A signature algorithm is a cryptographic scheme comprising key generation, signing, and verification procedures that lets a holder of a private key produce a value provably tied to a message, which anyone with the public key can verify. It provides authenticity, integrity, and non-repudiation, with families including RSA, ECDSA, EdDSA, and Schnorr. It is the cryptographic primitive underpinning digital signatures.
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- Schemes differ in key size, signature size, speed, and security assumptions: RSA relies on integer factoring, while ECDSA, EdDSA, and Schnorr rely on elliptic-curve discrete logs. Post-quantum candidates such as lattice- and hash-based signatures are being standardised to resist quantum attacks on current discrete-log schemes.