Most blockchains today rely on elliptic curve signatures such as secp256k1 or ed25519. A large scale quantum computer running Shor’s algorithm could break these schemes and derive private keys from public keys.
Post quantum schemes such as lattice based signatures are designed to resist known quantum attacks. Examples include Dilithium, Falcon and SPHINCS plus. They have very different performance characteristics. Key sizes and signature sizes are larger and verification cost can be higher.
For blockchains the migration path is constrained by existing addresses. When an account has never broadcast a transaction its public key is not on chain, which offers some protection. Once a user sends a transaction the public key becomes visible and should eventually be rotated to a quantum safe scheme.
The most realistic near term approach is to support hybrid signatures. A transaction is valid only when both a classical and a post quantum signature verify. This preserves compatibility while gradually hardening the system against future quantum advances.
