ENCRYPTION METHOD 1-CAESAR CIPHER

 

CAESAR CIPHER METHOD

* In the period of the Roman Empire(100BC—44BC), famous leader Julius Caesar communicated with his forces with this encryption method. Important  military messages were hidden in this way for many years and changed the course of wars. 

* Although it is easy to break this cipher in today's conditions, it has  provided secure communication for a long time when it was used.

* Caesar used the encryption tool called Caesar disk to make these shifts practically. 

* Curriculum topics related to Caesar Cipher/ Aim: Factorial, probability    (permutation), modular arithmetic...

HOW DOES IT WORKS?

* Caesar cipher is the technique of creating encrypted text by shifting the letters of the alphabet . Therefore, it is also called shift cipher.

* This cipher works by shifting the the letters in the alphabet by "k" unit . "k" is the  key.

EXAMPLE:

ENCRYPTION

*If you want to encrypt “ETWINNING” word with key “3”.

First of all, you need to replace each letter of the alphabet with the 3rd letter after it

You can see below cipher alphabet for key 3.

PlainAlphabet

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

CipherAlphabet

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

 

Then if you replace each letter with its equivalent in the table, you will get "HWZLQQLQJ" encrypted text

Method: Caesar, Key: 3, Plaintext: ETWINNING, Ciphertext:HWZLQQLQJ 

 

DECRYPTION

If you want to decrypt“RDXYJWNTZX”word for key 5 

First of all, you need to replace each letter of the alphabet with the 5rd letter before it.

CipherAlphabet

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

PlainAlphabet

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

 

Then if you replace each letter with it's equivalent in the table, you will get plain text “MYSTERIOUS”

Method:Caesar,Key:5,Ciphertext: RDXYJWNTZX, Plaintext: MYSTERIOUS

MIXED CAESAR CIPHER METHOD

The difference from Caesar method is that the key is not a number, but a word. When creating the encrypted alphabet, the key is written first and then the remaining letters of the alphabet are used.

EXAMPLE: 

ENCRYPTION

If you want to encrypt “PROJECT” word with key “FRUIT”.

Firstly you’ll write the key word. After than you’ll write the other letters in the alphabet( except the letters of the keyword).Via this way you’ll mixed the cipher alphabet.You can see below cipher alphabet.

PlainAlphabet

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

CipherAlphabet

F

R

U

I

T

V

W

X

Y

Z

A

B

C

D

E

G

H

J

K

L

M

N

O

P

Q

S

 

Then if you replace each letter with it's equivalent in the table, you will get cipher text “GJEZTUL”

Method:MixedCaesar,Key:FRUIT,Plaintext:PROJECT,Ciphertext: GJEZTUL

 

DECRYPTION

If we want to decrypt “ZCVYC”word for key “VEGETABLE”

Similarly you can create table below.

PlainAlphabet

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

CipherAlphabet

V

E

G

T

A

B

L

M

N

O

P

Q

R

S

U

W

X

Y

Z

C

D

F

H

I

J

K

 

Then if you replace each letter with it's equivalent in the table, you will get  plain text“START”

Method:Mixed Caesar,Key:VEGETABLE,Ciphertxt:ZCVYC,Plaintext:START