Reference no: EM132685808

Task 1:

1. Consider the following encryption system:
Input -> Monoalphabetic Encryption (Key: K1) -> Row Transposition Encryption (Key: K2) -> Output
Suppose the ciphertext Output of the encryption system is:
KNTGETRZTXRUQFACTIOSJNZAGTQ
The key values are:
K1 = QWERTYUIOPLKJHGFDSAZXCVBNM
K2 = 627158943
Find the corresponding Input plaintext text. Note that the plaintext is an intelligible English text.
Note: You must show all your solution steps.

Task 2:
1. Explain step by step the operation of DES.
2. In public-key cryptosystems, the RSA is the most commonly used algorithm. Answer the following questions:
a) Consider the following equation -
D= {(P-1)(Q-1)(E-1)+1}/E
where, E is an odd number, P&Q are prime numbers and {(P-1)(Q-1)-1} is evenly divisible by E, N = P X N.
Is this scheme equivalent to RSA? Justify your answer.
b) In the RSA algorithm, what is the security flaw with choosing e = 1 for the public key? (Hint: the RSA formula for encryption is c = Me mod n).
c) Answer the following scenario in relation to the RSA algorithm -
1. Suppose you are given a ciphertext C= 61 by a user whose public key is e=11, n=91. Break the code.
2. Suppose you have a set of encoded message blocks but you don't have the private key. If someone tells you that they know one of the plaintext blocks has a common factor with n (let n=pq and e is the public key). Does this help you in any way? Explain why and why not?

Attachment:- encryption system.rar