The origin of digital signature. In real life, some methods (such as handwriting, fingerprints, etc. ) has been used as proof of the identity of the signer. This is because: the signature is credible; Cannot be forged; Not reusable; Undeniable; The signed document is irrevocable. In the coming digital life, electronic documents will gradually replace paper documents as the main body of information exchange. The way to prove that the electronic document is made by the author is to make an electronic signature on the electronic document by simulating the ordinary handwritten signature. The author can identify himself by digital signature, and the reader can verify the identity of the author by digital signature. Because the process of information storage, transmission and processing is often carried out on the open communication network, information is more vulnerable to external or internal eavesdropping, interception, modification, forgery and replay attacks. Therefore, digital signature should have some special properties to resist these attacks. As an encryption technology, digital signature has the following functions and attributes:

1. Others can't forge the signature of the message, because the private key is only known to the signer, so others can't forge the correct signature result. Require private key holders to keep their private keys safe.

2. Anti-tampering For digital signatures, the signature and the original file form a mixed whole data, which cannot be tampered with, thus ensuring the integrity of the data.

3. Anti-replay in digital signature, if the technology of adding serial number and timestamp to the signature message is adopted, replay attack can be prevented.

4. Denial-proof digital signature can identify identity, and it is impossible to pretend to be forged. The signer cannot deny his signature. In order to prevent the receiver from denying it, in the digital signature system, the receiver is required to return the message signed by itself to the other party or the third party, or the third party arbitration mechanism is introduced. In this way, neither side can deny it.

5. Confidentiality With the guarantee of confidentiality, the interception attack will not succeed. The message to be signed is properly encrypted to ensure confidentiality, which involves encryption or signcryption theory.