1 Solve it with the Computer Rick Spillman CSCE 115 Spring 2012 Lecture 8

2 Outline Review History Autokey Cipher

3 Review

4 Turning Grille in CAP CAP will easily implement a Turning Grille

5 History of Ciphers

6 Censorship During WWII, the US set up a censorship service  By the end of the war it had over 14,000 employees at 90 sites throughout the country  It opened over 1 million pieces of mail a day  It listened to phone conversations, scanned movies, magazines and radio scripts To plug up steganographic channels it banned in advance whole classes of mail  Chess games by mail  Crossword puzzles  Newspaper clippings  One letter containing knitting instructions was held up until the examiner could actually knit the sweater  Loose stamps were replaced by others of equal value but of a different number and denomination

7 Null Ciphers One type of open code that was used to get by the censors was a null cipher where only certain words or letters are significant  Every fifth word  The first letter of every word Example of a letter sent by a German spy during WWI President’s embargo ruling should have immediate notice. Grave situation affecting international law. Statement forshadows ruin of many neutrals. Yellow journals unifying national excitement immensely. Pershing sails from NY June 1

8 Missed Opportunities 1 The allies had set up jargon coded messages to send to the underground in Europe  When the BBC broadcast “It is hot in Suez” the Resistance was to put into effect the Green Plan which called for sabotaging railroad tracks and equipment The most famous of these jargon code messages was the one announcing D-Day which the Nazis intercepted, recognized and ignored.

9 Missed Opportunities 2 Abwehr headquarters had discovered that D-Day would be signaled to the underground by a certain piece of music  So, the German 15 th Army set up a special 30-man interception crew to listen for the signal headed by Colonel Meyer  On June 1 at 9 pm Sergeant Walter Reichling of the team heard the signal and reported it to Colonel Meyer  Colonel Meyer telephoned the two German headquarters charged with the defense of France  But nothing was done about it – each headquarters had assumed that the other would sound the alarm

10 The Atomic Bomb As you would expect the development of atomic weapons during WWII was highly secret  The project sights were located in remote regions around the US  As a result, key personnel would travel from sight to sight and occasionally need to use the telephone  So the need arose for some sort of telephone cipher that could be easily used in the field  They developed a simple checkerboard cipher

11 The Atomic Cipher One of the 10 x 10 checkerboards used looked like: I P IO U O P N W E U T E K L O E UG NB T N S T T AZM D IO E S V TJ EYH N A OL SGH F C BA R S R I C WY U M N M V T H P IQ L S R E D A E N U O I RA D X HT E Encrypt “atom” A 42 T - 05 O - 69 M These would be spoken over the phone Why are there several squares with the same letter? Why are there so many U’s? - 88

12 More on Jargon Codes Jargon codes are frequently used with voice transmissions and that was the case with the atomic bomb program For example, when Enrico Fermi succeeded ahead of schedule in producing the first controlled chain reaction, Arthur Compton called James Conant using a on-the-fly jargon code: Arthur: “Jim, the Italian navigator has just landed in the new world. The earth is not as large as he had estimated and he arrived sooner than expected.” Conant: “Were the natives friendly?” Arthur: “Yes. Everyone landed safe and happy.”

13 AutoKey Ciphers

14 Fixing Vigenere Since a small key length is a weakness of a Vigenere cipher one fix that has been used is called an autokey cipher.  Select a keyword  Use the keyword to encipher the first segment of plaintext  Use the ciphertext (or the plaintext segment which was just enciphered) as the key for the next segment anautokeycipherprovidesalongkeyword cap cnp AutoKey-Ciphertext example wgd CAP will implement this cipher

15 Break This Autokey Cipher There is one major weakness in the autokey- ciphertext Consider what happens when you use the ciphertext as the key to decipher c n p w g d g k b i s q p w h a a a a a a a a a a a a a a a c n p w g d g k b i s q p w h l c h k x d e r h k y f h l c n p w g d g k b i s q p w h m j r h a h v y r i x g s c n p w g d g k b i s q p w h u t o k e y c i p h e r Key word

16 Autokey Plaintext Cipher So, it is not a good idea (though it has been done) to use the ciphertext as the running key The alternative is to use the plaintext as the key anautokeycipherprovidesalongkeyword cap cnp ana uao uto exm key... CAP will implement this cipher

17 Breaking the Autokey Plaintext Cipher This is not as easy to break as the autokey- ciphertext but... A Kasiski-like method exists to determine the “group length”  The group-length is the actual keyword length but since the keyword is not repeated, the group-length describes the length of segments of the running key  These segments define the distance between a plaintext letter being enciphered and becoming a key letter

18 Group Length For example, if the keyword is “alice” a possible cipher structure could be given by t h i s i s a n e x a m p l e a l i c e t h i s i s a n e x t t is enciphered t t is a key letter 5

19 Finding the Group Length It is possible to discover the group length from the ciphertext  Assume the group length is 5 then every plaintext letter will be enciphered by the letter 5 positions to its left and in turn will encipher the letter 5 positions to its right.  Since plaintext has a lot of repeated characters there will be an unusually large number of identical letters separated by the group length Example Key:... R... S Plaintext:... S... R Ciphertext:... J... J S S R There is a good chance that this kind of event will occur Group length

20 Procedure Find the distances between all letter repetitions The most common distances are strong candidates for the group-length CAP will automatically calculate these distances:

21 Using the Group Length Knowledge of the group length reveals how the plaintext is divided into segments.  If the group length is 5, then the first segment consists of every 5 th letter beginning with the first letter We know the encipher chain for this segment, for example: t h i s i s a n e x a m p l e a l i c e t h i s i s a n e x t s q u m l h v w f s m c p b t a s

22 Brute Force Attack We can use a brute force attack because each segment is defined by its beginning character (which is from the key word) Ciphertext (known) Key character (unknown) plaintext (unknown) t ? ? l ? ? s ? ? a Guess t t a s ts s Try all 26 guesses Use a low frequency character test

23 Example Given the ciphertext below created using an autokey – plaintext cipher, find the keyword and the plaintext: Find the key length Break the ciphertext into segments Try all possible keyword letters Run a low frequency character analysis nzmlw tsxyt mkmmp nawxl sskck zrziq ixnqm lqdql cbacx ksbbe nkugo exmmm njmgz xrjmi ezevz dnbui qajbu kdlcg spzzv qrxug gktuh gbwvh ytbcq favli dwcnp yllst qgvlv rllke itfw

24 Find the Group Length Run the keyword length option  Under the polyalphabetic tools click on Autokey Length Either 1 or 3 1 is a real possibility however it is weaker than longer keys so start by trying 3, if that doesn’t work then come back to 1

25 Solution With a good guess for the keyword length, run the autokey solution option Keyword found If “use” is not correct try combinations of these