the process of disguising information as “ciphertext,” or data unintelligible to an unauthorized person. Conversely, decryption, or decipherment, is the process of converting ciphertext back into its original format. Manual encryption has been used since Roman times, but the term has become associated with the disguising of information via electronic computers. Encryption is a process basic to cryptology (q.v.).

Computers encrypt data by applying an algorithm—i.e., a set of procedures or instructions for performing a specified task—to a block of data. A personal encryption key, or name, known only to the transmitter of the message and its intended receiver, is used to control the algorithm's encryption of the data, thus yielding unique ciphertext that can be decrypted only by using the key.

Since the late 1970s, two types of encryption have emerged. Conventional symmetric encryption requires the same key for both encryption and decryption. A common symmetric encryption system is the Data Encryption Standard (DES), an extremely complex algorithm approved as a standard by the U.S. National Bureau of Standards. Asymmetric encryption, or public-key cryptography, requires a pair of keys; one for encryption and one for decryption. It allows disguised data to be transferred between allied parties at different locations without also having to transfer the (not encrypted) key. A common asymmetric encryption standard is the RSA (Rivest-Shamir-Adleman) algorithm.

Encryption keys selected at random and of sufficient length are considered almost impregnable. A key 10 characters long selected from the 256 available ASCII characters could take roughly 40 billion centuries to decode, assuming that the perpetrator was attempting 10,000 different keys per second.