November 30, 1932

Cryptanalysis of the Enigma

Marian Rejewski reconstructs military Enigma and reads its first messages

Rejewski worked on the machine alone, after his colleagues went home — they were not allowed to know what he had been assigned.

December 1932, at the Saxon Palace

The documented breakthrough came during the last days of December 1932, after roughly ten weeks of work. Poland's Foreign Intelligence Agency dates the first successful decryption of German Enigma cryptograms at the Saxon Palace in Warsaw to 31 December 1932.

Marian Rejewski, then 27, had begun working against military Enigma in October 1932, alone and part-time after the other Cipher Bureau employees went home. Maksymilian Ciężki had assigned him the task in secret.

What arrived from Paris

French intelligence delivered past German daily-key tables — two months of them, for September and October 1932 — to Warsaw on 8 or 9 December.

Those photocopies contained obsolete keys, not the rotor wiring. They reduced the unknowns in Rejewski's permutation equations and enabled him to derive the military machine's rotor and reflector wiring mathematically.

The crucial packet reached him only about three weeks before the first successful decrypt.

Why 30 November does not work

The listed date is unsupported by any source consulted, and the material essential to the solution had not yet reached Rejewski by then. Sources differ by a day on the French delivery — 8 or 9 December — but both rule out a completed break in November.

"Breaking Enigma" was a process rather than a one-time solution: reconstructing the machine, recovering frequently changing daily settings and responding to German procedural changes were distinct achievements.

Rejewski performed the initial mathematical reconstruction alone; Jerzy Różycki and Henryk Zygalski were crucial to the continuing programme that followed.

Sources

Researched 23 Aug 2026 6 sources 2 audit passes Date disputed

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date disputed. Sources disagree; the research places it at 1932-12.

What the sources leave uncertain

The listed date, 30 November, is unsupported. Reliable accounts place the solution in late December, with one Polish official history naming 31 December.
Sources differ by one day on the French material's arrival—8 or 9 December—but both dates rule out a completed break on 30 November.
'Breaking Enigma' was a process rather than a permanent one-time solution: machine reconstruction, recovery of daily settings, and responses to later German changes were distinct achievements.