Post-Quantum Cryptography (PQC)
Signature and key-exchange schemes designed to resist quantum computers; NIST finalised the first standards in August 2024.
Post-quantum cryptography replaces problems a quantum computer can solve quickly (factoring, discrete logarithms) with problems it is not known to: structured lattices, hash functions, codes. NIST published the first final standards on 13 August 2024: FIPS 203 (ML-KEM, key encapsulation), FIPS 204 (ML-DSA, lattice signatures) and FIPS 205 (SLH-DSA, stateless hash-based signatures). For blockchains the cost is size: a post-quantum signature is hundreds to thousands of bytes against 64 for Schnorr, which is why migration designs such as BIP-360 focus on output types and script trees rather than a simple key swap. Hash-based schemes (XMSS, Winternitz, SLH-DSA) rely on the weakest assumptions and are the ones already deployed on a few chains. The readiness table on /quantum lists which chains have shipped what, with sources.