Internet DRAFT - draft-housley-lamps-cms-sphincs-plus
draft-housley-lamps-cms-sphincs-plus
Network Working Group R. Housley
Internet-Draft Vigil Security
Intended status: Standards Track S. Fluhrer
Expires: 7 March 2023 Cisco Systems
P. Kampanakis
Amazon Web Services
B. Westerbaan
Cloudflare
3 September 2022
Use of the SPHINCS+ Signature Algorithm in the Cryptographic Message
Syntax (CMS)
draft-housley-lamps-cms-sphincs-plus-01
Abstract
SPHINCS+ is a stateless hash-based signature scheme. This document
specifies the conventions for using the SPHINCS+ stateless hash-based
signature algorithm with the Cryptographic Message Syntax (CMS). In
addition, the algorithm identifier and public key syntax are
provided.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 7 March 2023.
Copyright Notice
Copyright (c) 2022 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.
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Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. ASN.1 . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. SPHINCS+ Hash-based Signature Algorithm Overview . . . . . . 3
3. SPHINCS+ Public Key Identifier . . . . . . . . . . . . . . . 4
4. Signed-data Conventions . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Appendix: ASN.1 Module . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
NOTICE: This document will be adjusted to match the SPHINCS+
specification that is published by NIST. Until that happens, just
about everything in this document is likely to change.
This document specifies the conventions for using the SPHINCS+ hash-
based signature algorithm (add reference to the NIST document here)
with the Cryptographic Message Syntax (CMS) [RFC5652] signed-data
content type.
SPHINCS+ offers three security levels. The parameters for each of
the security levels were chosen to provide 128 bits of security, 192
bits of security, and 256 bits of security. A separate algorithm
identifier has been assigned for SPHINCS+ at each of these security
levels.
SPHINCS+ is a stateless hash-based signature algorithm. Other hash-
based signature algorithms are stateful, including HSS/LMS [RFC8554]
and XMSS [RFC8391]. Without the need for state kept by the signer,
SPHINCS+ is much less fragile.
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1.1. ASN.1
CMS values are generated using ASN.1 [X680], using the Basic Encoding
Rules (BER) and the Distinguished Encoding Rules (DER) [X690].
1.2. Motivation
There have been recent advances in cryptanalysis and advances in the
development of quantum computers. Each of these advances pose a
threat to widely deployed digital signature.
If large-scale quantum computers are ever built, they will be able to
break many of the public-key cryptosystems currently in use,
including RSA, DSA, ECDSA, and EdDSA. A post-quantum cryptosystem
(PQC) is secure against quantum computers that have more than a
trivial number of quantum bits (qu-bits). It is open to conjecture
when it will be feasible to build such quantum computers; however, it
is prudent to use cryptographic algorithms that remain secure if a
large-scale quantum computer is invented. SPHINCS+ is a PQC
signature algorithm.
One use of a PQC signature algoritm is the protection of software
updates, perhaps using the format described in [RFC4108], to enable
deployment of software that implements other new PQC algorithms for
key management and confidentiality.
1.3. 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 interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. SPHINCS+ Hash-based Signature Algorithm Overview
SPHINCS+ is a hash-based signature scheme which consists of a few
time signature construction, namely Forest of Random Subsets (FORS)
and a hypertree. FORS signs a message with a private key. The
corresponding FORS public keys are the leaves in k binary trees. The
roots of these trees are hashed together to form a FORS root.
SPHINCS+ uses a one-time signature scheme called WOTS+. The FORS tree
roots are signed by a WOTS+ one-time signature private key. The
corresponding WOTS+ public keys form the leaves in d-layers of Merkle
subtrees in the SPHINCS+ hypertree. The bottom layer of that
hypertree signs the FORS roots with WOTS+. The root of the bottom
Merkle subtrees are then signed with WOTS+ and the corresponding
WOTS+ public keys form the leaves of the next level up subtree.
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Subtree roots are consequently signed by their corresponding subtree
layers until we reach the top subtree. The top layer subtree forms
the hypertree root which is trusted at the verifier.
A SPHINCS+ signature consists of the FORS signature, the WOTS+
signature in each layer and the path to the root of each subtree
until we reach the root of the hypertree.
A SPHINCS+ signature is verified by verifying the FORS signature, the
WOTS+ signatures and the path to the root of each subtree. When
reaching the root of the hypertree, the signature verifies only if it
hashes to the pre-trusted root of the SPHINCS+ hypertree.
SPHINCS+ is a stateless hash-based signature algorithm. Stateful
hash-based signature schemes require that the WOTS+ private key
(generated by using a state index) is never reused or the scheme
loses it security. Although its security decreases, FORS which is
used at the bottom of the SPHINCS+ hypertree does not collapse if the
same private key used to sign two or more different messages like in
stateful hash-based signature schemes. Without the need for state
kept by the signer to ensure it is not reused, SPHINCS+ is much less
fragile.
SPHINCS+ was designed to sign up to 2^64 messages and offers three
security levels. The parameters of the SPHINCS+ hypertree include
the security parameter, the hash function, the tree height, the
number of layers of subtrees, the Winternitz parameter of WOTS+, the
number of FORS trees and leaves in each. The parameters for each of
the security levels were chosen to provide 128 bits of security, 192
bits of security, and 256 bits of security.
3. SPHINCS+ Public Key Identifier
The AlgorithmIdentifier for a SPHINCS+ public key MUST use one of the
id-alg-sphincs-plus object identifiers listed below, based on the
security level used to generate the SPHINCS+ hypertree. The
parameters field of the AlgorithmIdentifier for the SPHINCS+ public
key 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; the certificate key usage extension MUST NOT contain
other values.
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pk-sphincs-plus-128 PUBLIC-KEY ::= {
IDENTIFIER id-alg-sphincs-plus-128
KEY SPHINCS-Plus-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
pk-sphincs-plus-192 PUBLIC-KEY ::= {
IDENTIFIER id-alg-sphincs-plus-192
KEY SPHINCS-Plus-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
pk-sphincs-plus-256 PUBLIC-KEY ::= {
IDENTIFIER id-alg-sphincs-plus-256
KEY SPHINCS-Plus-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
SPHINCS-Plus-PublicKey ::= OCTET STRING
NOTE: The values for these object identifiers will be assigned by
NIST. Once assigned, they will be added to a future revision of this
document.
The SPHINCS+ public key value is an OCTET STRING.
4. Signed-data Conventions
As specified in CMS [RFC5652], 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 SPHINCS+ 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 SPHINCS+ tree, and then a message-digest attribute is
constructed to contain the resulting hash value, and then the result
of DER encoding the set of signed attributes, which MUST include a
content-type attribute and a message-digest attribute, and then the
SPHINCS+ signature is computed over the DER-encoded output. In
summary:
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IF (signed attributes are absent)
THEN SPHINCS+_Sign(content)
ELSE message-digest attribute = Hash(content);
SPHINCS+_Sign(DER(SignedAttributes))
When using SPHINCS+, the fields in the SignerInfo are used as
follows:
digestAlgorithm:
The digestAlgorithm MUST contain the one-way hash function used to
in the SPHINCS+ tree. The algorithm identifiers for [FIPS180] and
[FIPS202] are repeated below for convenience.
mda-sha256 DIGEST-ALGORITHM ::= {
IDENTIFIER id-sha256
PARAMS TYPE NULL ARE preferredAbsent }
mda-shake256 DIGEST-ALGORITHM ::= {
IDENTIFIER id-shake256
PARAMS TYPE NULL ARE preferredAbsent }
hashalgs OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
country(16) us(840) organization(1) gov(101) csor(3)
nistAlgorithms(4) 2 }
id-sha256 OBJECT IDENTIFIER ::= { hashalgs 1 }
id-shake256 OBJECT IDENTIFIER ::= { hashAlgs 12 }
signatureAlgorithm:
The signatureAlgorithm MUST contain one of the the SPHINCS+
algorithm identifiers, and the algorithm parameters field MUST be
absent. The algorithm identifier MUST be one of the following:
id-alg-sphincs-plus-128, id-alg-sphincs-plus-192, or id-alg-
sphincs-plus-256.
signature:
The signature contains the signature value resulting from the
SPHINCS+ signing operation with the parameters associated with the
selected signatureAlgorithm. The SPHINCS+ signing operation and
the signature verification operation are specified in TBD.
5. Security Considerations
Implementations MUST protect the private keys. Compromise of the
private keys may result in the ability to forge signatures.
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When generating an SPHINCS+ key pair, an implementation MUST generate
each key pair independently of all other key pairs in the SPHINCS+
hypertree.
A SPHINCS+ tree MUST NOT be used for more than 2^64 signing
operations.
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, and [RFC4086] offers important guidance
in this area.
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.
When computing signatures, implementations SHOULD include protections
against fault injection attacks [CMP2018]. Protections against these
attacks include signature verification prior to releasing the
signature value to confirm that no error injected and generating the
signature a few times to confirm that the same signature value is
produced each time.
6. IANA Considerations
TBD
7. Acknowledgements
Thanks to Mike Ounsworth for his careful review and constructive
comments.
8. References
8.1. Normative References
[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>.
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[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>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
[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>.
[X680] ITU-T, "Information technology -- Abstract Syntax Notation
One (ASN.1): Specification of basic notation", ITU-T
Recommendation X.680, ISO/IEC 8824-1:2021, February 2021,
<https://www.itu.int/rec/T-REC-X.680>.
[X690] 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, ISO/IEC 8825-1-2021,
February 2021, <https://www.itu.int/rec/T-REC-X.690>.
8.2. Informative References
[CMP2018] Castelnovi, L., A, Martinelli, and T. Prest, "Grafting
Trees: A Fault Attack Against the SPHINCS Framework",
Post-Quantum Cryptography pp. 165-184, PQCrypto 2018,
Lecture Notes in Computer Science vol 10786, 2018,
<https://link.springer.com/
chapter/10.1007/978-3-319-79063-3_8>.
[FIPS180] National Institute of Standards and Technology (NIST),
"Secure Hash Standard (SHS)", FIPS PUB 180-4, August 2015.
[FIPS202] National Institute of Standards and Technology (NIST),
"SHA-3 Standard: Permutation-Based Hash and Extendable-
Output Functions", FIPS PUB 202, August 2015.
[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>.
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[RFC4108] 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>.
[RFC5911] 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>.
[RFC8391] Huelsing, A., Butin, D., Gazdag, S., Rijneveld, J., and A.
Mohaisen, "XMSS: eXtended Merkle Signature Scheme",
RFC 8391, DOI 10.17487/RFC8391, May 2018,
<https://www.rfc-editor.org/info/rfc8391>.
[RFC8554] 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>.
Appendix A. Appendix: ASN.1 Module
This ASN.1 Module builds upon the conventions established in
[RFC5911].
<CODE STARTS>
SPHINCS-Plus-Module-2022
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
id-smime(16) id-mod(0) id-mod-sphincs-plus-2022(TBD) }
DEFINITIONS IMPLICIT TAGS ::= BEGIN
EXPORTS ALL;
IMPORTS
PUBLIC-KEY, SIGNATURE-ALGORITHM, SMIME-CAPS
FROM AlgorithmInformation-2009 -- RFC 5911
{ 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-sphincs-plus-128 OBJECT IDENTIFIER ::= { TBD }
id-alg-sphincs-plus-192 OBJECT IDENTIFIER ::= { TBD }
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id-alg-sphincs-plus-256 OBJECT IDENTIFIER ::= { TBD }
--
-- Signature Algorithm and Public Key
--
sa-sphincs-plus-128 SIGNATURE-ALGORITHM ::= {
IDENTIFIER id-alg-sphincs-plus-128
PARAMS ARE absent
PUBLIC-KEYS { pk-sphincs-plus-128 }
SMIME-CAPS { IDENTIFIED BY id-alg-sphincs-plus-128 } }
sa-sphincs-plus-192 SIGNATURE-ALGORITHM ::= {
IDENTIFIER id-alg-sphincs-plus-192
PARAMS ARE absent
PUBLIC-KEYS { pk-sphincs-plus-192 }
SMIME-CAPS { IDENTIFIED BY id-alg-sphincs-plus-192 } }
sa-sphincs-plus-256 SIGNATURE-ALGORITHM ::= {
IDENTIFIER id-alg-sphincs-plus-256
PARAMS ARE absent
PUBLIC-KEYS { pk-sphincs-plus-256 }
SMIME-CAPS { IDENTIFIED BY id-alg-sphincs-plus-256 } }
pk-sphincs-plus-128 PUBLIC-KEY ::= {
IDENTIFIER id-alg-sphincs-plus-128
KEY SPHINCS-Plus-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
pk-sphincs-plus-192 PUBLIC-KEY ::= {
IDENTIFIER id-alg-sphincs-plus-192
KEY SPHINCS-Plus-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
pk-sphincs-plus-256 PUBLIC-KEY ::= {
IDENTIFIER id-alg-sphincs-plus-256
KEY SPHINCS-Plus-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
SPHINCS-Plus-PublicKey ::= OCTET STRING
--
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-- Expand the signature algorithm set used by CMS [RFC5911]
--
SignatureAlgorithmSet SIGNATURE-ALGORITHM ::=
{ sa-sphincs-plus-128 |
sa-sphincs-plus-192 |
sa-sphincs-plus-256,
... }
--
-- Expand the S/MIME capabilities set used by CMS [RFC5911]
--
SMimeCaps SMIME-CAPS ::=
{ sa-sphincs-plus-128.&smimeCaps |
sa-sphincs-plus-192.&smimeCaps |
sa-sphincs-plus-256.&smimeCaps,
... }
END
<CODE ENDS>
Authors' Addresses
Russ Housley
Vigil Security, LLC
Email: housley@vigilsec.com
Scott Fluhrer
Cisco Systems
Email: sfluhrer@cisco.com
Panos Kampanakis
Amazon Web Services
Email: kpanos@amazon.com
Bas Westerbaan
Cloudflare
Email: bas@westerbaan.name
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