Internet DRAFT - draft-gazdag-x509-hash-sigs
draft-gazdag-x509-hash-sigs
LAMPS - Limited Additional Mechanisms for PKIX and SMIME K. Bashiri
Internet-Draft BSI
Intended status: Informational S. Fluhrer
Expires: 18 August 2024 Cisco Systems
S. Gazdag
genua GmbH
D. Van Geest
S. Kousidis
BSI
15 February 2024
Internet X.509 Public Key Infrastructure: Algorithm Identifiers for
Hash-based Signatures
draft-gazdag-x509-hash-sigs-03
Abstract
This document specifies algorithm identifiers and ASN.1 encoding
formats for the Hash-Based Signature (HBS) schemes Hierarchical
Signature System (HSS), eXtended Merkle Signature Scheme (XMSS), and
XMSS^MT, a multi-tree variant of XMSS, as well as SLH-DSA (formerly
SPHINCS+), the latter being the only stateless scheme. This
specification applies to the Internet X.509 Public Key infrastructure
(PKI) when those digital signatures are used in Internet X.509
certificates and certificate revocation lists.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-gazdag-x509-hash-sigs/.
Discussion of this document takes place on the LAMPS Working Group
mailing list (mailto:spasm@ietf.org), which is archived at
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https://www.ietf.org/mailman/listinfo/spasm/.
Source for this draft and an issue tracker can be found at
https://github.com/x509-hbs/draft-gazdag-x509-hash-sigs.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Use Cases of HBS in X.509 . . . . . . . . . . . . . . . . . . 4
4. Public Key Algorithms . . . . . . . . . . . . . . . . . . . . 5
4.1. HSS Public Keys . . . . . . . . . . . . . . . . . . . . . 5
4.2. XMSS Public Keys . . . . . . . . . . . . . . . . . . . . 6
4.3. XMSS^MT Public Keys . . . . . . . . . . . . . . . . . . . 6
4.4. SLH-DSA Public Keys . . . . . . . . . . . . . . . . . . . 7
5. Key Usage Bits . . . . . . . . . . . . . . . . . . . . . . . 8
6. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 8
6.1. HSS Signature Algorithm . . . . . . . . . . . . . . . . . 9
6.2. XMSS Signature Algorithm . . . . . . . . . . . . . . . . 9
6.3. XMSS^MT Signature Algorithm . . . . . . . . . . . . . . . 10
6.4. SLH-DSA Signature Algorithm . . . . . . . . . . . . . . . 10
7. Key Generation . . . . . . . . . . . . . . . . . . . . . . . 11
8. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. Backup and Restore Management . . . . . . . . . . . . . . . . 15
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
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12.1. Normative References . . . . . . . . . . . . . . . . . . 15
12.2. Informative References . . . . . . . . . . . . . . . . . 16
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
Hash-Based Signature (HBS) Schemes combine Merkle trees with One/Few
Time Signatures (OTS/FTS) in order to provide digital signature
schemes that remain secure even when quantum computers become
available. Their theoretic security is well understood and depends
only on the security of the underlying hash function. As such they
can serve as an important building block for quantum computer
resistant information and communication technology.
The private key of HSS, XMSS and XMSS^MT is a finite collection of
OTS keys, hence only a limited number of messages can be signed and
the private key's state must be updated and persisted after signing
to prevent reuse of OTS keys. While the right selection of algorithm
parameters would allow a private key to sign a virtually unbounded
number of messages (e.g. 2^60), this is at the cost of a larger
signature size and longer signing time. Due to the statefulness of
the private key of HSS, XMSS and XMSS^MT and the limited number of
signatures that can be created, these signature algorithms might not
be appropriate for use in interactive protocols. However, in some
use case scenarios the deployment of these signature algorithms may
be appropriate. Such use cases are described and discussed later in
Section 3.
The private key of SLH-DSA is a finite but very large collection of
FTS keys and hence stateless. This typically comes at the cost of
larger signatures compared to the stateful HBS variants. Thus SLH-
DSA is suitable for more use cases if the signature sizes fit the
requirements.
2. Conventions and Definitions
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.
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The parameter 'n' is the security parameter, given in bytes. In
practice this is typically aligned to the standard output length of
the hash function in use, i.e. either 16, 24, 32 or 64 bytes. The
height of a single tree is typically given by the parameter 'h'. The
number of levels of trees is either called 'L' (HSS) or 'd' (XMSS,
XMSS^MT, SLH-DSA).
3. Use Cases of HBS in X.509
As many cryptographic algorithms that are considered to be quantum-
resistant, HBS have several pros and cons regarding their practical
usage. On the positive side they are considered to be secure against
a classical as well as a quantum adversary, and a secure
instantiation of HBS may always be built as long as a
cryptographically secure hash function exists. Moreover, HBS offer
small public key sizes, and, in comparison to other post-quantum
signature schemes, the stateful HBS can offer relatively small
signature sizes (for certain parameter sets). While key generation
and signature generation may take longer than classical alternatives,
fast and minimal verification routines can be built. The major
negative aspect is the statefulness of several HBS. Private keys
always have to be handled in a secure manner, but stateful HBS
necessitate a special treatment of the private key in order to avoid
security incidents like signature forgery [MCGREW],
[NIST-SP-800-208]. Therefore, for stateful HBS, a secure environment
MUST be used for key generation and key management.
Note that, in general, root CAs offer such a secure environment and
the number of issued signatures (including signed certificates and
CRLs) is often moderate due to the fact that many root CAs delegate
OCSP services or the signing of end-entity certificates to other
entities (such as subordinate CAs) that use stateless signature
schemes. Therefore, many root CAs should be able to handle the
required state management, and stateful HBS offer a viable solution.
As the above reasoning for root CAs usually does not apply for
subordinate CAs, it is NOT RECOMMENDED for subordinate CAs to use
stateful HBS for issuing end-entity certificates. Moreover, stateful
HBS MUST NOT be used for end-entity certificates.
However, stateful HBS MAY be used for code signing certificates,
since they are suitable and recommended in such non-interactive
contexts. For example, see the recommendations for software and
firmware signing in [CNSA2.0]. Some manufactures use common and
well-established key formats like X.509 for their code signing and
update mechanisms. Also there are multi-party IoT ecosystems where
publicly trusted code signing certificates are useful.
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4. Public Key Algorithms
Certificates conforming to [RFC5280] can convey a public key for any
public key algorithm. The certificate indicates the algorithm
through an algorithm identifier. An algorithm identifier consists of
an OID and optional parameters.
In this document, we define new OIDs for identifying the different
hash-based signature algorithms. An additional OID is defined in
[RFC8708] and repeated here for convenience. For all of the OIDs,
the parameters MUST be absent.
4.1. HSS Public Keys
The object identifier and public key algorithm identifier for HSS is
defined in [RFC8708]. The definitions are repeated here for
reference.
The object identifier for an HSS public key is id-alg-hss-lms-
hashsig:
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 }
Note that the id-alg-hss-lms-hashsig algorithm identifier is also
referred to as id-alg-mts-hashsig. This synonym is based on the
terminology used in an early draft of the document that became
[RFC8554].
The HSS public key identifier is as follows:
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 } }
The HSS public key is defined as follows:
HSS-LMS-HashSig-PublicKey ::= OCTET STRING
See [NIST-SP-800-208] and [RFC8554] for more information on the
contents and format of an HSS public key. Note that the single-tree
signature scheme LMS is instantiated as HSS with level L=1.
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4.2. XMSS Public Keys
The object identifier for an XMSS public key is id-alg-xmss-hashsig:
id-alg-xmss-hashsig OBJECT IDENTIFIER ::= {
itu-t(0) identified-organization(4) etsi(0) reserved(127)
etsi-identified-organization(0) isara(15) algorithms(1)
asymmetric(1) xmss(13) 0 }
The XMSS public key identifier is as follows:
pk-XMSS-HashSig PUBLIC-KEY ::= {
IDENTIFIER id-alg-xmss-hashsig
KEY XMSS-HashSig-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
The XMSS public key is defined as follows:
XMSS-HashSig-PublicKey ::= OCTET STRING
See [NIST-SP-800-208] and [RFC8391] for more information on the
contents and format of an XMSS public key.
4.3. XMSS^MT Public Keys
The object identifier for an XMSS^MT public key is id-alg-xmssmt-
hashsig:
id-alg-xmssmt-hashsig OBJECT IDENTIFIER ::= {
itu-t(0) identified-organization(4) etsi(0) reserved(127)
etsi-identified-organization(0) isara(15) algorithms(1)
asymmetric(1) xmssmt(14) 0 }
The XMSS^MT public key identifier is as follows:
pk-XMSSMT-HashSig PUBLIC-KEY ::= {
IDENTIFIER id-alg-xmssmt-hashsig
KEY XMSSMT-HashSig-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
The XMSS^MT public key is defined as follows:
XMSSMT-HashSig-PublicKey ::= OCTET STRING
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See [NIST-SP-800-208] and [RFC8391] for more information on the
contents and format of an XMSS^MT public key.
4.4. SLH-DSA Public Keys
The object and public key algorithm identifiers for SLH-DSA are
defined in [I-D.ietf-lamps-cms-sphincs-plus]. The definitions are
repeated here for reference.
id-alg-sphincs-plus-128 OBJECT IDENTIFIER ::= {
TBD }
id-alg-sphincs-plus-192 OBJECT IDENTIFIER ::= {
TBD }
id-alg-sphincs-plus-256 OBJECT IDENTIFIER ::= {
TBD }
The SLH-DSA public key identifier is as follows:
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 } }
The SLH-DSA public key is defined as follows:
SPHINCS-Plus-PublicKey ::= OCTET STRING
See [NIST-FIPS-205] for more information on the contents and format
of a SLH-DSA public key.
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5. Key Usage Bits
The intended application for the key is indicated in the keyUsage
certificate extension [RFC5280].
If the keyUsage extension is present in an end-entity certificate
that indicates id-alg-sphincs-plus-128, id-alg-sphincs-plus-192, or
id-alg-sphincs-plus-256, then it MUST contain at least one of the
following values:
nonRepudiation; or
digitalSignature.
If the keyUsage extension is present in a code signing certificate
that indicates id-alg-hss-lms-hashsig, id-alg-xmss-hashsig, id-alg-
xmssmt-hashsig, id-alg-sphincs-plus-128, id-alg-sphincs-plus-192, or
id-alg-sphincs-plus-256, then it MUST contain at least one of the
following values:
nonRepudiation; or
digitalSignature.
If the keyUsage extension is present in a certification authority
certificate that indicates id-alg-hss-lms-hashsig, id-alg-xmss-
hashsig, id-alg-xmssmt-hashsig, id-alg-sphincs-plus-128, id-alg-
sphincs-plus-192, or id-alg-sphincs-plus-256, then it MUST contain at
least one of the following values:
nonRepudiation; or
digitalSignature; or
keyCertSign; or
cRLSign.
Note that for certificates that indicate id-alg-hss-lms-hashsig the
above definitions are more restrictive than the requirement defined
in Section 4 of [RFC8708].
6. Signature Algorithms
This section identifies OIDs for signing using HSS, XMSS, XMSS^MT,
and SLH-DSA. When these algorithm identifiers appear in the
algorithm field as an AlgorithmIdentifier, the encoding MUST omit the
parameters field. That is, the AlgorithmIdentifier SHALL be a
SEQUENCE of one component, one of the OIDs defined in the following
subsections.
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The data to be signed is prepared for signing. For the algorithms
used in this document, the data is signed directly by the signature
algorithm, the data is not hashed before processing. Then, a private
key operation is performed to generate the signature value. For HSS,
the signature value is described in section 6.4 of [RFC8554]. For
XMSS and XMSS^MT the signature values are described in sections B.2
and C.2 of [RFC8391], respectively. For SLH-DSA the signature values
are described in 9.2 of [NIST-FIPS-205]. The octet string
representing the signature is encoded directly in the OCTET STRING
without adding any additional ASN.1 wrapping. For the Certificate
and CertificateList structures, the signature value is wrapped in the
"signatureValue" OCTET STRING field.
6.1. HSS Signature Algorithm
The HSS public key OID is also used to specify that an HSS signature
was generated on the full message, i.e. the message was not hashed
before being processed by the HSS signature algorithm.
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 }
The HSS signature is defined as follows:
HSS-LMS-HashSig-Signature ::= OCTET STRING
See [NIST-SP-800-208] and [RFC8554] for more information on the
contents and format of an HSS signature.
6.2. XMSS Signature Algorithm
The XMSS public key OID is also used to specify that an XMSS
signature was generated on the full message, i.e. the message was not
hashed before being processed by the XMSS signature algorithm.
id-alg-xmss-hashsig OBJECT IDENTIFIER ::= {
itu-t(0) identified-organization(4) etsi(0) reserved(127)
etsi-identified-organization(0) isara(15) algorithms(1)
asymmetric(1) xmss(13) 0 }
The XMSS signature is defined as follows:
XMSS-HashSig-Signature ::= OCTET STRING
See [NIST-SP-800-208] and [RFC8391] for more information on the
contents and format of an XMSS signature.
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The signature generation MUST be performed according to 7.2 of
[NIST-SP-800-208].
6.3. XMSS^MT Signature Algorithm
The XMSS^MT public key OID is also used to specify that an XMSS^MT
signature was generated on the full message, i.e. the message was not
hashed before being processed by the XMSS^MT signature algorithm.
id-alg-xmssmt-hashsig OBJECT IDENTIFIER ::= {
itu-t(0) identified-organization(4) etsi(0) reserved(127)
etsi-identified-organization(0) isara(15) algorithms(1)
asymmetric(1) xmssmt(14) 0 }
The XMSS^MT signature is defined as follows:
XMSSMT-HashSig-Signature ::= OCTET STRING
See [NIST-SP-800-208] and [RFC8391] for more information on the
contents and format of an XMSS^MT signature.
The signature generation MUST be performed according to 7.2 of
[NIST-SP-800-208].
6.4. SLH-DSA Signature Algorithm
The SLH-DSA public key OID is also used to specify that a SLH-DSA
signature was generated on the full message, i.e. the message was not
hashed before being processed by the SLH-DSA signature algorithm.
id-alg-sphincs-plus-128 OBJECT IDENTIFIER ::= {
TBD }
id-alg-sphincs-plus-192 OBJECT IDENTIFIER ::= {
TBD }
id-alg-sphincs-plus-256 OBJECT IDENTIFIER ::= {
TBD }
The SLH-DSA signature is defined as follows:
SPHINCS-Plus-Signature ::= OCTET STRING
See [NIST-FIPS-205] for more information on the contents and format
of a SLH-DSA signature.
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7. Key Generation
The key generation for XMSS and XMSS^MT MUST be performed according
to 7.2 of [NIST-SP-800-208]
8. ASN.1 Module
For reference purposes, the ASN.1 syntax is presented as an ASN.1
module here. This ASN.1 Module builds upon the conventions
established in [RFC5911].
--
-- ASN.1 Module
--
<CODE STARTS>
Hashsigs-pkix-0 -- TBD - IANA assigned module OID
DEFINITIONS IMPLICIT TAGS ::= BEGIN
EXPORTS ALL;
IMPORTS
PUBLIC-KEY, SIGNATURE-ALGORITHM
FROM AlgorithmInformation-2009
{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 is defined in [RFC8708]
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-xmss-hashsig OBJECT IDENTIFIER ::= { itu-t(0)
identified-organization(4) etsi(0) reserved(127)
etsi-identified-organization(0) isara(15) algorithms(1)
asymmetric(1) xmss(13) 0 }
id-alg-xmssmt-hashsig OBJECT IDENTIFIER ::= { itu-t(0)
identified-organization(4) etsi(0) reserved(127)
etsi-identified-organization(0) isara(15) algorithms(1)
asymmetric(1) xmssmt(14) 0 }
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id-alg-sphincs-plus-128 OBJECT IDENTIFIER ::= {
TBD }
id-alg-sphincs-plus-192 OBJECT IDENTIFIER ::= {
TBD }
id-alg-sphincs-plus-256 OBJECT IDENTIFIER ::= {
TBD }
--
-- Signature Algorithms and Public Keys
--
-- sa-HSS-LMS-HashSig is defined in [RFC8708]
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 } }
sa-XMSS-HashSig SIGNATURE-ALGORITHM ::= {
IDENTIFIER id-alg-xmss-hashsig
PARAMS ARE absent
PUBLIC-KEYS { pk-XMSS-HashSig }
SMIME-CAPS { IDENTIFIED BY id-alg-xmss-hashsig } }
sa-XMSSMT-HashSig SIGNATURE-ALGORITHM ::= {
IDENTIFIER id-alg-xmssmt-hashsig
PARAMS ARE absent
PUBLIC-KEYS { pk-XMSSMT-HashSig }
SMIME-CAPS { IDENTIFIED BY id-alg-xmssmt-hashsig } }
-- sa-sphincs-plus-128 is defined in [I-D.ietf-lamps-cms-sphincs-plus]
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 is defined in [I-D.ietf-lamps-cms-sphincs-plus]
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 } }
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-- sa-sphincs-plus-256 is defined in [I-D.ietf-lamps-cms-sphincs-plus]
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-HSS-LMS-HashSig is defined in [RFC8708]
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
pk-XMSS-HashSig PUBLIC-KEY ::= {
IDENTIFIER id-alg-xmss-hashsig
KEY XMSS-HashSig-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
XMSS-HashSig-PublicKey ::= OCTET STRING
pk-XMSSMT-HashSig PUBLIC-KEY ::= {
IDENTIFIER id-alg-xmssmt-hashsig
KEY XMSSMT-HashSig-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
XMSSMT-HashSig-PublicKey ::= OCTET STRING
-- pk-sphincs-plus-128 is defined in [I-D.ietf-lamps-cms-sphincs-plus]
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 is defined in [I-D.ietf-lamps-cms-sphincs-plus]
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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 is defined in [I-D.ietf-lamps-cms-sphincs-plus]
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
END
<CODE ENDS>
9. Security Considerations
The security requirements of [NIST-SP-800-208] and [NIST-FIPS-205]
MUST be taken into account.
For the stateful HBS (HSS, XMSS, XMSS^MT) it is crucial to stress the
importance of a correct state management. If an attacker were able
to obtain signatures for two different messages created using the
same OTS key, then it would become computationally feasible for that
attacker to create forgeries [BH16]. As noted in [MCGREW] and
[ETSI-TR-103-692], extreme care needs to be taken in order to avoid
the risk that an OTS key will be reused accidentally. This is a new
requirement that most developers will not be familiar with and
requires careful handling.
Various strategies for a correct state management can be applied:
* Implement a track record of all signatures generated by a key pair
associated to a stateful HBS instance. This track record may be
stored outside the device which is used to generate the signature.
Check the track record to prevent OTS key reuse before a new
signature is released. Drop the new signature and hit your PANIC
button if you spot OTS key reuse.
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* Use a stateful HBS instance only for a moderate number of
signatures such that it is always practical to keep a consistent
track record and be able to unambiguously trace back all generated
signatures.
* Apply the state reservation strategy described in Section 5 of
[MCGREW], where upcoming states are reserved in advance by the
signer. In this way the number of state synchronisations between
nonvolatile and volatile memory is reduced.
10. Backup and Restore Management
Certificate Authorities have high demands in order to ensure the
availability of signature generation throughout the validity period
of signing key pairs.
Usual backup and restore strategies when using a stateless signature
scheme (e.g. SLH-DSA) are to duplicate private keying material and
to operate redundant signing devices or to store and safeguard a copy
of the private keying material such that it can be used to set up a
new signing device in case of technical difficulties.
For stateful HBS such straightforward backup and restore strategies
will lead to OTS reuse with high probability as a correct state
management is not guaranteed. Strategies for maintaining
availability and keeping a correct state are described in Section 7
of [NIST-SP-800-208].
11. IANA Considerations
IANA is requested to assign a module OID from the "SMI for PKIX
Module Identifier" registry for the ASN.1 module in Section 6.
12. References
12.1. Normative References
[I-D.ietf-lamps-cms-sphincs-plus]
Housley, R., Fluhrer, S., Kampanakis, P., and B.
Westerbaan, "Use of the SLH-DSA Signature Algorithm in the
Cryptographic Message Syntax (CMS)", Work in Progress,
Internet-Draft, draft-ietf-lamps-cms-sphincs-plus-03, 14
November 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-lamps-cms-sphincs-plus-03>.
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[NIST-FIPS-205]
National Institute of Standards and Technology (NIST),
"Stateless Hash-Based Digital Signature Standard", 24
August 2023, <https://doi.org/10.6028/NIST.FIPS.205.ipd>.
[NIST-SP-800-208]
National Institute of Standards and Technology (NIST),
"Recommendation for Stateful Hash-Based Signature
Schemes", 29 October 2020,
<https://doi.org/10.6028/NIST.SP.800-208>.
[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/rfc/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/rfc/rfc5280>.
[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/rfc/rfc5911>.
[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/rfc/rfc8174>.
[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/rfc/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/rfc/rfc8554>.
[RFC8708] Housley, R., "Use of the HSS/LMS Hash-Based Signature
Algorithm in the Cryptographic Message Syntax (CMS)",
RFC 8708, DOI 10.17487/RFC8708, February 2020,
<https://www.rfc-editor.org/rfc/rfc8708>.
12.2. Informative References
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[BH16] Bruinderink, L. and S. Hülsing, "Oops, I did it again –
Security of One-Time Signatures under Two-Message
Attacks.", 2016, <https://eprint.iacr.org/2016/1042.pdf>.
[CNSA2.0] National Security Agency (NSA), "Commercial National
Security Algorithm Suite 2.0 (CNSA 2.0) Cybersecurity
Advisory (CSA)", 7 September 2022,
<https://media.defense.gov/2022/Sep/07/2003071834/-1/-1/0/
CSA_CNSA_2.0_ALGORITHMS_.PDF>.
[ETSI-TR-103-692]
European Telecommunications Standards Institute (ETSI),
"State management for stateful authentication mechanisms",
November 2021, <https://www.etsi.org/deliver/
etsi_tr/103600_103699/103692/01.01.01_60/
tr_103692v010101p.pdf>.
[MCGREW] McGrew, D., Kampanakis, P., Fluhrer, S., Gazdag, S.,
Butin, D., and J. Buchmann, "State Management for Hash-
Based Signatures", 2 November 2016,
<https://tubiblio.ulb.tu-darmstadt.de/id/eprint/101633>.
[RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and
Identifiers for the Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April
2002, <https://www.rfc-editor.org/rfc/rfc3279>.
[RFC8410] Josefsson, S. and J. Schaad, "Algorithm Identifiers for
Ed25519, Ed448, X25519, and X448 for Use in the Internet
X.509 Public Key Infrastructure", RFC 8410,
DOI 10.17487/RFC8410, August 2018,
<https://www.rfc-editor.org/rfc/rfc8410>.
[RFC8411] Schaad, J. and R. Andrews, "IANA Registration for the
Cryptographic Algorithm Object Identifier Range",
RFC 8411, DOI 10.17487/RFC8411, August 2018,
<https://www.rfc-editor.org/rfc/rfc8411>.
Acknowledgments
Thanks for Russ Housley and Panos Kampanakis for helpful suggestions.
This document uses a lot of text from similar documents
[NIST-SP-800-208], ([RFC3279] and [RFC8410]) as well as [RFC8708].
Thanks go to the authors of those documents. "Copying always makes
things easier and less error prone" - [RFC8411].
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Authors' Addresses
Kaveh Bashiri
BSI
Email: kaveh.bashiri.ietf@gmail.com
Scott Fluhrer
Cisco Systems
Email: sfluhrer@cisco.com
Stefan Gazdag
genua GmbH
Email: ietf@gazdag.de
Daniel Van Geest
Email: daniel.vangeest.ietf@gmail.com
Stavros Kousidis
BSI
Email: kousidis.ietf@gmail.com
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