Friday, August 10, 2012

Specialized cryptanalytic machines of WWII

Histories of WWII only tend to devote a few pages on codebreaking and when they do they usually focus on well known individuals such as William Friedman, Alan Turing, Gordon Welchman etc

The reason they do so is that we as humans like to connect a specific event with a face. For example Purple cipher machine=Friedman, Enigma success=Turing.

It’s undoubtedly a very simplistic way to view things but that’s what the average person wants. Of course only rarely can a specific success be traced back to one and only one person. Even back in WWII whole teams had to work to solve difficult crypto systems.

One thing that doesn’t get the attention it deserves is the use of specialized cryptanalytic devices for ‘breaking’ hard systems. Again I think the problem is our inherent need to identify humans as protagonists of important events.

Even so without bombes, duennas, autoscritchers, IBM punch card machines and various other specialized equipment many Allied codebreaking successes would be impossible.

Let’s take a quick look at some of the devices built and their targets.

Date Introduced
Date Introduced
3-rotor bombe
Plugboard Enigma
4-rotor bombe
M4 Enigma
Enigma with UKW-D
end 1944
Heath Robinson
Collosus I
Collosus II

Notice the long delay from the time a cipher machine is introduced till the time a cryptanalytic device is used against it. Building a specialized device took a long time and of course had the inherent problem that it could only be used against that specific cipher machine.

Postwar the Anglo-Americans realized that they needed more flexible equipment. This is explained briefly by the NSA’s Howard Campaigne [Source: NSA-OH-14-83, p73]:

We had in the past, before that time, we had built a special device for every problem. And we'd gotten some very effective devices. But it always took a long time to build it. We had to formulate the problem and design the equipment, and get it constructed, and debugged, and all that had to take place when we ought to be operating. And we saw that we thought with the flexible computer you can put a program on and get going right away.

The NSA’s need for a general purpose cryptanalytic device led them to invest great sums in developing the first computers postwar.

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