Encryption is a method of encoding data so that only authorized parties can access it. Encryption does not prevent interception or interference, but it denies the original data to a would-be attacker.
Encryption algorithms are called ciphers. An encryption cipher takes unencrypted data as input, referred to as plaintext. The cipher produces encrypted data, called ciphertext, as its output. The act of converting plaintext into ciphertext is called encryption, and the act of reversing it back is called decryption.
Modern ciphers use keys to control the encryption and decryption of data. Keys are typically relatively short, pseudo-random data sequences. Ciphertext encrypted with a given key cannot be decrypted without the proper key.
Broadly, there are two categories of ciphers—symmetric and asymmetric. A symmetric cipher uses the same key for both encryption and decryption, while an asymmetric cipher uses two different keys.