Chris Spackman's NeoCities Page

Early Modern Cryptanalysis

The traditional ciphers were broken by clever individuals with pencil and paper. But during World War I and the years that followed, codebreaking became a profession — and then a science. Governments created secret organizations dedicated to reading other nations' communications, and a handful of brilliant people developed the mathematical tools that made it systematic.

These pages cover the period roughly from 1914 to 1935 — from the desperate wartime codebreaking of the Zimmermann Telegram to William Friedman's transformation of cryptanalysis into a branch of applied mathematics. This era set the stage for everything that came later: Enigma, Bletchley Park, and eventually the computer-driven cryptography we use today.

The Pages

1. Codebooks: A History — how codes differ from ciphers, from Renaissance nomenclators to WWI diplomatic codebooks. Build your own codebook in the interactive exercise.
2. The Zimmermann Telegram — how British codebreakers in Room 40 decoded a secret German message that helped bring America into World War I. Includes an interactive codebook lookup.
3. The American Black Chamber — Herbert Yardley's MI-8 and its successor, the Cipher Bureau. How breaking Japanese diplomatic codes shaped the Washington Naval Conference — and why it was shut down.
4. Hitt, Friedman, and Scientific Cryptanalysis — Parker Hitt's foundational Manual and strip cipher device, followed by William Friedman's statistical revolution. Interactive tools for the Index of Coincidence, Kasiski examination, and chi-squared test.

Section Glossary — definitions of terms used on these pages.

Timeline

Key People

Parker Hitt (1878 – 1971)

An Army officer who wrote the first American textbook on military codebreaking. His 1916 Manual for the Solution of Military Ciphers taught techniques for breaking substitution and transposition ciphers. He also invented a strip cipher device — a set of rotating alphabet strips mounted on a cylinder — that was a direct ancestor of later cipher machines. Hitt trained many of the people who would go on to build America's codebreaking capability. Read more about Hitt's work.

Herbert O. Yardley (1889 – 1958)

A State Department code clerk who convinced the government to create its first dedicated codebreaking unit. He led MI-8 during World War I and then ran the "Black Chamber" (officially the Cipher Bureau) through the 1920s. His greatest success was breaking Japanese diplomatic codes before the Washington Naval Conference. After his unit was shut down, he wrote a tell-all book that became a bestseller and a cautionary tale about secrecy.

William F. Friedman (1891 – 1969)

Often called the "father of American cryptanalysis." Friedman transformed codebreaking from a craft into a branch of applied mathematics. His key innovation was applying statistical methods — particularly the Index of Coincidence — to systematically analyze ciphers. He founded the Army's Signal Intelligence Service, trained the team that broke the Japanese PURPLE machine, and developed techniques still used in cryptanalysis today.

Context