Faculty of Computer Studies T215B Communication and Information Technologies – Part B Tutor Marked Assignment Cut-Off Date: TBC Total Marks: 80 Contents Part A: Cryptography …..………………………………………………………... 2 Part B: Two Square Cipher ……………

Faculty of Computer Studies
T215B
Communication and Information Technologies – Part B
Tutor Marked Assignment

Cut-Off Date: TBC Total Marks: 80

Contents
Part A: Cryptography …..………………………………………………………... 2
Part B: Two Square Cipher ……………………………………………..……… 2
Part C: Two Square Cipher Algorithm - Encryption ………….……..……… 3

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Part A: Cryptography (20 marks)
During the study of T215B course you have studied several algorithms of encryption. This part focuses on the basics encryption; use your own words to answer the following questions.
1. Encryption: (6 Marks)
 What is encryption?
 What is it used for?
 What are its advantages and disadvantages?

2. Symmetric key cryptography: (6 Marks)
 What is it?
 What are its applications?
 What are its advantages and disadvantages?

3. Asymmetric key cryptography: (6 Marks)
 What is asymmetric key cryptography and why it is usually called public key cryptography?
 What are its applications?
 What are its advantages and disadvantages?

Note: you need to provide reliable references to your answer

Part B: Two Square Cipher (30 marks)
A two-square cipher [1] is a modification of the Playfair cipher and provides slightly better security of communication by encrypting the plaintext based on digraph principle which you studied in the Cease Cipher with Digraph.
This task aims to assist you in learning more about the two-square cipher. Your answer for this task should be as report which starting with introduction and ending with conclusion, the report should be within 1000 – 1200 words (long report, you should adhere to word count), the report must have proper citations and references. The body of your report should answer the following questions:
1. Define two-square cipher? (6 marks)
2. List the two varieties of the two-square cipher? (2 marks)
3. Describe the two-square encryption steps? (10 marks)
4. Describe the two-square cipher decryption steps? (4 marks)
5. The security of the two-square cipher cryptosystem has several advantages and disadvantages, list two advantages and two disadvantages? (4 marks)
Your answer should be within the range of (1000 – 1200) words count. (2 marks)
You should provide at least one figure or table. (2 marks)

Part C: Two Square Cipher Algorithm - Encryption (30 marks)
This part is a practical one. Based on the previous study of the two square cipher algorithm in Part B, you have to test the algorithm in order to obtain the correct ciphertext by following the next steps.
1. The first step of encryption is preparing the plaintext. The plaintext is your first, second and sure names, then select the first 12 letters of the name. (6 marks)
2. Use the two keywords “retreats” and “enemies” to generate two mixed squares one on top of the other of size 5x5, letters of alphabets are arranged line by line starting from the top left corner, the letter ‘x’ is dropped. You should provide the two resultant mixed squares letters as two strings, one each line. (12 marks)
3. Using the Two Square cipher algorithm, encrypt the plaintext of question 1 part C based on the generated two mixed squares of question 2 part C. (12 marks)
Your answer should be detailed, you should show each output of each step of the algorithm besides the final answers.

REFERENCES:

[1] "Solution of Polygraphic Substitution Systems", Chapter 7, IndaBook, 2015. Available at http://www.indabook.org/
[2] http://www.asciitable.pro/ascii_table.htm

NOTES

• Make sure to write your name and ID clearly.
• Answer all questions and do not exceed the word count.
• Always make citations and referencing (provide proper references using any format).
• Use your own words (copy and paste cause deduction of marks even if you provide proper references).
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End of TMA
Good Luck