Vigenère Cipher, Simple and Powerful Symmetric Encryption

Vigenère cipher is a method of encrypting alphabetic text by using a series of different Caesar ciphers based on the letters of a keyword. It is a simple form of polyalphabetic substitution.

Below we explain Vigenère Cipher which is a Symmetric cryptosystem. We have a table including 26 characters of alphabet each associated with a number from 0 to 25.

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
0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25

Message (Plain-Text) we are trying to encrypt is: “Network Security”

Encryption Key that we will use for this is: “ITC”

First, we find the Numbers for the key work on the table:

ITC = 8, 19, 2



Now we need to repeat the keyword to be the same size as message text. Once that’s done, next step is to shift each character to the right based on associated key number. For example, if the character is “N”, and associated Key character is “I”, then we shift “N” on the above table, 8 cells to the right and that makes it “V”.

Note: If we reach end of the table, we go back and start from the left side.



We will do this for all message text characters in the below table:

MC

N

E

T

W

O

R

K

S

E

C

U

R

I

T

Y

K

I

T

C

I

T

C

I

T

C

I

T

C

I

T

C

KN

8

19

2

8

19

2

8

19

2

8

19

2

8

19

2

CC

V

X

V

D

G

T

S

K

G

K

M

T

Q

L

A

MC: Message Character
K: Key
KN: Key Number
CC: Cipher Character

So, as it can be seen on the above table, the output Cipher-Text would be: “VXVDGTS KGKMTQLA”