1976, Professor E.Hellman of Stanford University, his research assistant W.Diffie and doctoral student Merckle (DHM for short) first created and published the so-called "public key cryptography", that is, using two different keys for encryption and decryption. Use the private key to decrypt. This key must be strictly managed and cannot be revealed. What's more, they also invented the so-called digital signature technology, that is, signing with a private key and then verifying with a public key.

In general references, it is considered that public key cryptosystem was invented by Duffy and Herman.