In the ISO 7498-2 standard, digital signature is defined as "some data attached to a data unit, or the cryptographic transformation of the data unit, which allows the receiver of the data unit to confirm the source and integrity of the data unit and protect the data from being forged by people (such as the receiver)".

The function of digital signature is an extension of our usual handwritten signature. Signing a written document has two main functions. First, it is difficult for me to deny my signature, so as to confirm the fact that the document is signed by myself. Second, because his signature is not easy to be imitated by others, it confirms that the document is true. With digital signature, you can also achieve the following functions:

(1) Confirm that the message was sent by the signer;

(2) Confirm that the information has not been modified since it was signed until it was received;

(3) The signer cannot deny that the information was sent by himself.