Cabinet Noir>Decrypt / Polybius square cipher

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Every letter of the message becomes the row and column numbers of its cell in a 5×5 grid.
Typesubstitution cipher
Breaking ittrivial to break
EraClassical Greece, 2nd century BC
NamePolybius' torch-signalling scheme, later the basis of tap code and fractionation
Modesencrypt · decrypt
Message

Square key

1
2
3
4
5
1
A
B
C
D
E
2
F
G
H
I
K
3
L
M
N
O
P
4
Q
R
S
T
U
5
V
W
X
Y
Z

The square — the highlighted cell (with its row and column) is the latest letter of the output.

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Created by Denys Grybov in 2021

v.0.4.0 // released on 25.10.2026