Cryptanalysis - the science of cracking secret codes - has always been an arms race between mathematicians and machine designers.
A newly declassified NSA document, titled “Fifty Years of Mathematical Cryptanalysis (1937–1987)”, provides a rare and sweeping look at how the U.S. developed world-leading capabilities in mathematical cryptanalysis.
The report chronicles how World War II, the Cold War, and the digital computing revolution transformed signals intelligence from pen-and-paper puzzles into a sprawling computational empire.
“Cryptanalysis is not just statistics or number crunching,” wrote author Glenn F. Stahly.
“It’s probability theory, abstract algebra, combinatorics - and psychology.”
🧠 From Poe to Turing
In the early 20th century, cryptology was still manual - relying on frequency counts, intuition, and educated guesses. By the time William F. Friedman built the U.S. Army’s Signal Intelligence Service (SIS), mathematicians were being embedded into code-breaking units.
By World War II, British and American cryptologic offices had drafted minds like:
- Alan Turing
- John von Neumann
- Claude Shannon
- I.J. Good
- Solomon Kullback
Many of these minds shaped not just wartime victory - but the very birth of modern computing.
⚙️ The Machines They Fought
A large portion of the NSA report traces the evolution of cipher machines - and the specialized technologies designed to defeat them. Among them:
- ENIGMA (Germany) – cracked by Polish and British mathematicians, later industrialized by the Allies
- TUNNY & STURGEON (Germany) – teleprinter ciphers that demanded both math and machines
- SIGABA (U.S.) – so complex it was never cracked during wartime
- Hagelin C-38/M-209 – widely deployed, easy to produce, but eventually vulnerable
To counter these, Allied codebreakers built revolutionary devices like the bombe, ROBIN, and COLOSSUS - the latter often considered the first programmable digital computer.
🖥️ Computers Reshape the Game
Post-war cryptanalysis shifted from mechanical tools to electronic computation.
Friedman’s early use of IBM punch cards laid the groundwork. By the 1950s and 60s, NSA was designing its own special-purpose computing devices to handle volume and speed far beyond human ability.
Every new generation of supercomputer brought fresh capabilities - not just for implementing old methods faster, but inventing entirely new attacks on cryptosystems.
“Computing power didn’t just amplify cryptanalysis,” the report states.
“It redefined it.”
📚 The Mathematicians Behind the Curtain
The NSA was, and likely still is, the largest employer of mathematicians in the world.
A few standout programs:
- Junior Mathematicians (1951): First post-war intake of talent
- Pl Cryptologic Mathematician Program (1963): Ongoing stream of recruits trained in applied mathematics
- SCAMP (1952–present): Summer cryptology programs bringing in academic elites
- IDA/CRD (1959–present): NSA’s “captive think tank” - a Princeton-based lab hosting names like Rosser, Knuth, and Albert
These efforts seeded decades of innovations - in everything from stepping rules and linear feedback shift registers to attacks on stream ciphers and public key systems.
📬 The Public Joins the Fray
By the late 1970s, NSA’s dominance faced a new challenge: academia.
The release of the Data Encryption Standard (DES) - and the controversy around its security - triggered an explosion of interest from civilian cryptographers like Whitfield Diffie, Martin Hellman, and Ron Rivest.
This led to the public discovery of public key encryption, including:
- RSA
- Knapsack systems
- McEliece’s code-based encryption
While these concepts had been theorized within classified channels, their public rediscovery blurred the line between state secrets and open science.
📈 The Cryptanalytic Arms Race
Technology is a double-edged sword.
As computers became faster, encryption did too. By the 1980s, NSA faced a field of over 300 commercial cipher machines - many designed indigenously abroad.
Worse still, encryption was migrating from hardware to software - making it cheap, fast, and easily changed.
“A system that can be rewritten overnight,” the report notes, “makes long-term cryptanalytic effort nearly impossible.”
This introduced an existential question: can codebreaking survive the agility of software?
📉 The Diminishing Advantage
The report concludes with a warning:
“Our lead is bound to diminish.”
While the U.S. and U.K. once enjoyed an overwhelming edge in cryptologic mathematics, the public explosion of cryptography - in conferences, journals, and open-source tools - means more eyes on every vulnerability.
Coupled with rising volumes of digital communication - from voice and video to telemetry and facsimile - the problem is no longer just one of math.
It’s logistics. It’s linguistics. It’s scale.
🧩 Takeaways from the Inside
This declassified document isn’t just a history. It’s a blueprint - showing how intellectual talent, war-driven urgency, and engineering ambition created the most advanced codebreaking infrastructure the world has ever seen.
But its most lasting message?
Even in cryptanalysis, the past is prologue. The battle for secure (and broken) communications continues - now fought in code, silicon, and qubits.
“The challenge,” the NSA concludes, “is for cryptomathematicians to remain no more than a few steps behind the cryptographers.”
