Which cryptographic signature scheme did Bitcoin Taproot add to the protocol?

Schnorr signatures are the cryptographic signature scheme added to Bitcoin through the Taproot upgrade.

Bitcoin’s original protocol used the Elliptic Curve Digital Signature Algorithm, or ECDSA, for ordinary transaction signatures. Taproot added Schnorr signatures through Bitcoin Improvement Proposal 340, which was activated as part of the wider upgrade in November 2021.

Schnorr signatures have useful mathematical properties for Bitcoin, including straightforward linearity. These properties help support signature aggregation and make certain multisignature or collaborative transactions more efficient and less distinguishable from ordinary single-key payments.

Schnorr signatures do not replace every signature format in Bitcoin overnight. Wallets and applications can continue using older formats, and adoption depends on software support. Schnorr is also not the name of the entire upgrade: Taproot is the broader protocol change, while Schnorr signatures are one of its central components.