replaces draft-housley-cms-mts-hash-sig
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Internet Engineering Task Force (IETF)                        R. Housley
Request for Comments: 8708                                Vigil Security
Category: Standards Track                                  February 2020
ISSN: 2070-1721

 Use of the HSS/LMS Hash-Based Signature Algorithm in the Cryptographic
                          Message Syntax (CMS)

Abstract

   This document specifies the conventions for using the Hierarchical
   Signature System (HSS) / Leighton-Micali Signature (LMS) hash-based
   signature algorithm with the Cryptographic Message Syntax (CMS).  In
   addition, the algorithm identifier and public key syntax are
   provided.  The HSS/LMS algorithm is one form of hash-based digital
   signature; it is described in RFC 8554.

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/rfc8708.

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
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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
     1.1.  ASN.1
     1.2.  Terminology
     1.3.  Motivation
   2.  HSS/LMS Hash-Based Signature Algorithm Overview
     2.1.  Hierarchical Signature System (HSS)
     2.2.  Leighton-Micali Signature (LMS)
     2.3.  Leighton-Micali One-Time Signature (LM-OTS) Algorithm
   3.  Algorithm Identifiers and Parameters
   4.  HSS/LMS Public Key Identifier
   5.  Signed-Data Conventions
   6.  Security Considerations
   7.  IANA Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Appendix A.  ASN.1 Module
   Acknowledgements
   Author's Address

1.  Introduction

   This document specifies the conventions for using the Hierarchical
   Signature System (HSS) / Leighton-Micali Signature (LMS) hash-based
   signature algorithm with the Cryptographic Message Syntax (CMS) [CMS]
   signed-data content type.  The LMS system provides a one-time digital
   signature that is a variant of Merkle Tree Signatures (MTS).  The HSS
   is built on top of the LMS system to efficiently scale for a larger
   numbers of signatures.  The HSS/LMS algorithm is one form of hash-
   based digital signature, and it is described in [HASHSIG].  The HSS/
   LMS signature algorithm can only be used for a fixed number of
   signing operations with a given private key, and the number of
   signing operations depends upon the size of the tree.  The HSS/LMS
   signature algorithm uses small public keys, and it has low
   computational cost; however, the signatures are quite large.  The
   HSS/LMS private key can be very small when the signer is willing to
   perform additional computation at signing time; alternatively, the
   private key can consume additional memory and provide a faster
   signing time.  The HSS/LMS signatures [HASHSIG] are currently defined
   to exclusively use SHA-256 [SHS].

1.1.  ASN.1

   CMS values are generated using ASN.1 [ASN1-B], using the Basic
   Encoding Rules (BER) and the Distinguished Encoding Rules (DER)
   [ASN1-E].

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

1.3.  Motivation

   Recent advances in cryptanalysis [BH2013] and progress in the
   development of quantum computers [NAS2019] pose a threat to widely
   deployed digital signature algorithms.  As a result, there is a need
   to prepare for a day when cryptosystems such as RSA and DSA that
   depend on discrete logarithms and factoring cannot be depended upon.

   If large-scale quantum computers are ever built, these computers will
   be able to break many of the public key cryptosystems currently in
   use.  A post-quantum cryptosystem [PQC] is a system that is secure
   against quantum computers that have more than a trivial number of
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