ECDSA

Elliptic Curve Digital Signature Algorithm — the signature scheme used by Bitcoin and pre-Taproot Ethereum. A private key produces a variable-length DER-encoded (r, s) signature (typically 71–72 bytes on Bitcoin) over a message hash; anyone with the corresponding public key can verify it without learning the private key. Bitcoin's secp256k1 curve is used for ECDSA; Ethereum uses the same curve but with an additional recovery parameter.