![]() ![]() Two-part codebooks have, according to Merriam-Webster, "an encoding part listing the plaintext segments in alphabetical and logical order each with its code group or groups assigned at random and a decoding part listing in alphabetical or numerical order the code groups with their plaintext equivalents." They are less vulnerable to guessing. For example, using English, if you know that 22667 stands for Vienna, then 24556 must be something that starts with W, X, Y, or Z. These are somewhat vulnerable to guessing because they are alphabetical for both plaintext and ciphertext. Buy as much as you can."Īs long as you maintain the sequence "Encrypt using A, Encrypt using B, send, Decrypt using B, Decrypt using A", the exact encryption steps can be replaced as long as the sender and receiver agree on the algorithms and keys.Īnyone could be confused by this, especially by the part about the Zimmermann telegram.Ĭodebooks come in three flavors: one-part, two-part, and hybrid. Since I am using a one-part code here, again go to pages 128 and 45 to get the original message "Small supplies of fruit expected. Step 5: The receiver then uses the code book to decrypt "06375 02221". This results in the message C1 equal to "06375 02221". Step 4: The receiver decrypts C2 by subtracting 13348 from each code number. Step 3: The message C2 ("19723 15569") is sent to the receiver. Step 2: For the second level of encryption, I will add 13348 to each code number (ignoring any carry or borrow beyond 5 digits). Moving to page 45, we find "Buy as much as you can." with the code number 02221. Step 1: On page 128, we have the phrase "Small supplies of fruit expected.", with the corresponding code number 06375. Buy as much as you can."įor my code book, I will use the A B C Universal Commercial Electric Telegraphic Code, 4th Edition. Suppose I want to send the message "Small supplies of fruit expected. ![]() The receiver then uses the code book to decrypt C1 and get the message M. ![]() The receiver uses the decryption algorithm for the second method on C2, obtaining C1.C1 is then treated as the plaintext, and enciphered using another method, resulting in a new ciphertext C2. ![]()
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