Imagine being able to turn an entire room of voice encryption machines into a device the size of a shoebox. Who could do that? Actually, someone did: it was called Alan Turing, and this is the story of his Delilah Project, an invention that remained hidden for decades.
Delilah Project: A Bridge Between Mathematics and Engineering
Il Delilah Project represents one of the lesser-known chapters of the career of the great Alan Turing, but also one of the most fascinating. During the Second World War, Turing did not only devote himself to deciphering Enigma, the German cryptographic machine. He also devoted himself to an ambitious goal: miniaturizing voice cryptography, making it portable and usable in the field. The result? It was a system composed of three units, each the size of a shoebox, weighing just 39 kg , including power.
“Delilah was one of the first systems based on rigorous cryptographic principles,” he recalled. Donald Bailey , Turing's assistant during the project.
The system was inspired by the principles of text cipher machines, such as the German SZ42, but he extended these concepts to the domain of the voice. Using a combination of advanced electronic circuitry and rotating wheels, Turing was able to generate a sequence of pseudorandom numbers that were added to the voice signal to encrypt it.
How did voice encryption work?
The heart of the Delilah Project was an analog-to-digital conversion process, similar to modern methods of digitizing sound. The voice signal was “broken down” into a series of numbers, each corresponding to the voltage of the signal at a given moment. To these numbers was then added a sequence of pseudo-random “keys”, generated by a module composed of five rotating wheels and eight multivibrators.
“The synchronization of keys between sender and receiver presented formidable difficulties,” Turing and Bayley wrote in their declassified reports.
Once transmitted, the encrypted audio signal was decoded by the receiver, who subtracted the same sequence of keys to reconstruct the original message. Although the result was often accompanied by background noise and distortion, the system worked and demonstrated an unprecedented level of safety.
Delilah: The Historical Context and Legacy of the Project
Il Delilah Project was born at a time when voice encryption represented the future of military communications. If the system SIGSALY was huge and required an entire room to operate, Turing envisioned something entirely different: a compact, portable device. However, with the end of the war, military interest in the project quickly waned.
“Delilah had little potential for further development,” Bayley commented in one of these manuscripts, “and was soon forgotten.”
Despite this, Turing's work on the project left a significant mark. The skills he acquired during his two years at Hanslope Park proved crucial to his later contributions to electronic computer design, such as theACE (Automatic Computing Engine).
Turing the Engineer: A Multidisciplinary Talent
Il Delilah Project offers a unique perspective on Turing: not only as a mathematician and logician, but also as an electronics engineer. Before 1943, his practical experience in electronics was limited, but his ability to learn quickly led him to master advanced concepts in a very short time.
The surviving documents, known as the “Bayley papers,” include detailed notes on experiments with multivibrators, Fourier analysis, and the bandwidth theorem, now known as Nyquist-Shannon theorem . These notes, together with the evening lectures Turing gave to young engineers, demonstrate his deep understanding of the mathematics applied to electronic circuits.
“I admired the originality of his mind,” Bayley recalled. “He taught me a lot, and I will always be grateful to him.”
Conclusion
Il Delilah Project is a remarkable example of how Turing’s genius extended far beyond the confines of mathematics and computer science. Although forgotten for decades, this project anticipated many of the innovations that would revolutionize modern communications. Today, thanks to the recent discovery of the “Bayley papers,” we can finally appreciate the importance of this invention and the role it played in shaping the future of technology.