Final answer:
Public-key encryption, proposed by Whitfield Diffie and Martin Hellman in 1976, uses two keys for secure communication and has been a major advancement in digital security.
Step-by-step explanation:
Whitfield Diffie and Martin Hellman first put forth the idea of public-key encryption in print in 1976. Two keys are used in this cryptographic system: a private key that the owner keeps private and a public key that is freely shared. Public-key encryption is special because it makes it possible to communicate securely over an unsecure channel without requiring a shared secret key beforehand. This was a big development for the fields of cryptography and digital security.