Historical question: Longevity of Colossus.

[Paul Leyland]

> From: Quentin Campbell [mailto:Q.G.Campbell@newcastle.ac.uk]
> A couple of things I recall from talks given here:
> 
> 1. At the end of the War, Donald Michie and others tried "programming"
>    a Colossus to do some non-cryptographic computations. I 
> also understand
>    it was tried on some cryptographic tasks for which it was not
>    originally designed. It may be it had some utility in 
> these other areas
>    that extended its useful life.

Thank you, that is information I had not heard before.

> 2. Tony Sale has also said that there are some analysis 
> algorithms that
>    are built into the logic of Colossus and which could be selected as
>    part of its set-up menu that remain classified still. He was told
>    that some of these techniques were still in use at Cheltenham until
>    fairly recently.


This ties in nicely with a tale I can relate.

Bob Morris, the retired chief scientist at NSA, gave a talk at Cambridge
about 3 years ago.  In the pub afterwards he claimed that none of the WW2
machine cryptography was anything but of historical interest.  I asked him
why aspects of the Colossus design were still classified.  He immediately
backtracked, giving essentially the same answer as Tony Sale gave to you.

About a year ago, New Scientist (I think) revealed one of those aspects that
had recently been declassified.  Incorporating a one-bit delay in the
keystream (using a single capacitor in Colossus) and then correlating gave a
useful attack on a class of stream ciphers and that this trick was not
previously widely known.


Paul