In cryptography, a simple substitution cipher is a method of encryption in which a symbol in the original message (plaintext) is replaced with a single coded symbol (ciphertext) according to a fixed system. The receiver of the message deciphers the text by performing the inverse substitution. One easy example of a simple substitution cipher is to replace every letter in the message with the one that immediately follows it in the alphabet; in this way, the plaintext hello becomes the ciphertext ifmmp because h maps to i, e maps to f, l maps to m, and o maps to p. To decrypt this message, you perform the inverse operation, which is to replace each letter in the ciphertext ifmmp with the letter that immediately precedes it in the alphabet instead. We describe the encryption method by defining a key, a string of 26 letters that identifies what the ciphertext character is for each character in the string "", in order. Thus for the above cipher, the key would be ""