Complexity of Substitution Encryption and Decryption

An important issue in using any cryptosystem is the time it takes to turn plaintext into ciphertext, and vice versa. Especially in the field it is essential that the scrambling and unscrambling do not deter the authorized parties from completing their missions. The timing is directly related to the complexity of the encryption algorithm. For example encryption and decryption with substation ciphers can be performed by direct lookup in a table illustrating the correspondence, like the ones shown in example. One way thinking of this expression is that if one message is twice as long as another, it will take twice as long to encrypt.