Use of the Hash-based Merkle Tree Signature (MTS) Algorithm in the Cryptographic Message Syntax (CMS)
draft-housley-cms-mts-hash-sig-03

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INTERNET-DRAFT                                                R. Housley
Intended Status: Proposed Standard                        Vigil Security
Expires: 20 April 2016                                   18 October 2015

      Use of the Hash-based Merkle Tree Signature (MTS) Algorithm
               in the Cryptographic Message Syntax (CMS)
                  <draft-housley-cms-mts-hash-sig-03>

Abstract

   This document specifies the conventions for using the Merkle Tree
   Signatures (MTS) digital signature algorithm with the Cryptographic
   Message Syntax (CMS).  The MTS algorithm is one form of hash-based
   digital signature.

Status of this Memo

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

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Housley                                                         [Page 1]
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Copyright and License Notice

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  MTS Digital Signature Algorithm  . . . . . . . . . . . . .  3
     1.2.  LM-OTS One-time Signature Algorithm  . . . . . . . . . . .  4
     1.3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Algorithm Identifiers and Parameters . . . . . . . . . . . . .  4
   3.  Signed-data Conventions  . . . . . . . . . . . . . . . . . . .  5
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  5
     4.1.  Implementation Security Considerations . . . . . . . . . .  6
     4.2.  Algorithm Security Considerations  . . . . . . . . . . . .  6
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   6.  Normative References . . . . . . . . . . . . . . . . . . . . .  7
   7.  Informative References . . . . . . . . . . . . . . . . . . . .  7
   Appendix: ASN.1 Module . . . . . . . . . . . . . . . . . . . . . .  8
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10

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1.  Introduction

   This document specifies the conventions for using the Merkle Tree
   Signatures (MTS) digital signature algorithm with the Cryptographic
   Message Syntax (CMS) [CMS] signed-data content type.  The MTS
   algorithm is one form of hash-based digital signature that can only
   be used for a fixed number of signatures.  The MTS algorithm is
   described in [HASHSIG].  The MTS algorithm uses small private and
   public keys, and it has low computational cost; however, the
   signatures are quite large.

   CMS values are generated using ASN.1 [ASN1-02], using the Basic
   Encoding Rules (BER) and the Distinguished Encoding Rules (DER).

1.1.  MTS Digital Signature Algorithm

   Merkle Tree Signatures (MTS) are a method for signing a large but
   fixed number of messages.  An MTS system is an N-time signature
   system, meaning that the private key can be used to generate at most
   N signatures.

   An MTS system uses two cryptographic components: a one-time signature
   method and a collision-resistant hash function.  Each MTS
   public/private key pair is associated with a k-way tree.  Each leaf
   of the tree can be used to generate a one-time signature (OTS), which
   can be used to securely sign exactly one message, but cannot securely
   sign more than one.

   This specification makes use of the MTS algorithm specified in
   [HASHSIG], which is the Leighton and Micali adaptation [LM] of the
   original Lamport-Diffie-Winternitz-Merkle one-time signature system
   [M1979][M1987][M1989a][M1989b]. It makes use of the LM-OTS one-time
   signature scheme and the SHA-256 [SHS] one-way hash function.

   An LMS system has two parameters.  The height of the tree, h, which
   is the number of levels in the tree minus one.  The [HASHSIG]
   specification supports three values for this parameter: h=20; h=10;
   and h=5.  The number of bytes associated with each node in the tree,
   n, is defined by the hash function.  The [HASHSIG] specification
   supports two hash functions: SHA-256 [SHS], with n=32; and
   SHA-256-16, which is the same as SHA-256, except that the hash result
   is truncated to 16 bytes, with n=16.  Note that there are 2^h leaves
   in the tree.

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   Six tree sizes are specified in [HASHSIG]:
      lms_sha256_n32_h20;
      lms_sha256_n32_h10;
      lms_sha256_n32_h5;
      lms_sha256_n16_h20;
      lms_sha256_n16_h10; and
      lms_sha256_n16_h5.

   An LMS signature consists of three things: a typecode indicating the
   particular LMS algorithm, an LM-OTS signature, and an array of values
   that is associated with the path through the tree from the leaf
   associated with the LM-OTS signature to the root.  The array of
   values contains the siblings of the nodes on the path from the leaf
   to the root but does not contain the nodes on the path itself.  The
   array for a tree with height h will have h values.  The first value
   is the sibling of the leaf, the next value is the sibling of the
   parent of the leaf, and so on up the path to the root.

1.2.  LM-OTS One-time Signature Algorithm

   Merkle Tree Signatures (MTS) depend on a LM-OTS one-time signature
   method.  An LM-OTS has four parameters.  The number of bytes
   associated with the has function, n, which is the same as the LMS
   parameter.  Again, the [HASHSIG] specification supports two hash
   functions: SHA-256 [SHS], with n=32; and SHA-256-16, with n=16.  The
   the Winternitz parameter, w.  The [HASHSIG] specification supports
   four values for this parameter: w=1; w=2; w=4; and w=8.  The number
   of n-byte string elements that make up the LM-OTS signature, p.  The
   number of left-shift bits used in the checksum function, ls.  The
   values of p and ls are dependent on the choices of the parameters n
   and w, as described in Appendix A of [HASHSIG].

   Eight LM-OTS variants are defined in [HASHSIG]:
      LMOTS_SHA256_N32_W1;
      LMOTS_SHA256_N32_W2;
      LMOTS_SHA256_N32_W4;
      LMOTS_SHA256_N32_W8;
      LMOTS_SHA256_N16_W1;
      LMOTS_SHA256_N16_W2;
      LMOTS_SHA256_N16_W4; and
      LMOTS_SHA256_N16_W8.

1.3.  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 RFC 2119 [KEYWORDS].

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2.  Algorithm Identifiers and Parameters

   The algorithm identifier for an MTS signature is id-alg-mts-hashsig:

      id-smime  OBJECT IDENTIFIER ::= { iso(1) member-body(2)
                  us(840) rsadsi(113549) pkcs(1) pkcs9(9) 16 }

      id-alg  OBJECT IDENTIFIER ::= { id-smime  3 }

      id-alg-mts-hashsig  OBJECT IDENTIFIER ::= { id-alg 17 }

   When the id-alg-mts-hashsig algorithm identifier is used for a
   signature, the AlgorithmIdentifier parameters field MUST be absent.

   The first 4 bytes of the signature value contains the
   mls_algorithm_type as defined in Section 5.5 of [HASHSIG].  This type
   tells how to parse the remaining parts of the signature value, which
   is composed of an LM-OTS signature and an array of values that is
   associated with the path through the tree from the leaf associated
   with the LM-OTS signature to the root.

   The first 4 bytes of the LM-OTS signature value  contains the
   ots_algorithm_type as defined in Section 4.10 of [HASHSIG].  This
   type is followed by n*p bytes of signature value.

   The signature format is designed for easy parsing.  Each format
   starts with a 4-byte enumeration value that indicates all of the
   details of the signature algorithm, indirectly providing all of the
   information that is needed to parse the value during signature
   validation.

3.  Signed-data Conventions

   digestAlgorithms SHOULD contain the one-way hash function used to
   compute the message digest on the eContent value.  Since the hash-
   based signature algorithms all depend on SHA-256, it is strongly
   RECOMMENDED that SHA-256 also be used to compute the message digest
   on the content.

   Further, the same one-way hash function SHOULD be used to compute the
   message digest on both the eContent and the signedAttributes value if
   signedAttributes exist.  Again, since the hash-based signature
   algorithms all depend on SHA-256, it is strongly RECOMMENDED that
   SHA-256 be used.

   signatureAlgorithm MUST contain id-alg-mts-hashsig.  The algorithm
   parameters field MUST be absent.

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   signature contains the single value resulting from the signing
   operation as specified in [HASHSIG].

4.  Security Considerations

4.1.  Implementation Security Considerations

   Implementations must protect the private keys.  Compromise of the
   private keys may result in the ability to forge signatures.  Along
   with the private key, the implementation must maintain a counter
   value that indicates which leaf nodes in the tree have been used.
   Loss of integrity of this counter can cause an one-time key to be
   used more than once.  As a result, when a private key and an
   associated counter value are stored on non-volatile media or stored
   in a virtual machine environment, care must be taken to preserve
   these properties.

   An implementation must ensure that a LDWM private key is used only
   one time, and ensure that the LDWM private key cannot be used for any
   other purpose.

   The generation of private keys relies on random numbers.  The use of
   inadequate pseudo-random number generators (PRNGs) to generate these
   values can result in little or no security.  An attacker may find it
   much easier to reproduce the PRNG environment that produced the keys,
   searching the resulting small set of possibilities, rather than brute
   force searching the whole key space.  The generation of quality
   random numbers is difficult.  RFC 4086 [RANDOM] offers important
   guidance in this area.

   When computing signatures, the same hash function SHOULD be used for
   all operations.  This reduces the number of failure points in the
   signature process.

4.2.  Algorithm Security Considerations

   At Black Hat USA 2013, some researchers gave a presentation on the
   current sate of public key cryptography.  They said: "Current
   cryptosystems depend on discrete logarithm and factoring which has
   seen some major new developments in the past 6 months" [BH2013].
   They encouraged preparation for a day when RSA and DSA cannot be
   depended upon.

   A post-quantum cryptosystem is a system that is secure against
   quantum computers that have more than a trivial number of quantum
   bits.  It is open to conjecture whether it is feasible to build such
   a machine.  RSA, DSA, and ECDSA are not post-quantum secure.

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   The LM-OTP one-time signature and LMS do not depend on discrete
   logarithm or factoring, and these algorithms are considered to be
   post-quantum secure.

   Today, RSA is often used to digitally sign software updates.  This
   means that the distribution of software updates could be compromised
   if a significant advance is made in factoring or a quantum computer
   is invented.  The use of MTS signatures to protect software update
   distribution, perhaps using the format described in [FWPROT], will
   allow the deployment of software that implements new cryptosystems.

5.  IANA Considerations

   {{ RFC Editor: Please remove this section prior to publication. }}

   This document has no actions for IANA.

6.  Normative References

   [ASN1-02]  ITU-T, "ITU-T Recommendation X.680, X.681, X.682, and
              X.683", ITU-T X.680, X.681, X.682, and X.683, 2002.

   [CMS]      Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <http://www.rfc-editor.org/info/rfc5652>.

   [HASHSIG]  McGrew, D., and M. Curcio, "Hash-Based Signatures", Work
              in progress. <draft-mcgrew-hash-sigs-03>

   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI
              10.17487/RFC2119, March 1997, <http://www.rfc-
              editor.org/info/rfc2119>.

   [SHS]      National Institute of Standards and Technology (NIST),
              FIPS Publication 180-3: Secure Hash Standard, October
              2008.

7.  Informative References

   [BH2013]   Ptacek, T., T. Ritter, J. Samuel, and A. Stamos, "The
              Factoring Dead: Preparing for the Cryptopocalypse", August
              2013.  <https://media.blackhat.com/us-13/us-13-Stamos-The-
              Factoring-Dead.pdf>

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   [CMSASN1]  Hoffman, P. and J. Schaad, "New ASN.1 Modules for
              Cryptographic Message Syntax (CMS) and S/MIME", RFC 5911,
              DOI 10.17487/RFC5911, June 2010, <http://www.rfc-
              editor.org/info/rfc5911>.

   [FWPROT]   Housley, R., "Using Cryptographic Message Syntax (CMS) to
              Protect Firmware Packages", RFC 4108, DOI
              10.17487/RFC4108, August 2005, <http://www.rfc-
              editor.org/info/rfc4108>.

   [LM]       Leighton, T. and S. Micali, "Large provably fast and
              secure digital signature schemes from secure hash
              functions", U.S. Patent 5,432,852, July 1995.

   [M1979]    Merkle, R., "Secrecy, Authentication, and Public Key
              Systems", Stanford University Information Systems
              Laboratory Technical Report 1979-1, 1979.

   [M1987]    Merkle, R., "A Digital Signature Based on a Conventional
              Encryption Function", Lecture Notes in Computer Science
              crypto87, 1988.

   [M1989a]   Merkle, R., "A Certified Digital Signature", Lecture Notes
              in Computer Science crypto89, 1990.

   [M1989b]  Merkle, R., "One Way Hash Functions and DES", Lecture Notes
              in Computer Science crypto89, 1990.

   [PKIXASN1] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
              Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
              DOI 10.17487/RFC5912, June 2010, <http://www.rfc-
              editor.org/info/rfc5912>.

   [PQC]      Bernstein, D., "Introduction to post-quantum
              cryptography", 2009.
              <http://www.pqcrypto.org/www.springer.com/cda/content/
              document/cda_downloaddocument/9783540887010-c1.pdf>

   [RANDOM]   Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005, <http://www.rfc-
              editor.org/info/rfc4086>.

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Appendix: ASN.1 Module

   MTS-HashSig-2013
     { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
       id-smime(16) id-mod(0) id-mod-mts-hashsig-2013(64) }

   DEFINITIONS EXPLICIT TAGS ::= BEGIN

   EXPORTS ALL;

   IMPORTS
     SIGNATURE-ALGORITHM PUBLIC-KEY
       FROM AlgorithmInformation-2009  -- RFC 5911 [CMSASN1]
         { iso(1) identified-organization(3) dod(6) internet(1)
           security(5) mechanisms(5) pkix(7) id-mod(0)
           id-mod-algorithmInformation-02(58) }

     mda-sha256
       FROM PKIX1-PSS-OAEP-Algorithms-2009  -- RFC 5912 [PKIXASN1]
         { iso(1) identified-organization(3) dod(6)
           internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
           id-mod-pkix1-rsa-pkalgs-02(54) } ;

   --
   -- Object Identifiers
   --

   id-smime  OBJECT IDENTIFIER ::= { iso(1) member-body(2)
               us(840) rsadsi(113549) pkcs(1) pkcs9(9) 16 }

   id-alg  OBJECT IDENTIFIER ::= { id-smime  3 }

   id-alg-mts-hashsig  OBJECT IDENTIFIER ::= { id-alg 17 }

   --
   -- Signature Algorithm and Public Key
   --

   sa-MTS-HashSig SIGNATURE-ALGORITHM ::= {
        IDENTIFIER id-alg-mts-hashsig
        HASHES { mda-sha256, ... }
        PUBLIC-KEYS { pk-MTS-HashSig } }

   pk-MTS-HashSig PUBLIC-KEY ::= {
       IDENTIFIER id-alg-mts-hashsig
       KEY MTS-HashSig-PublicKey }

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   MTS-HashSig-PublicKey ::= OCTET STRING

   HashSignatureAlgs SIGNATURE-ALGORITHM ::= {
       sa-MTS-HashSig, ... }

   END

Author's Address

   Russ Housley
   Vigil Security, LLC
   918 Spring Knoll Drive
   Herndon, VA 20170
   USA

   EMail: housley@vigilsec.com

Housley                                                        [Page 10]