RFC 8708

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

Okay bestie, let's talk about RFC 8708 💖 It's an IETF Request for Comments, and its author is R. Housley from Vigil Security. It's a Standards Track document, dated February 2020, with ISSN 2070-1721. The header doesn't list anything it obsoletes or updates, so there's no drama there 🎀

Abstract

This doc lays out the rules for using the Hierarchical Signature System (HSS) / Leighton-Micali Signature (LMS) hash-based signature algorithm with the Cryptographic Message Syntax (CMS) 🔐 It also gives you the algorithm identifier and the public key syntax. HSS/LMS is one flavour of hash-based digital signature, and it's described in RFC 8554 🦋

Status of This Memo

This is an Internet Standards Track document 💅

It's a product of the Internet Engineering Task Force (IETF), so it represents the consensus of the IETF community. It went through public review and was approved for publication by the Internet Engineering Steering Group (IESG). If you want more on Internet Standards, check Section 2 of RFC 7841 🌸

For the current status, any errata, and how to send feedback, go to 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 Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) as they stand on the publication date. Please read these carefully, because they spell out your rights and restrictions for this document 📜 Any Code Components pulled out of this document must include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come without warranty, as the Simplified BSD License describes.

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 doc is all about using HSS/LMS with the Cryptographic Message Syntax (CMS) [CMS] signed-data content type 💖 LMS gives you a one-time digital signature, and it's a variant of Merkle Tree Signatures (MTS). HSS sits on top of LMS so it can scale up to a bigger number of signatures efficiently 🧚 HSS/LMS is one form of hash-based digital signature, and [HASHSIG] describes it.

Here's the catch: an HSS/LMS signature algorithm can only be used for a fixed number of signing operations with a given private key, and that number depends on the size of the tree 🙈 The public keys are small and the computational cost is low, but the signatures are quite large. An HSS/LMS private key can be really tiny if the signer is okay doing extra computation at signing time. Or the private key can eat more memory and sign faster, so you pick your poison 🍓 For now, the HSS/LMS signatures [HASHSIG] are defined to use exclusively SHA-256 [SHS].

1.1. ASN.1

CMS values are made with ASN.1 [ASN1-B], encoded 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 read as described in BCP 14 [RFC2119] [RFC8174], but only when they show up in all capitals, exactly like that 📖 Lowercase versions don't count, bestie 💅

1.3. Motivation

Recent advances in cryptanalysis [BH2013] and progress on quantum computers [NAS2019] are a real threat to digital signature algorithms that are widely deployed 😭 We need to get ready for a day when cryptosystems like RSA and DSA, which rely on discrete logarithms and factoring, can no longer be counted on.

If large-scale quantum computers ever get built, they'll be able to break a lot of the public key cryptosystems we use today. A post-quantum cryptosystem [PQC] is one that stays secure against quantum computers with more than a trivial number of quantum bits (qubits) 👑 Nobody knows when we'll be able to build those machines. But RSA, DSA, Elliptic Curve Digital Signature Algorithm (ECDSA), and Edwards-curve Digital Signature Algorithm (EdDSA) are all vulnerable if large-scale quantum computers ever show up.

HSS/LMS doesn't depend on the difficulty of discrete logarithms or factoring, so it's considered post-quantum secure ✨ One great use for post-quantum-secure signatures is protecting software updates, maybe using the format in [FWPROT], so people can roll out software that implements new cryptosystems 🦋

2. HSS/LMS Hash-Based Signature Algorithm Overview 🌸

Merkle Tree Signatures (MTS) are a way to sign a large but fixed number of messages 🎀 An MTS system relies on a one-time signature method and a collision-resistant hash function.

This spec uses the hash-based algorithm from [HASHSIG], which is the Leighton and Micali adaptation [LM] of the original Lamport-Diffie-Winternitz-Merkle one-time signature system [M1979] [M1987] [M1989a] [M1989b] 🧠

As the name suggests, the hash-based signature algorithm depends on a collision-resistant hash function. The one in [HASHSIG] uses only the SHA-256 one-way hash function [SHS], but it sets up an IANA registry [IANA-LMS] so more one-way hash functions can be registered in the future 🔮

2.1. Hierarchical Signature System (HSS)

The MTS system in [HASHSIG] uses a hierarchy of trees. The N-time Hierarchical Signature System (HSS) lets the signer generate subordinate trees when they're needed 🌳 Otherwise, generating the whole tree could take weeks or longer, and nobody has time for that 😩

An HSS signature from [HASHSIG] carries the number of signed public keys (Nspk), then that many signed public keys, and then the LMS signature from Section 2.2. The public key of the topmost LMS tree is the public key of the HSS system 👑 The LMS private key in the parent tree signs the LMS public key of the child tree. The LMS private key in the bottom-most tree signs the actual message. The signatures over the public key and over the actual message are both LMS signatures from Section 2.2.

For a standalone tree (a top tree with no children), the elements of the HSS signature value look like this:

      u32str(0) ||
      lms_signature  /* signature of message */

Here, u32str() and || work the way they're defined in [HASHSIG] 💜

For a tree with Nspk signed public keys, the elements of the HSS signature value look like this:

      u32str(Nspk) ||
      signed_public_key[0] ||
      signed_public_key[1] ||
         ...
      signed_public_key[Nspk-2] ||
      signed_public_key[Nspk-1] ||
      lms_signature  /* signature of message */

As Section 3.3 of [HASHSIG] defines it, a signed_public_key structure holds the lms_signature over the public key, followed by the public key itself. Also, Nspk is the number of levels in the tree hierarchy minus 1 🫶

2.2. Leighton-Micali Signature (LMS)

Every tree in the system from [HASHSIG] uses the Leighton-Micali Signature (LMS) system 🦋 LMS has two parameters. The first is the height of the tree, h, which is the number of levels in the tree minus one. [HASHSIG] supports five values for it: h=5, h=10, h=15, h=20, and h=25. Remember, a tree has 2^h leaves ✨ The second parameter, m, is the number of bytes the hash function outputs, which is the amount of data for each node in the tree. [HASHSIG] supports only the SHA-256 hash function [SHS], with m=32. So [HASHSIG] supports five tree sizes, identified as:

• LMS_SHA256_M32_H5
• LMS_SHA256_M32_H10
• LMS_SHA256_M32_H15
• LMS_SHA256_M32_H20
• LMS_SHA256_M32_H25

[HASHSIG] sets up an IANA registry [IANA-LMS] so more hash functions and more tree sizes can be registered later 🔥

As [HASHSIG] specifies, the LMS public key has four elements: the lms_algorithm_type from the list above, the otstype that identifies the Leighton-Micali One-Time Signature (LM-OTS) type (see Section 2.3), the private key identifier (I) from Section 5.3 of [HASHSIG], and the m-byte string for the root node of the tree (T[1]) 💖 The LMS public key looks like this:

      u32str(lms_algorithm_type) || u32str(otstype) || I || T[1]

Also per [HASHSIG], an LMS signature has four elements: the number of the leaf (q) tied to the LM-OTS signature value, an LM-OTS signature value (see Section 2.3), a typecode for the particular LMS algorithm, and an array of values for the path through the tree from the leaf tied to the LM-OTS signature value up to the root 🌈 The array holds the siblings of the nodes on that path, but not the nodes on the path itself. A tree of height h has h values in that array. The first value is the sibling of the leaf, the next is the sibling of the leaf's parent, and so on up to the root. The four elements of the LMS signature value look like this:

      u32str(q) ||
      ots_signature ||
      u32str(type) ||
      path[0] || path[1] || ... || path[h-1]

---

Part 1 of 3 is done, bestie! 💜 Part 2 is coming up next, so stay tuned 🎀

2.3. Leighton-Micali One-Time Signature (LM-OTS) Algorithm ✨

Okay bestie, Merkle Tree Signatures (MTS) depend on a one-time signature method 🌸, and [HASHSIG] specifies LM-OTS, which has five parameters:

n: The length in bytes of the hash function output. [HASHSIG] supports only SHA-256 [SHS], with n=32. 🔥

H: A preimage-resistant hash function that accepts byte strings of any length and returns an n-byte string. 💅

w: The width in bits of the Winternitz coefficients. [HASHSIG] supports four values for this parameter: w=1, w=2, w=4, and w=8. 🦋

p: The number of n-byte string elements that make up the LM-OTS signature value. 🧚

ls: The number of bits that are left-shifted in the final step of the checksum function, which is defined in Section 4.4 of [HASHSIG]. 💜

The values of p and ls depend on your choices of n and w, as described in Appendix B of [HASHSIG]. It's giving math homework, but it's worth it ngl 🙈

The [HASHSIG] specification supports four LM-OTS variants:

• LMOTS_SHA256_N32_W1
• LMOTS_SHA256_N32_W2
• LMOTS_SHA256_N32_W4
• LMOTS_SHA256_N32_W8

The [HASHSIG] specification also sets up an IANA registry [IANA-LMS] so more variants can be registered later. Future-proof queen behavior 👑

Signing involves generating C, an n-byte random value. Random values, bestie, always! 🎀

The LM-OTS signature value can be summarized as the identifier of the LM-OTS variant, the random value, and a sequence of hash values (y[0] through y[p-1]) that correspond to the elements of the public key, as described in Section 4.5 of [HASHSIG]:

u32str(otstype) || C || y[0] || ... || y[p-1]

3. Algorithm Identifiers and Parameters 💜

The algorithm identifier for an HSS/LMS hash-based signature is:

id-alg-hss-lms-hashsig OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) alg(3) 17 }

When this object identifier is used for an HSS/LMS signature, the AlgorithmIdentifier parameters field MUST be absent (that is, the parameters are not present, and the parameters are not set to NULL). Absent means absent, not NULL, no exceptions 🙅‍♀️

The signature value is a large OCTET STRING, as described in Section 2 of this document. The signature format is designed for easy parsing. The HSS, LMS, and LM-OTS components of the signature value each include a counter and a typecode that indirectly provide all of the information that is needed to parse the value during signature validation. So the parser has everything it needs, no guessing, very organized 🗂️✨

The signature value identifies the hash function used in the HSS/LMS tree. [HASHSIG] uses only the SHA-256 hash function [SHS], but it establishes an IANA registry [IANA-LMS] to permit the registration of additional hash functions in the future. 🌈

4. HSS/LMS Public Key Identifier 🔑

The AlgorithmIdentifier for an HSS/LMS public key uses the id-alg-hss-lms-hashsig object identifier, and the parameters field MUST be absent.

When this AlgorithmIdentifier appears in the SubjectPublicKeyInfo field of an X.509 certificate [RFC5280], the certificate key usage extension MAY contain digitalSignature, nonRepudiation, keyCertSign, and cRLSign; however, it MUST NOT contain other values. So you get a short, specific list of allowed key usages, and that's the whole vibe 💅

pk-HSS-LMS-HashSig PUBLIC-KEY ::= {
    IDENTIFIER id-alg-hss-lms-hashsig
    KEY HSS-LMS-HashSig-PublicKey
    PARAMS ARE absent
    CERT-KEY-USAGE
      { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

HSS-LMS-HashSig-PublicKey ::= OCTET STRING

Note that id-alg-hss-lms-hashsig is also referred to as id-alg-mts-hashsig. This synonym comes from the terminology used in an early draft version of the document that became [HASHSIG]. Two names, one identifier, zero drama 🦋

The public key value is an OCTET STRING. Like the signature format, it is designed for easy parsing. The value is the number of levels in the public key, L, followed by the LMS public key.

The HSS/LMS public key value can be described as:

u32str(L) || lms_public_key

Note that the public key for the topmost LMS tree is the public key of the HSS system. When L=1, the HSS system is a single tree. Simple, clean, iconic 🌸

5. Signed-Data Conventions 📝

As specified in [CMS], the digital signature is produced from the message digest and the signer's private key. The signature is computed over different values depending on whether signed attributes are absent or present.

When signed attributes are absent, the HSS/LMS signature is computed over the content. When signed attributes are present, a hash is computed over the content using the same hash function that is used in the HSS/LMS tree. Then a message-digest attribute is constructed with the hash of the content, and then the HSS/LMS signature is computed over the DER-encoded set of signed attributes (which MUST include a content-type attribute and a message-digest attribute). In summary:

IF (signed attributes are absent)
THEN HSS_LMS_Sign(content)
ELSE message-digest attribute = Hash(content);
     HSS_LMS_Sign(DER(SignedAttributes))

When using [HASHSIG], the fields in the SignerInfo are used as follows:

• digestAlgorithm MUST contain the one-way hash function used in the HSS/LMS tree. In [HASHSIG], SHA-256 is the only supported hash function, but other hash functions might be registered in the future. For convenience, the AlgorithmIdentifier for SHA-256 from [PKIXASN1] is repeated here:

mda-sha256 DIGEST-ALGORITHM ::= {
    IDENTIFIER id-sha256
    PARAMS TYPE NULL ARE preferredAbsent }

id-sha256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
    country(16) us(840) organization(1) gov(101) csor(3)
    nistAlgorithms(4) hashalgs(2) 1 }

• signatureAlgorithm MUST contain id-alg-hss-lms-hashsig, and the algorithm parameters field MUST be absent.
• signature contains the single HSS signature value resulting from the signing operation as specified in [HASHSIG].

6. Security Considerations 🚨

Okay, bestie, this section is SERIOUS, so read it carefully 😭

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 keep track of which leaf nodes in the tree have been used. Loss of integrity of this tracking data can cause a one-time key to be used more than once. As a result, when a private key and the tracking data are stored on non-volatile media or in a virtual machine environment, failed writes, virtual machine snapshotting or cloning, and other operational concerns must be considered to ensure confidentiality and integrity. Reusing a one-time key is the ultimate ick, so guard that tracking data like it's your diary 💀

When generating an LMS key pair, an implementation MUST generate each key pair independently of all other key pairs in the HSS tree.

An implementation MUST ensure that an LM-OTS private key is used to generate a signature only one time and ensure that it cannot be used for any other purpose. One signature per key, period, no sharing 🙅‍♀️💅

The generation of private keys relies on random numbers. The use of inadequate pseudorandom 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, and [RFC4086] offers important guidance in this area. Weak randomness is a whole horror movie 😱, so go read [RFC4086] for real.

The generation of hash-based signatures also depends on random numbers. While the consequences of an inadequate pseudorandom number generator (PRNG) to generate these values is much less severe than in the generation of private keys, the guidance in [RFC4086] remains important. Less severe does not mean ignore it, periodt ✨

When computing signatures, the same hash function SHOULD be used to compute the message digest of the content and the signed attributes, if they are present.

7. IANA Considerations 🌷

In the "SMI Security for S/MIME Module Identifier (1.2.840.113549.1.9.16.0)" registry, IANA has updated the reference for value 64 to point to this document.

In the "SMI Security for S/MIME Algorithms (1.2.840.113549.1.9.16.3)" registry, IANA has updated the description for value 17 to "id-alg-hss-lms-hashsig" and updated the reference to point to this document.

IANA has also added the following note to the "SMI Security for S/MIME Algorithms (1.2.840.113549.1.9.16.3)" registry:

Value 17, "id-alg-hss-lms-hashsig", is also referred to as "id-
alg-mts-hashsig".

8. References 📚

8.1. Normative References

[ASN1-B]   ITU-T, "Information technology -- Abstract Syntax Notation
           One (ASN.1): Specification of basic notation",
           ITU-T Recommendation X.680, August 2015.

[ASN1-E]   ITU-T, "Information technology -- ASN.1 encoding rules:
           Specification of Basic Encoding Rules (BER), Canonical
           Encoding Rules (CER) and Distinguished Encoding Rules
           (DER)", ITU-T Recommendation X.690, August 2015.

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

[HASHSIG]  McGrew, D., Curcio, M., and S. Fluhrer, "Leighton-Micali
           Hash-Based Signatures", RFC 8554, DOI 10.17487/RFC8554,
           April 2019, <https://www.rfc-editor.org/info/rfc8554>.

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

[RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
           Housley, R., and W. Polk, "Internet X.509 Public Key
           Infrastructure Certificate and Certificate Revocation List
           (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
           <https://www.rfc-editor.org/info/rfc5280>.

[RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
           2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
           May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[SHS]      National Institute of Standards and Technology (NIST),
           "Secure Hash Standard (SHS)", FIPS PUB 180-4,
           DOI 10.6028/NIST.FIPS.180-4, August 2015,
           <https://doi.org/10.6028/NIST.FIPS.180-4>.

8.2. Informative References 📚✨

Okay bestie, these are the extra reads that back up the whole spec. They're not required to implement it, but they're where the history and the deep background live 🤓💖

[BH2013] Ptacek, T., Ritter, T., Samuel, J., 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, DOI 10.17487/RFC5911, June 2010, <https://www.rfc-editor.org/info/rfc5911>.

[CMSASN1U] Schaad, J. and S. Turner, "Additional New ASN.1 Modules for the Cryptographic Message Syntax (CMS) and the Public Key Infrastructure Using X.509 (PKIX)", RFC 6268, DOI 10.17487/RFC6268, July 2011, <https://www.rfc-editor.org/info/rfc6268>.

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

[IANA-LMS] IANA, "Leighton-Micali Signatures (LMS)", <https://www.iana.org/assignments/leighton-micali-signatures/>.

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

[M1979] Merkle, R., "Secrecy, Authentication, and Public Key Systems", Technical Report No. 1979-1, Information Systems Laboratory, Stanford University, 1979.

[M1987] Merkle, R., "A Digital Signature Based on a Conventional Encryption Function", Advances in Cryptology -- CRYPTO '87 Proceedings, Lecture Notes in Computer Science Vol. 293, DOI 10.1007/3-540-48184-2_32, 1988, <https://doi.org/10.1007/3-540-48184-2_32>.

[M1989a] Merkle, R., "A Certified Digital Signature", Advances in Cryptology -- CRYPTO '89 Proceedings, Lecture Notes in Computer Science Vol. 435, DOI 10.1007/0-387-34805-0_21, 1990, <https://doi.org/10.1007/0-387-34805-0_21>.

[M1989b] Merkle, R., "One Way Hash Functions and DES", Advances in Cryptology -- CRYPTO '89 Proceedings, Lecture Notes in Computer Science Vol. 435, DOI 10.1007/0-387-34805-0_40, 1990, <https://doi.org/10.1007/0-387-34805-0_40>.

[NAS2019] National Academies of Sciences, Engineering, and Medicine, "Quantum Computing: Progress and Prospects", The National Academies Press, DOI 10.17226/25196, 2019, <https://doi.org/10.17226/25196>.

[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, <https://www.rfc-editor.org/info/rfc5912>.

[PQC] Bernstein, D., "Introduction to post-quantum cryptography", DOI 10.1007/978-3-540-88702-7_1, 2009, <http://www.springer.com/cda/content/document/cda_downloaddocument/9783540887010-c1.pdf>.

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

---

Appendix A. ASN.1 Module 🧩

Here's the official ASN.1 module, copied over character for character. Don't touch a single thing in here 🙈

<CODE STARTS>

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 IMPLICIT TAGS ::= BEGIN

EXPORTS ALL;

IMPORTS
  PUBLIC-KEY, SIGNATURE-ALGORITHM, SMIME-CAPS
    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) } ;

--
-- Object Identifiers
--

id-alg-hss-lms-hashsig OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) alg(3) 17 }

id-alg-mts-hashsig OBJECT IDENTIFIER ::= id-alg-hss-lms-hashsig

--
-- Signature Algorithm and Public Key
--

sa-HSS-LMS-HashSig SIGNATURE-ALGORITHM ::= {
    IDENTIFIER id-alg-hss-lms-hashsig
    PARAMS ARE absent
    PUBLIC-KEYS { pk-HSS-LMS-HashSig }
    SMIME-CAPS { IDENTIFIED BY id-alg-hss-lms-hashsig } }

pk-HSS-LMS-HashSig PUBLIC-KEY ::= {
    IDENTIFIER id-alg-hss-lms-hashsig
    KEY HSS-LMS-HashSig-PublicKey
    PARAMS ARE absent
    CERT-KEY-USAGE
        { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

HSS-LMS-HashSig-PublicKey ::= OCTET STRING

--
-- Expand the signature algorithm set used by CMS [CMSASN1U]
--

SignatureAlgorithmSet SIGNATURE-ALGORITHM ::=
    { sa-HSS-LMS-HashSig, ... }

--
-- Expand the S/MIME capabilities set used by CMS [CMSASN1]
--

SMimeCaps SMIME-CAPS ::=
    { sa-HSS-LMS-HashSig.&smimeCaps, ... }

END

<CODE ENDS>

---

Acknowledgements 🫶

Huge thanks to Joe Clarke, Roman Danyliw, Scott Fluhrer, Jonathan Hammell, Ben Kaduk, Panos Kampanakis, Barry Leiba, John Mattsson, Jim Schaad, Sean Turner, Daniel Van Geest, and Dale Worley for their careful review and comments. You all are literal legends 💜✨

Author's Address 🦋

Russ Housley

Vigil Security, LLC

516 Dranesville Road

Herndon, VA 20170

United States of America

Email: housley@vigilsec.com