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On August 5th, 1857,
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a 4,300 km long cable was laid across the Atlantic Ocean,
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it provided a link between Britain and the Americas,
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further strengthening their social and economic alliances.
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Now information could be represented
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as a pattern of electrical pulses,
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and sent across the world almost instantaneously.
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Stock tickers, and money transfers,
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these were commercial applications invented by Western Union
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which ushered in a new era of global communication.
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Please stand by for this announcement.
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Germany has invaded Poland.
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And it has bombed many towns.
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General mobilization has been ordered in Britain and France.
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And consequently this country is at war with Germany.
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Throughout the world, which is the real cause of the war
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that today threatens the freedom of mankind.
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(Italian words)
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(Japanese words)
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The Japanese has attacked Pearl Harbor Hawaii by air.
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President Roosevelt has just announced.
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(German words)
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During World War II, Germany, Italy, and Japan
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were far outnumbered by the allies.
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Their only conceivable path to victory
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was the ability to launch widespread surprise attacks.
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So the goal of encryption technology
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was to automate the one time pad
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using an encryption machine.
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Ideally, this machine would accept an input letter,
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apply a random shift, and output the encrypted letter.
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However, all machine follow the same principle.
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They begin in some initial configuration known as a state.
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They accept some input. They do an operation with the input,
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and then they produce an output.
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The operation from the initial state to final state
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is always predictable, and repeatable.
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So the goal was to produce identical machines
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that output a scrambled sequence of shifts,
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which took a long time to repeat.
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Therefore Alice and Bob could generate
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an identical shift sequence as follows:
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First, they need to share identical machines,
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and agree on an initial position
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which is defined as the key setting.
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Then, they align their machines to the same position
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and finally cycle through the identical operations
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to achieve identical sequences.
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Now, the state-of-the-art technology of the time
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was called a rotor encryption machine.
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We're all familiar with the mechanical process of an odometer,
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which takes a long time to finally repeat its cycle.
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Now imagine we scramble the numbers on the wheels of the odometer.
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When it ticks forward,
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a new shift could be generated
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by adding up each number on the rotors.
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This is the rough idea behind rotor encryption machines.
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For example, the message "Attack northwest"
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would be encrypted as follows:
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Notice how a new shift is used
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at each position in the message.
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With 3 rotors, each with 26 numbers,
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the length of the sequence before repeating is 26x26x26.
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This is equivalent to having
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a list of shifts 17,576 numbers long.
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Understand that each rotor position
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is equivalent to a location in the sequence.
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The initial machine state is known as the key setting,
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and the collection of all possible key settings
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defines the key space.
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This key space increases
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if the number of ways to initially configure the machine increases.
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For example, if the rotors can be rearranged,
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then the order can be selected in 6 ways.
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Let's visualize the key space at this point.
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First, we choose from 1 of 6 possible rotor orderings.
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Then we select an initial position from the rotor sequence.
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This gives us a key space with over a 100,000 key settings.
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Remember, every machine configuration
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is a point in this space.
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When we select a key setting,
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we're selecting a starting point in this space,
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which then determines the rest of the shift sequence.
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Give away the key setting,
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and you give away the entire sequence.
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The security of rotor machines
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depends on both the size of this key space,
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and the randomness of the key setting.
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During World War II,
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one of the most important encryption technologies
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used by the German military was known as the Enigma.
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It was an electromechanical rotor machine
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invented by a German engineer at the end of the World War I.
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Each rotor wheel had electrical contacts
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on either side with a maze of wirings within.
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So at each rotor position, there's an electrical path
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from every input letter to every output letter.
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When the rotor advanced,
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an entirely new path was defined for each letter.
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During the war,
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they continually tried to increase the key space of the Enigma,
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in order to make it stronger.
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For example, some changes they made
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were to add a fourth rotor wheel,
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and increase the number of possible rotors
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you could put into the machine to 60.
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This has the effect of massively increasing the key space.
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Near the end of the war,
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the Enigma could be set up in
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over 150 million million million ways.
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Guessing the key setting which was used for a given message
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was about as likely as guessing the outcome of 26 dice rolls.
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This gave the German confidence that the allies,
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even if they have the copy of the Enigma,
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could never check all possible key settings.
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For two parties to communicate using the Enigma,
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it required that they first shared the daily key settings.
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This allowed them to align their machines to the same position.
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This protocol changed over and over during the war,
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but generally involved distributing key sheets in advance
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to all operators.
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Each day, the operator would cut off the daily settings,
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and this would tell them the daily configuration of their machine,
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such as what rotors to use and the order of the rotors.
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This key setting was then to be destroyed after use.
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However one vital step was left to the operator.
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They were to select a random initial position of each rotor
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before communication began,
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and a very simple mistake was made
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by some fatigued operators.
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We make this exact same mistake
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every time we set a bike lock combination,
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because we tend to rotate the cylinders
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only a few clicks from the initial state,
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or we reused a common password.
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This destroyed the uniform distribution of the initial rotor position,
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and after repeated observations,
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it allowed the allies
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to reverse engineer the rotor wirings completely.
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The second major error was a design error,
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not a procedural one.
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The Enigma was designed
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so that an input letter would never encrypt to itself.
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So given an encrypted letter, such as L,
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you can now eliminate the possibility that
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L was the original letter.
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What they thought was a strength
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was actually a weakness in design,
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and this lead to a code-breaking machine,
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initially designed by the Poles,
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and later improved by the British-American effort.
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The Bombe was multiple Enigma rotors chained together,
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allowing it to rapidly test different key settings.
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It took advantage of the fact that
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common words were known to be in the original message,
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such as weather, and these came to be known as crypts.
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For a given messaging crypt,
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the Bombe could scan through
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all possible rotor positions and orders,
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in order to find possible key settings in a matter of minutes.
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This machine allowed the allies
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to read German commands within hours of them being issued.
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It was a fatal blow to their combat strategy,
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as the allies could anticipate their next move.
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One fact remains,
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this initial attempts at automating the one time pad failed.
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If the operators had instead rolled dice
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to decide their initial rotor positions,
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the starting points in the sequence
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could have been uniformly distributed.
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This would have prevented
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the reverse engineering of the rotor wirings,
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and if the Enigma allows the letters to
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be encrypted to themselves,
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the Bombe couldn't have taken advantage of crypts,
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and this would require the allies to check the entire key space,
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which was impossible even with the fastest computer.
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Repetition reduced the key space.
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Otherwise the outcome of World War II
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could have been drastically different.