Netting the Big Tuna

Intercepting and decrypting enemy messages was an important part of the Allies' strategy during World War II.  Beginning in July 1941, Germany's high command communication used a machine called the Lorenz SZ40 or SZ42, which British intelligence referred to as "Tunny" (named after the fish that Americans call "tuna").  Although the British did not obtain a Lorenz machine until late in the war, the codebreakers at Bletchley Park were able to deduce the machine's operation in January 1942.

The Tunny machine used a typewriter-style keyboard to enter text which was combined with a pseudo-random byte string to produce the cypher text.  This was then transmitted by radio or telegraph to a Tunny machine which was set up to generate the same byte string and combine it with the cypher text to get the plaintext message (a symmetric cypher using a pseudo-random one-time pad).
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Don't curse, recurse

Recursion is a concept in mathematics, computability theory, and computer programming, although the usage differs. In computability theory, a recursive set is one where membership can be confirmed or refuted using a process that terminates, and a recursively enumerable set is one for which there is a process that terminates if membership should be confirmed but may not terminate if membership should be refuted.  In mathematics, recursion refers to the embedding of something within itself, such as a function that uses itself in its own definition.  In computer programming, a recursive algorithm is a description of a computation that includes the same computation, but using different parameters.
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