Signing a document as proof of identity and intention has been done for centuries, and it’s still the preferred method of providing authentication and liability to a legal act (note: not intended as legal advice). More recently, public key infrastructure and the concept of digital signatures have laid the foundation for implementing an electronic method for signing documents. A digital signature adds the following properties to an electronic document or other type of stream file:
Integrity — The sender and receiver are assured that the message has not been altered during transmission. If a message is digitally signed, any change in the message invalidates the signature.
Authentication — Signatures are used to authenticate the source of messages. Ownership of the private key binds that key to a specific user, so a valid signature calculated using the related public key confirms that the message was sent by that user.