What is a Schnorr signature?

A digital signatureDigital signature (ECDSA, Schnorr)Proof, made with a private key, that the owner approved a payment. Anyone can check it; practical forgery is infeasible under current assumptions. proves that the owner of a private keyPrivate keyThe secret number that lets you spend your bitcoin. Whoever knows it controls the coins, so it must never be shared. approved a payment. Bitcoin used a method called ECDSA from 2009, and the TaprootTaprootA 2021 upgrade that added Schnorr signatures and addresses starting bc1p, making complex payments cheaper and more private. upgrade of November 2021 added Schnorr signatures, named after the German mathematician Claus Peter Schnorr and defined for Bitcoin in BIP-340. They work with the same keys, and each one is a fixed 64 bytes.

Their most useful property is that keys and signatures can be added together. With a scheme such as MuSig2 (BIP-327), a group who must all sign can make one shared key and one joint signature, so their payment looks like an ordinary one from a single person and costs less.

Like ECDSA, Schnorr signatures rely on elliptic-curve maths that 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, in theory, undo.