Re: M4 Steckers

philmarks-L+Gohi/[email protected] wrote:
> Tony Sale wrote:
> 
> > All, In thinking about the M4 "find the Steckers" problem I decided to
> > do what BP would have done, look for human errors in the preparation
> > of setting sheets, and I found them.
> > In a 1944 months setting sheet, the person preparing it had obviously
> > got tired of doing them. On any one day there are sequences, sometimes
> > four long of incremented letters such as, AL BM CN DO.
> > I suggest that in working through letter pairs, at least two and
> > possibly three successive letter increments are tried at the same time.
> 
> I don't have any more examples, but it is clear that Bletchley Park was 
> looking out for this kind of thing throughout the war.
> 
> There is a wartime memo in the US National Archives showing that in late 
> 1944 BP detected examples of Umkehrwalze D pairings from one Luftwaffe key 
> having been used to construct the Stecker pairings for another.  This memo 
> was written by the same Reg Parker mentioned by Gordon Welchman in "The Hut 
> 6 Story" as having detected repeated portions of Enigma keys back in 1942.
> 
> I'm not aware of any similar examples from German Naval traffic, and in 
> general the Luftwaffe was much less conscious of cipher security than its 
> marine counterpart.
> 
> Tony's example is rather more egregious.  I believe there were instances 
> where local Luftwaffe offices made up their own keys rather than receiving 
> them from a central cipher office, and in those cases it seems more likely 
> that poor practices could be adopted.  Presumably all of these organizations 
> were getting pretty short on staff by that stage of the war, while the 
> demand for key sheets was increasing as the Luftwaffe (and for that matter 
> the German Navy) started to segregate their networks into more and more 
> separate keys.

Tony,

we found some bad Stecker pairs in 1941 (for example connections like A/X, B/Y, C/X, D/W). Certain other pairs were favoured. The 1945 messages seemed to be more random. So these two networks had different practices.

If you are lucky enough to guess 3 Stecker, you may see little plaintext in the decrypt (about 1 in 5 letters correct on average). Finding the first few is difficult.

Geoff