Where this game comes from
The cipher wheel
The Roman writer Suetonius says Julius Caesar wrote private letters with each letter moved three places along the alphabet. Around 1467 the Italian architect Leon Battista Alberti described a cipher disk — two rings of letters, the inner one turning — in a short book, De componendis cifris.
One thing to hold: Two discs of card or metal, one inside the other, pinned through the middle.
Why it matters: Alberti turned his disk part-way through a message, so one letter could be written many different ways. That idea shaped secret writing for the next 400 years.
What we don’t know: None of Caesar’s own coded letters survive; we know of his shift only because Suetonius wrote it down, about 150 years later.
Counting letters (frequency analysis)
The scholar al-Kindi, working in Baghdad in the 800s, wrote the oldest known description of breaking a code by counting how often each letter turns up, in a book now called A Manuscript on Deciphering Cryptographic Messages.
One thing to hold: A tally: one mark for every time a letter appears.
Why it matters: A code that swaps letters hides each letter but not how often it is used. In English, E is the commonest, so the commonest letter in a long coded message is a good first guess for E.
What we don’t know: His book was lost for a long time; a copy was found in 1987 in the Süleymaniye Library in Istanbul. Exactly when in the 800s he wrote it is not known.
Morse code
Samuel Morse and Alfred Vail built a telegraph code of short and long signals in the late 1830s. The international code used today, which changes many of the American letters, was agreed at a telegraph conference in Paris in 1865.
One thing to hold: A brass telegraph key: press briefly for a dot, hold for a dash.
Why it matters: The same pattern can travel as clicks, tones, flashes of light or taps on a pipe. The message is the pattern, not the sound — so it can be seen as well as heard.
What we don’t know: People still argue over how much of the code was Vail’s work rather than Morse’s.
Dates:
- 1844 Morse sends “What hath God wrought” from Washington to Baltimore.
- 1865 A conference in Paris agrees an international version of the code.
The wheel of disks
In the 1790s Thomas Jefferson described a cipher made of 36 disks on one rod, each disk with the alphabet around its edge in a different order. You turn the disks until your message reads along one row, then copy down the letters of any other row.
One thing to hold: A stack of lettered disks threaded on a rod, like coins on a stick.
Why it matters: The key is the ORDER of the disks on the rod. A friend with the same disks in the same order lines up the code on one row and finds the message on another. In 1891 Etienne Bazeries, a French officer, invented a similar device of his own, with 20 disks.
What we don’t know: Exactly when in the 1790s Jefferson invented his wheel is not clear.
Dates:
- 1790s Jefferson describes a wheel of 36 disks.
- 1891 Bazeries invents a 20-disk version on his own.
- 1922 The US Army starts using the M-94, 25 aluminium disks on a spindle, until 1942.