Hexahue

Hexahue is a monoalphabetic substitution cipher that emerged in the 2000s within the escape-room and recreational cryptography community. Its hallmark: each letter is represented not by an abstract glyph but by a 2×3 mosaic of six fixed colours, and only the spatial arrangement of those colours changes from one letter to the next.

Principle

The six colours

🟥 Red       🟨 Yellow    🟩 Green
🟦 Blue      🟪 Magenta   🬨 Cyan

These six hues stay identical for every letter. What distinguishes one letter from another is purely the position of each colour within the 2×3 grid.

Combinatorics

With 6 colours placed in 6 cells, you have 6! = 720 possible arrangements — far more than the 26 letters of the alphabet. The Hexahue table uses only 26 of those 720, chosen to be visually distinctive:

A : R Y G        B : Y R G        C : G Y R
    B M C            B M C            B M C
…

(Read: top row, bottom row, left to right.)

A Hexahue letter fits in a square tile of about 1×1 cm, readable from 2–3 metres away. Beyond that, the eye can no longer distinguish the colour layout — hence the typical use in escape rooms at short range.

Cryptographic characteristics

Strengths

• Unique aesthetic: a Hexahue message looks like a mosaic or a strip of pixel art, not classical ciphertext.
• Fast reading once the table is memorised — a trained player decodes 1–2 words per second.
• Partially colourblind-friendly: with six hues spread evenly across the colour wheel (R, Y, G, C, B, M), most colourblind individuals can still distinguish the arrangements.

Weaknesses

• Standard monoalphabetic substitution: the arrangement frequencies follow the source language (E is most common in English/French).
• Solvable in minutes by anyone with the public table.
• Production cost is non-negligible: colour printing or physical cards required, whereas a glyph-based mono substitution can be hand-written.

Variants

• Black-and-white Hexahue — replaces colours with six different hatching patterns. Survives photocopying.
• Octohue — extension to 8 colours and a 2×4 grid; covers 26 letters + 10 digits + punctuation.
• Trihue — reduced to 3 colours and a 1×3 grid, only covers 6 letters; used for very short messages.

Uses

Hexahue has emerged as the de-facto standard in French escape rooms during the 2010s–2020s:

• Visual hint embedded in décor (paintings, posters, coloured lighting).
• Notebook: players receive a paper table they consult during the game.
• Videos / screens: decodable in real time on dynamic displays.
• Board games: integrated into several detective games (Mysterium, Detective Club).

It also turns up in digital treasure hunts (geocaching) as an intermediate code to signal coordinates.

Why it’s pedagogically interesting

Hexahue introduces a rare dimension in classical cryptography: the purely visual dimension. The player learns that the signifier of a substitution does not have to be a character — it can be:

• A colour (Hexahue).
• A human posture (Dancing Men).
• A geometric drawing (Pig Pen).
• A sound (Tap code, DTMF).
• A movement (sign language, semaphore).

It is a useful bridge to modern multimodal codes (2D barcodes, QR codes, ArUco markers).

The 26 hexagons

The full alphabet as coloured hexagons. Each letter, digit or punctuation mark has its own glyph — Hexahue is one of the few ciphers where every cleartext character (not only letters) gets a dedicated symbol.

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

Digits and punctuation

0

1

2

3

4

5

6

7

8

9

.

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