Pers Z S

The Pers Z S was the symbol and the code name of the Chiffrierdienst, i.e. the Cryptanalysis Department or Signal Intelligence Agency of the German Foreign Office (German: Auswärtiges Amt) before and during World War II. Pers Z S was also called Special Service of Z Branch of the Foreign Office Personnel Department (German: Sonderdienst des Referats Z in der Personalabteilung des Auswärtigen Amtes) Though similar in nature and operation to the OKW/Chi cipher bureau, it was a civilian operation as opposed to the military operation at OKW/Chi. According to TICOM interrogators it evinced an extraordinary degree of competence, primarily driven by a consistency of development not found in any other German signals bureau of the period.

The letter "Chi" for the Chiffrierabteilung is, contrary to what one might expect, not the Greek letter Chi, nor anything to do with the chi test, a common cryptographic test used as part of deciphering of enciphered message, and invented by Solomon Kullback, but only to the first three letters of the word Chiffrierabteilung (English:cipher department).

Little was known about Pers Z S before April 1945, when the first section was captured. TICOM, the United States effort to capture German intelligence assets after the war, found that captured documents provided little information on the execution of the unit, with the records of the Mathematical and Cryptological section having been destroyed. The field covered by Pers Z S, over 25 countries for a period of 25 years, stymied TICOM as so few interrogators were available, who also lacked experience in cryptographic diplomatic system, as this was the first TICOM investigation. Inevitably there were some areas which were not covered.

In May 1945, the usual approach by TICOM to force captured personnel to write homework describing processes used in a particular intelligence unit under interrogation was not fully developed. The only document prepared as homework was prepared on 6 August 1945 by Professor Dr Hans Rohrbach, along with several of his Pers Z S colleagues, which described the cryptanalysis of the American O-2 strip cypher, which was considered a most significant piece of work.

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