How Can Bitcoin Resist Quantum Computers? A Comparison of Three Lattice-Based Signature Schemes
"Bitcoin's Quantum Defense: A Comparison of Three Lattice-Based Signature Schemes" by the Blockstream Research Team explores how Bitcoin can transition to quantum-resistant digital signatures, as current schemes like Schnorr and ECDSA are vulnerable to quantum computers. The report evaluates three lattice-based signature candidates—Dilithium, Falcon, and Hawk—against criteria like on-chain cost (key/signature size), implementation complexity, deployment risks, and support for Bitcoin's key derivation standard (BIP-32).
The analysis recommends a minimum Security Level 3 for Bitcoin due to its long-term security needs. Dilithium (ML-DSA) is praised for its simplicity and integer-only operations, making it easier to implement securely, but it has the largest signature size (~5.3 KB for Level 3). Falcon (FN-DSA) offers the most compact signatures (e.g., ~3.1 KB for Level 5) and the fastest verification, though its signing requires complex floating-point sampling—a solvable engineering challenge. Hawk, despite its small size, was withdrawn from NIST standardization after a security vulnerability was discovered, highlighting the importance of conservative security margins.
Currently, neither Dilithium nor Falcon has a fully viable, production-ready BIP-32 key derivation method. The report concludes that if a lattice-based scheme had to be chosen now, Falcon-1024 would be the preferred option for its balance of size, speed, and mature security assumptions. However, the short-term recommendation remains hash-based signatures (like SPHINCS+) for their lower risk, with a potential future hybrid or full transition to Falcon once its standard (FN-DSA) is finalized and well-supported.
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