COSE A. R. Mott Internet-Draft RustyKey Intended status: Standards Track 29 April 2026 Expires: 31 October 2026 CBOR Object Signing and Encryption (COSE) and JSON Object Signing and Encryption (JOSE) Registrations for SQIsign draft-mott-cose-sqisign-02 Abstract *NOTE: This document describes a signature scheme based on an algorithm currently under evaluation in the NIST Post-Quantum Cryptography standardization process. Be aware that the underlying primitive may change as a result of that process.* This document specifies the algorithm encodings and representations for the SQIsign digital signature scheme within the CBOR Object Signing and Encryption (COSE) and JSON Object Signing and Encryption (JOSE) frameworks. SQIsign is an isogeny-based post-quantum signature scheme that provides the most compact signature and public key sizes of any candidate in the NIST Post-Quantum Cryptography (PQC) standardization and on-ramp-to-standardization processes. The standardization of SQIsign will be helpful to address current infrastructure bottlenecks, specifically the FIDO2 CTAP2 specification used by billions of in-service devices and browser installations. Depending on authenticator implementation, transport (USB/NFC/BLE) and message fragmentation support. Some deployments of CTAP2-based authenticators enforce limits near 1024 bytes for external key communication, and some standardized post-quantum signature schemes increase message sizes and may stress constrained authenticators or transports. As a result CBOR-encoded messages may hit limits in some authenticators. SQIsign-L1, L2 and L5 signatures are small enough to enable delivery over constrained networks like 802.15.4 and may be more suitable for constrained networks due to smaller signature sizes. Mott Expires 31 October 2026 [Page 1] Internet-Draft cose-sqisign April 2026 This document clarifies that SQIsign does not expose the auxiliary torsion-point information exploited in the SIDH/SIKE attacks. Consequently, the specific attack techniques of Castryck–Decru do not directly apply. However, the scheme remains subject to ongoing cryptanalysis of isogeny-based constructions. By establishing stable COSE and JOSE identifiers, this document ensures the interoperability required for the seamless integration of post-quantum security into high-density, bandwidth-constrained, and legacy-compatible hardware environments. 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-mott-cose-sqisign/. Discussion of this document takes place on the COSE Working Group mailing list (mailto:cose@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/cose/. Subscribe at https://www.ietf.org/mailman/listinfo/cose/. Source for this draft and an issue tracker can be found at https://github.com/https://github.com/antonymott/quantum-resistant- rustykey. 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 31 October 2026. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. Mott Expires 31 October 2026 [Page 2] Internet-Draft cose-sqisign April 2026 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. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Background and Motivation . . . . . . . . . . . . . . . . 5 1.1.1. Pressing Need for Smaller PQC Signatures . . . . . . 5 1.1.2. Estimated Constrained Device Footprint . . . . . . . 6 1.1.3. Pressing need: Limit or Stop 'Harvest now; decrypt later' Attacks . . . . . . . . . . . . . . . . . . . 7 1.2. Scope and Status . . . . . . . . . . . . . . . . . . . . 8 1.3. Relationship to Other Work . . . . . . . . . . . . . . . 8 1.4. Constrained Device Applicability . . . . . . . . . . . . 8 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 9 3. Resistance to "Torsion Point" attack . . . . . . . . . . . . 9 3.1. SIKE Vulnerability (The "Torsion Point" Attack) of 2022 . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Why SQISign appears unaffected by the SIKE Vulnerability . . . . . . . . . . . . . . . . . . . . . . 10 4. SQIsign Algorithm Overview . . . . . . . . . . . . . . . . . 10 4.1. Cryptographic Foundation . . . . . . . . . . . . . . . . 10 4.2. Security Levels . . . . . . . . . . . . . . . . . . . . . 10 4.3. Performance Characteristics . . . . . . . . . . . . . . . 11 5. COSE Integration . . . . . . . . . . . . . . . . . . . . . . 11 5.1. SQIsign Algorithms . . . . . . . . . . . . . . . . . . . 11 5.2. SQIsign Key Types . . . . . . . . . . . . . . . . . . . . 11 5.3. SQIsign Key Parameters . . . . . . . . . . . . . . . . . 12 5.4. SQIsign-Specific Key Parameters . . . . . . . . . . . . . 12 5.5. COSE Key Format Examples . . . . . . . . . . . . . . . . 12 5.5.1. Public Key (COSE_Key) . . . . . . . . . . . . . . . . 12 5.5.2. Private Key (COSE_Key) . . . . . . . . . . . . . . . 12 5.6. COSE Signature Format . . . . . . . . . . . . . . . . . . 13 5.6.1. Protected Headers . . . . . . . . . . . . . . . . . . 13 5.6.2. Example COSE_Sign1 Structure . . . . . . . . . . . . 13 6. JOSE Integration . . . . . . . . . . . . . . . . . . . . . . 13 6.1. JSON Web Signature (JWS) Algorithm Registration . . . . . 13 6.2. JSON Web Key (JWK) Representation . . . . . . . . . . . . 14 6.2.1. Public Key Parameters . . . . . . . . . . . . . . . . 14 6.2.2. Private Key Parameters . . . . . . . . . . . . . . . 14 6.3. JWK Examples . . . . . . . . . . . . . . . . . . . . . . 14 6.3.1. Public Key (JWK) Example . . . . . . . . . . . . . . 14 Mott Expires 31 October 2026 [Page 3] Internet-Draft cose-sqisign April 2026 6.3.2. Private Key (JWK) Example . . . . . . . . . . . . . . 15 6.4. JWS Compact Serialization . . . . . . . . . . . . . . . . 15 6.4.1. Example JWS Protected Header . . . . . . . . . . . . 15 6.4.2. Complete JWS Example . . . . . . . . . . . . . . . . 15 7. Implementation Considerations . . . . . . . . . . . . . . . . 15 7.1. Signature and Key Generation . . . . . . . . . . . . . . 15 7.2. Randomness Requirements . . . . . . . . . . . . . . . . . 16 7.3. Side-Channel Protections . . . . . . . . . . . . . . . . 16 7.4. Performance Trade-offs . . . . . . . . . . . . . . . . . 16 7.5. Interoperability Testing . . . . . . . . . . . . . . . . 16 8. Security Considerations . . . . . . . . . . . . . . . . . . . 16 8.1. Algorithm Security . . . . . . . . . . . . . . . . . . . 16 8.2. Quantum Security . . . . . . . . . . . . . . . . . . . . 17 8.3. Current Cryptanalysis Status . . . . . . . . . . . . . . 17 8.4. Implementation Security . . . . . . . . . . . . . . . . . 17 8.4.1. Random Number Generation . . . . . . . . . . . . . . 17 8.4.2. Side-Channel Resistance . . . . . . . . . . . . . . . 17 8.4.3. Key Management . . . . . . . . . . . . . . . . . . . 18 8.5. Cryptographic Agility . . . . . . . . . . . . . . . . . . 18 8.6. Constrained Device Specific Risks . . . . . . . . . . . . 18 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 9.1. Additions to Existing Registries . . . . . . . . . . . . 18 9.1.1. New COSE Algorithms . . . . . . . . . . . . . . . . . 18 9.1.2. New COSE Key Types . . . . . . . . . . . . . . . . . 19 9.1.3. New COSE Key Type Parameters . . . . . . . . . . . . 19 9.1.4. New JWS Algorithms . . . . . . . . . . . . . . . . . 20 9.1.5. New JSON Web Key Types . . . . . . . . . . . . . . . 20 9.1.6. New JSON Web Key Parameters . . . . . . . . . . . . . 20 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 11.1. Normative References . . . . . . . . . . . . . . . . . . 21 11.2. Informative References . . . . . . . . . . . . . . . . . 21 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 12.1. Normative References . . . . . . . . . . . . . . . . . . 21 12.2. Informative References . . . . . . . . . . . . . . . . . 22 Appendix A. Test Vectors . . . . . . . . . . . . . . . . . . . . 23 A.1. SQIsign-L1 Test Vectors . . . . . . . . . . . . . . . . . 23 A.1.1. Example 1: Simple Message Signing . . . . . . . . . . 23 A.1.2. COSE_Sign1 Complete Example . . . . . . . . . . . . . 24 A.1.3. JWS Complete Example . . . . . . . . . . . . . . . . 24 A.2. SQIsign-L3 Test Vectors . . . . . . . . . . . . . . . . . 24 A.3. SQIsign-L5 Test Vectors . . . . . . . . . . . . . . . . . 24 Appendix B. Implementation Status . . . . . . . . . . . . . . . 25 B.1. Open Source Implementations . . . . . . . . . . . . . . . 25 B.1.1. Reference Implementation . . . . . . . . . . . . . . 25 B.1.2. Rust Implementation . . . . . . . . . . . . . . . . . 25 B.2. Commercial Implementations . . . . . . . . . . . . . . . 25 B.3. Interoperability Testing . . . . . . . . . . . . . . . . 25 Mott Expires 31 October 2026 [Page 4] Internet-Draft cose-sqisign April 2026 Appendix C. Design Rationale . . . . . . . . . . . . . . . . . . 26 C.1. Algorithm Identifier Selection . . . . . . . . . . . . . 26 C.2. Key Type Design . . . . . . . . . . . . . . . . . . . . . 26 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 26 D.1. draft-mott-cose-sqisign-02 . . . . . . . . . . . . . . . 26 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 26 1. Introduction This document registers algorithm identifiers and key type parameters for SQIsign in COSE and JOSE. 1.1. Background and Motivation Post-quantum cryptography readiness is critical for constrained devices. As of 2026, while FIDO2/WebAuthn supports various COSE algorithms, some hardware authenticators and platform authenticators (like TPMs) have strict memory/storage constraints, effectively limiting public keys to 1024 bytes or less, hindering the adoption of large-key post-quantum algorithms. 1.1.1. Pressing Need for Smaller PQC Signatures FN-DSA (Falcon) and ML-DSA (Dilithium) have larger signatures that may not fit in constrained environments. The fundamental differences between ML-DSA, FN-DSA, and SQIsign lie in their underlying hard mathematical problems, implementation complexity, and performance trade-offs. Falcon (NIST secondary) uses NTRU lattices to achieve very small signatures and fast verification, but requires complex floating-point math. Dilithium (NIST primary) is a balanced, high-efficiency lattice scheme using Module-LWE/SIS, easy to implement. SQIsign [SQIsign-Spec] [SQIsign-Analysis] is a non-lattice, isogeny- based scheme that offers the smallest signature sizes but suffers from significantly slower signature generation where even vI may take seconds to minutes, or longer with WASM implementations for browsers of particular relevance to signatures required for WebAuthn PassKeys [WebAuthn-PQC-Signature-size-constraints]. SQIsign is an isogeny- based digital signature scheme participating in NIST's Round 2 Additional Digital Signature Schemes, not yet a NIST standard [NIST-Finalized-Standards]. Speed: SQIsign is significantly slower at signing (roughly 100x to 1000x) compared to ML-DSA, though the math is changing fast and variants improve this. Mott Expires 31 October 2026 [Page 5] Internet-Draft cose-sqisign April 2026 Table 1 compares representative parameter sets; note that these schemes are at different stages of standardization and evaluation. +=============+=================+================+==============+ | Algorithm | Public Key Size | Signature Size | PK + Sig | | | | | Fits < 1024? | +=============+=================+================+==============+ | ML-DSA-44 | 1,312 bytes | 2,420 bytes | ❌ | +-------------+-----------------+----------------+--------------+ | ML-DSA-65 | 1,952 bytes | 3,293 bytes | ❌ | +-------------+-----------------+----------------+--------------+ | ML-DSA-87 | 2,592 bytes | 4,595 bytes | ❌ | +-------------+-----------------+----------------+--------------+ | FN-DSA-512 | 897 bytes | 666 bytes | ❌ (1,563 | | | | | total) | +-------------+-----------------+----------------+--------------+ | FN-DSA-1024 | 1,793 bytes | 1,280 bytes | ❌ | +-------------+-----------------+----------------+--------------+ | SQIsign-L1 | 65 bytes | 148 bytes | ✅ (213 | | | | | total) | +-------------+-----------------+----------------+--------------+ | SQIsign-L3 | 97 bytes | 224 bytes | ✅ (321 | | | | | total) | +-------------+-----------------+----------------+--------------+ | SQIsign-L5 | 129 bytes | 292 bytes | ✅ (421 | | | | | total) | +-------------+-----------------+----------------+--------------+ Table 1 1.1.2. Estimated Constrained Device Footprint The total addressable market for SQIsign in constrained devices is estimated at ~6.25 billion units. 1.1.2.1. Device Category Breakdown 1.1.2.1.1. Legacy Hardware Security Keys: ~120 - 150 million * Security keys in Service: ~120 - 150 million legacy keys in active circulation (Series 5 and older). Some firmware introduced PQC readiness. Some older keys cannot be updated to increase buffer sizes. Mott Expires 31 October 2026 [Page 6] Internet-Draft cose-sqisign April 2026 1.1.2.1.2. Constrained TPMs and Platform Modules: ~1.1 billion Trusted Platform Modules (TPMs) are integrated into PCs and servers, but their WebAuthn implementation often inherits protocol-level constraints. Estimated ~2.5 billion active chips worldwide. Constrained Subset: We estimate ~1.1 billion of these are in older Windows 10/11 or Linux machines where the OS "virtual authenticator" or TPM driver still enforces the 1024-byte message default to maintain backward compatibility with external CTAP1/2 tools. 1.1.2.1.3. Browser and Software Implementations: ~5 billion This category refers to the "User-Agent" layer that mediates between the web and the hardware. Global Browser Agents: There are over 5 billion active browser instances across mobile and desktop (Chrome, Safari, Edge, Firefox). Legacy Protocols: Even on modern hardware, browsers often use the FIDO2 CTAP2 specification which, unless explicitly negotiated for larger messages, maintains a 1024-byte default for external key communication. 1.1.2.1.4. Critical Infrastructure: ~300 Million includes Energy (electric, nuclear, oil, gas), Water & Wastewater, Transportation Systems, Communications, Government, Emergency Services, Healthcare and Financial Services Industrial/Government: Agencies like the U.S. Department of Defense rely on high-security FIPS-certified keys that are notoriously slow to upgrade. We estimate ~50 million "frozen" government keys. IoT Security: Of the ~21 billion connected IoT devices in 2026, only a fraction use WebAuthn. However, for those that do (smart locks, secure gateways), approximately 250 million are estimated to use older, non-upgradable secure elements limited to 1024-byte payloads. Recent government-level initiatives highlight the necessity to "...effectively deprecate the use of RSA, Diffie-Hellman (DH), and elliptic curve cryptography (ECDH and ECDSA) when mandated." [CNSA-2], Page 4. 1.1.3. Pressing need: Limit or Stop 'Harvest now; decrypt later' Attacks Adversaries are collecting encrypted data today to decrypt when quantum computers become available. The transition to post-quantum cryptography (PQC) is critical for ensuring long-term security of digital communications against adversaries equipped with large-scale quantum computers. The National Institute of Standards and Technology (NIST) has been leading standardization efforts, having selected initial PQC algorithms and continuing to evaluate additional candidates. Mott Expires 31 October 2026 [Page 7] Internet-Draft cose-sqisign April 2026 CBOR Object Signing and Encryption (COSE) [RFC9052] is specifically designed for constrained node networks and IoT environments where bandwidth, storage, and computational resources are limited. The compact nature of SQIsign makes it an ideal candidate for COSE deployments. 1.2. Scope and Status This document is published on the *Standards* track rather than Informational Track for the following reasons: 1. *Algorithm Maturity*: SQIsign is currently undergoing evaluation in NIST's on-ramp process 2. *Continued Cryptanalysis*: The algorithm has active ongoing review by the cryptographic research community, including the IRTF CFRG 3. *High anticipated demand*: This specification enables experimentation and early deployment to gather implementation experience *This document does not represent Working Group consensus on algorithm innovation.* The COSE and JOSE working groups focus on algorithm _integration_ and _encoding_, not cryptographic algorithm design. The cryptographic properties of SQIsign are being evaluated through NIST's process and academic peer review. 1.3. Relationship to Other Work This document follows the precedent established by [I-D.ietf-cose-falcon] and [I-D.ietf-cose-dilithium] for integrating NIST PQC candidate algorithms into COSE and JOSE. The structure and approach are intentionally aligned to provide consistency across post-quantum signature scheme integrations. 1.4. Constrained Device Applicability SQIsign is particularly attractive for: * *IoT sensors* with limited flash memory * *Firmware updates* over low-bandwidth networks (LoRaWAN, NB-IoT) * *Embedded certificates* in constrained devices * *Blockchain and DLT* where transaction size affects fees Mott Expires 31 October 2026 [Page 8] Internet-Draft cose-sqisign April 2026 * *Satellite communications* with bandwidth constraints 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. This document uses the following terms: * *PQC*: Post-Quantum Cryptography * *COSE*: CBOR Object Signing and Encryption * *JOSE*: JSON Object Signing and Encryption * *JWS*: JSON Web Signature * *JWK*: JSON Web Key * *CBOR*: Concise Binary Object Representation [RFC7049] * *ECDH*: Elliptic Curve Diffie-Hellman * *IANA*: Internet Assigned Numbers Authority 3. Resistance to "Torsion Point" attack 3.1. SIKE Vulnerability (The "Torsion Point" Attack) of 2022 SIKE (Supersingular Isogeny Key Encapsulation) was a key exchange, more specifically, a Key Encapsulation Mechanism (KEM). In the SIKE protocol, users had to share more than just the target elliptic curve. To make the math work for key exchange, they shared the images of specific points (called torsion points) under the secret isogeny. * The Info: If the secret isogeny is 𝜙, SIKE gave away 𝜙(𝑃) and 𝜙(𝑄) for specific basis points 𝑃 and 𝑄. * The Break: In 2022, Castryck and Decru showed that this auxiliary information allowed an attacker to allowed an attacker to construct a higher-dimensional abelian variety linking the public data. In this setting, the secret isogeny can be recovered efficiently using techniques based on Kani’s results on isogenies between products of elliptic curves. Mott Expires 31 October 2026 [Page 9] Internet-Draft cose-sqisign April 2026 * The Oversight: For years, cryptanalysts thought this extra info was harmless. Related techniques existed in the algebraic geometry literature but had not previously been applied in this cryptographic context. 3.2. Why SQISign appears unaffected by the SIKE Vulnerability SQIsign is a signature scheme in which the prover demonstrates knowledge of an isogeny through a zero-knowledge protocol. Unlike SIDH/SIKE, it does not publish images of torsion basis points under secret isogenies. The Castryck–Decru attack relies critically on this auxiliary torsion-point information to construct additional structure (e.g., via abelian surfaces) that enables efficient recovery of the secret isogeny. Because SQIsign does not provide such auxiliary data, these techniques do not directly apply. Attacks would instead need to solve instances of the isogeny path problem or related problems in the endomorphism ring, for which no comparable shortcut is currently known. 4. SQIsign Algorithm Overview 4.1. Cryptographic Foundation SQIsign is based on the hardness of finding isogenies between supersingular elliptic curves over finite fields. The security assumption relies primarily on the difficulty of the *Isogeny Path Problem* Unlike lattice-based schemes, isogeny-based cryptography offers: * *Smaller key and signature sizes* * *Algebraic structure* based on elliptic curve isogenies * *Different security assumptions* (diversification from lattice- based schemes) 4.2. Security Levels SQIsign is defined with three parameter sets corresponding to NIST security levels: Mott Expires 31 October 2026 [Page 10] Internet-Draft cose-sqisign April 2026 +===============+============+============+===========+===========+ | Parameter Set | NIST Level | Public Key | Signature | Classical | | | | | | Sec | +===============+============+============+===========+===========+ | SQIsign-L1 | I | 65 bytes | 148 bytes | ~128 bits | +---------------+------------+------------+-----------+-----------+ | SQIsign-L3 | III | 97 bytes | 224 bytes | ~192 bits | +---------------+------------+------------+-----------+-----------+ | SQIsign-L5 | V | 129 bytes | 292 bytes | ~256 bits | +---------------+------------+------------+-----------+-----------+ Table 2 4.3. Performance Characteristics * *Signing*: Computationally intensive (slower than lattice schemes) * *Verification*: Moderate computational cost * *Key Generation*: Intensive computation required * *Size*: Exceptional efficiency: substantially smaller than many lattice-based alternatives at comparable security levels *Recommended Use Cases:* - Sign-once, verify-many scenarios (firmware, certificates) - Bandwidth-constrained environments - Storage-limited devices - Applications where signature/key size dominates performance considerations 5. COSE Integration This section defines the identifiers for SQIsign in COSE [RFC8152]. 5.1. SQIsign Algorithms The algorithms defined in this document are: * SQIsign-L1: SQIsign NIST Level I (suggested value -61) * SQIsign-L3: SQIsign NIST Level III (suggested value -62) * SQIsign-L5: SQIsign NIST Level V (suggested value -63) 5.2. SQIsign Key Types A new key type is defined for SQIsign with the name "SQIsign". Mott Expires 31 October 2026 [Page 11] Internet-Draft cose-sqisign April 2026 5.3. SQIsign Key Parameters SQIsign keys use the following COSE Key common parameters: +===============+============+===========+==========================+ | Key Parameter | COSE Label | CBOR Type | Description | +===============+============+===========+==========================+ | kty | 1 | int | Key type: IETF | | | | | (SQIsign) | +---------------+------------+-----------+--------------------------+ | kid | 2 | bstr | Key ID (optional) | +---------------+------------+-----------+--------------------------+ | alg | 3 | int | Algorithm identifier | | | | | (-61, -62, or -63) | +---------------+------------+-----------+--------------------------+ | key_ops | 4 | array | Key operations | | | | | (sign, verify) | +---------------+------------+-----------+--------------------------+ Table 3 5.4. SQIsign-Specific Key Parameters +===============+=======+===========+====================+ | Key Parameter | Label | CBOR Type | Description | +===============+=======+===========+====================+ | pub | -1 | bstr | SQIsign public key | +---------------+-------+-----------+--------------------+ | priv | -2 | bstr | SQIsign private | | | | | key (sensitive) | +---------------+-------+-----------+--------------------+ Table 4 5.5. COSE Key Format Examples 5.5.1. Public Key (COSE_Key) cbor { 1: IETF, / kty: SQIsign / 3: -61, / alg: SQIsign-L1 / -1: h'[PUBLIC_KEY]' / pub: SQIsign public key bytes / } 5.5.2. Private Key (COSE_Key) cbor { 1: IETF, / kty: SQIsign / 3: -61, / alg: SQIsign-L1 / -1: h'[PUBLIC_KEY]', / pub: SQIsign public key bytes / -2: h'[PRIVATE_KEY]' / priv: SQIsign private key bytes / } Mott Expires 31 October 2026 [Page 12] Internet-Draft cose-sqisign April 2026 5.6. COSE Signature Format SQIsign signatures in COSE follow the standard COSE_Sign1 structure [RFC9052]: COSE_Sign1 = [ protected: bstr .cbor header_map, unprotected: header_map, payload: bstr / nil, signature: bstr ] The signature field contains the raw SQIsign signature bytes. 5.6.1. Protected Headers The protected header MUST include: cbor { 1: -61 / alg: SQIsign-L1, -62 for L3, -63 for L5 / } 5.6.2. Example COSE_Sign1 Structure cbor 18( / COSE_Sign1 tag / [ h'A10139003C', / protected: {"alg": -61} / {}, / unprotected / h'546869732069732074686520636F6E74656E742E', / payload / h'[SQISIGN_SIGNATURE_BYTES]' / signature / ] ) 6. JOSE Integration 6.1. JSON Web Signature (JWS) Algorithm Registration The following algorithm identifiers are registered for use in the JWS "alg" header parameter for JSON Web Signatures [RFC7515]: +================+==============+=============================+ | Algorithm Name | Description | Implementation Requirements | +================+==============+=============================+ | SQIsign-L1 | SQIsign NIST | Optional | | | Level I | | +----------------+--------------+-----------------------------+ | SQIsign-L3 | SQIsign NIST | Optional | | | Level III | | +----------------+--------------+-----------------------------+ | SQIsign-L5 | SQIsign NIST | Optional | | | Level V | | +----------------+--------------+-----------------------------+ Table 5 Mott Expires 31 October 2026 [Page 13] Internet-Draft cose-sqisign April 2026 6.2. JSON Web Key (JWK) Representation SQIsign keys are represented in JWK [RFC7517] format as follows: 6.2.1. Public Key Parameters +===========+========+===============================+ | Parameter | Type | Description | +===========+========+===============================+ | kty | string | Key type: "SQIsign" | +-----------+--------+-------------------------------+ | alg | string | Algorithm: "SQIsign-L1", | | | | "SQIsign-L3", or "SQIsign-L5" | +-----------+--------+-------------------------------+ | pub | string | Base64url-encoded public key | +-----------+--------+-------------------------------+ | kid | string | Key ID (optional) | +-----------+--------+-------------------------------+ | use | string | Public key use: "sig" | | | | (optional) | +-----------+--------+-------------------------------+ | key_ops | array | Key operations: [verify] | | | | (optional) | +-----------+--------+-------------------------------+ Table 6 6.2.2. Private Key Parameters Private keys include all public key parameters plus: +===========+========+===============================+ | Parameter | Type | Description | +===========+========+===============================+ | priv | string | Base64url-encoded private key | +-----------+--------+-------------------------------+ Table 7 6.3. JWK Examples 6.3.1. Public Key (JWK) Example json { "kty": "SQIsign", "alg": "SQIsign-L1", "pub": "KxtQx8s8RcBEU67wr57K37fdPEztN4M8NUC_\ 5xZuqgMwkaeJhM94YHi_- 2UsQllbnmm-W4XFSLm2hUwiMylrAh0", "kid": "2027-01-device-key", "use": "sig", "key_ops": ["verify"] } Mott Expires 31 October 2026 [Page 14] Internet-Draft cose-sqisign April 2026 6.3.2. Private Key (JWK) Example json { "kty": "SQIsign", "alg": "SQIsign-L1", "pub": "KxtQx8s8RcBEU67wr57K37fdPEztN4M8NUC_\ 5xZuqgMwkaeJhM94YHi_- 2UsQllbnmm-W4XFSLm2hUwiMylrAh0", "priv": "KxtQx8s8RcBEU67wr57K37fdPEztN4M8NUC_5xZuqgMwkaeJhM94YHi_\ - 2UsQllbnmm-W4XFSLm2hUwiMylrAh1VwP9vNkBZH0Bjj2wc-\ p7sUgQAAAAAAAAAAAAAAAAAAN68tviJbcCpQ84fh-4IJB4-\ ____________________P38m3fKOhfhMspQU9GmA4CD5___\ _______________________________________________\ ___________wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA\ AAAAAAA5cP9aha40v- 8mFd_bdAgpR93Ug2iPhu4_NxG97C7\ 8wBvVMGOrQTCli7NxrR2KlPZR1AC5VddGf4p- ZjCzrWfAJv\ xhEh4uOKXq1MmuS9TwZGuz1YIYMIguu1wqjdmfaQAfOmK2g\ WWO3vcld5s7GR2AcrTv65ocK_pVUWY8eJDcQA", "kid": "2027-01-device-key", "use": "sig", "key_ops": ["sign"] } 6.4. JWS Compact Serialization A JWS using SQIsign follows the standard compact serialization: BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload) || '.' || BASE64URL(JWS Signature) 6.4.1. Example JWS Protected Header json { "alg": "SQIsign-L1", "typ": "JWT" } Base64url-encoded: eyJhbGciOiJTUUlzaWduLUwxIiwidHlwIjoiSldUIn0 6.4.2. Complete JWS Example eyJhbGciOiJTUUlzaWduLUwxIiwidHlwIjoiSldUIn0 . [BASE64URL_PAYLOAD] . [BASE64URL_SQISIGN_SIGNATURE] 7. Implementation Considerations 7.1. Signature and Key Generation Implementations MUST follow the SQIsign specification [SQIsign-Spec] for: * Key pair generation * Signature generation * Signature verification Mott Expires 31 October 2026 [Page 15] Internet-Draft cose-sqisign April 2026 7.2. Randomness Requirements SQIsign signature generation requires high-quality randomness. Implementations MUST use a cryptographically secure random number generator (CSRNG) compliant with [RFC4086] or equivalent. 7.3. Side-Channel Protections Implementations SHOULD implement protections against: * Timing attacks * Power analysis * Fault injection attacks Particularly for constrained devices deployed in physically accessible environments. 7.4. Performance Trade-offs Implementers should be aware: * *Signing is computationally expensive*: Consider pre-signing or batch operations * *Verification is moderate*: Suitable for resource-constrained verifiers * *Size is exceptional*: Minimizes bandwidth and storage 7.5. Interoperability Testing Early implementations SHOULD participate in interoperability testing to ensure: * Consistent signature generation and verification * Proper encoding in COSE and JOSE formats * Cross-platform compatibility 8. Security Considerations 8.1. Algorithm Security The security of SQIsign relies primarily on the hardness of finding isogenies between supersingular elliptic curves. Mott Expires 31 October 2026 [Page 16] Internet-Draft cose-sqisign April 2026 These assumptions are *different from lattice-based schemes*, providing cryptographic diversity in the post-quantum landscape. 8.2. Quantum Security SQIsign is designed to resist attacks by large-scale quantum computers. The three parameter sets provide security equivalent to AES-128, AES-192, and AES-256 against both classical and quantum adversaries. 8.3. Current Cryptanalysis Status As of this writing, SQIsign is undergoing active cryptanalytic review: * *NIST Round 2 evaluation*: [NIST-Finalized-Standards] * *Academic research*: Ongoing analysis of isogeny-based cryptography * *Known attacks*: No attacks are currently known that recover private keys for the standardized parameter sets within their claimed security levels. However, the scheme and its underlying assumptions remain under active study. *Implementers are advised*: - Monitor NIST announcements and updates - Follow academic literature on isogeny cryptanalysis - Be prepared to deprecate or update as cryptanalysis evolves 8.4. Implementation Security 8.4.1. Random Number Generation Poor randomness can completely compromise SQIsign security. Implementations MUST use robust CSRNGs, especially on constrained devices with limited entropy sources. 8.4.2. Side-Channel Resistance Constrained devices may be physically accessible to attackers. Implementations SHOULD: * Use constant-time algorithms where possible * Implement countermeasures against DPA/SPA * Consider fault attack mitigations Mott Expires 31 October 2026 [Page 17] Internet-Draft cose-sqisign April 2026 8.4.3. Key Management * Private keys MUST be protected with appropriate access controls * Consider hardware security modules (HSMs) or secure elements for key storage * Implement key rotation policies appropriate to the deployment 8.5. Cryptographic Agility Organizations deploying SQIsign SHOULD: * Maintain hybrid deployments with classical algorithms during transition * Plan for algorithm migration if cryptanalysis reveals weaknesses * Monitor NIST and IRTF guidance on PQC deployment 8.6. Constrained Device Specific Risks IoT devices face unique challenges: * *Physical access*: Devices may be deployed in hostile environments * *Limited update capability*: Firmware updates may be infrequent or impossible * *Long deployment lifetimes*: Devices may operate for 10+ years Design systems with: - Defense in depth (multiple security layers) - Remote update capability when possible - Graceful degradation if algorithm is compromised 9. IANA Considerations 9.1. Additions to Existing Registries IANA is requested to add the following entries to the COSE and JOSE registries. The following completed registration actions are provided as described in [RFC9053] and [RFC9054]. 9.1.1. New COSE Algorithms IANA is requested to register the following entries in the "COSE Algorithms" registry: Mott Expires 31 October 2026 [Page 18] Internet-Draft cose-sqisign April 2026 +==========+=====+===========+==============+======+========+=====+ |Name |Value|Description| Capabilities |Change|Ref |Rec'd| | | | | |Cont | | | +==========+=====+===========+==============+======+========+=====+ |SQIsign-L1|-61 |SQIsign | kty |IETF |THIS-RFC|No | | | |NIST L I | | | | | +----------+-----+-----------+--------------+------+--------+-----+ |SQIsign-L3|-62 |SQIsign | kty |IETF |THIS-RFC|No | | | |NIST L III | | | | | +----------+-----+-----------+--------------+------+--------+-----+ |SQIsign-L5|-63 |SQIsign | kty |IETF |THIS-RFC|No | | | |NIST L V | | | | | +----------+-----+-----------+--------------+------+--------+-----+ Table 8 9.1.2. New COSE Key Types IANA is requested to register the following entry in the "COSE Key Types" registry: +=========+=======+=============+==============+========+==========+ | Name | Value | Description | Capabilities | Change | Ref | | | | | | Cont | | +=========+=======+=============+==============+========+==========+ | SQIsign | IETF | SQIsign pub | sign, verify | IETF | THIS-RFC | | | | key | | | | +---------+-------+-------------+--------------+--------+----------+ Table 9 9.1.3. New COSE Key Type Parameters IANA is requested to register the following entries in the "COSE Key Type Parameters" registry: +==========+======+=======+======+=========+========+===========+ | Key Type | Name | Label | CBOR | Desc | Change | Reference | | | | | Type | | Cont | | +==========+======+=======+======+=========+========+===========+ | SQIsign | pub | -1 | bstr | Public | IETF | THIS-RFC | | | | | | key | | | +----------+------+-------+------+---------+--------+-----------+ | SQIsign | priv | -2 | bstr | Private | IETF | THIS-RFC | | | | | | key | | | +----------+------+-------+------+---------+--------+-----------+ Table 10 Mott Expires 31 October 2026 [Page 19] Internet-Draft cose-sqisign April 2026 9.1.4. New JWS Algorithms IANA is requested to register the following entries in the "JSON Web Signature and Encryption Algorithms" registry: +============+==========+==========+======+==========+=============+ | Algorithm | Desc | Impl Req |Change| Ref | Recommended | | Name | | |Cont | | | +============+==========+==========+======+==========+=============+ | SQIsign-L1 | SQIsign | Optional |IETF | THIS-RFC | No | | | NIST L I | | | | | +------------+----------+----------+------+----------+-------------+ | SQIsign-L3 | SQIsign | Optional |IETF | THIS-RFC | No | | | NIST L | | | | | | | III | | | | | +------------+----------+----------+------+----------+-------------+ | SQIsign-L5 | SQIsign | Optional |IETF | THIS-RFC | No | | | NIST L V | | | | | +------------+----------+----------+------+----------+-------------+ Table 11 9.1.5. New JSON Web Key Types IANA is requested to register the following entry in the "JSON Web Key Types" registry: +===================+====================+=============+===========+ | "kty" Param Value | Key Type Desc | Change Cont | Reference | +===================+====================+=============+===========+ | SQIsign | SQIsign public key | IETF | THIS-RFC | +-------------------+--------------------+-------------+-----------+ Table 12 9.1.6. New JSON Web Key Parameters IANA is requested to register the following entries in the "JSON Web Key Parameters" registry: Mott Expires 31 October 2026 [Page 20] Internet-Draft cose-sqisign April 2026 +============+=========+=====================+========+===========+ | Param Name | Desc | Used with "kty" Val | Change | Reference | | | | | Cont | | +============+=========+=====================+========+===========+ | pub | Public | SQIsign | IETF | THIS-RFC | | | key | | | | +------------+---------+---------------------+--------+-----------+ | priv | Private | SQIsign | IETF | THIS-RFC | | | key | | | | +------------+---------+---------------------+--------+-----------+ Table 13 10. Acknowledgments The authors would like to thank: * Luca DeFeo for reviewing draft-00 and providing valuable feedback. Any remaining errors are solely the responsibility of the authors. * The SQIsign design team for groundbreaking work on isogeny-based signatures * The NIST PQC team for managing the standardization process * The COSE and JOSE working groups for guidance on integration * The IRTF Crypto Forum Research Group for ongoing cryptanalytic review * Early implementers who provide valuable feedback This work builds upon the template established by [I-D.ietf-cose-falcon] and similar PQC integration efforts. 11. References 11.1. Normative References _Populated automatically from metadata_ 11.2. Informative References _Populated automatically from metadata_ 12. References 12.1. Normative References Mott Expires 31 October 2026 [Page 21] Internet-Draft cose-sqisign April 2026 [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE): Structures and Process", STD 96, RFC 9052, DOI 10.17487/RFC9052, August 2022, . [RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE): Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053, August 2022, . [RFC9054] Schaad, J., "CBOR Object Signing and Encryption (COSE): Hash Algorithms", RFC 9054, DOI 10.17487/RFC9054, August 2022, . 12.2. Informative References [CNSA-2] National Security Agency, "Commercial National Security Algorithm Suite 2.0", May 2025, . [I-D.ietf-cose-dilithium] Prorock, M. and O. Steele, "ML-DSA for JOSE and COSE", Work in Progress, Internet-Draft, draft-ietf-cose- dilithium-11, 15 November 2025, . Mott Expires 31 October 2026 [Page 22] Internet-Draft cose-sqisign April 2026 [I-D.ietf-cose-falcon] Prorock, M., Steele, O., and H. Tschofenig, "FN-DSA for JOSE and COSE", Work in Progress, Internet-Draft, draft- ietf-cose-falcon-04, 15 March 2026, . [NIST-Finalized-Standards] NIST, ""NIST Releases First 3 Finalized Post-Quantum Encryption Standards"", August 2024, . [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, DOI 10.17487/RFC4086, June 2005, . [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013, . [SQIsign-Analysis] IACR ePrint Archive, ""SQIsign: Compact Post-Quantum Signatures from Quaternions and Isogenies"", January 2021, . [SQIsign-Spec] SQIsign team, "SQIsign: Compact Post-Quantum Signatures from Quaternions and Isogenies (Round 2)", February 2025, . [WebAuthn-PQC-Signature-size-constraints] University of Quantum Science, "WebAuthn PQC Signature size constraints", April 2026, . Appendix A. Test Vectors A.1. SQIsign-L1 Test Vectors A.1.1. Example 1: Simple Message Signing The following test vector exhibits a SQIsign Level I signature over a short message. Mott Expires 31 October 2026 [Page 23] Internet-Draft cose-sqisign April 2026 Message (hex): d81c4d8d734fcbfbeade3d3f8a039faa2a2c9957e835ad55b2 \ 2e75bf57bb556ac8 Message (ASCII): MsO=?*,W5U.uWUj Public Key (hex): 07CCD21425136F6E865E497D2D4D208F0054AD81372066E \ 817480787AAF7B2029550C89E892D618CE3230F23510BFBE68FCCDDAEA51DB1436 \ B462ADFAF008A010B Public Key (Base64url): B8zSFCUTb26GXkl9LU0gjwBUrYE3IGboF0gHh6r3s \ gKVUMieiS1hjOMjDyNRC_vmj8zdrqUdsUNrRirfrwCKAQs Signature (hex): 84228651f271b0f39f2f19f2e8718f31ed3365ac9e5cb303 \ afe663d0cfc11f0455d891b0ca6c7e653f9ba2667730bb77befe1b1a3182840428 \ 4af8fd7baacc010001d974b5ca671ff65708d8b462a5a84a1443ee9b5fed721876 \ 7c9d85ceed04db0a69a2f6ec3be835b3b2624b9a0df68837ad00bcacc27d1ec806 \ a44840267471d86eff3447018adb0a6551ee8322ab30010202 Signature (Base64url): hCKGUfJxsPOfLxny6HGPMe0zZayeXLMDr-Zj0M_BHw \ RV2JGwymx- ZT-bomZ3MLt3vv4bGjGChAQoSvj9e6rMAQAB2XS1ymcf9lcI2LRipahK \ FEPum1_tchh2fJ2Fzu0E2wppovbsO-g1s7JiS5oN9og3rQC8rMJ9HsgGpEhAJnRx2G \ 7_NEcBitsKZVHugyKrMAECAg A.1.2. COSE_Sign1 Complete Example cbor 18( [ h'a10139003c', / protected: {"alg": -61} / {}, / unprotected / h'd81c4d8d734fcbfbeade3d3f8a039faa2a2c9957e835ad55b22e75bf57bb \ 556ac8', / payload / h'84228651f271b0f39f2f19f2e8718f31ed3365ac9e5cb303afe663d0cfc1 \ 1f0455d891b0ca6c7e653f9ba2667730bb77befe1b1a31828404284af8fd7b \ aacc010001d974b5ca671ff65708d8b462a5a84a1443ee9b5fed7218767c9d \ 85ceed04db0a69a2f6ec3be835b3b2624b9a0df68837ad00bcacc27d1ec806 \ a44840267471d86eff3447018adb0a6551ee8322ab30010202' ] ) A.1.3. JWS Complete Example eyJhbGciOiJTUUlzaWduLUwxIiwidHlwIjoiSldUIn0 . 2BxNjXNPy_vq3j0_igOfqiosmVfoNa1Vsi51v1e7VWrI . hCKGUfJxsPOfLxny6HGPMe0zZayeXLMDr-Zj0M_BHwRV2JGwymx-ZT-bomZ3MLt3vv \ 4bGjGChAQoSvj9e6rMAQAB2XS1ymcf9lcI2LRipahKFEPum1_tchh2fJ2Fzu0E2wpp \ ovbsO-g1s7JiS5oN9og3rQC8rMJ9HsgGpEhAJnRx2G7_NEcBitsKZVHugyKrMAECAg A.2. SQIsign-L3 Test Vectors [PLACEHOLDER FOR L3 TEST VECTORS] A.3. SQIsign-L5 Test Vectors [PLACEHOLDER FOR L5 TEST VECTORS] Mott Expires 31 October 2026 [Page 24] Internet-Draft cose-sqisign April 2026 Appendix B. Implementation Status [RFC Editor: Please remove this section before publication] This section records the status of known implementations at the time of writing. B.1. Open Source Implementations B.1.1. Reference Implementation * *Organization*: SQIsign team * *Repository*: https://github.com/SQISign/the-sqisign * *Language*: C * *License*: MIT * *Status*: Active development * *COSE/JOSE Support*: Not yet integrated B.1.2. Rust Implementation * *Organization*: IETF - Community implementation * *Repository*: IETF * *Language*: Rust * *License*: IETF * *COSE Support*: Planned * *Status*: Development B.2. Commercial Implementations [RFC EDITOR: To be populated as vendors implement] B.3. Interoperability Testing * *Test Suite Location*: IETF * *Participating Organizations*: IETF Mott Expires 31 October 2026 [Page 25] Internet-Draft cose-sqisign April 2026 Appendix C. Design Rationale C.1. Algorithm Identifier Selection The requested algorithm identifiers (-61, -62, -63) are: * In the range designated for experimental/informational use * Sequential for the three parameter sets * Not conflicting with existing registrations * Consistent with the approach used for other PQC algorithms C.2. Key Type Design The SQIsign key type is intentionally simple: * Only two parameters (pub, priv) following minimalist design * Binary encoding (bstr) for efficiency * No algorithm-specific encoding—raw bytes from SQIsign spec This approach: - Minimizes CBOR encoding overhead (critical for constrained devices) - Simplifies implementation - Provides future flexibility for parameter set evolution Appendix D. Change Log [RFC Editor Note:** Please remove this section before publication] D.1. draft-mott-cose-sqisign-02 * Incorporated technical corrections and feedback from Luca De Feo on draft-00 * Updated the Abstract and Introduction to utilize more neutral, objective language * Removed vendor-specific branding in favor of generic cryptographic terminology * fixed various formatting issues Author's Address Mott Expires 31 October 2026 [Page 26] Internet-Draft cose-sqisign April 2026 Antony R. Mott RustyKey United States of America Email: antony@rustykey.io Mott Expires 31 October 2026 [Page 27]