Process of disguising information as “ciphertext,” or data that will be unintelligible to an unauthorized person. Decryption is the process of converting ciphertext back into its original format, sometimes called plaintext (see cryptography). Computers encrypt data by applying an algorithm to a block of data. A personal key known only to the message's transmitter and intended receiver is used to control the encryption. Well-designed keys are almost impregnable. A key 16 characters long selected at random from 256 ASCII characters could take far longer than the 15-billion-year age of the universe to decode, assuming the perpetrator attempted 100 million different key combinations per second. Symmetric encryption requires the same key for both encryption and decryption. Asymmetric encryption, or public-key cryptography, requires a pair of keys, one for encryption and one for decryption. Encyclopædia Britannica Concise