McCormick Notes

McCormick's family stated he had used 'his own coded writing' since boyhood and that no one had ever read it back. The notes contain about 30 lines of mixed letters and numbers, organised into apparent paragraphs with parenthetical asides. The FBI CRRU — the same unit that worked the Unabomber and Zodiac materials — concluded that the notes are 'almost certainly genuine cipher' rather than random scribbling, but that the encryption may be entirely private: a system of personal abbreviations with no algorithmic structure that an outsider could reverse-engineer.

Statistically the notes show real linguistic structure: repeated bigrams, periodic capitalisation, paragraph breaks. They do not match any standard cipher (Vigenère, Playfair, Hill, columnar transposition, Polybius). The leading hypothesis is that they are an idiolectic cipher — a system invented and used by a single person, where the 'key' is not a string but a lifetime of personal associations. Such ciphers are functionally one-time pads from the cryptanalyst's point of view: even with all the ciphertext in the world, recovering the plaintext requires recovering the author's mental model.

The McCormick notes are a leading example used in arguments for crowdsourced cryptanalysis: the FBI explicitly opened them to the public hoping that someone — perhaps a relative, perhaps a stranger with the right insight — would recognise a personal pattern. They are also a sobering counterpoint to fictional 'genius detective' decipherments: a real intelligence agency, with full access to context and a 12-year head start, could not crack a barely-literate man's personal notes.