A coding system in which encryption and decryption are done with public and private keys, allowing users who don't know each other to send secure or verifiable messages. Suppose Fred wants to send a message. He would encrypt it with his private key, which no one else knows; then the recipient would decrypt it using Fred's publicly available key, thus verifying that the message came from Fred. Alternately, suppose Fred wants to receive an encrypted message. The sender would encrypt the message with Fred's public key and only Fred would be able to decrypt it using his private key. This method, also known as dual-key or symmetric cryptography, in which the sender and recipient must agree on and use the same private for encryption and decryption.
An encryption system that uses a matched pair of mathematical keys, one private and the other public. Private keys are used to digitally sign electronic payments or other documents and to decrypt email messages and electronic payments. Keyholders provide the matching public keys to their correspondents, who use them to verify the digital signatures and to encrypt email and electronic payment instructions.