Digital signatures provide authenticity, integrity and non-repudiation to electronic documents by using public key infrastructure. Digital signatures are generated by encrypting a document hash with a private key. Anyone can verify the signature using the corresponding public key. Digital signatures vary with document content and cannot be forged, unlike paper signatures. Private keys must be securely stored in smart cards, hardware tokens or password protected soft tokens to maintain non-repudiation. A certifying authority issues digital certificates that bind users to their public keys to facilitate trust in electronic transactions.