An electro-mechanical rotor cipher machine created by the German engineer Arthur Scherbius.

How does it work ? Let’s find out.

The Enigma Structure

Why is the Enigma Machine special ? The wires inside the rotors are actually circuits connecting the battery to a bulb. The rotors move automatically when a key is pressed. Why is this important ? Let’s see

How can we retrieve the Ciphered Text ? Set similar initial configurations as the Enigma machine on which the encryption was done. How did the Germans send this information ? By radio using Morse code. Decryption

Can we exhaust all possible configurations of the Enigma Machine ?.NO. But Why ?But Why ? Let us see the total possible configurations.Let us see the total possible configurations. 3 Rotors can be arranged in 3! Ways=6 ways.3 Rotors can be arranged in 3! Ways=6 ways. Possible initial configuration of the Enigma Machine=26*26*26=Possible initial configuration of the Enigma Machine=26*26*26= ways. Now introducing plugboards.There are maximum 10 pairs.Now introducing plugboards.There are maximum 10 pairs. Total ways we can pair=C(26,2)*C(24,2)*..*C(8,2)=Total ways we can pair=C(26,2)*C(24,2)*..*C(8,2)= Since we don’t care about pair orders we divide by 10!. Therefore the total possible ways=Since we don’t care about pair orders we divide by 10!. Therefore the total possible ways= 150,738,274,937,250 ways. = 150,738,274,937,250 ways. Therefore total possible ways=6*17576* 150,738,274,937,250 ≈ 15,000,000,000,000,000,000 ways.Therefore total possible ways=6*17576* 150,738,274,937,250 ≈ 15,000,000,000,000,000,000 ways. Even a Modern computer would take almost an year to compute that many configurations !!!!Even a Modern computer would take almost an year to compute that many configurations !!!!

Flaw of the Enigma The flaw of the Enigma machine was that a letter could never map to itself. Another flaw was that for a particular rotor configuration, the Enigma encoding was symmetrical. Using this flaw, Alan Turing and Gordon Welchman created a machine which would crack the Enigma code in 20 minutes. The machine was called the Bombe.

Breaking the Enigma Code The most common technique used at Bletchley Park was the known-plaintext attack, in which the codebreakers guess that a particular sequence of characters exists somewhere in the decoded message. A sequence of characters that you guess is part of the plaintext is called a crib. Breaking an Enigma message required the following steps: –Align the crib with the ciphertext to eliminate crashes in which a letter appears to map to itself. –Create a menu recording the links between letter pairs in the crib and ciphertext. –Identify loops in the menu at which a chain of letter pairs cycles back to the original letter. –Use the loops in the menu to create a wiring pattern for an electromechanical device called a Bombe that searches for settings of the Enigma rotors that produce the observed pattern.

Step 1: Align the Crib and Ciphertext UAENFVRLBZPWMEPMIHFSRJXFMJKWRAXQEZ KEINEBESONDERENEREIGNISSEKEINEBESONDERENEREIGNISSEKEINEBESONDERENEREIGNISSEKEINEBESONDERENEREIGNISSEKEINEBESONDERENEREIGNISSEKEINEBESONDERENEREIGNISSE No crashes exist in this alignment, so it is a feasible solution.

Step 2: Construct the Menu V K 0 R E 1 L I 2 B N 3 Z E 4 P B 5 W E 6 M S 7 E O 8 P N 9 M D 10 I E 11 H R 12 F E 13 S N 14 R E 15 J R 16 X E 17 F I 18 M G 19 J N 20 K I 21 W S 22 R S 23 A E 24 LKV OFIHPB ZERJNG AXWSMD , V K 0 R E 1 L I 2 B N 3 Z E 4 P B 5 W E 6 M S 7 E O 8 P N 9 M D 10 I E 11 H R 12 F E 13 S N 14 R E 15 J R 16 X E 17 F I 18 M G 19 J N 20 K I 21 W S 22 R S 23 A E 24

Step 3: Find the Loops V K 0 R E 1 L I 2 B N 3 Z E 4 P B 5 W E 6 M S 7 E O 8 P N 9 M D 10 I E 11 H R 12 F E 13 S N 14 R E 15 J R 16 X E 17 F I 18 M G 19 J N 20 K I 21 W S 22 R S 23 A E 24 LKV OFIHPB ZERJNG AXWSMD ,

References: The Code Book-Simon Singh

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