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Table 14 - 1. Encrypting each letter with the multiplicative cipher with key 7.
Plaintext
SymbolNumber Encryption with
Key 7Ciphertext
Symbol
A 0 ( 0 * 7) % 26 = 0 A
B 1 (1 * 7) % 26 = 7 H
C 2 (2 * 7) % 26 = 14 O
D 3 (3 * 7) % 26 = 21 V
E 4 (4 * 7) % 26 = 2 C
F 5 (5 * 7) % 26 = 9 J
G 6 (6 * 7) % 26 = 16 Q
H 7 (7 * 7) % 26 = 23 X
I 8 (8 * 7) % 26 = 4 E
J 9 (9 * 7) % 26 = 11 L
K 10 (10 * 7) % 26 = 18 S
L 11 (11 * 7) % 26 = 25 Y
M 12 (12 * 7) % 26 = 6 G
N 13 (13 * 7) % 26 = 13 N
O 14 (14 * 7) % 26 = 20 U
P 15 (15 * 7) % 26 = 1 B
Q 16 (16 * 7) % 26 = 8 I
R 17 (17 * 7) % 26 = 15 P
S 18 (18 * 7) % 26 = 22 W
T 19 (19 * 7) % 26 = 3 D
U 20 (20 * 7) % 26 = 10 K
V 21 (21 * 7) % 26 = 17 R
W 22 (22 * 7) % 26 = 24 Y
X 23 (23 * 7) % 26 = 5 F
Y 24 (24 * 7) % 26 = 12 M
Z 25 (25 * 7) % 26 = 19 TYou will end up with this mapping for the key 7: to encrypt you replace the top letter with the
letter under it, and vice versa to decrypt:
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
↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕ ↕
A H O V C J Q X E L S Y G N U B I P W D K R Y F M T
It wouldn’t take long for an attacker to brute-force through the first 7 keys. But the good thing
about the multiplicative cipher is that it can work with very large keys, like 8 , 953 , 851 (which has
the letters of the alphabet map to the letters AXUROLIFCZWTQNKHEBYVSPMJGD). It would
take quite some time for a computer to brute-force through nearly nine million keys.