In cryptography, a cipher is a set of established rules that can be used to encrypt or decrypt text messages. The process of encryption includes converting evident data into an incomprehensible or impenetrable form. The unencrypted form of the text is referred to as ciphertext, and the original text that can be understood clearly is known as plaintext. Although both texts contain the same information, the ciphertext is written in a format that can only be read or accessed by those who know the right decryption procedure. The use of a particular secret piece of information known as a cryptographic key is a key component in the majority of encryption algorithms. Numerous encryption techniques are employed depending on the key type, and cipher algorithms can be categorized as symmetric or asymmetric. Symmetric ciphers use the same key for both encryption and decryption while asymmetric ciphers use different keys for each operation. The majority of modern encryption methods are handled by computers, but ciphers have been used to encrypt messages since around 400 BC, a long time before the time of the ancient Greeks. Famous Roman statesman Julius Caesar frequently utilized substitution ciphers, replacing each letter in a message with the letter three letters down the alphabet.