Pigpen Cipher: How to Read and Decode It

The pigpen cipher is a substitution cipher that swaps every letter for a fragment of a grid: the symbol for each letter is the shape of the cell it sits in. There is no shifting and no keyword. Learn the layout once and you can read it on sight, which is exactly why the Freemasons trusted it with a century of lodge records.

What is the pigpen cipher?

Write the alphabet into four frames: two tic-tac-toe grids and two crosses. A to I fill the first grid. J to R fill the second, and each of those cells carries a dot. S to V take the pockets of the first cross, W to Z the second, dotted again.

Your letter’s symbol is the walls around it. A sits in the top left corner of the first grid, so its mark is a corner: one wall below, one to the right. E sits dead centre, so its mark is a full box. N sits dead centre of the dotted grid, so its mark is the same box with a dot inside.

That is the whole machine. No arithmetic, no key phrase to remember, just geometry. The name comes from the picture: the grid pens the letters in like pigs.

You will also see it called the masonic cipher, the Freemason’s cipher, or the tic-tac-toe cipher. Same animal, same pen.

How do you decode a pigpen cipher?

Three steps, and the first one is the only real work.

1. Draw the key. Two grids, two crosses, dots on the second of each. Fill in A to Z in order.
2. Read each symbol’s shape. Count the walls and check for the dot. A full box is E; a full box with a dot is N.
3. Match the shape to its cell and write the letter down.

Take the four symbols above. The first is a box missing its left wall, with a dot: middle left of the dotted grid, M. The second and third are full boxes, no dot: E, twice. The last is a chevron opening left: the left pocket of the first cross, T. MEET.

Once the key is in your head you stop translating and start reading. Most people get there inside an hour.

Who used the pigpen cipher?

The Freemasons, most famously. Eighteenth-century lodges used it for correspondence and record keeping, enough that the system still carries their name.

The best surviving example is carved in stone. In Trinity Church cemetery in New York, the headstone of James Leeson, who died in 1794, carries a strip of pigpen symbols above his name. It kept its secret for the better part of a century before anyone published a reading. Decoded, it says REMEMBER DEATH.

The cipher never retired. It turns up in scout troops, escape rooms, and puzzle books, and it earns its place: it looks like sorcery and reads like the alphabet.

Is the pigpen cipher secure?

No, and it never was. Pigpen is a monoalphabetic substitution cipher: one symbol per letter, the same symbol every time. Dress the alphabet in geometry and the mathematics does not change. Count the symbols, and the most frequent one is almost certainly E. The one-symbol words are A or I. From there it unravels like any newspaper cryptogram, and the standard key is so well known that most of the time there is nothing to break at all.

That fragility is the lesson. A cipher that hides the shape of the letters, and not their pattern, falls to anyone with a pencil and patience. If you want the full toolkit, our guide to solving cryptograms walks the whole method: frequency counts, pattern words, and the footholds that open any substitution.