![]() Now imagine the Venona team trying to break the code without the benefit of captured Soviet code books or one-time pads. He sends this series of six five-letter words and one five-digit number to Moscow.ħ.where another clerk deciphers it, reversing these steps. The example in Figure 14-2 shows the letter. Finally, he adds a five-digit number, which gives the message a serial number and indicates the date on which it was enciphered. Unless you know the key (the number used to encrypt the message), you wont be able to decrypt the secret code. ![]() They are also a way to explore data representation, and an important part of computational. The clerk appends another five-letter group (corresponding to the next number from the one-time pad) to signal the end of the message. Ciphers are a great way to play with numbers and arithmetic. Next the clerk converts the numerical groups to letter groups, using the formula:Ħ. (For instance, 8 + 6 = 4, not 14, because nothing is carried):ĥ. The key for this cipher is a letter which represents the number. and adds them to the four groups that make up the message, using non-carrying arithmetic. The Caesar cipher shifts all the letters in a piece of text by a certain number of places. Then the clerk takes the next four five-digit groups from the one-time pad. That first number will alert the recipient, who has the same one-time pad, which page of the pad to consult.Ĥ. At the upper-left corner is a number-26473, in this case-which is inserted before the first group in the series: The Caesar Shift Cipher is a simple substitution cipher where the ciphertext alphabet is shifted a given number of spaces. Now the clerk consults a unique “one-time pad.” Each page bears 60 five-digit numbers and is supposed to be used just once. The clerk shifts one digit to the first group from the second, two digits to the second group from the third, and so on, yielding:ģ. An agent hands the text to a cipher clerk, who uses a code book to convert the words to four-digit numbers:Ģ. The best candidate we can find is ‘wtbsfdoesksjd’ it. The message-“Pilot delivered report about rockets”-is hypothetical, but it makes reference to an actual American spy, William Ullmann, an Army officer assigned to the Pentagon, whom the Soviets code-named “Pilot.” A U.S.-based Soviet agent might send this message to Moscow alerting superiors to check the diplomatic pouch for a dispatch from Pilot.ġ. If we can use a computer and a program such as CrypTool 2 (free open-source software available at ), we can use an even more efficient method to break the encrypted advertisement in The Times: we look for a word in the ciphertext that has a distinctive letter pattern. Here’s how it worked, as explained by John Earl Haynes and Harvey Klehr in their book Venona: Decoding Soviet Espionage in America. To get a hint of the monstrously difficult task undertaken by the Venona code breakers, consider all the elaborate steps that Soviet agents took to encrypt a secret message.
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