It uses the Hebrew alphabet where the first letter of the Hebrew alphabet is replaced by the last letter, the 2nd letter is replaced by the 2nd to last letter and so on. The earliest known example is the Atbash cipher which is found in the Old Testament and dates from around 600-500BC. Each plaintext letter is substituted by a unique ciphertext letter. One of the oldest of cipher types was the simple substitution or monoalphabetic substitution ciphers in which each letter of the alphabet is replaced by another letter. Print(mon_Sub(ainAlphabet, args.cipherAlphabet,Īrgs.message, args.blocks_of_five, args.crypt_mode, args.keep_char)) Parser.add_argument("-ka", "-keep-non-alp", help="keep non-alphabet characters", dest="keep_char", action="store_true") Parser.add_argument("-m", "-message", help="text to decrypt / encrypt", type=str, required=True) Parser.add_argument("-bf", "-blocks-of-five", dest="blocks_of_five", action="store_true") Parser.add_argument("-d", "-decrypt", dest="crypt_mode", action="store_false") Parser.add_argument("-e", "-encrypt", dest="crypt_mode", action="store_true") Parser.add_argument("-pa", "-plainAlphabet", help="set plaintext alphabet", type=str) Parser.add_argument("-ca", "-cipherAlphabet", help="set ciphertext alphabet", type=str) If(len(decrypted_message.replace(" ", "")) % 5 = 0):ĭecrypted_message = decrypted_message + " " # if b_blocks_of_five is true, then there are no spaces in decrypted_message, so if length is % 5 = 0 append space # if b_blocks_of_five is false then take all chars, even spaces # if b_blocks_of_five is true skip spaces in message # if character is not in plaintextalphabet New_char_index = inputAlphabet.index(character) # if the character is in the plaintextalphabet Please enter your text here.' -keep-non-alpĭef mon_Sub(plainAlp, cipherAlp, message, b_blocks_of_five, b_crypt_mode, b_keep_char): One can simply try to decode the message with all 26 of them, being aware that only one is likely to result in a meaningful message.Ĭuriously, this method of encryption does still find use even in modern times in one context: ROT13.Python monoalpha.py -plainAlphabet 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz' -cipherAlphabet 'BCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyzA' -encrypt -message 'Hello this is a test. One can easily decrypt such messages whether they have the secret key or not - as there are only 26 possible "keys" that could have been used. Knowledge of this secret key makes decrypting easy - so it should be shared with the intended recipient of your secret message.ĭespite the fact that Julius Caesar used it to protect messages of military significance - this is actually a really terrible means of encryption. The number of letters shifted functions as the secret key. When we encrypt something in this way, we are using what is called a Caeser cipher. Then, each letter of the encrypted message should be replaced with the letter on the outer dial that lines up with it as found on the inner dial. One would rotate the outer dial so that "C" on the inner dial is lined up with the "A" on the outer one. Replacing each letter of our intended message "AWESOME" with its outer-ring counterpart, we arrive at the encrypted message: "CYGUQOG"ĭecrypting is just as easy. ( note: the shift forward will always be one less than the number shown in the window) For letters "Y" and "Z", since we don't have enough letters to go "forward 2" without surpassing the end of the alphabet, so we wrap around to the beginning, matching "Y" with "A" and "Z" with "B". Upon inspection, we can see that almost every letter of the inner ring is now paired with a letter on the outer ring that is 2 letters "forward" in the alphabet. In this particular model, one can also see a small "3" in the window below the inner ring's "A", since "A" is lined up "C" and "C" is the third letter of the alphabet. In the ring shown, we see this is the letter "C". To do this with the secret decoder ring shown below, we would turn the outside ring by some amount, noting the letter on the outer ring that then matches up with the letter "A" on the inner ring. Secret Decoder Rings and the Caeser CipherA secret decoder ring is a device which allows one to encrypt or decrypt a message using a simple Caeser cipher.Īs an example, suppose you wanted to encode the word "AWESOME". Secret Decoder Rings and the Caeser Cipher
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