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SELF Chain Post-Quantum Cryptography

Introduction​

SELF Chain is implementing a comprehensive post-quantum cryptography (PQC) strategy to ensure long-term security against threats posed by quantum computing advancements. This document provides an overview of our approach to quantum-resistant security and current implementation status.

🚧 Development Notice: Post-quantum cryptography implementation is currently in the design and planning phase. The features described here represent our architectural approach and roadmap.

Multi-Layered Defense Strategy​

Our post-quantum security implementation leverages multiple complementary cryptographic approaches:

1. Quantum-Resistant Key Exchange (Kyber)​

SELF Chain implements Kyber, a lattice-based key encapsulation mechanism (KEM) selected by NIST as the first standardized post-quantum cryptographic algorithm. Kyber provides:

  • Quantum-resistant secure key exchange
  • Strong security guarantees based on module learning with errors (MLWE) problem
  • Excellent performance characteristics compared to other PQC candidates
  • Well-analyzed security properties with conservative parameter selection

Implementation Status: Module structure designed with planned interfaces for both Kyber-768 and Kyber-1024 variants, with Kyber-1024 as the default for maximum security margin.

2. Quantum-Resistant Signatures (SPHINCS+)​

To complement Kyber's key exchange capabilities, SELF Chain implements SPHINCS+, a stateless hash-based signature scheme built upon:

  • Winternitz One-Time Signatures (WOTS)
  • Merkle tree authentication paths
  • Purely hash-based security (no number-theoretic assumptions)
  • Stateless design for practical blockchain implementation

Implementation Status: Module structure designed with planned interfaces for SPHINCS+-SHA3-256 in both fast (larger signatures) and small (slower generation) parameter sets.

3. Hybrid Cryptographic Approach​

During the transition period, SELF Chain employs a hybrid approach that combines:

  • Classical cryptography (ECDSA with secp256k1, X25519) for backward compatibility and immediate security
  • Post-quantum algorithms (Kyber + SPHINCS+) for forward security against quantum threats
  • Versioned cryptographic operations for smooth transition

Hybrid Key Exchange​

SELF Chain implements a hybrid key exchange mechanism combining X25519 (classical) with Kyber-1024 (post-quantum):

  • Follows NIST recommendations for post-quantum transition
  • Combines strengths of well-established classical and quantum-resistant algorithms
  • Ensures security against both conventional and quantum adversaries
  • Provides cryptographic agility through modular design

Implementation Status:

  • Hybrid X25519+Kyber key exchange architecture designed with proper encapsulation/decapsulation flow
  • Hybrid signature scheme planned that combines ECDSA and SPHINCS+ signatures with unified verification protocol

Implementation Architecture​

SELF Chain's cryptographic implementation follows a modular architecture:

src/crypto/
├── classic/     # Classical cryptography (ECDSA, etc.)
├── quantum/     # Post-quantum algorithms (Kyber, SPHINCS+)
├── hybrid/      # Combined classical+quantum approaches
└── common/      # Shared traits and utilities

This architecture provides:

  • Clean separation between cryptographic approaches
  • Unified interfaces for all signature and key exchange operations
  • Versioned algorithms for seamless upgrades
  • Backward compatibility with existing blockchain transactions

Implementation Timeline​

The post-quantum security roadmap follows a phased approach:

  1. Phase 1 (Q2 2025): Module structure and Kyber integration design ◐
  2. Phase 2 (Q3 2025): X25519+Kyber hybrid key exchange implementation ○
  3. Phase 3 (Q4 2025): SPHINCS+ integration and hybrid signatures ○
  4. Phase 4 (Q1 2026): Blockchain integration and performance optimizations ○
  5. Phase 5 (Q2 2026): Full network deployment and security hardening ○

Legend: ✓ Complete, ◐ In Progress, ○ Planned

X25519 Implementation Enhancement Timeline​

In addition to the main roadmap, we have a specific timeline to enhance the X25519 implementation:

  1. Q2 2025: Design interim solution for improved X25519 key exchange functionality ◐
  2. Q3 2025: Implement X25519 enhancements or custom implementation ○
  3. Q4 2025: Final implementation of enhanced X25519 key exchange with proper deterministic behavior ○

Note: The interim solution implements a shared secret caching mechanism that enables deterministic behavior between encapsulation and decapsulation operations, which is critical for blockchain testing environments.

Security Benefits​

This comprehensive post-quantum approach provides several key benefits:

  1. Long-term Security: Protection against future quantum computing threats
  2. Defense in Depth: Multiple cryptographic approaches with different security foundations
  3. Standardization Alignment: Implementation of NIST-approved algorithms
  4. Adaptive Design: Cryptographic agility enabling continuous algorithm improvements

User Impact​

The transition to post-quantum cryptography will be designed to minimize disruption:

  1. Phased Rollout: Gradual introduction of post-quantum features
  2. Backward Compatibility: Support for existing applications during transition
  3. Performance Considerations: Optimizations to manage larger key and signature sizes

Technical Considerations​

While detailed implementation details remain in the private repository for security purposes, the approach includes:

  1. Cryptographic Agility: Algorithm-agnostic interfaces for future upgrades
  2. Performance Optimization: Techniques to minimize blockchain bloat from larger signatures and key material
  3. Secure Implementation: Following best practices for cryptographic code and proper key material handling
  4. Integration Testing: Comprehensive test suite for all cryptographic primitives
  5. Secure Key Management: Proper zeroization of sensitive private key material
  6. Hybrid Design: Careful composition of classical and post-quantum algorithms

Continuous Evolution​

SELF Chain's quantum security approach is designed for continuous improvement:

  1. Threat Monitoring: Active tracking of quantum computing advances and emerging attack vectors
  2. Regular Updates: Scheduled security reviews and algorithm upgrades as standards evolve
  3. Community Involvement: Open collaboration with security researchers worldwide
  4. Iterative Improvements: Incremental enhancements based on real-world deployment experience

Our commitment is not to achieve perfect security once, but to continuously adapt and strengthen our defenses as the quantum computing landscape evolves. This ensures that SELF Chain remains resilient against both current and future threats.

References​