Codes (Codes And Ciphers)

Affine Cipher

AFFINE CIPHER
Type: Substitution
(Note: it's formula for encryption is f(x)=(ax+b)mod n, and for decryption is f(y)=a^-1(y-b)mod n, where "a" should be coprime of "n", "x" or "y" corresponds on the position of the letter in the alphabet (see rotation code), and "b" is any value of input, and mod n is the limit of rotation)
Example: (encryption)
Plaintext: AFFINE
a=5, b=8, n=26
F(x)=(ax+b)mod26
A=0, F(0)=(5(0)+8)mod26=8
F=5, F(5)=(5(5)+8)mod26=3­­3
F=5, F(5)=(5(5)+8)mod26=3­­3
I =8, F(8)=(5(8)+8)mod26=4­­8
N=13, F(13)=(5(13)+8)mod26­­=73
E=4, F(4)=(5(4)+8)mod26=2­­8
A=08=I
F=33=H
F=33=H
I =48=W
N=73=V
E=28=C

Ciphertext: IHHWVC
Example: (decryption)
Ciphertext: IHHWVC
a=5, b=8, n=26
F(y)=a^-1(y-b)mod n
I =08, f(8)=5^-1(8-8)mod26=­­0
H=33, f(33)=5^-1(33-8)mod2­­6=5
H=33, f(33)=5^-1(33-8)mod2­­6=5
W=48, f(48)=5^-1(48-8)mod2­­6=8
V=73, f(73)=5^-1(73-8)mod2­­6=13
C=28, f(28)=5^-1(28-8)mod2­­6=4
I =0=A
H=5=F
H=5=F
W=8=I
V=13=N
C=5=E
Plaintext: AFFINE