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January 2015The monthly newsletter by Felgall Pty Ltd

My Word

Encryption

I watched "The Imitation Games" earlier this month - which supposedly showed how Alan Turing developed a mechanical way to decrypt German messages sent using the Enigma machine. As I watched I noticed a number of obvious inaccuracies in what the movie depicted.I confirmed these inaccuracies and discovered more when I looked up an historical account of the events afterward.

Now the Enigma machine in its original form had 158,962,555,217,826,360,000 different settings (the movie rounded this off to 159,000,000,000,000,000,000 which is reasonable enough). For manual decryption processes this would have been sufficient provided that the settings were changed frequently enough and provided that messages were not too repetitive in their content. When you add in mechanical processes to speed up testing and when you consider that many of the German messages were of a repetitive nature this proved to be totally inadequate.

The Enigma was first broken broken by the Poles in December 1932. At the time the Germans were only changing the settings once a month. The repetitive nature of some of the messages allowed the Poles to reverse engineer the Enigma machine and also created mechanical devices to aide in decryption. By 1938 the Germans had built further complexity into the Enigma and the Poles handed over their Enigma replica and other mechanical devices to England as the resources required now exceeded what Poland could reasonably handle plus there was the knowledge that Germany would likely attack Poland before much longer (having already taken over Austria and Czechoslovakia).

So the movie was somewhat inaccurate in that Alan Turing didn't build the first mechanical device while being opposed by the rest of the group. They started off with mechanical devices already supplied to them by the Poles and simply built more complex versions to handle the more complex versions of Enigma. Also while the movie portrayed one machine for performing decryptions which toward the end of the movie provided a complete solution, there were actually 200 such machines built and they relied on partial decryption of the messages to start with and then only gave possible solutions which then needed to be checked. One thing the movie did get right was that it was the repetitive nature of the weather report messages that assisted in breaking the encryptions.

Another aspect that the movie got wrong was in claiming that the device Turing built to break Enigma was the first computer. In fact those devices (known as 'The bombe') could only perform the one task - that of finding possible solutions to the Enigma encryption - it was in fact another machine also built by the code breakers at Bletchley Park and called 'Colossus' that was the first computer as it used valves, had no moving parts, and was semi-programmable very different from the mechanical device used to break Enigma.

Perhaps the most important thing that the movie got right was the weakness that resulted from the way that the Germans were using these encryptions. While the messages were kept reasonably short (or split into pieces sent using different settings) the information being sent was too repetitive and the Germans didn't always reset the start position as frequently as they should have. If we look at this in terms of encryption today, this same weakness needs to be overcome if you expect data encrypted using any encryption system to be secure. The other big weakness of Enigma was the symmetrical nature of the encryption where feeding the encrypted message through with the same settings as was used to produce that encryption would convert the encrypted message back to plain text. Modern encryption uses asymmetric keys where the key required to decrypt the message is different from that used to encrypt the message so that working out the key used to encrypt the message does not assist you in any way in decoding the message.

While the number of combinations that Enigma could handle might appear to be a large number, in modern terms it is relatively small and messages encrypted using Enigma could be quickly decrypted using current computer technology. Modern encryption techniques use far more complex algorithms that the one built into Enigma. These are made possible by being able to use computers to perform the encryption and decryption tasks and are also made necessary by the fact that any simpler algorithm can be quickly decrypted using computers.

Encryption has had a long history with computers with the first computers (and related mechanical devices) being used to decrypt messages and more modern computers being used to develop far more sophisticated encryption algorithms.
 

On Site

This last month I uploaded the last of the new XHTML reference pages as well as a variety of other pages. Also now available at felgall.com.au is my new hosted club membership system with a demo of both the ordinary member and committee member options as well as all the help pages (including those for the membership officer which does not currently have a demo but it works fine for the one club so far using the system). There have also been a number of new tutorials added to javascriptexample.net over the past month. Probably not so many new things over the coming months so if you have ideas for anything you'd like me to write about please let me know.
 

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