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Post by James Starbird on Dec 4, 2016 1:06:38 GMT
BANBURISMUS: Banburismus refers to an optical aid to comparing two messages against each other, looking for characters which match in both. It is done by placing the messages (represented by holes punched in sheets of card) on top of each other over a light-box and counting places where the light shines through. Light can only shine through where two holes are in the same place - representing matching characters at that position in the messages. ( It seems that there was a variation on this theme where the two messages would be put on top of each other over a dark table-top. Where the holes lined up the dark table-top would be visible and would contrast with the light-coloured card. ) The card sheets were printed in Banbury (a town in central England, not far from Bletchley Park) and were known as "banburies" - and the technique was "banburismus". You might Google this for further information on the early code breaking efforts.
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Post by lpaseen on Dec 4, 2016 4:09:26 GMT
Thanks for the info, it's actually first time I hear about it. At first I thought it was what I know as jeffrey sheets (or Zygalski sheets) and when the holes lined up you had a drop. That method of breaking became obsolete in May 10 1940 (the day they invaded France) when the Germens changed the procedure to no longer repeat the initial message key. Luckily they had broken enough messages that they found patterns and habits in operators so when the jeffrey sheets no longer worked they had to move over to Herivel tips and sillies to break it (the bombe came later).
Reading wikipedia I see that Banburismus was used to better guess what right and middle rotors to load the bombe with and depended on other things than the jeffrey sheets did so they kept working until it was enough bombes where built to have a specific set of rotors available all the time.
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