public key cryptography A cryptographic system in which two different keys are used for encryption and decryption. Also called asymmetric cryptography. The sender of the message looks up the public key of the intended recipient and uses the public key to encrypt the message. The recipient then uses his or her private key, which is not made public to decrypt the message. This method of encryption is considered more secure than symmetrical cryptography because one of the keys is kept strictly private. See also public key, private key.