Internet DRAFT - draft-uni-qsckeys-falcon
draft-uni-qsckeys-falcon
Internet Engineering Task Force C. V. Vredendaal
Internet-Draft NXP Semiconductors
Intended status: Informational S. Dragone
Expires: 26 April 2023 B. Hess
T. Visegrady
M. Osborne
IBM Research GmbH
D. Bong
Utimaco IS GmbH
J. Bos
NXP Semiconductors
23 October 2022
Quantum Safe Cryptography Key Information for FALCON
draft-uni-qsckeys-falcon-00
Abstract
This proposal defines key management approaches for the Quantum Safe
Cryptographic (QSC) algorithm FALCON which has been selected for
standardization by the NIST Post Quantum Cryptography (PQC) process.
This includes key identification and key serialization. The purpose
is to provide guidance such that the adoption of quantum safe
algorithms is not hampered with the fragmented evolution of necessary
key management standards. Early definition of key material standards
will help expedite the adoption of new quantum safe algorithms and at
the same time as improving interoperability between implementations
and minimizing divergence across standards.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 26 April 2023.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Algorithm Identification . . . . . . . . . . . . . . . . 3
1.3. Algorithm and Algorithm Parameter Object Identifier . . . 3
2. Overview of FALCON and parameter OIDs . . . . . . . . . . . . 4
2.1. Key Formats . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Public Key Format based on RFC5280 . . . . . . . . . . . 5
2.3. Overview of Memo Definitions - PQC Key Formats . . . . . 5
3. FALCON . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Algorithm Parameter Identifiers . . . . . . . . . . . . . 6
3.2. Key Details . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Private Key Full Encoding . . . . . . . . . . . . . . . . 7
3.4. Public Key Full Encoding . . . . . . . . . . . . . . . . 8
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Additional Stuff . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
QSC algorithms being standardized in the NIST PQC Process have
evolved through several rounds and iterations. Keys are neither
easily identifiable nor compatible across rounds. It is also
expected that algorithms will evolve after final candidates have been
selected. The lack of binary compatibility between algorithm
versions and variants means that it is important to clearly identify
key material. Parallel to the NIST process, industry is evaluating
the impact of adopting new PQC algorithms, in particular key
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management. Here it is important to define and standardize key
serialization and encoding formats. Finally, we have seen that many
platforms and protocols are very constrained when it comes to the
amount of memory or space available for key objects. This makes it
important to define and standardize key compression formats. This
proposal addresses aspects of key identification and key
serialization for the future NIST Digital Signature standard, FALCON.
For the other schemes, see draft-uni-qsckeys-kyber, draft-uni-
qsckeys-falcon, draft-uni-qsckeys-dilithium and the previous
Internet-Draft [draft-uni-qsckeys-01]. This proposal will be updated
when the final NIST standard for CRYSTALS-Kyber becomes available.
1.1. Requirements Language
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 RFC 2119 [RFC2119] .
1.2. Algorithm Identification
Algorithm identification is important for several reasons:
* Managing a smooth transition from early adoption algorithm
versions to production versions where there is no compatibility.
* Supporting different algorithm versions from different NIST rounds
* Identifying different key serialization strategies
* Identifying compressed and uncompressed keys
The current standardization of quantum safe algorithms does not
address the definition of serialization structures for keys. As a
result, it has become commonplace for the cryptographic community
working on and with these algorithms to define their own approaches.
This leads to proprietary and internal representations for key
material. This has certain advantages in terms of ease of
experimentation while focusing on finding the best-performing QSC
algorithms. In terms of longer-term support where algorithm versions
change this is a problem. This proposal defines in section 2 a long-
term structured key representation format useful to address the goals
outlined above.
1.3. Algorithm and Algorithm Parameter Object Identifier
Algorithm and algorithm parameter information shall have ASN.1 type
AlgorithmIdentifier as given in [RFC5280] and shall be extended by an
pqcAlgorithmParameterName type in the optional parameters field:
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AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER, - OID: algorithm and algo parameter
parameters pqcAlgorithmParameterName OPTIONAL
}
pqcAlgorithmParameterName ::= PrintableString
2. Overview of FALCON and parameter OIDs
FALCON consists of two different parameter sets. This memo
attributes a name and a placeholder for an OID to the different
parameter sets of FALCON. The following table gives an overview of
the possible OIDs in the algorithm field and possible parameters set
names in the parameters field of the AlgorithmIdentifier type. Each
name or OID represents a single parameter set of given security.
Details can be found in the next section.
|=========+=====+===============================================|
| FALCON (PQC Digital Signature) |
|=========+=====+===============================================|
| falcon512-r3 |
|---------+-----+-----------------------------------------------|
| |ASN.1| {..*.. pqc-ds-falcon falcon512-r3} |
| |dot. | |
|---------+-----+-----------------------------------------------|
| falcon1024-r3 |
|---------+-----+-----------------------------------------------|
| |ASN.1| {..*.. pqc-ds-falcon falcon1024-r3} |
| |Dot | |
|=========+=====+===============================================|
Figure 1
2.1. Key Formats
The private key format defined is from PKCS#8 [RFC5208] . PKCS#8
PrivateKeyInfo is defined as:
PrivateKeyInfo ::= SEQUENCE {
version INTEGER -- PKCS#8 syntax ver
privateKeyAlgorithm AlgorithmIdentifier -- see chapter above
privateKey OCTET STRING, -- see chapter below
attributes [0] IMPLICIT Attributes OPTIONAL
}
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Distributing a PQC private key requires a PKCS#8 PrivateKeyInfo with
a joined PQC algorithm and algorithm parameter OID in the algorithm
field of AlgorithmIdentifier and a PQC algorithm specific private key
object in the privateKey field of PrivateKeyInfo. Both objects are
defined in the specific algorithm sections of this document. For an
overview see tables above and below.
2.2. Public Key Format based on [RFC5280]
RFC5280 subjectPublicKeyInfo is defined in as:
SubjectPublicKeyInfo := SEQUENCE {
algorithm AlgorithmIdentifier -- see chapter above
subjectPublicKey BIT STRING -- see chapter below
}
Distributing a PQC public key requires a [RFC5480]
subjectPublicKeyInfo with a joined PQC algorithm and algorithm
parameter OID in the algorithm field of AlgorithmIdentifier and a PQC
algorithm specific public key object in the subjectPublicKey field of
subjectPublicKeyInfo. Both objects are defined in the specific
algorithm sections of this document. For an overview see tables
above and below.
2.3. Overview of Memo Definitions - PQC Key Formats
The privateKey field in the PrivateKeyInfo type [RFC5480] is an OCTET
STRING whose contents are the value of the private key. The
interpretation of the content differs from PQC algorithm to
algorithm. The subjectPublicKey field in the subjectPublicKeyInfo
type [RFC5480] is a BIT STRING whose contents are the value of the
public key. Here also the interpretation of the content differs from
PQC algorithm to algorithm.
3. FALCON
FALCON is a lattice-based signature scheme that uses the short
integer solution problem (SIS) over NTRU lattices as its underlying
hard problem.
* Project Website: https://falcon-sign.info/
* NIST Round 3 Submission:
https://csrc.nist.gov/CSRC/media/Projects/post-quantum-
cryptography/documents/round-3/submissions/Falcon-Round3.zip
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3.1. Algorithm Parameter Identifiers
FALCON uses OIDs to identify parameters sets.
|=========================+=====================================|
| falcon512-r3 |
|=========================+=====================================|
| Parameter OID | {..*.. falcon512-r3} |
| | <.> |
| NIST Level Security | Level 1 |
|-------------------------|-------------------------------------|
| Parameters | Dimension/Degree n = 512 |
| | Polynomial Phi = 1+x^n |
| | Modulus q = 12289 |
| | Max. signature square norm |
| | floor (beta^2) = 34034726 |
| | Standard deviation = 165.736617183 |
| | sigma_{max} = 1.8205 |
| | sigma_{min} = 1.27783369 |
|=========================+=====================================|
| falcon1024-r3 |
|=========================+=====================================|
| Parameter OID | {..*.. falcon1024-r3} |
| | <.> |
| NIST Level Security | Level 5 |
|-------------------------|-------------------------------------|
| Parameters | Dimension/Degree n = 1024 |
| | Polynomial Phi = 1+x^n |
| | Modulus q = 12289 |
| | Max. signature square norm |
| | floor (beta^2) = 34034726 |
| | Standard deviation = 168.388571447 |
| | sigma_{max} = 1.8205 |
| | sigma_{min} = 1.298280334 |
|=========================+=====================================|
Figure 2
3.2. Key Details
The FALCON private key contains the key components f, g and F. Each
coefficient of f and g is encoded over a fixed number of bits, which
depends on the degree of f and g: 6 bits each for degree 512
(parameter name = falcon512-r3) and 5 bits each for degree 1024
(parameter name = falcon1024-r3). Coefficients of F use 8 bits each,
regardless of its degree. Each coefficient uses signed encoding,
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with two's complement for negative values. Moreover, the minimal
value is forbidden, e.g. when using degree 512, the valid range for a
coefficient of f or g is -31 to +31; -32 is not allowed.
|==========================+=========+===========|
| Algorithm OID | Params | Private |
| | | Key |
| | | Length |
|==========================+=========+===========+
| falcon512-r3 | f=384 | 1280 |
| | g=384 | |
| | F=512 | |
|--------------------------+---------+-----------|
| falcon1024-r3 | f=640 | 2304 |
| | g=640 | |
| | F=1024 | |
|==========================+=========+===========+
Figure 3
3.3. Private Key Full Encoding
Encoding a FALCON private key with PKCS#8 must include the following
two fields:
* falcon-(degree)-r3 in the algorithm field of AlgorithmIdentifier
* FALCONPrivateKey in the privateKey field, which is an OCTET
STRING.
When a FALCON public key is included in the distributed
PrivateKeyInfo, the PublicKey field in FALCONPrivateKey is used (see
description of FALCONPublicKey below). ASN.1 Encoding for a FALCON
private key:
FALCONPrivateKey ::= SEQUENCE {
version INTEGER {v2(1)} -- syntax version 2 (round 3)
f OCTET STRING, -- short integer polynomial f
g OCTET STRING, -- short integer polynomial g
f OCTET STRING, -- short integer polynomial F
publicKey [0] IMPLICIT FALCONPublicKey OPTIONAL
-- see next section
}
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3.4. Public Key Full Encoding
The FALCON public key contains a series of coefficients encoded into
parameter h. Each coefficient of h is encoded as a 14 bit sequence
(since q = 12289, 14 bits per coefficient are used). Coefficients
are then concatenated. The final bit string is zero padded to fit
into a byte sequence.
|==========================+=========+==========|
| Algorithm | Public Key Length |
|==========================+====================+
| falcon512-r3 | 896 |
|--------------------------+--------------------|
| falcon1024-r3 | 1792 |
|==========================+====================|
Figure 4
FALCONPublicKey := SEQUENCE {
h OCTET STRING -- integer polynomial h
}
4. Acknowledgements
This template was derived from an initial version written by Pekka
Savola and contributed by him to the xml2rfc project.
This document is part of a plan to make xml2rfc indispensable.
5. IANA Considerations
This memo includes no request to IANA.
6. Security Considerations
Any processing of the ASN.1 private key structures, such as base64
en/decoding shall be performed in "constant-time", meaning without
secret-dependent control flow and table lookups. The ASN.1
structures in this document are defined with fixed tag-lengths. The
purpose is to prevent side-channel leakage of variable lengths during
DER parsing. Any DER parsing of the private key ASN.1 key structures
shall be performed with these fixed lengths.
7. References
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7.1. 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>.
[RFC5208] Kaliski, B., "Public-Key Cryptography Standards (PKCS) #8:
Private-Key Information Syntax Specification Version 1.2",
BCP 14, RFC 5208, DOI 10.17487/RFC5208, May 2008,
<hhttps://www.rfc-editor.org/info/rfc5208>.
[RFC5280] Cooper, D., "Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL)
Profile", BCP 14, RFC RFC5280, DOI 10.17487/RFC5280, May
2008, <hhttps://www.rfc-editor.org/info/rfcRFC5280>.
[RFC5480] Turner, S., "Elliptic Curve Cryptography Subject Public
Key Information", BCP 14, RFC RFC5480,
DOI 10.17487/RFC5480, May 2009,
<hhttps://www.rfc-editor.org/info/rfc5480>.
7.2. Informative References
[draft-uni-qsckeys-01]
Vredendaal, C. V., Dragone, S., Hess, B., Visegrady, T.,
Osborne, M., Bong, D., and J. Bos, "Quantum Safe
Cryptography Key Information", Work in Progress, Internet-
Draft, draft-uni-qsckeys-01, 12 May 2022,
<https://www.ietf.org/archive/id/draft-uni-qsckeys-
01.txt>.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
DOI 10.17487/RFC2629, June 1999,
<https://www.rfc-editor.org/info/rfc2629>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
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Appendix A. Additional Stuff
This becomes an Appendix.
Authors' Addresses
Christine van Vredendaal
NXP Semiconductors
High Tech Campus 60
5656 AE Eindhoven
Netherlands
Email: cvvrede@gmail.com
Silvio Dragone
IBM Research GmbH
Saeumerstrasse 4
CH-8803 Rueschlikon
Switzerland
Email: sid@zurich.ibm.com
Basil Hess
IBM Research GmbH
Saeumerstrasse 4
CH-8803 Rueschlikon
Switzerland
Email: bhe@zurich.ibm.com
Tamas Visegrady
IBM Research GmbH
Saeumerstrasse 4
CH-8803 Rueschlikon
Switzerland
Email: tvi@zurich.ibm.com
Michael Osborne
IBM Research GmbH
Saeumerstrasse 4
CH-8803 Rueschlikon
Switzerland
Email: osb@zurich.ibm.com
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Dieter Bong
Utimaco IS GmbH
Germanusstrasse 4
52080 Aachen
Germany
Email: dieter.bong@utimaco.com
Joppe Bos
NXP Semiconductors
High Tech Campus 60
5656 AE Eindhoven
Netherlands
Email: joppe.bos@nxp.com
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