Cracking the Enigma Machine - Rejewski, Turing and the Math that saved the world
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The Math That Saved the WorldBrad Youngbrad@clearpoint.co.ilA Mathematical and Historical Analysis of the Cryptographic Attacks on the Nazi Enigma Machine Marian RejewskiAlan TuringAgendaDevelopment…
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The Math That Saved the World Brad Young brad@clearpoint.co.il A Mathematical and Historical Analysis of the Cryptographic Attacks on the Nazi Enigma Machine Marian Rejewski Alan Turing
Agenda Development of Enigma Machine – Why/How/What The Rejewski Crack The Turing Crack Historical Impact
WWI Cryptology First major war with radio + telegraph Very large volume of communications Hand-ciphers Playfair, ADFGVX etc. Bigraph substitution + transformation Encryption/Decryption Inefficient …Became bottleneck Cryptanalysis Difficult, time-consuming… But successful (mainly)
Zimmermann Telegram
Invention of Enigma Machine Arthur Scherbius Efficient! (oh, and also Secure, by the way) Business, Military versions Early 1920’s – very poor sales German economy in trouble
Oops Publishes history book Reveals the impact of crypto on WWI Now, the Germans want Enigma!
A B C D E F G H Reflector 3rd Rotor 2nd Rotor 1st Rotor Lightbulbs Keyboard Enigma Schematic
A B C D E F G H Reflector Lightbulbs 3rd Rotor 2nd Rotor 1st Rotor Keyboard Electric Circuit
A B Pressing ‘A’ on the keyboard… C D E F … lights the ‘B’ lightbulb G H NOTE: Because it is a electric circuit, no letter can map to itself. Minor detail combinatorically speaking, but very important for the Turing crack. Reflector Lightbulbs 3rd Rotor 2nd Rotor 1st Rotor Keyboard Electric Circuit
A B C D E After each letter, the first rotor shifts one step. So now, pressing ‘A’ lights a different lightbulb….’F’ F G H Reflector Lightbulbs 3rd Rotor 2nd Rotor 1st Rotor Keyboard Rotor Shift
A B C D E F Sits between keyboard and rotors. Each plug cable swaps signal between two letters. 6 cables connect 12 letters. 14 other letters are not plugged at all. G H Reflector Lightbulbs Plugboard 3rd Rotor 2nd Rotor 1st Rotor Keyboard Plugboard
Plugboard
Keysize A B Rotor Order Rotor Setting Plugboard Wiring I – III - II VYJ A/G, D/Q, J/Z,L/S, M/V, N/T 3! = 6 263 =17,576 C(26,2) x C(24,2) x C(22,2) x C(20,2) x C(18,2) x C(16,2) x 1/6! (26!)3 x C(26,2)…C(2,2)x1/13! C ? 105 D E F ? 1011 ? 1092 G H Total Key Size ? 10108 Variable Key Size ? 1016
German Use of Enigma
German Use of Enigma Day Keys (RO, RS, PB) distributed monthly in key books
For each message, sender chooses Message Key (Rotor Setting only)
Encode Message Key using Day Key, twice Move rotor to Message Key setting Encode actual message Set to Day Key(VYJ) Change to Message Key (CIL) CILCILATTACKFROMNORTHATNINETHIRTYBOKJRVSQIGPQTMNWJRAKOBYTKMTKGBBRQ
Agenda Development of Enigma Machine – Why/How/What The Rejewski Crack The Turing Crack Historical Impact
Biuro Szyfrów 1918 – Polish Independence 1919 – Creation (and success) of Cipher Bureau 1926 – Germany goes dark as Enigma is adopted 1930 – Bring in the mathematicians (?!?) Marian Rejewski Jerzy Ró?ycki Henryk Zygalski
The Rejewski Crack Intuition,Espionage,Engineering Understand how Enigma works Reverse-engineer the wiring Be able to crack the key each day Permutational Mathematics
The Math of Permutation Cycles P = P-1 =
Cycle Notation P = P = (AECH)(BFD)(G) = (BFD)(G) (AECH) = (FDB)(G)(CHAE) P-1 = (HCEA)(DFB)(G) Benefits of cycle notation: Concise Easier to take inverse (These are benefits of efficiency)
Cycle Structure = (AECH)(BFD)(G) P = 4 3 1 = (AFC)(BG)(D)(EH) Q = 3 2 1 2 Benefits of cycle notation: Concise Easier to take inverse Gives more info – Cycle Structure (This is a benefit of value-add information)
Composition P = = (AECH)(BFD)(G) Q = = (AFC)(BG)(D)(EH) Q ? P = Q(P()) = (AHFDGBCE) Q ? P ? P ? Q - NOT Commutative Q ? ( P ? R ) = ( Q ? P ) ? R - Associative
Identity = (A)(B)(C)(D)(E)(F)(G)(H) I = P ? I = I ? P = P P ? P -1 = I I ? I = I i.e. I = I -1 (ab) ? I , but (ab) ? (ab) = (a)(b) i.e. (ab) = (ab)-1
Conjugation Conjugation of Q by P is defined as P ? Q ? P-1 P = (AECH)(BFD)(G) P-1 = (HCEA)(DFB)(G) Q = (AFC)(BG)(D)(EH) 1-2-2-3 1-2-2-3 This is not a coincidence! This is not a coincidence! P ? Q ? P-1 = (AC)(B)(DHE)(FG)
Theorem: Cycle structure is invariant under conjugation Proof: Suppose Q: i?j, that is Q(i) = j. Consider P ? Q ? P-1 (P(i)). P ? Q ? P-1 (P(i)) = P ? Q ? (P-1 ? P)(i) = P ? Q(i) = P(j) i.e. P ? Q ? P-1: P(i)?P(j) Therefore… If Q has k-cycle (i1, i2 … ik) then P ? Q ? P-1 has k-cycle (P(i1), P(i2)…P(ik)) QED
Using Permuation Cycles on Enigma A B Suppose we intercept a message: BOLJRVSQIGPQTMNWJRAKOBYTKMTTGBBRQUPWLHSOLNFEQTHJOVX Plaintext: abcabcCiphertext: BOLJRV Define En as the permutation that occurs when Enigma machine is in state n. So, in the first state, a?B. In the fourth state, a?J E1 = (aB …E4 = (aJ … Now…Recall the effect of the Reflector, which creates 2-letter circuits So, if a?B, then B?a. So the cycle is closed. E1 = (aB) …E4 = (aJ) … So, we can now compute E4 ? E1 = (BJ … C These are the variablesa,b,c, not the actual letters D E F G H
Using Permuation Cycles on Enigma If we have many intercepts from the same day, then they were produced with the same day settings. So we can calculate the entire compositions… E4 ? E1 = (BJUMPWTCFE)(ARDNHSLYZK)(G)(I)(O)(Q)(X)(V)E5 ? E2 = (ORJCLVHGXKF)(AUYMPZQNDWB)(ES)(IT)E6 ? E3 = (BWOIKTZHXB)(EPQJYLVGN)(ARCU)(DSMF) Good news: abc variables have been eliminated! We’ve found a unique identifier! Bad news: It is one of 10,000,000,000,000,000 possibilities
Explore the nature of En A B En = P ? Rn ? P where P is the plugboard permutation and Rn is rotor permutation when in state n E4 ? E1 = P ? R4 ? P ? P ? R1 ? P Now, recall the plugboard… P = (ab)(cd)(ef)(gh)(ij)(kl)(m)(n)(o)(p)(q)(r)(s)(t)(u)(v)(w)(x)(y)(z) All 2-cycles and 1-cycles, therefore P = P-1 ! E4 ? E1 = P ? R4 ? P ? P ? R1 ? P = P ? R4 ? P ? P-1 ? R1 ? P = P ? R4 ? (P ? P-1 ) ? R1 ? P = P ? R4 ? R1 ? P = P ? (R4 ? R1 ) ? P = P ? (R4 ? R1 ) ? P-1 C P R D E F G H Conjugation:Cycle structure of E4 ? E1 is same as cycle structure of R4 ? R1 and is not affected at all by the plugboard! E4 ? E1 = (BJUMPWTCFE)(ARDNHSLYZK)(G)(I)(O)(Q)(X)(V)E5 ? E2 = (AUYMPZQNDWB)(CLVHGXKFORJ)(ES)(IT)E6 ? E3 = (BWOIKTZHXB)(EPQJYLVGN)(ARCU)(DSMF) 1-1-1-1-1-1-10-10 ; 2-2-11-11 ; 4-4-9-9 Remember: Keysize(R) ? 105 Keysize(P) ? 1011
Now, where are we? Figuring out En is problem of size 1016 Now, we have Rn, a smaller problem: 105 Just barely small enough to attack brute force
Recovering the Plugboard Plugboard is the biggest problem combinatorically But… It is trivial to solve E4 ? E1 = (BJUMPWTCFE)(ARDNHSLYZK)(G)(I)(O)(Q)(X)(V) R4 ? R1 = (MGWTREFBJU)(AKZCINLSHY)(P)(D)(O)(Q)(V)(X) (BJUMPWTCFE) (BJUMGWTREF) Plugboard settings: P/G , C/R , E/F , etc.
Paradox of Decreasing Benefit Keysize # Cables
Agenda Development of Enigma Machine – Why/How/What The Rejewski Crack The Turing Crack Historical Impact
1939 – Brink of War Polish deliver Enigma replica and training to England and France Biuro Szyfrów is dismantled
Bletchley Park HQ of British Government Code and Cypher School (GCCS)
New Challenges Combinatoric More rotors to choose from Increase # of plugs Ring settings Procedural Eliminate Message Key repetition Navy / Air Force / Army mods Keysize now 1023
Turing’s Solution Known-Plaintext attack Heil Hitler Wetterbericht Seeding values Plaintext Crib:Ciphertext: Try to place the crib without letter any letter mapping to itself WETTERBERICHT WETTERBERICHT WETTERBERICHT WETTERBERICHT WETTERBERICHT EXLMBTWZXBITWZCIQ P(false hit) = (25/26)length of crib
J Q F b E E1 E1: W?E E5: E?B E7: B?W a W J Q J B b E E5 c J Q L B E7 c a W
J Q F b E1 a J Q J b E5 c J Q L E7 c a
M V C b E1 a M Z C b E5 c M B D E7 c a
M V C b a E1 M Z C b E5 c M B D E7 P(false hit) = (1/26)length of cycle-1 a c
Turing’s Bombe NOT a computer Multi-Enigma Wiring 120 rpm ? max 6 hrs to solve ~70% of days cracked Accurate crib? Location of crib in message? Find cycle in message? Not too many false hits? Crib seeding Fake missions – Get spotted 18’26”N, 72’49”E = einachtzweisechsnordensiebenzweivierneunosten Reimann zeta zeros
Agenda Development of Enigma Machine – Why/How/What The Rejewski Crack The Turing Crack Historical Impact
6 : 60,000,000 :: 8 : ?
Secrecy Bletchley Park is gutted Enigma machines captured (and distributed!) Top Secret status until 1973!
Marian Rejewski – During and After the War
1939 – Romania
1939 – France
French cipher bureau
1940 – Algeria
1940 – Back to France
Rozycki dies in transit
Underground cryptography
1942 – Spain
Betrayed mid-crossing
Arrested + Jailed
1942 – Portugal, Gibraltar
1942 – England
No security clearance (Vichy France)
Polish Army – hand ciphers
1945 – Poland
1950 – Cable salesman
Secret Service meddling
1955 – Bookkeeper
Until retirement
1973 – Finally learns about ULTRA
1980 – Dies at age 73
Alan Turing –Timeline 1936-8 – Computability, Turing Machine, Decidability, Riemann 1939-45 – Bletchley Park 1946 – Automatic Computing Engine 1947-48 – Algorithms, Neural Nets, AI 1948 – Almost an Olympian 1948-50 – Manchester Mark I Mersenne + ??? (Was he on a secret nuclear program?? Might explain the gov’t paranoia) 1950 – Turing Test 1951 – Mathematical Biology 1952 – Arrest 1954 – Death at age 41
Colossus Computer Cracks Lorenz cipher High-level German communications History of Computers Z3 Colossus ENIAC Mark I
NSA
Addenda, Errata, Anecdotes Wiring analysis Hans Thilo-Schmidt TTTTTTTTTTTT Entry wheel order Why E1-E6, instead of E0-E5 ? Ring Settings and Rotor Stepping “Turing. Alan Turing.” Other WWII Cryptanalysis Disguising ULTRA intelligence Suggested Reading David Kahn – The Codebreakers Simon Singh – The Code Book
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