**Question 1:**

Use the following steps to determine the value of N:

Choose the last two digits of your NCI student Let’s assume the digits are AB. For example, if your student ID number is x12345867, then A is 6 and B is 7.

Calculate S by adding A and B e., S = A + B.

Select a random number between 15 and Let R be the number.

Add R and S to calculate N, e., N = R + S.

**Question 2: **

Follow the steps below to encrypt and decrypt a random text:

Select a random plaintext of N characters and split the plaintext into at least four blocks. Here, N is obtained in Question 1.

Encrypt the blocks generated in step a) with Electronic Code Book (ECB) and find the associated

Decrypt the ciphertexts generated in step b) with ECB and find their corresponding

Apply Counter (CTR) encryption to the blocks from step a) and find the associated

Decrypt the ciphertexts generated in step d) with CTR and find the corresponding plaintexts

**Question 3: **

Explain the Diffie–Hellman key exchange when the sender and receiver agree on a prime number which is a number greater than N and the generator which is equal to G. Assume that G is equal to A + 10, and N and A are determined in Question 1.

**Question 4:**

Compare Hash functions, Message Authentication Code, and Digital Signature with an example. Provide at least three comparisons.

**Question 5:**

A sender encrypts a message using symmetric key encryption according to the following algorithm: m ⊕ k ⊕ ……N times………⊕K.

Here, m is the message, k is the key, N is the number calculated in Question 1, and ⊕ is the XOR operator. Answer the following questions:

Is the above algorithm a valid encryption algorithm and why?

If the answer to Q(2A) is “yes”, what would be the symmetric key decryption algorithm? What number would you add to the value of N to make this algorithm valid if the answer to Q(5a) is “no”?

**Question 6:**

Suppose that a sender needs to send plaintext equal to the number N to a destination. Explain how you will use public-key cryptography to meet confidentiality, authentication, integrity, and nonrepudiation security requirements (all together) for plaintext equal to number N.

Select the RSA public-key cryptography algorithm and use the method given in question a) to meet all security requirements. Note that the plaintext is the number N in this question. There is no word limit for this You are free to choose any parameter of the RSA algorithm.

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