RFC 9708

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

📅 published January 2025, from ietf

RFC 9708 🎀 Use of the HSS/LMS Hash-Based Signature Algorithm in the Cryptographic Message Syntax (CMS)

okay bestie, here's the vibe check on this doc 💅 It's from the IETF (Request for Comments: 9708, ISSN 2070-1721). R. Housley of Vigil Security wrote it, it came out in January 2025, and it's a Standards Track doc. It obsoletes RFC 8708 🦋 so if you're still reading the old one, it's time to update your life.

Abstract ✨

so this doc explains how to use the HSS/LMS hash-based signature algorithm with CMS, and it also gives you the algorithm identifier and the public key syntax 🫶 HSS/LMS is one flavor of hash-based digital signature, and it's described in RFC 8554. Tea: this doc obsoletes RFC 8708. 🍓

Status of This Memo 📜

this is an Internet Standards Track document. It's an IETF product, and it's got the consensus of the IETF community behind it. It went through public review and got the green light from the Internet Engineering Steering Group (IESG). If you want more on Internet Standards, check Section 2 of RFC 7841 ✨

for the current status, errata, or to send feedback, head to https://www.rfc-editor.org/info/rfc9708 💖

Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved.

this doc 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. Read them closely, bestie, because they spell out your rights and restrictions for this doc 🙈 Any Code Components pulled out of this doc have to include Revised BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come with no warranty, same as the Revised BSD License says.

Table of Contents 🧚

1.  Introduction
  1.1.  ASN.1
  1.2.  Terminology
  1.3.  Motivation
  1.4.  Changes Since RFC 8708
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 ✨

okay so this doc is all about using the Hierarchical Signature System (HSS) / Leighton-Micali Signature (LMS) hash-based signature algorithm with the CMS [CMS] signed-data content type 💅 LMS gives you a one-time digital signature, and it's a variant of the Merkle Tree Signature (MTS) scheme. HSS sits on top of LMS so it can scale up to a bigger number of signatures without melting down 🔥 HSS/LMS is one form of hash-based digital signature, and it's 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 how many you get depends on the size of the tree 🌸

the good news is that HSS/LMS uses small public keys and has low computational cost. The tea is that the signatures are quite large 🙈 The HSS/LMS private key can be super small if the signer is cool with doing more computation at signing time. Or the private key can eat more memory and give you faster signing 🧚 The HSS/LMS signatures are defined in [HASHSIG]. Right now, there are parameter sets that use SHA-256 [SHS] and SHAKE256 [SHA3].

1.1. ASN.1 🎀

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

1.2. Terminology 📖

here's the deal with the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this doc. They get read the way BCP 14 [RFC2119] [RFC8174] describes, but only when they show up in all capitals, exactly like that 💖

1.3. Motivation 🦋

advances in cryptanalysis [BH2013] and progress in building quantum computers [NAS2019] are a future threat to the digital signature algorithms everyone uses right now. So we need to get ready for a day when cryptosystems like RSA and DSA, which rely on discrete logarithms and factoring, can't be depended on anymore 😭

if cryptographically relevant quantum computers (CRQCs) ever get built, they'll be able to break lots 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 it'll be feasible to build such computers. Still, RSA, DSA, Elliptic Curve Digital Signature Algorithm (ECDSA), and Edwards-curve Digital Signature Algorithm (EdDSA) are all vulnerable if CRQCs ever show up 💀

the HSS/LMS signature algorithm doesn't depend on how hard discrete logarithms or factoring are. It depends on a second-preimage-resistant cryptographic hash function, so it's considered post-quantum secure ✨ One use for post-quantum-secure signatures is protecting software updates, maybe using the format described in [FWPROT], so people can roll out software that implements new cryptosystems 🌈

1.4. Changes Since RFC 8708 🍓

when RFC 8708 came out, there were no plans to put an HSS/LMS public key in a certificate. The assumption was that the public key would get distributed some other way. Today, there are plans to put an HSS/LMS public key in a certificate [X.509-S-HBS] 👑 The KEY field of the pk-HSS-LMS-HashSig definition in the ASN.1 module doesn't come into play when you use HSS/LMS signatures in CMS. It still needs to be consistent with the rules for carrying an HSS/LMS public key in a certificate, though. The pk-HSS-LMS-HashSig definition is updated so there's no ASN.1 wrapping for the public key. These changes resolve [Err7960] and [Err7963] 🫶

more HSS/LMS tree sizes got defined, and the list in Section 2.2 was expanded to include the new ones 🌸

more LM-OTS Signatures got defined too, and the list in Section 2.3 grew to cover them 🧚

Section 4 now has more detail on the allowed values in the X.509 certificate key usage extension for an HSS/LMS public key. It's giving thorough ✨

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

the Merkle Tree Signature (MTS) scheme is a way to sign a large but fixed number of messages. An MTS system depends 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] only uses the SHA-256 one-way hash function [SHS], but it sets up an IANA registry [IANA-LMS] so more one-way hash functions can get registered later on 🎀

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 😭

an HSS signature, as specified in [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 for 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 in the child tree, and the LMS private key in the bottom-most tree signs the actual message. Both the signature over the public key and the signature over the message are LMS signatures, as described in Section 2.2 🌸

here's the HSS signature value for a standalone tree (a top tree with no children), summed up:

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

u32str() and || are used the way they're defined in [HASHSIG] ✨

here's the HSS signature value for a tree with Nspk signed public keys:

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 defined in Section 3.3 of [HASHSIG], the signed_public_key structure holds the lms_signature over the public key, followed by the public key itself. Note that 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. The tree has 2^h leaves. The second parameter, m, is the number of bytes the hash function outputs, which is also the amount of data tied to each node in the tree. [HASHSIG] supports the SHA-256 hash function [SHS] with m=32. More LMS Signature parameter sets have been registered at [IANA-LMS] 💖

as specified in [HASHSIG], 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) described in Section 5.3 of [HASHSIG], and the m-byte string tied to the root node of the tree (T[1]) 🦋

the LMS public key can be summed up like this:

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

also as specified in [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 tied to the path through the tree from the leaf with the LM-OTS signature value up to the root. That array holds the siblings of the nodes on the path from the leaf to the root, but not the nodes on the path itself. For a tree with height h, the array has h values. 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 can be summed up like this:

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

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

okay so Merkle Tree Signatures (MTS) depend on a one-time signature method, and [HASHSIG] specifies the use of the LM-OTS, which has five parameters 💅

  • n: the length in bytes of the hash function output. 🌸
  • H: a preimage-resistant hash function that takes 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]. Bestie, the math is all there 🤓

[HASHSIG] specifies four LM-OTS variants (as listed in Table 1 of [HASHSIG]). Additional LM-OTS Signature parameter sets have been registered at [IANA-LMS]. So many options, it's giving buffet 🍓

Signing involves generating C, an n-byte random value. 🎲

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]. Here's the whole vibe:

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

3. Algorithm Identifiers and Parameters 🎀

okay so the algorithm identifier for an HSS/LMS hash-based signature is this ✨

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

When you use this object identifier for an HSS/LMS signature, the AlgorithmIdentifier parameters field MUST be absent. That means the parameters are not present, and they are not set to NULL. Not NULL, not empty, just gone 🙈

In the CMS, the HSS/LMS signature value is a large OCTET STRING. The HSS/LMS signature generation is described in Section 2 of this document. The signature format is designed for easy parsing, which is so considerate 🥹 The HSS, LMS, and LM-OTS components of the signature value each include a counter and a typecode. Together they indirectly give you all the info you need to parse the value during signature validation. Iconic. 👑

The signature value identifies the hash function used in the HSS/LMS tree. 🔥

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. Same energy as before, no parameters allowed 🙅‍♀️

When this AlgorithmIdentifier appears in the SubjectPublicKeyInfo field of a certification authority (CA) X.509 certificate [RFC5280], the certificate key usage extension MUST contain at least one of the following values: digitalSignature, nonRepudiation, keyCertSign, and cRLSign. However, it MUST NOT contain other values. Strict but make it cute 🎀

When this AlgorithmIdentifier appears in the SubjectPublicKeyInfo field of an end-entity X.509 certificate [RFC5280], the certificate key usage extension MUST contain at least one of the following: digitalSignature, nonRepudiation, or cRLSign. However, it MUST NOT contain other values. Different rules for end-entities, noted 📝

pk-HSS-LMS-HashSig PUBLIC-KEY ::= {
    IDENTIFIER id-alg-hss-lms-hashsig
    -- KEY no ASN.1 wrapping --
    PARAMS ARE absent
    CERT-KEY-USAGE
      { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

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

The id-alg-hss-lms-hashsig algorithm identifier 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]. Ooh, a nickname with a whole origin story 🦋

When the public key appears outside a certificate, it is an OCTET STRING. Like the signature format, it's 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

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, no drama 🌈

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. After that, 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. It's a whole chain, bestie 🫶 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. For convenience, the AlgorithmIdentifier for SHA-256 from [PKIXASN1] and the AlgorithmIdentifier for SHAKE256 from [RFC8692] are 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 }

mda-shake256 DIGEST-ALGORITHM ::= {
    IDENTIFIER id-shake256 }

id-shake256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
    country(16) us(840) organization(1) gov(101) csor(3)
    nistAlgorithm(4) hashAlgs(2) 12 }
  • signatureAlgorithm MUST contain id-alg-hss-lms-hashsig, and the algorithm parameters field MUST be absent. 🎯
  • signature contains the single HSS/LMS signature value that results from the signing operation, as specified in [HASHSIG]. 💅

6. Security Considerations 🚨

Okay, this part is SERIOUS, so listen up 🙏 Implementations MUST protect the private keys. If the private keys are compromised, someone can forge signatures, and that is a full-on disaster 💀 Along with the private key, the implementation MUST keep track of which leaf nodes in the tree have been used. If the integrity of this tracking data is lost, a one-time key can be used more than once. So when a private key and the tracking data are stored on non-volatile media or in a virtual machine environment, you have to think about failed writes, virtual machine snapshotting or cloning, and other operational concerns. Confidentiality and integrity are the goal 😭

When generating an LMS key pair, an implementation MUST generate each key pair independently of all other key pairs in the HSS tree. No copy-pasting keys, bestie 🙅‍♀️

An implementation MUST ensure that an LM-OTS private key is used to generate a signature only one time, and MUST ensure that it cannot be used for any other purpose. One time means ONE TIME 🔑

The generation of private keys relies on random numbers. Inadequate pseudorandom number generators (PRNGs) used 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 and search the resulting small set of possibilities, rather than brute-force searching the whole key space. Quality random numbers are genuinely hard to make, and [RFC4086] offers important guidance in this area. Do not skip this one 🧠

The generation of hash-based signatures also depends on random numbers. The consequences of an inadequate PRNG for these values are much less severe than in the generation of private keys, but the guidance in [RFC4086] remains important. Less scary, still important 🫠

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 changed the reference for value 64 to this document. 📋

In the "SMI Security for S/MIME Algorithms (1.2.840.113549.1.9.16.3)" registry, IANA has changed the reference for value 17 to this document. 🦋

8. References 📚

8.1. Normative References 🧾

8.2. Informative References ✨

Okay, now for the bonus reading list 📚 These are the extra references that give background and context, but nothing here is required to implement the spec, so you can relax 💅

[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.

[Err7960] RFC Errata, Erratum ID 7960, RFC 8708, https://www.rfc-editor.org/errata/eid7960.

[Err7963] RFC Errata, Erratum ID 7963, RFC 8708, https://www.rfc-editor.org/errata/eid7963.

[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", Information Systems Laboratory, Stanford University, Technical Report No. 1979-1, 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", Post-Quantum Cryptography, Springer, pp. 1-14, DOI 10.1007/978-3-540-88702-7_1, 2009, https://doi.org/10.1007/978-3-540-88702-7_1.

[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.

[X.509-S-HBS] Van Geest, D., Bashiri, K., Fluhrer, S., Gazdag, S., and S. Kousidis, "Use of the HSS and XMSS Hash-Based Signature Algorithms in Internet X.509 Public Key Infrastructure", Work in Progress, Internet-Draft, draft-ietf-lamps-x509-shbs-13, 12 December 2024, https://datatracker.ietf.org/doc/html/draft-ietf-lamps-x509-shbs-13.

Appendix A. ASN.1 Module 🧚

Okay, the ASN.1 module in this appendix is built on top of the modules in [CMSASN1] and [CMSASN1U] 🎀 Here's the whole thing, copied exactly:

<CODE BEGINS>
MTS-HashSig-2013
  { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(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) pkcs-9(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 no ASN.1 wrapping --
    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 everyone who gave comments on the drafts that became RFC 8708 💖 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 literally the best 🌸

Also a massive thank you to Daniel Van Geest for motivating the creation of this document 👑

Author's Address 💌

Russ Housley
Vigil Security, LLC
516 Dranesville Road
Herndon, VA 20170
United States of America
Email: housley@vigilsec.com
📦 where this page comes from