Breaking the WW2 German Enigma Historical APT Perspective Richard - PowerPoint PPT Presentation

Breaking the WW2 German Enigma Historical “APT” Perspective Richard Brisson Email: richardbrisson@sympatico.ca 6/27/2019 1

Overview • Enigma Background … • “Getting In”! • “Staying In”! • “Getting Back In”! • “The Imitation Game” Movie – Some facts, some fiction 6/27/2019 2

Early 20 th Century Cryptography Rotor Machines Arthur Scherbius patents Enigma in 1923 6/27/2019 3

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1930’s - Enigma firm taken over by German Government & Military Main Features  Electro-mechanical device  Keyboard  Stecker or Plugboard  3 rotors - indexed I, II, III  Mechanism for stepping the rotors  Reflector  Lampboard 6/27/2019 6

German Enigma Rotors  26 spring loaded contacts on right face  26 flat contacts on the left face  Rotors I, II, III - secret wiring/permutation  Has a ring which has the letters/numbers for the reading station and a single notch  This notch ring can be rotated relative to the rotor itself (26 positions) 6/27/2019 7

German Enigma 6/27/2019 8

German Enigma Motion of Rotors  3 rotors are selected and inserted in a specific order from left to right in the Enigma  Rightmost rotor always single steps with every keystroke  Middle rotor will single step if a) its right neighboring rotor’s notch is in the appropriate position, or b) its own notch is in the appropriate position  Leftmost rotor steps if the notch of the middle rotor is in appropriate position  On average, middle rotor steps every 26th keystrokes  On average the leftmost rotor steps every 676th keystrokes 6/27/2019 9

German Enigma Reflector  Returns the electrical impulse back through the rotors (along a different path)  Encryption process is reciprocal => If E(x | s) = y, then E(y | s) = x for any configuration/state “s”  E(x | s) is never equal to x for any state “s”. 6/27/2019 10

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German Enigma Enigma Cryptovariables • Plugboard wiring (usually 6 or 10 plug wires) – daily • Order of rotors – daily • Relative location of notch ring to main rotor (ringstellung) – daily • Starting positions for 3 rotors (chosen at random by operator and typically changed for each message) 6/27/2019 12

German Enigma 6/27/2019 13

German Enigma WW-II Cryptography The German Enigma At the beginning of WW-II, the German military increases the number of available rotors from 3 to 5. In 1941, the Kriegsmarine increases the number even further from 5 to 8 with those numbered 6, 7 and 8 having two ring notches each. 6/27/2019 14

German Enigma WW-II Cryptography The German Enigma In 1941, the Kriegsmarine introduces a fourth functional rotor! That rotor is the leftmost with a now compressed reflector to its left. The 4 th rotor is typically red coded for which there are two to choose from. 6/27/2019 15

World War II An urgent problem warrants a timely and effective plan to achieve the ultimate solution! 6/27/2019 16

Getting in … How does the German Enigma work? Work by the Poles in the 1930’s including: • Acquiring a commercial version of Enigma; • Benefitting from French information extracted from a HUMINT source on Enigma (Hans-Thilo Schmidt – codename Asché); • Correctly guessing the entry ring (alphabetical sequence); • Recovering the wiring for rotors #1, #2 and #3 in the early 1930’s and rotors #4 and #5 just before WW2 in 1939; • Weeks before the German invasion in 1930, the Poles share their work/secrets with the French and British – suggestion by Gustave Bertrand … 6/27/2019 17

Getting in … How does the German Enigma work? • With the information obtained from the Poles, the Allies completely understand the 3-rotor Enigma as used by the German Army and Luftwaffe; • To exploit the Kriegsmarine Enigma messages, the Allies had to recover the wiring of rotors #6, #7 and #8; • Attempt to understand the variety of ways the German elements impart knowledge of the starting positions for the rotors to initiate encipherment of actual plaintext messages (e.g. in the clear, grundstellung and double encipherment of starting positions, codebooks, etc.). 6/27/2019 18

Getting in … Is it possible to cryptanalytically break Enigma? Cryptanalytic work by the Poles in the 1930’s including: • Exploited the twice enciphered indicator in the 3-rotor Enigma to first recover the rotor wirings; • Analyzed the cycle structure underlying the twice encrypted indicators to exploit traffic – the analysis involved attempting all possible rotor combinations and starts (i.e. 6 * 17576 = 105,456) and seeing how many characters lit up in two interconnected Enigmas (with the second Enigma being 3 steps ahead of the first Enigma) – the number of lit characters is independent of ringstellung and stecker connections! 6/27/2019 19

Getting in … Developing cryptanalytic attacks against Enigma Attacks that were crib based rather than the focus on the twice encrypted indicators • Use of stereotypical words or phrases in Enigma messages; • Advancing technological progress in regards to hypothesis validation or rejection through rapid paced mechanical/electrical components; • Taking advantage of a character never encrypting to itself 6/27/2019 20

Getting in … Development of the Cryptanalytic UK Bombe • Bombe required a menu which was derived from matching the plaintext from a crib to a specific position in cipher; • Each Bombe ran against a specific rotor order and exhausted all possible rotor positions against the supplied menu; • Early Bombe runs assumed that only the rightmost rotor stepped and none of the others to its left – so the length of the crib was critical! Long enough to not give too many false hits but not too long to greatly increase the probability of the middle rotor stepping. Apparently later Bombes took account of the possibility of the middle rotor stepping as well. 6/27/2019 21

Getting in … Development of the Cryptanalytic UK Bombe • The Bombe occasionally gave you an incorrect answer – otherwise it gave only part of the right answer! It typically provided a candidate solution that had to be secondary tested. If it was validated, it yielded the true rotor order, initial rotor positions for the (crib, cipher) placement and one stecker or plugboard value. So more work had to be done to recover the rest of the Enigma settings!!! • The Welchman diagonal board idea (which took advantage of the fact that the stecker was reciprocal) vastly improved Bombe efficiency and was incorporated from the 2nd Bombe manufactured onwards; • A key figure in the development of the UK Bombes was Harold “Doc” Keene (electrical engineer). 6/27/2019 22

Getting in … Is it possible to cryptanalytically break Enigma? Developing other cryptanalytic approaches and attacks: • Observing and taking advantage of “CILLIES”; • The Turing “EINS” catalog; • Banburismus scoring methods developed by Turing. 6/27/2019 23

Staying in … After breaking the first few Enigma messages, what next? Improving the cribs: • Profile cribs based on network and users (actual plaintext and where most likely in the ciphertext); • Aided by “Traffic Analysis” developed by Gordon Welchman. 6/27/2019 24

Staying in … After breaking the first few Enigma messages, what next? Developing and/or managing opportunities: • North African German post commonly having “Nothing to report” as its daily plaintext message for Enigma encipherment – Allied Forces under strict orders not to go anywhere near this post and assuring that they intercept his Enigma message; • Expand infrastructure and partnerships to intercept, collect and forward Enigma traffic worldwide; • “Intelligence Analysis” of decrypts and general “Traffic Analysis” assist in focussing on prioritizing selection of Enigma messages to be submitted for breaking on Bombes. 6/27/2019 25

Staying in … Once you break Enigma messages on a regular basis … Developing and/or managing opportunities/risks: • Development of “ULTRA” clearance and the strict need -to- know principle; • Winterbotham’s book “The Ultra Secret” – Coventry … • Kriegsmarine Enigma decrypts typically reported U-boat positions based on fine grids of the North Atlantic – the Brits typically sent reconnaissance planes in their direction so that the U-boats would assume that they were spotted before they were attacked. 6/27/2019 26

Getting back in … The Kriegsmarine adds a 4th functional rotor in 1942… Moving towards a solution: • Have to recover the missing new components to 4-rotor Enigma (new Beta and Gamma rotors as well as new selectable reflectors); • Understanding the bigram and trigram tables for indicator encipherment; • Information sharing with Allies – U.S. develops a more resilient and faster Bombes (e.g. codebreaking rotors rotate at about 1725 rpm compared to 120 rpm for the UK Bombes) – “Joe Desch story. 6/27/2019 27