How digital signature works: "When sending a message, the sender uses a hash function to generate a message digest from the message body, and then encrypts the digest with his own private key. This encrypted digest will be sent to the receiver as a digital signature of the message. The receiver first calculates the message digest from the received original message using the same hash function as the sender, and then decrypts the digital signature attached to the message using the sender's public key. If the two digests are the same, then the receiver will digitally sign them for two purposes: first, it can be sure that the message is indeed signed by the sender and sent out, because others cannot forge the sender's signature. Secondly, the digital signature can determine the integrity of the message. Because the characteristic of digital signature is that it represents the characteristics of the file, if the file changes, the value of digital signature will also change. Different files will get different digital signatures. Digital signature involves hash function, sender's public key and sender's private key. " Description of the message authentication! Digital signature is not that complicated. Digital signature: the sender performs D operation on message X with his own key to generate unreadable ciphertext Dsk, and then sends Dsx to the receiver. In order to verify the signature, the receiver performs an e operation with the sender's key to recover the message.
Everyone has a pair of "keys" (digital identity), one of which is known only by her/him (key) and the other is public (public key). Use the key when signing, and use the public key when verifying the signature. And because anyone can claim that she/he is you, the public key must be registered with the person (certification authority) that the receiver trusts. After registration, the authentication institution will issue you a digital certificate. After signing the document, you send this digital certificate to the receiver together with the document and signature, and the receiver asks the authentication institution whether it is really a document signed with your key.