Thursday, February 11, 2016

Castle Feuerstein Laboratorium

There are many stories, some more fiction than others, about mysterious Nazi laboratories in dark castle dungeons where SS scientists perform all kinds of occult experiments. Return to Castle Wolfenstein and Mortyr are some well known PC games that portrait the Nazi obsession with the Ahnenerbe, the occult and paranormal experiments. Wewelsburg, the elite SS school and a center for archaeological excavations, is probably the most sinister of all.

What if I told you that scientists, lead by Dokter Oskar Vierling, worked in a secretive laboratorium in Castle Feuerstein. Does this sound to you like a sequel to Castle Wolfenstein? Not quite! Burg Feuerstein, located in Ebermannstadt, close to Nürnberg (Eng. Nuremberg), was all but fiction. A physicist in a mysterious laboratorium, how could that possibly relate to cryptology and intelligence? Exactly!

Feuerstein was an important target of TICOM, a secret Allied project to capture German scientists and seize SIGINT stations,  cryptographic and communications equipment, just before Germany surrendered. The mission of TICOM (Target Intelligence Committee) was to collect as much as possible German science and technology, preferably before Soviet forces got their hands on it. To achieve this, TICOM sent fast-moving special teams to pre-determined valuable locations inside the collapsing Germany, sometimes ahead of Allied troops.

Burg Feuerstein in Ebermannstadt

Is there a better way to hide a secret laboratorium than to build a typical Frankischen Schweiz style castle on top of a mountain in plain sight? It was so obtrusive that no one would suspect its purpose. Castle Feuerstein was build from scratch in 1941 by Dr Vierling with private funds. He was a physicist, electronics engineer and professor in high-frequency technology and electroacoustics. Laboratorium Feuerstein started its research in 1942 and developed experimental communications systems. At its peak, Feuerstein housed 200 staff and workers. TICOM only learned about Feuerstein's existence from decoded intercepts that referred to its research.

The scientists, lead by Dr Vierling, worked on a variety of projects, including high speed transmitters for covert agents, receivers, wave traps, accurate filter design, speech scramblers, voice frequency spectography, teleprinter cipher (crypto) attachments, improvements on cipher machines, a synchronisation system for the Lorenz SZ42 cipher teleprinter, acoustics and filter components for acoustic torpedoes, anti-radar coating for submarines, a night fighter control system, various frequency generators and an electronic calculator to solve sine and cosine equations. They were a busy bunch!

Dr. Oskar Vierling
Just before the German collapse, Dr Vierling was ordered to relocate his speech projects to Berchtesgaden in the Bavarian Alps and to destroy all other projects and equipment. Vierling, however, had other plans with his Feuerstein legacy. Once the Nazi's were off to Berchtesgaden with the speech equipment, he stored the most valuable equipment and plans in a large bomb proof walk-in vault, hidden behind a false wall in Feuerstein. There, he awaited the end of the war.

Castle Feuerstein was used as a German Army hospital at the time the TICOM team arrived. They rounded up the scientists and Dr Vierling proved very willing to cooperate with TICOM. Vierling and his group rushed to restore the laboratory and continued their work on selected projects under control of TICOM investigators.

NSA's declassified AXIS SIGINT in WWII, Vol II, Notes on German High Level Cryptography and Cryptanalysis contains some interesting crypto related info. The Lorenz SZ-42c cipher teleprinter with synchronisation, named SK-44 and SK-45, would generate and send a continuous pseudo-random five-bit stream. The receiver mixed its identical stream, by XOR-ing, with the incoming stream, resulting in nothing to print, since (K ⊕ K) = 0. When sending a message, the plain teleprinter message was mixed into the stream. The receiver mixed, as usual, the received signal with its own stream, which results in canceling out the stream and the original plain message being printed instantly, since (K ⊕ M) ⊕ K = M.

An eavesdropper would not know if or when the random stream contained an actual message or how long it was, thus effectively preventing traffic analysis. The U.S. Army Security Agency (ASA) suggested that analysis of the continuous mostly non-message-carrying pseudo-random stream, generated by the  SZ-42c, might compromise the machine's secret key settings. This would enable them to predict the stream and decipher all message that follow. The principle of continuous random stream was also used in the 1950s on the more advanced U.S. KWR-37 JASON and KWT-37 Fleet Broadcast crypto system.

Speech scrambling research by Dr Vierling's team produced little result. In 1943, only Dr Vierling and Telefunken still worked on ciphony (encrypted voice) and from 1944 on only Dr Vierling. At war ends, Feuerstein's research on ciphony focused on synthetic speech, encrypted by triple wobbling. The speech was separated in eight frequency bands. These were encrypted in a three stage ring wobbling (shifting the frequencies up and down) where the stage was split in half and these halves wobbled separately. However, speech quality after de-wobbling was very bad and ASA considered the German scientists several years away from developing any usable ciphony.

More details about the Feuerstein laboratory and Dr Vierling's work is available in chapter VIII, page 37 from Volume 8 Miscellaneous (alternative link here) of NSA's declassified files on European Axis Signal Intelligence in World War II. The rebuild of the lab under control of TICOM is described the Interim Report on Laboratorium Feuerstein (first pages are double, start reading from page 5) from the NARA archive. Another excellent source is the TICOM Archive. These documents contain enough inspiration for a few Wolfenstein sequels.

The importance of Feuerstein for TICOM is shown in ASA documents. The Temporary Duty Report of Mr William Friedman, the renowned U.S. cryptologist, is a resume of his tour in Germany from July to September 1945, in cooperation with TICOM. Vierling's Laboratorium, noted as important TICOM target, was one of the sites he visited in July 1945. NSA has a few more documents related to Dr Vierling.

After the war, Prof Dr Oskar Vierling continued working at his 1941 established firm VIERLING GmbH but relocated to Ebermannstadt, a mere kilometer from Castle Feuerstein. He had quite a prolific career, developing crypto machines, covert radio transmitters, eavesdropping devices, radio direction finding and various measuring and test equipment. He worked for Organisation Gehlen (post-war West-German intelligence), its successor the Bundesnachrichtendienst (foreign intelligence), the Zentralstelle für Chiffrierwesen (central cryptologic service) and the Deutsche Bundespost. From the 1930s until the 1950s he was also an important pioneer in the development of electronic and electro-acoustic instruments.

Due to legal restrictions on crypto export, Dr Vierling sold the rights for his crypto equipment to Crypto AG's predecessor Hagelin Cryptos. NSA archives show that Dr Vierling developed crypto machines in cooperation with ASA and NSA, at least until 1953 (see here and here). These documents show that ASA supplied tranistors for Vierling's crypto research. Transistors were quite novel in 1953 and their use in crypto equipment pretty unique.

Vierling's firm is currently still located in Ebermannstadt. Today, Burg Feuerstein is a catholic youth center.

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