Pigpen cipher (Freemason)

The Pigpen cipher (sometimes called the masonic cipher) is a monoalphabetic substitution with geometric glyphs. Each letter is represented by the shape of its « pen » in a mentally drawn grid.

Its use by Freemasons from the 18th century onward to seal their archives gave it its popular name. Before them, Templars and Rosicrucians used variants of the same geometric idea.

Principle

The reference grid

Two superimposed structures are imagined:

3×3 grid (plain cells):          3×3 grid (dotted cells):
  A │ B │ C                        J │ K │ L
  ──┼───┼──                        ──┼───┼──
  D │ E │ F                        M │ N │ O
  ──┼───┼──                        ──┼───┼──
  G │ H │ I                        P │ Q │ R

Two-crossing X (plain):          Two-crossing X (dotted):
    S                                W
  T   U                            X   Y
    V                                Z

Each letter is placed into a cell — for letters J to R and W to Z, a dot is added inside to distinguish them from the former set.

A letter’s glyph

The glyph is simply the outline of its cell in the grid. For instance:

• A (top-left corner of the plain grid) → an inverted L (⌐).
• E (center) → an empty square (□).
• I (bottom-right corner) → an L shape (¬).
• N (center of the dotted grid) → a dotted square (⊡).

The sender writes the glyph sequence; the recipient reads it by finding each outline’s position in the grid.

Variants

• Templar cipher — same principles, a cross-shaped grid.
• Rosicrucian cipher — four-branch grid, esoteric variant.
• Tic-tac-toe cipher — limited to the first 9 letters (no dotted variant).
• Double-grid masonic cipher — enriched with two full grids (up to 52 possible cells).

Weaknesses

• No key: if the attacker knows the method (and Pigpen is in every crypto book today), decryption is instant.
• It’s a disguised monoalphabetic substitution: glyph distribution betrays it under frequency analysis, like any simple substitute.
• The glyph geometry is rigid: the dotted variant is visually detectable.

Pigpen has no modern cryptographic value. Its appeal is aesthetic and cultural.

The 26 glyphs

The full table of masonic glyphs as found in most modern sources.

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z