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INTERNET-DRAFT                                                R. Housley
Intended Status: Proposed Standard                        Vigil Security
Expires: 24 October 2014                                   24 April 2014


      Use of the Hash-based Merkle Tree Signature (MTS) Algorithm
               in the Cryptographic Message Syntax (CMS)
                  <draft-housley-cms-mts-hash-sig-01>


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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
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Housley                                                         [Page 1]

INTERNET-DRAFT                                             24 April 2014


Copyright and License Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  MTS Digital Signature Algorithm  . . . . . . . . . . . . .  3
     1.2.  LDWM One-time Signature Algorithm  . . . . . . . . . . . .  4
     1.3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Algorithm Identifiers and Parameters . . . . . . . . . . . . .  5
   3.  Signed-data Conventions  . . . . . . . . . . . . . . . . . . .  6
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
     4.1.  Implementation Security Considerations . . . . . . . . . .  6
     4.2.  Algorithm Security Considerations  . . . . . . . . . . . .  6
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     6.1.  Normative References . . . . . . . . . . . . . . . . . . .  7
     6.2.  Informative References . . . . . . . . . . . . . . . . . .  8
   Appendix: ASN.1 Module . . . . . . . . . . . . . . . . . . . . . .  8
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  9


















Housley                                                         [Page 2]

INTERNET-DRAFT                                             24 April 2014


1.  Introduction

   This document specifies the conventions for using the 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 specific 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 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 with each node containing an n-byte value.  Each leaf of
   the tree contains the value of the public key of an Lamport, Diffie,
   Winternitz, and Merkle (LDWM) public/private key pair [HASHSIG].  The
   LDWM algorithm requires a robust one-way function to underpin the
   signature generation and verification.  The algorithms in this
   document all make use of the SHA-256 [SHS] one-way hash function,
   which produces a 32 byte result.

   The value at the root of the tree is the MTS public key.  Each
   interior node is computed by applying the hash function to the
   concatenation of the values of its children nodes.  Once again, the
   algorithms in this document all make use of the SHA-256 [SHS] one-way
   hash function.

   An MTS signature consists of an LDWM signature, a node number that
   identifies the leaf node associated with the signature, and an array
   of values associated with the path through the tree from the LDWM
   signature leaf to the root.  The array of values contains 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 branching number k and height h will have (k-1)*h values.  The
   first (k-1) values are the siblings of the leaf, the next (k-1)
   values are the siblings of the parent of the leaf, and so on.








Housley                                                         [Page 3]

INTERNET-DRAFT                                             24 April 2014


   Four tree sizes are specified in [HASHSIG]:

      MTS_SHA256_K2_H20:
         o  k = 2  (2 child nodes for each interior node),
         o  h = 20 (20 levels in the tree),
         o  n = 32 (32 bytes associated with each node), and
         o  mts_algorithm_type = 0x00000001.

      MTS_SHA256_K4_H10:
         o  k = 4  (4 child nodes for each interior node),
         o  h = 10 (10 levels in the tree),
         o  n = 32 (32 bytes associated with each node), and
         o  mts_algorithm_type = 0x00000002.

      MTS_SHA256_K8_H7:
         o  n = 8  (8 child nodes for each interior node),
         o  h = 7  (7 levels in the tree), and
         o  n = 32 (32 bytes associated with each node), and
         o  mts_algorithm_type = 0x00000003.

      MTS_SHA256_K16_H5:
         o  k = 16 (16 child nodes for each interior node),
         o  h = 5  (5 levels in the tree),
         o  n = 32 (32 bytes associated with each node), and
         o  mts_algorithm_type = 0x00000004.

   There are k^h leaves in the tree.

1.2.  LDWM One-time Signature Algorithm

   Merkle Tree Signatures (MTS) depend on a LDWM one-time signature
   method.  The four variants described in [HASHSIG] depend on SHA-256
   [SHS] and SHA-256-20, which is the same as SHA-256, except that the
   hash result is truncated to 20 bytes.

   Four LDWN one-time signature algorithms are defined in [HASHSIG]:

      LDWM_SHA256_M20_W1:
         o  ldwm_algorithm_type = 0x00000001; and
         o  the signature value is the 4-byte ldwm_algorithm_type
            followed by 265 20-byte values.

      LDWM_SHA256_M20_W2:
         o  ldwm_algorithm_type = 0x00000002; and
         o  the signature value is the 4-byte ldwm_algorithm_type
            followed by 133 20-byte values.





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      LDWM_SHA256_M20_W4:
         o  ldwm_algorithm_type = 0x00000003; and
         o  the signature value is the 4-byte ldwm_algorithm_type
            followed by 67 20-byte values.

      LDWM_SHA256_M20_W8:
         o  ldwm_algorithm_type = 0x00000004; and
         o  the signature value is the 4-byte ldwm_algorithm_type
            followed by 32 20-byte values.

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].

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
   mts_algorithm_type as defined in Section 4.5 of [HASHSIG].  For
   convenience, these values are repeated in above in Section 1.1 of
   this document.  This value tells how to parse the remaining parts of
   the signature value, which is composed of an LDWM signature value, a
   4-byte signature leaf number, and the MTS path.

   The first 4 bytes of the LDWM signature value  contains the
   ldwm_algorithm_type as defined in Section 3.10 of [HASHSIG].  For
   convenience, these values are repeated in above in Section 1.2 of
   this document.

   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.




Housley                                                         [Page 5]

INTERNET-DRAFT                                             24 April 2014


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.

   signature contains the single value resulting from the signing
   operation.

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.  Further,
   a LDWM private key MUST be used only one time, and the LDWM private
   key MUST NOT 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].



Housley                                                         [Page 6]

INTERNET-DRAFT                                             24 April 2014


   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.

   The LDWM one-time signature and MTS system 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, September 2009.

   [HASHSIG]  McGrew, D., and M. Curcio, "Hash-Based Signatures", Work
              in progress. <draft-mcgrew-hash-sigs-01>

   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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








Housley                                                         [Page 7]

INTERNET-DRAFT                                             24 April 2014


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]

   [CMSASN1]  Hoffman, P. and J. Schaad, "New ASN.1 Modules for
              Cryptographic Message Syntax (CMS) and S/MIME", RFC 5911,
              June 2010.

   [FWPROT]   Housley, R., "Using Cryptographic Message Syntax (CMS) to
              Protect Firmware Packages", RFC 4108, August 2005.

   [PKIXASN1] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
              Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
              June 2010.

   [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,
              June 2005.




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;











Housley                                                         [Page 8]

INTERNET-DRAFT                                             24 April 2014


   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 }

   MTS-HashSig-PublicKey ::= OCTET STRING

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

   END






Housley                                                         [Page 9]

INTERNET-DRAFT                                             24 April 2014


Author's Address

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

   EMail: housley@vigilsec.com










































Housley                                                        [Page 10]


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