Question 2 RSA

In an RSA cryptosystem, you intercept a ciphertext C = 2023 sent to a user whose public key is (e = 148363, n = 369389). What is the plaintext M? Show your steps, assuming that your calculator can only handle a maximum of 12 decimal digits.

Question 3 Mode of Operation

Suppose there is a symmetric encryption scheme, CS, that on input an 8-bit message, P, and a key, K, procedures a ciphertext, C. K is a positive integer. CS performs a right circular shift on P based on K. For example, if P is 01011011 and K is 3, C is 01101011. You are given a string, S, which is having a value of POLYU. Perform the following tasks:

Write down the binary form of S, based on 8-bit ASCII code representation. [4 marks]

Encrypt S using CS. The mode of operation is ECB. K is 4. Represent C in binary representation. [6 marks]

Encrypt S using CS. The mode of operation is CBC. K is the last numeric digit of your student ID. Represent C in binary representation. The initialization vector is X.

[10 marks]