John Cairncross - the man who made Soviet victory at Kursk Possible

In the event of loss of capture of machines or code books, a reserve hand cipher was used, possibly Doppelkastenschlüssel.
We found evidence of this from the batch of original messages from 1941 on the eastern front. Some message forms were a different cipher, possibly Doppelkastenschlüssel, unlike the Enigma we were not able to break these by computer. They were very short. Rejewski, who worked on this cipher while in England, said a minimu of 1000 characters on the same key was needed for a comfortable break.

 

Period 43/44:

And most crucially on Kursk:

And his assessment:

Captured machines would help. Captured keys however would not allow later traffic to be read without cryptanalysis, since the keys would be changed. There appears to be no evidence this happened, unless you have other sources contradicting Christos.

All the best

Andreas


If machines were captured it is quite likely that operators and documentation, even records were captured with them. Having captured machines the NKVD would immediately go looking among the PoWs for those who used them. Their methods of information extraction were probably successful when they found those men.

 

Personnel Security at Bletchley Park - Part One

From the website of Tony Comer, the former GCHQ Historian, on a broad theme and this excerpt concerns John Cairncross. A teaser passage:

Link: Sigint Historian: Personnel Security at Bletchley Park - Part One

Personnel Security at Bletchley Park - Part Two

Has a related theme and the teaser now is:

Yes more on John Cairncross!

Link: Sigint Historian: Personnel Security at Bletchley Park - Part Two

Part Three tomorrow if you're good.

 

One way to get a handle on this would be to read through what was actually being intercepted at Bletchley in the Spring and Summer of 1943. That would establish what there was for him to leak, if not what he did hand over. But you'd really have to be dedicated. UK National Archives files HW 5/220 – HW 5/325 more or less cover the period from the planning in March through to the conclusion of the Soviet counterattack in late August and would, at a guess, take about 10–15 full days to go through (inc. the necessary food/coffee/ibuprofen breaks).

 

Part Three has a different theme:

Link and Ian Fleming has a part: Sigint Historian: Personnel Security at Bletchley Park - Part Three