The good newsThe war diary of the German Army’s signal intelligence agency Inspectorate 7/VI and the reports of the cryptanalytic centre in the East Horchleitstelle Ost (later named Leitstelle der Nachrichtenaufklärung) are available for the period 1941-43. Also summaries on the solution of Soviet codes are available for the period October 1944-March 1945.
The bad newsI haven’t been able to find the reports of Horchleitstelle Ost for the second half of 1941 and for the period February- September 1944.
The unexpectedAccording to a recently declassified TICOM report the Germans were able to read the first version of the Soviet diplomatic one time pad code in the 1930’s and the codes of the Comintern. In the first case their success was due to the fact that the system was not true one time pad in that one additive page was assigned to each message. If the values were not enough to encipher the entire message then they were reused.
In the case of the Comintern it seems that the main system used by Communist Parties around the world was a numerical code used together with a letter to number substitution table. The table was used as a ‘key’ generator for additive sequences used to encipher the coded message. A common book would be used for this purpose and the user would identify through the indicator the page and line that the sequence would start from. In one such case the Germans solved the ‘encipherment sequence of about five million digits’ and identified the five books used as cipher.