In 1984, adi shamir, one of the famous inventors of RSA public key system, suggested that directly using identity as public key without relying on digital certificate might be the best way to simplify public key encryption system. In 2000, Dr. Dan Bona and Dr. Matt Franklin.
A major breakthrough was made in mathematics, and the first practical ID-based digital signature system (IBE system) was invented. IBE (Identity-based Encryption) is a public key encryption algorithm, and any character string can be used as a valid public key.