Cryptography - Basic

HYBRID PLAYFAIR - CAESAR
SYMMETRIC KEY CRYPTOGRAPHY
HYBRID PLAYFAIR - CAESAR SYMMETRIC KEY
CRYPTOGRAPHY. 1Tuesday, April 17, 2018

PRESENTED BY
PAPER – VII-B
AKASH DEY
SOUVIK SARKAR
ROLL NO- 318111103969 ROLL NO- 318111103974
RAJESH PAL
ROLL NO- 318111103966
Under the guidance of
TUMPA CHAKRABORTY
Dept. of Computer ScienceHYBRID PLAYFAIR - CAESAR SYMMETRIC KEY 2Tuesday, April 17, 2018

CONTENTS
 INTRODUCTION (4-9)
 PLAYFAIR CIPHER (10-16)
 CAESAR CIPHER (17-22)
 COMBINATION OF PLAYFAIR & CAESAR CIPHER (23-28)
 RESULT (29–32)
 ADVANTAGES (33)
 FUTURE SCOPE (34)
 RESOURCES (35)
 CONCLUSION (36)
3
CRYPTOGRAPHY Tuesday, April 17, 2018

WHAT IS CRYPTOGRAPHY
Cryptography
* Cryptography is the science of using mathematics to encrypt
and decrypt data.
* Cryptography enables us to store sensitive information or
transmit it across secure networks so that it can not be read by
anyone except the intended recipient.
Cryptanalysis
* The study of methods for obtaining the meaning of encrypted
information without accessing the secret information.
4

CATEGORIES OF CRYPTOGRAPHY
5

SECURITY SERVICES OF CRYPTOGRAPHY
6

SECURITY ATTACKS
Passive Attacks
* Obtain message contents
* Monitoring traffic flows
Active Attacks
* Masquerade of one entity as some other
* Replay previous messages
* Modify messages in transmit
* Add, delete messages
* Denial of service
7

BASIC TERMS
Plain Text: The original message
Cipher Text: The coded message
Encryption: The method of converting plain text to cipher text.
Decryption: The method of re-converting cipher text to plain text.
Key: Information used in cipher known only to sender/receiver.
Cryptographers: People who do cryptography.
Cryptology: The field of both cryptography and cryptanalysis.
8

ENCRYPTION & DECRYPTION
PROCESS
9

WHAT IS CIPHER
Cipher is an algorithm for transforming original message to coded
message.
Example of cipher:
* Caesar Cipher
* Playfair Cipher
* Shift Cipher
* Additive Cipher
* Multiplicative Cipher
* Affine(Additive + Multiplicative) Cipher
10

PLAYFAIR CIPHER
 Playfair cipher was invented by Wheatstone on 26 March 1854,but it
was promoted by Lord Playfair.
 The Playfair cipher is a dual alphabetic substitution cipher.
 The cipher uses a key consisting of a string of unique characters.
11

PLAYFAIR CIPHER
The Playfair cipher operates on pair of letters. The key is a 5x5 matrix
consisting of every letter except ‘J’.
Before encrypting, the plain text must be transformed:
* Replace all J’s with I’s
* Write the plain text in pair of letters
* Identical letters which occur in a pair must be separated by an ‘X’
* If the number of letters is odd, add a ‘Z’ to the end.
* Replace the spaces with ‘Z’
12

PLAYFAIR KEY MATRIX
 A 5x5 matrix of letters based on a keyword.
 Fill in letters of keyword (no duplicate letters).
 Fill the rest of the matrix with remaining letters
 Eg. Using the keyword KEYWORD
13
CRYPTOGRAPHY
K E Y W O
R D A B C
F G H I L
M N P Q S
T U V X Z
Tuesday, April 17, 2018

RULES FOR
Letters appear on the same row:
Replace them with the letters to their immediate right respectively
(left for decryption)
Letters appear on the same column:
Replace them with the letters immediately below respectively
(top for decryption)
Neither on the same row nor on column:
Replace them with the letters on the same row respectively but at
the other pair of corners of the rectangle defined by the original pair.
14HYBRID PLAYFAIR - CAESAR SYMMETRIC KEY
CRYPTOGRAPHY
K E Y W O
R D A B C
F G H I L
M N P Q S
T U V X Z

ENCRYPTION PROCESS
Plain text: SECRET MESSAGE
After space remove: SECRETZMESSAGE
Separate into pair: SE CR ET ZM ES SA GE
Encryption Process: SE=NO CR=RD ET=KU ZM=TS ES=ON SA=PC
GE=ND
Cipher Text: NORDKUTSONPCND
CRYPTOGRAPHY

DECRYPTION PROCESS
Cipher Text: NORDKUTSONPCND
Decryption Process: NO=SE RD=CR KU=ET TS=ZM ON=ES
PC=SA ND=GE
Plain Text: SECRETMESSAGE
After replacing ‘Z’ with space: SECRET MESSAGE
CRYPTOGRAPHY 16Tuesday, April 17, 2018

CAESAR CIPHER
 The Caesar Cipher is earliest known Substitution cipher.
 It was invented by Julius Caesar.
 Each letter is replaced with a letter at certain distance away
from that letter.
17

WHAT IS CAESAR CIPHER
 Caesar Cipher is used to encrypt messages using a very
simple algorithm, which could be easily decrypted if the key is
known.
Each letter of the alphabet is replaced with a letter at certain
distance away from that letter. At the end, wrap back around to
the beginning.
 Example with a shift of 3 :
18
CRYPTOGRAPHY

PROCESS OF
When we use a Caesar Cipher , we assign each letter to an index starting
from 0.
 Rules for encryption:
c=(p+k) mod 26
 Rules for decryption:
p=(c-k) mod 26
This will give us the index of the encrypted letter!
19

ENCODING PROCESS
Let’s have a 5 letter alphabet with only the letters A-E
First, we assign each letter an index, starting from 0.
We then have to choose a key. For this example, we’ll use 2.
Let’s try encoding the word CADE using the formula for the previous slide.
The index of the letter D is 3. The key is 2. The modulus is 5, since the
alphabet has 5 letters.
Let’s use the algorithm: (3+2) = 5. 5 mod 5 = 0. The index of A is 0, so D
would become the letter A.
Using algorithm on each letter, we can encode the word to:ECAB
20HYBRID PLAYFAIR - CAESAR SYMMETRIC KEY Tuesday, April 17, 2018

HOW DOES MOD WORK
The mod is used for wrapping back around once we reach at the end
of the alphabet.
When converting the letter D using the key 2, we first add 3 + 2,
which gives us 5. As we can see, the index 5 is beyond the scope of
this alphabet. When we do 5 mod 5, we get the remainder of 0, which
is how much we need to go back and count from the beginning of the
alphabet.
21
CRYPTOGRAPHY

DECODING PROCESS
To decode, we do the following:
(cipher letter index – key) mod (total number of letters)
Here the key is 2 and the encoded text is ECAB
The index of the letter E is 4. The modulus is 5, since the alphabet has 5
letters.
Let’s use the algorithm: (4-2) = 2. 2 mod 5 =2 . The index of C is 2, so E
would become the letter C.
Using algorithm on each letter, we can decode the word to:CADE
22
CRYPTOGRAPHY

COMBINATION OF
PLAYFAIR & CAESAR CIPHER
This is a combine method of PLAYFAIR and CAESAR Ciphers.
We combine these two methods to encode and decode a
message to provide better and stronger security.
23
CRYPTOGRAPHY

PROCESS FOR ENCRYPTION & DECRYPTION
At first the plain text is encoded using PLAYFAIR Cipher.
Then the encoded text is again encoded using CAESAR Cipher.
Then the caesar text is decoded by CAESAR Cipher.
Finally the decoded text is again decoded by PLAYFAIR Cipher to
get back the original text.
CRYPTOGRAPHY

PROCESS OF ENCODING
CAESAR ENCODING:
The plain text (playfair encrypted text) is: NORDKUTSONPCND
The key is : 3
The caesar encrypted text is :QRUGNXWVRQSFQG
25

PROCESS OF DECODING
CAESAR DECRYPTION:
The text for decryption is: QRUGNXWVRQSFQG
The key is: 3
The caesar decrypted text is: NORDKUTSONPCND
26

PROCESS OF DECODING
PLAYFAIR DECRYPTION :
The text for decryption is: NORDKUTSONPCND
The key matrix is:
The playfair decrypted text is: SECRETZMESSAGE
The plain text is: SECRET MESSAGE
CRYPTOGRAPHY
K E Y W O
R D A B C
F G H I L
M N P Q S
T U V X Z

RESULT
SET 1:
CRYPTOGRAPHY
28Tuesday, April 17, 2018

RESULT
SET 1:
CRYPTOGRAPHY

RESULT
SET 2:
CRYPTOGRAPHY

ADVANTAGES
OF THIS METHOD
 A brute force attack on a playfair cipher is very difficult
 The encipherment hides the single letter frequency of the characters
 A strong large key is very difficult to crack
 The combination of these two methods provide better and stronger
security
to the messages
32

FUTURE SCOPE
Though the brute force attack on this cipher is very difficult, the other
attacks can crack the cipher easily
One method to avoid this problem in future is to use a large size of
matrix instead of 5X5 matrix, consisting of only 25 characters
Another method is to use a large and strong key to provide stronger
security

RESOURCES
Regarding this project, we gather basic ideas and information from
various books, pdfs and Wikipedia. This resources are following:
Cryptography and Network Security - Behrouz A. Forouzan
Cryptography and Network Security - William Stallings
Internet Resources – i) www.stackexchange.com
ii) www.youtube.com
iii) www.techopedia.com

CONCLUSION
Cryptography is the study and practice of hiding information and
private messages.
It can be done by using any of these techniques discussed previous.
By using the encryption techniques a fair unit of confidentiality,
authentication,
integrity, access control and availability of data is maintained.
35

THANK YOU
CRYPTOGRAPHY

Cryptography - Basic

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