What is a digital signature in Bitcoin?
Proof, made with a private key, that the owner approved a payment. Anyone can check it; practical forgery is infeasible under current assumptions.
Bitcoin has used a signature scheme called ECDSA since 2009. Since TaprootTaprootA 2021 upgrade that added Schnorr signatures and addresses starting bc1p, making complex payments cheaper and more private. it also uses Schnorr signaturesSchnorr signatureA kind of digital signature Bitcoin added with Taproot in 2021. Several people can combine keys so their joint signature looks like one person's., which are simpler and let several signers combine into one.
Both rely on elliptic-curve maths that, in theory, a large enough quantum computerQuantum computer (qubit)A computer that uses quantum physics to solve some problems far faster than ordinary ones. Its working parts are called qubits. could undo.
References
- Bitcoin Improvement Proposals, “BIP-340: Schnorr Signatures for secp256k1”.