So plaintext letter A is replaced by ciphertext letter D, B is replaced by E and so on. In this type each plaintext letter was replaced by the letter standing three places further along in the alphabet. Using the English alphabet the Atbash substitution is:Īnother example is the Caesar cipher which was used by the Roman general and statesman Julius Caesar (100 BC-44 BC) to exchange messages with Marcus Tullius Cicero (106 BC-43 BC) and others. 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): Python monoalpha.py -plainAlphabet 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz' -cipherAlphabet 'BCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyzA' -encrypt -message 'Hello this is a test.
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