Editing Weak key (section)

== Historical origins ==
Virtually all rotor-based cipher machines (from 1925 onwards) have implementation flaws that lead to a substantial number of weak keys being created. Some [[rotor machine]]s have more problems with weak keys than others, as modern block and stream ciphers do.

The first [[stream cipher]] machines were also rotor machines and had some of the same problems of weak keys as the more traditional rotor machines. The [[Siemens and Halske T52|T52]] was one such stream cipher machine that had weak key problems.

The British first detected T52 traffic in Summer and Autumn of 1942. One link was between [[Sicily]] and [[Libya]], codenamed "[[Sturgeon]]", and another from [[Aegean Sea|the Aegean]] to [[Sicily]], codenamed "[[Mackerel]]". Operators of both links were in the habit of enciphering several messages with the same machine settings, producing large numbers of [[Cryptanalysis#Depth|depths]].

There were several (mostly incompatible) versions of the T52: the T52a and T52b (which differed only in their electrical noise suppression), T52c, T52d and T52e. While the T52a/b and T52c were cryptologically weak, the last two were more advanced devices; the movement of the wheels was intermittent, the decision on whether or not to advance them being controlled by logic circuits which took as input data from the wheels themselves.

In addition, a number of conceptual flaws (including very subtle ones) had been eliminated. One such flaw was the ability to reset the [[keystream]] to a fixed point, which led to key reuse by undisciplined machine operators.