Hans Rohrbach was born on February 27th, 1903

Written by: Victor Malone

Hans Rohrbach: The Mathematician Who Cracked the American Diplomatic O2 Cipher

Hans Rohrbach is best known for his remarkable achievement in breaking the American diplomatic O2 cipher, a variant of the M138A strip cipher, during World War II. This groundbreaking feat earned him recognition as one of the most skilled cryptanalysts of his time.

Early Life and Education

Rohrbach was born on February 27, 1903, in Berlin, Germany, to journalist Paul Rohrbach and his wife Clara (née Müller). He showed an early interest in mathematics and physics, attending the Gymnasium school at Berlin-Friedenau and later the Fichte Gymnasium in Berlin-Wilmersdorf.

After completing his school leaving exam in 1921, Rohrbach pursued higher education at the Friedrich-Wilhelm University in Berlin, where he studied mathematics, physics, and philosophy. During his university days, he became involved with the Berlin student organization Mathematisch-Physikalische Arbeitsgemeinschaft (Mathematics and Physics Working Group), which gave him the opportunity to visit the United States in 1923.

Academic Pursuits and Cryptanalysis

Rohrbach resumed his studies at the University of Berlin in 1924, eventually completing his PhD thesis, "Die Charaktere der projektiven Gruppen," in 1929. His academic focus on algebra and number theory laid the foundation for his future work in cryptanalysis.

In the 1930s, Rohrbach began working at Pers Z S, the German Foreign Office cipher bureau, where he applied his mathematical expertise to crack various encryption codes. His most notable achievement was breaking the American diplomatic O2 cipher in 1943, a feat that showcased his exceptional skills as a cryptanalyst.

War Years and Capture

During World War II, Rohrbach continued to work at Pers Z S, using his expertise to support the German war effort. However, in 1945, he was captured by TICOM (Target Intelligence Committee), the Allied effort to round up and seize captured German intelligence personnel and material.

After his capture, Rohrbach wrote a report detailing his methods for breaking the O2 cipher, which provided valuable insights into the workings of the German cryptanalytic efforts during World War II.

Legacy and Impact

Hans Rohrbach's remarkable achievements in cryptanalysis have had a lasting impact on the field of cryptography. His work on the O2 cipher and other encryption codes has contributed significantly to our understanding of code-breaking and encryption techniques.

Today, Rohrbach is remembered as one of the most skilled cryptanalysts of the 20th century, and his work continues to influence the development of cryptography and secure communication systems.

• Rohrbach's work on the O2 cipher is still studied by cryptographers and historians, providing valuable insights into the cryptographic techniques used during World War II.
• His report on breaking the O2 cipher has become a seminal work in the field of cryptanalysis, shedding light on the methods and techniques used by German cryptanalysts during the war.
• Rohrbach's contributions to algebra and number theory have also had a lasting impact on the development of modern mathematics.

Hans Rohrbach passed away on December 19, 1993, leaving behind a legacy of groundbreaking work in cryptanalysis and mathematics that continues to inspire and inform researchers today.