To transmit messages in critical situations when the value of information and Data is high, For example in the military, we need to encrypt messages. Different ways to encrypt messages have been invented, the subject of this project is encoding the message in the sender and decoding the message in the receiver using the Playfair method over the network platform. we used #c for programming this project.

1. Encrypted Message Transmitter On Public Network
Eastern Mediterranean University
Famagusta, North Cyprus
Instructor:
Assoc.Prof.Dr.Duygu Çelik Ertuğrul
Roshina Nikzad
Fall Semester 2019

2. Contents
• Definition
• Algorithms for encryption
• Diagram Cryptography
• Proposed System
• Existing System Limitation
• Solution
• Method and language for programming
• Functions
• Encryption Function
• Decryption Function
• Connection Function
• Softeware interface
• Environment of user interface
• Hardware Requirement
• Diagram(E-R ,Use Case , Sequence , Activity)
• Conclusion

3. Definition
The project entitled “Encrypted MessageTransmitter On Public Network” is a new messaging
technique used for the secure transfer of messages from one person to another.
This application comprises one main technique called cryptography.
This application first encrypts the message using cryptographic algorithm
Then sends encrypted data to the receiver he has the knowledge about the key so he tries to
decrypt it.
Only the intended receiver will know the key to resolve the encrypted message

4. Algorithms For Encryption
The
algorithms
that are used
for encryption
are
Ceaser
cipher
Play fair
Hill cipher
Vigeners
cipher

5. Definition of Play fair:
The Playfair Cipher was first described by CharlesWheatstone in 1854,
it was the first example of a Digraph Substitution Cipher.
It is named after Lord Playfair, who heavily promoted the use of the cipher to the military.
When it was first put to the British Foreign Office as a cipher, it was rejected due to its perceived
complexity.
However, it was later adopted as a military cipher due to it being reasonably fast to use, and it
requires no special equipment,
whilst also providing a stronger cipher than a “Monoalphabetic” Substitution Cipher.
It was used in the Second BoerWar, and bothWorldWar I andWorldWar II to different degrees.
It is no longer used by military forces since the advent of powerful computers, but in its day it
provided a relatively secure cipher which was easy to implement quite quickly.

6. Play fair Encryption:
In order to encrypt using the Playfair Cipher, we must first draw up a Polybius Square (but without
the need for the number headings).This is usually done using a keyword, and either combining "i"
and "j" or omitting "q" from the square.We must now split the plaintext up into digraphs (that is
pairs of letters). On each digraph we perform the following encryption steps:
• If the digraph consists of the same letter twice (or there is only one letter left by itself at the end
of the plaintext) then insert the letter "X" between the same letters (or at the end), and then
continue with the rest of the steps.
• If the two letters appear on the same row in the square, then replace each letter by the letter
immediately to the right of it in the square (cycling round to the left hand side if necessary).
• If the two letters appear in the same column in the square, then replace each letter by the letter
immediately below it in the square (cycling round to the top of the square if necessary).
• Otherwise, form the rectangle for which the two plaintext letters are two opposite corners.Then
replace each plaintext letter with the letter that forms the other corner of the rectangle that lies
on the same row as that plaintext letter (being careful to maintain the order).

7. Play fair Decryption:
Decryption is nearly identical to the encryption process, except
for rules 2 and 3 (in section 2) we must take the letters to the
left and above respectively. Also, we remove any extra "X" in
the decrypted text to reveal the final plaintext.
• We shall decipher the cipher text "UA ARBED EXAPO PR
QNX AXANR" which has been encrypted using the keyword
example. Firstly we must generate the Polybius Square
which we are using, as shown to the right. (Fig. 1)

8. Play fair Encryption:(continue)
• The next step is to split the cipher text into digraphs.There is no need
to add any "X" in the decryption process as these will be revealed as
we decrypt. (Fig. 2)
• Now we apply the rules as needed to each digraph in the cipher text.
We now combine all the digraphs together in Fig. 3.
• So we get the message "we wilxl mexet at thex exit". When we
remove the unnecessary "x"s we get a final plaintext of "we will meet
at the exit". Note that we cannot just remove all the "x"s as one is part
of the word "exit".

9. Play fair Samples:
As an example we shall encrypt the plaintext "hide the gold in the tree
stump" using the key phrase playfair example. Firstly we must generate
the Polybius Square that we are going to use.We do this by setting out
a 5x5 grid, and filling it with the alphabet, starting with the letters of
the key phrase, and ignoring any letters we already have in the square.
We are also going to combine "I" and "J" in the square. (Fig. 4)

10. Play fair Samples: (continue)
We must now split the plaintext into digraphs.At this point it is a good idea to apply Rule 1, and split up
any double letter digraphs by inserting an "x" between them.The first image below (Fig. 5) shows the
initial digraph split of the plaintext, and the second image (Fig. 6) displays how we split up the "ee" into
"ex" and "es". In this case, when we insert this extra "x", we no longer need to have one at the end of
the plaintext.
We can now take each of the cipher text digraphs that we produced and put them all together. It is
illustrated in Fig. 7.
We can now write out the cipher text as a long string "BMODZBXDNABEKUDMUIXMMOUVIF" or split
it into block of 5 "BMODZ BXDNA BEKUD MUIXM MOUVI F" or even give it the same layout as the
original "BMOD ZBX DNAB EK UDM UIXMMOUVIF".

11. Main Features of Play fair Cipher:
The Playfair Cipher was an ingenious new way to encipher messages. It was the first of its kind, and
opened up the world of cryptography to a whole new type of cipher: the “polygraphic” cipher.
Although not secure in terms of modern cryptography, it was a substantial improvement over
“Monoalphabetic” Substitution Ciphers, and significantly easier to use in the field than
“Polyalphabetic” Substitution Ciphers.
We can see in the decryption example above that there are three digraphs the same in the cipher
text, namely "XA", and we also see that all three decrypt to the same plaintext "ex".This shows us
that Digraph Substitution Ciphers are still susceptible to Frequency Analysis, but it has to be done on
pairs of letters.
Because it is done on pairs of letters, this Frequency Analysis is significantly harder to crack. Firstly,
for a “monoalphabetic” cipher we have 26 possible letters to check. For a general DigraphCipher we
have 26 x 26 = 676 possible pairings we need to check in our frequency analysis. In the instance of
the PlayfairCipher, we cannot encrypt to a double letter, so we remove the 26 possibilities of double
letters, giving us 650 possible digraphs we need to check. By hand this task in monumental, but with
the help of a computer, it can be done in a matter of seconds.
Another useful weakness of the Playfair Cipher that can be exploited in cryptanalysis is the fact that
the same pair of letters reversed will produce the same pair of letters reversed. For example, if the
plaintext "er" encrypts to "HY", then the plaintext "re" will encrypt "YH".This is useful in some words
in English such as "departed" which start and end with the same pair of letter in reverse.

12. Diagram Cryptography:

13. Proposed System
It hides the message and your privacy is safe..
You can write whatever you want and however you want (any theme any symbol for
the code) to keep your code a secret by using encryption
A third party can only access the text if he has the key
which is shared by the sender and the receiver
We use of Play fair algorithm
for encrption

14. Existing System Limitation
There is no option to try all the
algorithms together in one system.
There is no privilege for the
user to send the encrypted
message to other person as a
mail. There is no database
storage for the existing
system. Further
retrieval of the code is
not possible.
The system do not check for any
authentication. Any user can encrypt
and decrypt.

15. Solution
To be more professional,
it is better to divide tasks
into sections, for
example,
Use of the different types
of specialized software
for centralized
management (for user
accounts checks, access
control and
authentication work such
as audit system and etc )
we can be encrypt the
content of our message
to different destinations,
using a text messaging
system.

16. Method and language for programming
we have employed offline application to encrypt and decrypt messages
transmitted in communication network.
• There are several programming languages such as
• PHP,
• JAVA,
• C#,
• C++
In this project, the C# programming language is selected for implementation
playfair Encryption and Decryption since
C# language has many user-friendly and appropriate characteristics.

17. Functions:
Encryption Function :
Decryption Function :
Connection Function (Communication Network):

18. Encryption Function
Plaintext
as
“sInput”
Key
as
“sKey”
output
as
“sEncryptedText”
the encryption function is named “PlayfairEncryption” In the encryption is as follow function; we have two string input
“sInput” and “sKey” which are as plaintext and key respectively.And also we have one string output named as
“sEncryptedText” that will be our cipher text.

19. Decryption Function
In this part of project, Decryption function (“PlayfairDecryption”) of playfair cipher is provided
we have one output named “sOutput” which is our original plaintext (string value).
the algorithm need two strings (inputs or arguments) and key .

20. Connection Function (Communication Network):
The connection section of the project is one of the most important parts which is responsible
to send and receive encrypted messages.
The communication part of project is divided into three subsections included :
• IP Address Extraction
• Sending Function
• Receiving Function presented

21. Software Interfaces
• Language used: C#
• For the convenience of working with software
and being user friendly,We have used the
Windows form in its known form in theWindows
software.
• The software's user interface environment with
the necessary instructions and explanations helps
the user to properly use the software and does not
require training.

22. Environment of user interface:

23. Environment of user interface:
(encryption and decryption)

24. Environment of user interface:
(IP address , help and Exit)

25. Environment of user interface:(help menu)

26. Hardware Requirements
we need at least 2
computers that
should be
connected together
via Internet (WIFI or
port Ethernet
10/100 Mbps that
connected to LAN
,WAN or Campus
LAN Switches )
Processor: Pentium,
AMD or Higher
version
Operation system:
Windows 7, 8, 10,
Linux
RAM: 256 MB, 2 GB
recomme

27. Diagrams -ER

28. Use Case Diagram

29. Sequence Diagram

30. Activity Diagram

31. Conclusion
Security is one of the main
factor that is considered
everywhere This program will help in providing
Security,Intergrity,Confidentiality,and
Authentication while transferring a
message

32. The end
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