Saramsha

No. 006  ·  22 September 2026

The Shape of a Secret

Every message carries a fingerprint: how often each letter turns up. A cipher's real job is to rub it out. Three machines take the same message, two thousand years apart.

Shift

3

Turn the inner ring. Every letter moves the same distance along the alphabet: A becomes D. Suetonius says this is exactly what Caesar did, with a shift of three.

Message

Ciphertext

The tape

message key cipher every e

About this piece

Rubbing out the fingerprint

Count the letters in any page of English and you get the same lopsided shape: E towers over everything, T A O I N S H R crowd behind it, and J Q X Z barely appear. The shape is so stable that it survives translation into a cipher — which is the oldest hole in cryptography, and the one every machine on this page is trying to plug.

Around the year 850 in Baghdad, al-Kindi wrote it down: to read an enciphered message, count its symbols, compare the counts with a long piece of ordinary writing in the same language, and match the commonest to the commonest. His manuscript sat unread in an Ottoman archive in Istanbul until 1987. Europe had to work the same trick out for itself, six hundred years late.

Caesar's cipher cannot survive that for a second. Shifting every letter by the same amount slides the whole fingerprint sideways without changing its shape, so the tall bar is still E wearing a different name. There are only 25 keys; the desk tries all of them and scores each against English with a χ² test, and on any decent length of text the right one wins by a mile.

The cipher named after Blaise de Vigenère was actually published by Giovan Battista Bellaso in 1553, and it hides the fingerprint properly: with a keyword of nine letters, E is enciphered nine different ways and the bars flatten out. It was called unbreakable for three hundred years. Then Charles Babbage broke it around 1854 and told nobody, and Friedrich Kasiski published the method in 1863. The flaw is the repeat: take every ninth letter and you are back to a single Caesar shift.

That is what the gauge measures. William Friedman's index of coincidence, from 1922, is the chance that two letters picked at random from the text are the same one: about 0.067 for English, 0.038 for letters drawn from a hat. Caesar leaves it untouched — the whole tell. Vigenère pushes it down. Try key lengths one by one and the true length is the one where it springs back up; the desk does this, then solves each column as a separate Caesar.

Enigma answers with a key that never repeats. Three rotors out of five, chosen and ordered and set, step like an odometer between every keystroke, so the wiring is different for every letter; the plugboard swaps ten pairs on the way in and back out again. The index of coincidence lands on noise and stays there. Marian Rejewski of the Polish Cipher Bureau had nevertheless reconstructed the machine's internal wiring by 1932, from permutation theory and operator sloppiness, and handed the work to Britain and France five weeks before the invasion.

The last weakness is in the panel on the right. The reflector that makes Enigma so convenient — the same setting encodes and decodes, as the run it back through button shows — also guarantees that no letter is ever enciphered as itself. That single negative fact lets you slide a guessed word along a message and throw away every position where a letter collides. Every crib the bombes chewed through started there.

Everything runs in your browser and nothing is sent anywhere. The Enigma is a faithful three-rotor Wehrmacht machine, rotors I–V with reflector B, including the middle rotor's double step; ring settings are fixed at A. Type 1 2 3 to change rooms.