A Digital Signature is an electronic Signature that can be used to authenticate the identity of the sender of a message or a singer of a document, and possibly to ensure that the original content of the message or document that has been send is unchanged. Digital Signatures are easily transportable, cannot be imitated by someone else, and can be automatically time stamped. The ability to ensure that the original signed message arrived means that the sender cannot easily repudiate it later.

A Digital Signature can be used with any kind of message, whether it is encrypted or not, simply so simply so that the receiver can be sure of the sender’s identity and that the message arrived intact. A Digital certificate contains the Digital Signature of the certificate – issuing authority so that anyone can verify that the certificate is real.

Digital Signatures are often used in the context of Public key infrastructure ( PKI ) schemes in which the public key used in the Signature scheme is tied to a user by a Digital identity certificate issued by a certificate authority, usually run by a third party commercial firm. PKI systems use asymmetric key cryptography to unbreakably bind user information ( name, address, phone number etc ) to a public key, the underlying idea is closely akin to that of a notary endorsement.