Cabinet Noir
>Cryptoanalysis / 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.
Type
substitution cipher
Breaking it
trivial to break
Era
Classical Greece, 2nd century BC
Name
Polybius' torch-signalling scheme, later the basis of tap code and fractionation
Modes
encrypt · decrypt · cryptoanalysis
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Tool
Cryptoanalysis
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Practice
Ciphertext to break
Hints
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Custom
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Crib panel
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1. Square
Each pair of digits names a cell of the unknown square: assign letters by frequency, pairs run 11–55.
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11
·
0
12
·
0
13
·
0
14
·
0
15
·
0
21
·
0
22
·
0
23
·
0
24
·
0
25
·
0
31
·
0
32
·
0
33
·
0
34
·
0
35
·
0
41
·
0
42
·
0
43
·
0
44
·
0
45
·
0
51
·
0
52
·
0
53
·
0
54
·
0
55
·
0
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
Clear
Probable word (crib):
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Created by Denys Grybov in 2021
v.0.4.0 // released on 25.10.2026