Leighton-Micali Hash-Based Signatures
RFC 8554

Document Type RFC - Informational (April 2019; No errata)
Last updated 2019-04-29
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Internet Research Task Force (IRTF)                            D. McGrew
Request for Comments: 8554                                     M. Curcio
Category: Informational                                       S. Fluhrer
ISSN: 2070-1721                                            Cisco Systems
                                                              April 2019

                 Leighton-Micali Hash-Based Signatures

Abstract

   This note describes a digital-signature system based on cryptographic
   hash functions, following the seminal work in this area of Lamport,
   Diffie, Winternitz, and Merkle, as adapted by Leighton and Micali in
   1995.  It specifies a one-time signature scheme and a general
   signature scheme.  These systems provide asymmetric authentication
   without using large integer mathematics and can achieve a high
   security level.  They are suitable for compact implementations, are
   relatively simple to implement, and are naturally resistant to side-
   channel attacks.  Unlike many other signature systems, hash-based
   signatures would still be secure even if it proves feasible for an
   attacker to build a quantum computer.

   This document is a product of the Crypto Forum Research Group (CFRG)
   in the IRTF.  This has been reviewed by many researchers, both in the
   research group and outside of it.  The Acknowledgements section lists
   many of them.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Research Task Force
   (IRTF).  The IRTF publishes the results of Internet-related research
   and development activities.  These results might not be suitable for
   deployment.  This RFC represents the consensus of the Crypto Forum
   Research Group of the Internet Research Task Force (IRTF).  Documents
   approved for publication by the IRSG are not candidates for any level
   of Internet Standard; see 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/rfc8554.

McGrew, et al.                Informational                     [Page 1]
RFC 8554                LMS Hash-Based Signatures             April 2019

Copyright Notice

   Copyright (c) 2019 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  CFRG Note on Post-Quantum Cryptography  . . . . . . . . .   5
     1.2.  Intellectual Property . . . . . . . . . . . . . . . . . .   6
       1.2.1.  Disclaimer  . . . . . . . . . . . . . . . . . . . . .   6
     1.3.  Conventions Used in This Document . . . . . . . . . . . .   6
   2.  Interface . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Notation  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  Data Types  . . . . . . . . . . . . . . . . . . . . . . .   7
       3.1.1.  Operators . . . . . . . . . . . . . . . . . . . . . .   7
       3.1.2.  Functions . . . . . . . . . . . . . . . . . . . . . .   8
       3.1.3.  Strings of w-Bit Elements . . . . . . . . . . . . . .   8
     3.2.  Typecodes . . . . . . . . . . . . . . . . . . . . . . . .   9
     3.3.  Notation and Formats  . . . . . . . . . . . . . . . . . .   9
   4.  LM-OTS One-Time Signatures  . . . . . . . . . . . . . . . . .  12
     4.1.  Parameters  . . . . . . . . . . . . . . . . . . . . . . .  13
     4.2.  Private Key . . . . . . . . . . . . . . . . . . . . . . .  14
     4.3.  Public Key  . . . . . . . . . . . . . . . . . . . . . . .  15
     4.4.  Checksum  . . . . . . . . . . . . . . . . . . . . . . . .  15
     4.5.  Signature Generation  . . . . . . . . . . . . . . . . . .  16
     4.6.  Signature Verification  . . . . . . . . . . . . . . . . .  17
   5.  Leighton-Micali Signatures  . . . . . . . . . . . . . . . . .  19
     5.1.  Parameters  . . . . . . . . . . . . . . . . . . . . . . .  19
     5.2.  LMS Private Key . . . . . . . . . . . . . . . . . . . . .  20
     5.3.  LMS Public Key  . . . . . . . . . . . . . . . . . . . . .  21
     5.4.  LMS Signature . . . . . . . . . . . . . . . . . . . . . .  22
       5.4.1.  LMS Signature Generation  . . . . . . . . . . . . . .  23
       5.4.2.  LMS Signature Verification  . . . . . . . . . . . . .  24
   6.  Hierarchical Signatures . . . . . . . . . . . . . . . . . . .  26
     6.1.  Key Generation  . . . . . . . . . . . . . . . . . . . . .  29
     6.2.  Signature Generation  . . . . . . . . . . . . . . . . . .  30
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