ENCRYPTION METHOD 5- VIGENERE CIPHER

 

* After most monoalphabetic ciphers were broken with the frequency analysis method, the search for a safer method has begun.

* French cryptographer Blaise de Veginere developed Veginere cipher  in 1586.

* This method is a derivative of the Caesar technique. It's differenses from Caesar is that it is shifted according to an unstable periodic number sequence. Therefore, repeating letters correspond to another letter each time. In other words, these cipher cannot be decrypted using the frequency method.

* Curriculum topics related to Vigenere Cipher/ Aim: Sequences, Matrix, Permutation

HOW DOES IT WORK?

*   A square matrix board of type nxn is used for the alphabet with n letters.The standart table is as follows.

Vigenere

PLAİNTEXT

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

KEY TEXT

A

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

B

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

C

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

B

D

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

E

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

F

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

G

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

H

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

I

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

J

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

K

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

L

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

M

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

N

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

O

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

P

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

Q

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

R

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

S

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

T

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

U

U

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

V

V

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

W

W

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

X

X

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

Y

Y

Z

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Z

Z

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

Vigenere Board (Tabula Recta)

There is a common key text that the sender and recipient know. From the first row (first horizontal) find the letters of the plain text, from the first column (first vertical) find the letters of the key text, and then combined. Intersection points create the encrypted text.

 

EXAMPLE

ENCRYPTION

If you want to encrypt " HELP ME QUICKLY PLEASE" plaitext with the "NİCE DAY"

Plaintext

H

E

L

P

M

E

Q

U

I

C

K

L

Y

P

L

E

A

S

E

Keytext

N

I

C

E

D

A

Y

H

E

L

P

M

E

Q

U

I

C

K

L

Ciphertext

U

M

N

T

P

E

O

B

M

N

Z

X

C

F

F

M

C

C

P

You find "UMNTPEOBMNZXCFFMCCP" ciphertext.

Method:Vigenere, Plaintext: HELP ME QUICKLY PLEASE, Keytext= NICE DAY, Ciphertext= UMNTPEOBMNZXCFFMCCP

 

DECRYPTION

Decryption can make simularly with Vigenere board. If you want decrypt ciphertext "UMNTPEOBMNZXCFFMCCP"  with keytext "NİCE DAY"

Ciphertext

U

M

N

T

P

E

O

B

M

N

Z

X

C

F

F

M

C

C

P

Keytext

N

I

C

E

D

A

Y

H

E

L

P

M

E

Q

U

I

C

K

L

Plaintext

H

E

L

P

M

E

Q

U

I

C

K

L

Y

P

L

E

A

S

E

You find Plaintext: HELP ME QUICKLY PLEASE