digital signature 
A means of verifying that a file or e-mail message was created by a specific person, usually the sender. Signatures come in several varieties, but all rely on encryption. For example, a sender may attach an encrypted summary of a message to serve as a signature, which the recipient decrypts and matches against the actual message for verification. A match also verifies that a message has not been tampered with. Digital signatures are often used in combination with encryption software and/or a digital certificate to create a secure channel of communication.