The message sender signs the message digest with his own private key.

The message sender sends the message itself together with the signed message digest.

The information receiver generates a new message digest by using the same one-way HASH function as the information sender, and then verifies the message digest by using the public key of the information sender to confirm the identity of the information sender and whether the information has been modified.

trait

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.