Post-quantum cryptography

Post-quantum cryptography is not quantum cryptography. It is classical software that replaces today's public-key algorithms with ones whose underlying problem resists Shor's algorithm, which would break RSA factoring and ECDSA discrete logarithms in polynomial time. Grover's algorithm only gives a quadratic speedup against symmetric and hash cryptography, which stays secure by doubling key sizes such as AES-256 and SHA-512.

Chains sign transactions with ECDSA or EdDSA, precisely what a cryptographically relevant quantum computer would render vulnerable. Risk concentrates on public keys already exposed on-chain, for example reused addresses or old P2PK outputs. Add the Harvest Now, Decrypt Later model, where an adversary captures signed data today to decrypt it once the machine exists, and the case for migrating ahead of time becomes clear.

The standards already exist. In August 2024 NIST published its first three final norms: FIPS 203 (ML-KEM, derived from Kyber), FIPS 204 (ML-DSA, from Dilithium) and FIPS 205 (SLH-DSA, from SPHINCS+). In March 2025 it selected HQC as an additional algorithm, with a final standard expected around 2027, while FN-DSA (FALCON) remains in development. In production, QRL uses XMSS hash-based signatures, Algorand certifies its state with FALCON, Cloudflare and Chrome deploy hybrid X25519+ML-KEM TLS, and Ethereum's roadmap contemplates quantum-resistant signatures. This layer shapes the longevity of any on-chain infrastructure.