Rotor

Rotor

Positions Rotor

Civil Rotor

So in this picture, you see that rotor four is spinning faster and rotor two is spinning slower.

This is the rough idea behind rotor encryption machines.

First, we choose from 1 of 6 possible rotor orderings.

Then we select an initial position from the rotor sequence.

And there's a rotor there that this motor is spinning.

And if you manipulate the speed of this rotor, you are actually able to crack the rotor and eventually even have the centrifuge explode.

And the other way around, if you increase the speed of rotor three and decrease the speed of rotor one, then the robot pitches forward.

This destroyed the uniform distribution of the initial rotor position, and after repeated observations, it allowed the allies to reverse engineer the rotor wirings completely.

Understand that each rotor position is equivalent to a location in the sequence.

When the rotor advanced, an entirely new path was defined for each letter.

So we were able to associate the small digital warhead with the rotor control.

Each rotor wheel had electrical contacts on either side with a maze of wirings within.

The rotor is that moving part within the centrifuge, that black object that you see.

The reason why a battery might not charge is that the alternator might be broken or the fan belt might be broken.

Now, the state of the art technology of the time was called a rotor encryption machine.

So at each rotor position, there's an electrical path from every input letter to every output letter.

It was an electromechanical rotor machine invented by a German engineer at the end of the World War I.

You wish to make sure that a helicopter can be recognized, no matter what angle it's rotor blades currently have.

The security of rotor machines depends on both the size of this key space, and the randomness of the key setting.

If the operators had instead rolled dice to decide their initial rotor positions, the starting points in the sequence could have been uniformly distributed.

They were to select a random initial position of each rotor before communication began, and a very simple mistake was made by some fatigued operators.

For example, some changes they made were to add a fourth rotor wheel, and increase the number of possible rotors you could put into the machine to 60.

For a given messaging crypt, the Bombe could scan through all possible rotor positions and orders, in order to find possible key settings in a matter of minutes.

We can observe things like the oil light and the lights and the battery meter and then compute probabilities of the hypothesis, like the alternator is broken or the fan belt is broken or the battery is dead.

The same way as, at the moment, the power stations burn the fuel to create steam, to run the turbine, to create a rotating magnetic...object what we call a rotor, which has got magnets mounted on it, within the generator, to create electricity.

This would have prevented the reverse engineering of the rotor wirings, and if the Enigma allows the letters to be encrypted to themselves, the Bombe couldn't have taken advantage of crypts, and this would require the allies to check the entire key space, which was impossible even with the fastest computer.