Submission Deadline: Week 5, March 30 2018 11:59pm
(a) Decrypt the ciphertext
This message was encrypted with a double transposition (of the type discussed in the lecture and tute) using a matrix of 7 rows and 10 columns. Hint: The first word is “there.”
(b) Find the plaintext and the key, given the cipher-text
(c) Decrypt the following message that was encrypted using a simple substitution cipher:
Q2 Using the letter encodings in Table I, the following two cipher-text messages were encrypted with the same one-time pad:
KHHLTK and KTHLLE
Find all possible plaintexts for each message and the corresponding one-time pad.
Q3 Bob is a receiver and Alice is a sender. Bob generates public and private keys using RSA encryption algorithm and sends the public key to Alice. Alice has a message M=8596 to send. Bob uses parameter p=89 and q=191, and chooses a small public key parameter e. What are the values of suitable public and private keys? How would Alice encrypt message M=8596? How would Bob decrypt the encrypted message C with the private key?
Q4 Alice has a message M=37 to send to Bob securely using ElGamal encryption algorithm. Bob chooses p=8081, g=2849, x=53. Alice chooses r=78. Show the encryption and decryption steps.
Q5 Alice has a message M=186 to send to Bob securely using Paillier encryption algorithm. Bob chooses p=11, q=17,and selects an integer g =188. Alice selects a random number r=97. Show the encryption and decryption steps.