COSE T. Looker
Internet-Draft Mattr
Intended status: Standards Track M. Jones
Expires: 27 April 2023 Microsoft
24 October 2022
Barreto-Lynn-Scott Elliptic Curve Key Representations for JOSE and COSE
draft-ietf-cose-bls-key-representations-01
Abstract
This specification defines how to represent cryptographic keys for
the pairing-friendly elliptic curves known as Barreto-Lynn-Scott
(BLS), for use with the key representation formats of JSON Web Key
(JWK) and COSE (COSE_Key).
Discussion Venues
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/tplooker/draft-ietf-cose-bls-key-representations.
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Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
2.1. Representation Definition . . . . . . . . . . . . . . . . 3
2.1.1. JSON Web Key Representation . . . . . . . . . . . . . 4
2.1.2. COSE_Key Representation . . . . . . . . . . . . . . . 4
2.1.3. Curve Parameter Registration . . . . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
4.1. JSON Web Key (JWK) Elliptic Curve Registrations . . . . . 6
4.2. COSE Elliptic Curve Registrations . . . . . . . . . . . . 7
5. Normative References . . . . . . . . . . . . . . . . . . . . 9
6. Informative References . . . . . . . . . . . . . . . . . . . 9
Appendix A. Appendix . . . . . . . . . . . . . . . . . . . . . . 11
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 12
Appendix C. Document History . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
This specification defines how to represent cryptographic keys for
the pairing-friendly elliptic curves known as Barreto-Lynn-Scott
[BLS], for use with the key representation formats of JSON Web Key
(JWK) and COSE_Key. This specification registers the elliptic curves
in appropriate IANA JOSE and COSE registries.
There are a variety of applications for pairing based cryptography
including schemes already published as RFCs, such as Identity-Based
Cryptography [RFC5091] Sakai-Kasahara Key Encryption (SAKKE)
[RFC6508], and Identity-Based Authenticated Key Exchange (IBAKE)
[RFC6539]. SAKKE is applied to Multimedia Internet KEYing (MIKEY)
[RFC6509].
This branch of cryptography has also been used to develop privacy-
preserving cryptographic hardware attestations schemes, including the
Elliptic Curve Direct Anonymous Attestation (ECDAA) in the Trusted
Platform Modules [TPM] specified by the Trusted Computing Group.
Further work on similar schemes has also occurred at the FIDO
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Alliance [ECDAA]. Similarly, Intel released [EPID] which provides a
solution to remote hardware attestation for Intel Software Guard
Extension (SGX) enabled environments.
More recently, applications of pairing based cryptography using the
Barreto-Lynn-Scott curves include the standardization effort for BLS
Signatures [id.draft.bls-signature-04], which are used extensively in
multiple blockchain projects due to their unique signature
aggregation properties, including [Ethereum] [DFINITY] [Algorand].
Additionally, efforts are under way to standardize the general
purpose short group signature scheme of BBS Signatures [BBS], which
features novel properties such as multi-message signing and selective
disclosure alongside zero knowledge proving. It is intended that
this draft will help with these efforts by standardizing the
associated cryptographic key representation in the popular formats of
JWK and COSE_Key.
Other relevant work to this draft includes [JWP] which is extending
the JOSE family of specifications to provide support for representing
a variety of new proof based cryptographic schemes such as [BBS]
which as referred to above uses the Barreto-Lynn-Scott curves.
There are multiple different pairing-friendly curves in active use;
however, this draft focuses on a definition for the Barreto-Lynn-
Scott curves due to them being the most "widely used" and "efficient"
whilst achieving 128-bit and 256-bit security (BLS12-381 and
BLS48-581 respectively).
More extensive discussion on the broader application of pairing based
cryptography and the assessment of various elliptic curves (including
the BLS family) can be found in
[id.draft.pairing-friendly-curves-10].
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.
2.1. Representation Definition
The following definitions apply to the pairing-friendly elliptic
curves known as the Barreto-Lynn-Scott (BLS) curves.
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2.1.1. JSON Web Key Representation
When expressing a cryptographic key for these curves in JSON Web Key
(JWK) form, the following rules apply:
* The parameter "kty" MUST be present and set to "OKP".
* The parameter "crv" MUST be present and value MUST be one defined
in Section 2.1.3.
* The parameter "x" MUST be present whose value represents the curve
point for the public key. This value MUST be encoded using the
serialization defined in [id.draft.pairing-friendly-curves-10]
Appendix C and MUST be base64url encoded without padding as
defined in [RFC7515] Appendix C.
* The parameter "d" MUST be present for private key representations
whose value MUST contain the little-endian representation of the
private key base64url encoded without padding as defined in
[RFC7515] Appendix C. This parameter MUST NOT be present for
public keys.
2.1.2. COSE_Key Representation
When expressing a cryptographic key for these curves in COSE_Key
form, the following rules apply:
* The parameter "kty" (1) MUST be present and set to "OKP" (1).
* The parameter "crv" (-1) MUST be present and value MUST be one
defined in Section 2.1.3.
* The parameter "x" (-2) MUST be present whose value represents the
curve point for the public key. This value MUST be encoded using
the serialization defined in [id.draft.pairing-friendly-curves-10]
Appendix C.
* The parameter "d" (-4) MUST be present for private key
representations whose value MUST contain the little-endian
representation of the private key. This parameter MUST NOT be
present for public keys.
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2.1.3. Curve Parameter Registration
+============+============+=====================================+
| JWK "crv" | COSE_Key | Description |
| value | "crv" | |
| | value | |
+============+============+=====================================+
| Bls12381G1 | TBD (13 | A cryptographic key on the Barreto- |
| | requested) | Lynn-Scott (BLS) curve featuring an |
| | | embedding degree 12 with 381-bit p |
| | | in the subgroup of G1 defined as |
| | | E(GF(p)) of order r |
+------------+------------+-------------------------------------+
| Bls12381G2 | TBD (14 | A cryptographic key on the Barreto- |
| | requested) | Lynn-Scott (BLS) curve featuring an |
| | | embedding degree 12 with 381-bit p |
| | | in the subgroup of G1 defined as |
| | | E(GF(p^2)) of order r |
+------------+------------+-------------------------------------+
| Bls48581G1 | TBD (15 | A cryptographic key on the Barreto- |
| | requested) | Lynn-Scott (BLS) curve featuring an |
| | | embedding degree 48 with 581-bit p |
| | | in the subgroup of G1 defined as |
| | | E(GF(p)) of order r |
+------------+------------+-------------------------------------+
| Bls48581G2 | TBD (16 | A cryptographic key on the Barreto- |
| | requested) | Lynn-Scott (BLS) curve featuring an |
| | | embedding degree 48 with 581-bit p |
| | | in the subgroup of G1 defined as |
| | | E(GF(p^8)) of order r |
+------------+------------+-------------------------------------+
Table 1
3. Security Considerations
See [id.draft.pairing-friendly-curves-10] for additional details on
security considerations for the curves used. Implementers should
also consider the general guidance provided in Section 9 of [RFC7517]
and Section 17 of [RFC8152] when using this specification.
Furthermore, because this specification only defines the
cryptographic key representations and not the usage of these keys
with specific algorithms, implementers should be aware to follow any
guidance that may be provided around appropriate usage of the keys
and or additional steps that may be required to validate the keys
within the context of particular algorithms.
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4. IANA Considerations
4.1. JSON Web Key (JWK) Elliptic Curve Registrations
This section registers the following values in the IANA "JSON Web Key
Elliptic Curve" registry [IANA.JOSE.Curves].
Bls12381G1
* Curve Name: Bls12381G1
* Curve Description: 381 bit with an embedding degree of 12 Barreto-
Lynn-Scott pairing-friendly curve using the r-order subgroup of
E(GF(p))
* JOSE Implementation Requirements: Optional
* Change Controller: IESG
* Specification Document(s): Section 2.1.1
Bls12381G2
* Curve Name: Bls12381G2
* Curve Description: 381 bit with an embedding degree of 12 Barreto-
Lynn-Scott pairing-friendly curve using the r-order subgroup of
E'(GF(p^2))
* JOSE Implementation Requirements: Optional
* Change Controller: IESG
* Specification Document(s): Section 2.1.1
Bls48581G1
* Curve Name: Bls48581G1
* Curve Description: 581 bit with an embedding degree of 48 Barreto-
Lynn-Scott pairing-friendly curve using the r-order subgroup of
E(GF(p))
* JOSE Implementation Requirements: Optional
* Change Controller: IESG
* Specification Document(s): Section 2.1.1
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Bls48581G2
* Curve Name: Bls48581G2
* Curve Description: 581 bit with an embedding degree of 48 Barreto-
Lynn-Scott pairing-friendly curve using the r-order subgroup of
E'(GF(p^8))
* JOSE Implementation Requirements: Optional
* Change Controller: IESG
* Specification Document(s): Section 2.1.1
4.2. COSE Elliptic Curve Registrations
This section registers the following value in the IANA "COSE Elliptic
Curves" registry [IANA.COSE.Curves].
Bls12381G1
* Curve Name: Bls12381G1
* Value: TBD (13 requested)
* Key Type: OKP
* Curve Description: 381 bit with an embedding degree of 12 Barreto-
Lynn-Scott pairing-friendly curve using the r-order subgroup of
E(GF(p))
* JOSE Implementation Requirements: Optional
* Change Controller: IESG
* Specification Document(s): Section 2.1.2
* Recommended: Yes
Bls12381G2
* Curve Name: Bls12381G2
* Value: TBD (14 requested)
* Key Type: OKP
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* Curve Description: 381 bit with an embedding degree of 12 Barreto-
Lynn-Scott pairing-friendly curve using the r-order subgroup of
E'(GF(p^2))
* JOSE Implementation Requirements: Optional
* Change Controller: IESG
* Specification Document(s): Section 2.1.2
* Recommended: Yes
Bls48581G1
* Curve Name: Bls48581G1
* Value: TBD (15 requested)
* Key Type: OKP
* Curve Description: 581 bit with an embedding degree of 48 Barreto-
Lynn-Scott pairing-friendly curve using the r-order subgroup of
E(GF(p))
* JOSE Implementation Requirements: Optional
* Change Controller: IESG
* Specification Document(s): Section 2.1.2
* Recommended: Yes
Bls48581G2
* Curve Name: Bls48581G2
* Value: TBD (16 requested)
* Key Type: OKP
* Curve Description: 581 bit with an embedding degree of 48 Barreto-
Lynn-Scott pairing-friendly curve using the r-order subgroup of
E'(GF(p^8))
* JOSE Implementation Requirements: Optional
* Change Controller: IESG
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* Specification Document(s): Section 2.1.2
* Recommended: Yes
5. Normative References
[BLS] Barreto, P., Lynn, B., and M. Scott, "Constructing
Elliptic Curves with Prescribed Embedding Degrees", 2003.
[IANA.COSE.Curves]
IANA, "COSE Elliptic Curves",
.
[IANA.JOSE.Curves]
IANA, "JOSE Elliptic Curves",
.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, .
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
.
[id.draft.bls-signature-04]
IETF CFRG, "BLS Signature",
.
[id.draft.pairing-friendly-curves-10]
IETF CFRG, "Pairing-Friendly Curves",
.
6. Informative References
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[BBS] Decentralized Identity Foundation, "The BBS Signature
Scheme", .
[ECDAA] FIDO Alliance, "ECDAA Algorithm", 2018,
.
[EPID] Intel Corporation, "Intel (R) SGX: Intel (R) EPID
Provisioning and Attestation Services",
.
[JWP] Miller, J. and M. Jones, "JSON Web Proof", .
[RFC5091] Boyen, X. and L. Martin, "Identity-Based Cryptography
Standard (IBCS) #1: Supersingular Curve Implementations of
the BF and BB1 Cryptosystems", RFC 5091,
DOI 10.17487/RFC5091, December 2007,
.
[RFC6508] Groves, M., "Sakai-Kasahara Key Encryption (SAKKE)",
RFC 6508, DOI 10.17487/RFC6508, February 2012,
.
[RFC6509] Groves, M., "MIKEY-SAKKE: Sakai-Kasahara Key Encryption in
Multimedia Internet KEYing (MIKEY)", RFC 6509,
DOI 10.17487/RFC6509, February 2012,
.
[RFC6539] Cakulev, V., Sundaram, G., and I. Broustis, "IBAKE:
Identity-Based Authenticated Key Exchange", RFC 6539,
DOI 10.17487/RFC6539, March 2012,
.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, .
[TPM] Trusted Computing Group, "Trusted Platform Module",
.
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Appendix A. Appendix
The following examples showcase JWKs for both the G1 and G2 subgroups
of the Bls12381 curve. Note, the examples also include the
corresponding private key, expressed through the inclusion of the "d"
parameter.
An example JWK for the Bls12381 curve where the public key is in the
G1 subgroup.
{
"kty": "OKP",
"crv": "Bls12381G1",
"d": "Mt_OyD9IAsYvobHJ9NCipm6-G7zAu28FCc-saRnXhjQ",
"x": "iXmOmxttBniHSpyoq-vBr82BexrqG7WDTsxCY4ngUOERVxwpwUT7yKqSKqJeIr7J"
}
Another example of a different JWK for the Bls12381 curve where the
public key is in the G1 subgroup.
{
"kty": "OKP",
"crv": "Bls12381G1",
"d": "PV21Ysd3RNtDBzx94WOkIItSdMkMx0xdjtVFWen9xy8",
"x": "jQb7AerHCU1Zf7oUCMYioqAkK_Q35-hDmg9cKhIJzGyZmQgb4saO376vjmGkvaLC"
}
An example JWK for the Bls12381 curve where the public key is in the
G2 subgroup.
{
"kty": "OKP",
"crv": "Bls12381G2",
"d": "CUrC9Xp5pEonbFaykalWlbNYYwueJlcuoOexhEhpu0k",
"x": "rvdKcdkxwlj0Y-XZsFpz1hDPJGjnLN27IJipbmaLlaKdYfICGG6dzakG6EkdcvW0AtVV6hXBSKtdFnKQKmmD759tMYYuvKYf5o2cZnROLN5iWQ2H6vp6FlLi71a_AE5I"
}
Another example of a different JWK for the Bls12381 curve where the
public key is in the G2 subgroup.
{
"kty": "OKP",
"crv": "Bls12381G2",
"d": "oF2xFR6Iu3aWQARjHFdmNjeZBKuSO6q1DA1t2ucNHyc",
"x": "pHufIAzbxDG-oaD0Kb1BcRsDpjw0JX3h6FHRJQpuYSpqQr_sZigCD3UOTrDO2YEvAxiC6GZXZvlwkqSIOVHRWAwRt2loaqAu6jFiL0L0r8LuXhBxX0tvfPX1UhYgcl3_"
}
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Appendix B. Acknowledgments
The authors would like to acknowledge the work of Kyle Den Hartog,
which was used as the foundation for this draft.
Appendix C. Document History
-00
* Created draft-ietf-cose-bls-key-representations-00 from draft-
looker-cose-bls-key-representations-00 following working group
adoption.
Authors' Addresses
Tobias Looker
Mattr
Email: tobias.looker@mattr.global
Michael B. Jones
Microsoft
Email: mbj@microsoft.com
URI: https://self-issued.info/
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