🔐 Playfair Cipher

Playfair Cipher — 5×5 Digraphic Substitution Cipher (I/J merged)

📊 5×5 Key Matrix

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

I/J are treated as the same cell (I/J merged)

Three substitution rules:

  1. Same row: shift right one (wrap around)
  2. Same column: shift down one (wrap around)
  3. Different row and column: swap corners