Network Working Group D. Van Geest
Internet-Draft ISARA Corporation
Intended status: Standards Track S. Fluhrer
Expires: September 12, 2019 Cisco Systems
March 11, 2019
Algorithm Identifiers for HSS and XMSS for Use in the Internet X.509
Public Key Infrastructure
draft-vangeest-x509-hash-sigs-03
Abstract
This document specifies algorithm identifiers and ASN.1 encoding
formats for the Hierarchical Signature System (HSS), eXtended Merkle
Signature Scheme (XMSS), and XMSS^MT, a multi-tree variant of XMSS.
This specification applies to the Internet X.509 Public Key
infrastructure (PKI) when digital signatures are used to sign
certificates and certificate revocation lists (CRLs).
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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This Internet-Draft will expire on September 12, 2019.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Subject Public Key Algorithms . . . . . . . . . . . . . . . . 3
2.1. HSS Public Keys . . . . . . . . . . . . . . . . . . . . . 3
2.2. XMSS Public Keys . . . . . . . . . . . . . . . . . . . . 4
2.3. XMSS^MT Public Keys . . . . . . . . . . . . . . . . . . . 4
3. Key Usage Bits . . . . . . . . . . . . . . . . . . . . . . . 5
4. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 5
4.1. HSS Signature Algorithm . . . . . . . . . . . . . . . . . 6
4.2. XMSS Signature Algorithm . . . . . . . . . . . . . . . . 6
4.3. XMSS^MT Signature Algorithm . . . . . . . . . . . . . . . 6
5. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6.1. Algorithm Security Considerations . . . . . . . . . . . . 9
6.2. Implementation Security Considerations . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
The Hierarchical Signature System (HSS) is described in
[I-D.mcgrew-hash-sigs].
The eXtended Merkle Signature Scheme (XMSS), and its multi-tree
variant XMSS^MT, are described in [RFC8391].
These signature algorithms are based on well-studied Hash Based
Signature (HBS) schemes, which can withstand known attacks using
quantum computers. They combine Merkle Trees with One Time Signature
(OTS) schemes in order to create signature systems which can sign a
large but limited number of messages per private key. The private
keys are stateful; a key's state must be updated and persisted after
signing to prevent reuse of OTS keys. If an OTS key is reused,
cryptographic security is not guaranteed for that key.
Due to the statefulness of the private key and the limited number of
signatures that can be created, these signature algorithms might not
be appropriate for use in interactive protocols. While the right
selection of algorithm parameters would allow a private key to sign a
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virtually unbounded number of messages (e.g. 2^60), this is at the
cost of a larger signature size and longer signing time. Since these
algorithms are already known to be secure against quantum attacks,
and because roots of trust are generally long-lived and can take
longer to be deployed than end-entity certificates, these signature
algorithms are more appropriate to be used in root and subordinate CA
certificates. They are also appropriate in non-interactive contexts
such as code signing. In particular, there are multi-party IoT
ecosystems where publicly trusted code signing certificates are
useful.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Subject 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
[I-D.ietf-lamps-cms-hash-sig] and repeated here for convenience. For
all of the OIDs, the parameters MUST be absent.
2.1. HSS Public Keys
The object identifier and public key algorithm identifier for HSS is
defined in [I-D.ietf-lamps-cms-hash-sig]. 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
[I-D.mcgrew-hash-sigs].
The HSS public key's properties are defined as follows:
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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
[I-D.ietf-lamps-cms-hash-sig] contains more information on the
contents and format of an HSS public key.
2.2. XMSS Public Keys
The object identifier for an XMSS public key is id-alg-xmss:
id-alg-xmss 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's properties are defined as follows:
pk-XMSS PUBLIC-KEY ::= {
IDENTIFIER id-alg-xmss
KEY XMSS-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
XMSS-PublicKey ::= OCTET STRING
The format of an XMSS public key is is formally defined using XDR
[RFC4506] and is defined in Appendix B.3 of [RFC8391]. In
particular, the first 4 bytes represents the big-ending encoding of
the XMSS algorithm type.
2.3. XMSS^MT Public Keys
The object identifier for an XMSS^MT public key is id-alg-xmssmt:
id-alg-xmssmt 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's properties are defined as follows:
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pk-XMSSMT PUBLIC-KEY ::= {
IDENTIFIER id-alg-xmssmt
KEY XMSSMT-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
XMSSMT-PublicKey ::= OCTET STRING
The format of an XMSS^MT public key is is formally defined using XDR
[RFC4506] and is defined in Appendix C.3 of [RFC8391]. In
particular, the first 4 bytes represents the big-ending encoding of
the XMSS^MT algorithm type.
3. Key Usage Bits
The intended application for the key is indicated in the keyUsage
certificate extension.
If the keyUsage extension is present in an end-entity certificate
that indicates id-alg-xmss or id-alg-xmssmt in SubjectPublicKeyInfo,
then the keyUsage extension MUST contain one or both of the following
values:
nonRepudiation; and
digitalSignature.
If the keyUsage extension is present in a certification authority
certificate that indicates id-alg-xmss or id-alg-xmssmt, then the
keyUsage extension MUST contain one or more of the following values:
nonRepudiation;
digitalSignature;
keyCertSign; and
cRLSign.
[I-D.ietf-lamps-cms-hash-sig] defines the key usage for id-alg-hss-
lms-hashsig, which is the same as for the keys above.
4. Signature Algorithms
This section identifies OIDs for signing using HSS, XMSS, and
XMSS^MT. 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 below.
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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 3.3 of
[I-D.mcgrew-hash-sigs]. For XMSS and XMSS^MT the signature values
are described in sections B.2 and C.2 of [RFC8391] respectively. The
octet string representing the signature is encoded directly in the
BIT STRING without adding any additional ASN.1 wrapping. For the
Certificate and CertificateList structures, the signature value is
wrapped in the "signatureValue" BIT STRING field.
4.1. 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 }
[I-D.ietf-lamps-cms-hash-sig] contains more information on the
contents and format of an HSS signature.
4.2. 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 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 format of an XMSS signature is is formally defined using XDR
[RFC4506] and is defined in Appendix B.2 of [RFC8391].
4.3. 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.
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id-alg-xmssmt 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 format of an XMSS^MT signature is is formally defined using XDR
[RFC4506] and is defined in Appendix C.2 of [RFC8391].
5. ASN.1 Module
For reference purposes, the ASN.1 syntax is presented as an ASN.1
module here.
-- ASN.1 Module
Hashsigs-pkix-0 -- TBD - IANA assigned module OID
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
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 [ietf-lamps-cms-hash-sig]
--
-- 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 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 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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-- Signature Algorithms and Public Keys
--
-- sa-HSS-LMS-HashSig is defined in [ietf-lamps-cms-hash-sig]
--
-- 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 is defined in [ietf-lamps-cms-hash-sig]
--
-- 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
sa-XMSS SIGNATURE-ALGORITHM ::= {
IDENTIFIER id-alg-xmss
PARAMS ARE absent
PUBLIC-KEYS { pk-XMSS }
SMIME-CAPS { IDENTIFIED BY id-alg-xmss } }
pk-XMSS PUBLIC-KEY ::= {
IDENTIFIER id-alg-xmss
KEY XMSS-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
XMSS-PublicKey ::= OCTET STRING
sa-XMSSMT SIGNATURE-ALGORITHM ::= {
IDENTIFIER id-alg-xmssmt
PARAMS ARE absent
PUBLIC-KEYS { pk-XMSSMT }
SMIME-CAPS { IDENTIFIED BY id-alg-xmssmt } }
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pk-XMSSMT PUBLIC-KEY ::= {
IDENTIFIER id-alg-xmssmt
KEY XMSSMT-PublicKey
PARAMS ARE absent
CERT-KEY-USAGE
{ digitalSignature, nonRepudiation, keyCertSign, cRLSign } }
XMSSMT-PublicKey ::= OCTET STRING
END
6. Security Considerations
6.1. Algorithm Security Considerations
The cryptographic security of the signatures generated by the
algorithms mentioned in this document depends only on the hash
algorithms used within the signature algorithms and the pre-hash
algorithm used to create an X.509 certificate's message digest.
Grover's algorithm [Grover96] is a quantum search algorithm which
gives a quadratic improvement in search time to brute-force pre-image
attacks. The results of [BBBV97] show that this improvement is
optimal, however [Fluhrer17] notes that Grover's algorithm doesn't
parallelize well. Thus, given a bounded amount of time to perform
the attack and using a conservative estimate of the performance of a
real quantum computer, the pre-image quantum security of SHA-256 is
closer to 190 bits. All parameter sets for the signature algorithms
in this document currently use SHA-256 internally and thus have at
least 128 bits of quantum pre-image resistance, or 190 bits using the
security assumptions in [Fluhrer17].
[Zhandry15] shows that hash collisions can be found using an
algorithm with a lower bound on the number of oracle queries on the
order of 2^(n/3) on the number of bits, however [DJB09] demonstrates
that the quantum memory requirements would be much greater.
Therefore a parameter set using SHA-256 would have at least 128 bits
of quantum collision-resistance as well as the pre-image resistance
mentioned in the previous paragraph.
Given the quantum collision and pre-image resistance of SHA-256
estimated above, the current parameter sets used by id-alg-hss-lms-
hashsig, id-alg-xmss and id-alg-xmssmt provide 128 bits or more of
quantum security. This is believed to be secure enough to protect
X.509 certificates for well beyond any reasonable certificate
lifetime.
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6.2. Implementation Security Considerations
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 stored in a virtual machine environment, care must
be taken to preserve confidentiality and integrity.
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. [RFC4086] offers important guidance in
this area.
The generation of hash-based signatures also depends on random
numbers. While the consequences of an inadequate pseudo-random
number generator (PRNGs) to generate these values is much less severe
than the generation of private keys, the guidance in [RFC4086]
remains important.
7. Acknowledgements
Thanks for Russ Housley for the helpful suggestions.
This document uses a lot of text from similar documents ([RFC3279]
and [RFC8410]) as well as [I-D.ietf-lamps-cms-hash-sig]. Thanks go
to the authors of those documents. "Copying always makes things
easier and less error prone" - [RFC8411].
8. 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 5.
9. References
9.1. Normative References
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[I-D.ietf-lamps-cms-hash-sig]
Housley, R., "Use of the HSS/LMS Hash-based Signature
Algorithm in the Cryptographic Message Syntax (CMS)",
draft-ietf-lamps-cms-hash-sig-07 (work in progress), March
2019.
[I-D.mcgrew-hash-sigs]
McGrew, D., Curcio, M., and S. Fluhrer, "Hash-Based
Signatures", draft-mcgrew-hash-sigs-15 (work in progress),
January 2019.
[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>.
[RFC4506] Eisler, M., Ed., "XDR: External Data Representation
Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May
2006, <https://www.rfc-editor.org/info/rfc4506>.
[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>.
[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>.
9.2. Informative References
[BBBV97] Bennett, C., Bernstein, E., Brassard, G., and U. Vazirani,
"Strengths and weaknesses of quantum computing", SIAM J.
Comput. 26(5), 1510-1523, 1997.
[DJB09] Bernstein, D., "Cost analysis of hash collisions: Will
quantum computers make SHARCS obsolete?", SHARCS 9, p.
105, 2009.
[Fluhrer17]
Fluhrer, S., "Reassessing Grover's Algorithm", Cryptology
ePrint Archive Report 2017/811, August 2017,
<https://eprint.iacr.org/2017/811.pdf>.
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[Grover96]
Grover, L., "A fast quantum mechanical algorithm for
database search", 28th ACM Symposium on the Theory of
Computing p. 212, 1996.
[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/info/rfc3279>.
[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>.
[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/info/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/info/rfc8411>.
[Zhandry15]
Zhandry, M., "A note on the quantum collision and set
equality problems", Quantum Information & Computation 15,
7-8, 557-567, May 2015.
Authors' Addresses
Daniel Van Geest
ISARA Corporation
560 Westmount Rd N
Waterloo, Ontario N2L 0A9
Canada
Email: daniel.vangeest@isara.com
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Scott Fluhrer
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
USA
Email: sfluhrer@cisco.com
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