Exercise Sheet 1

1.Decipher the following ciphertext that has been doubly enciphered with a rail fence of height 5 and a monoalphabetic substitution cipher with keyword CRYPTOGRAPHY: WHAWPAVNAMTLPTTUTHLVTWMCV

 

  1. Carry out the following computations on residue classes:

(a) [8]11 + [5]11                       (b) [5]14 − [7]14

Save your time - order a paper!

Get your paper written from scratch within the tight deadline. Our service is a reliable solution to all your troubles. Place an order on any task and we will take care of it. You won’t have to worry about the quality and deadlines

Order Paper Now

(c) [5]13 ∗ [7]13                      (d) [8]12 ∗ [11]12

 

3.Assume a simple two round Feistel block cipher with an 8 bit key and 16 bit block size. Key derivation is defined as Ki = K +75·i( mod 256) where Ki is the ith subkey and K is the decimal representation of the key. The encryption function is f(Ki , Ri) = 127 · (Ki + Ri)(mod256) where Ri is the decimal representation of the right 8 bit of the input block.

Encrypt the message block M = (V, S) with key K = Y. Use the ASCII encoding of capital letters where A is encoded as 65. It is sufficient to give your result as a pair of decimal numbers.

 

  1. By defining a suitable strategy for the attacker, show that the one-time pad is not a secure block cipher.

 

Order Description

Q1- Monoalphabetic Substitution Ciphers

1. choosing a keyword,
2. removing all duplicate letters from the keyword
3. start the cipher-alphabet with the letters from duplicate-free keyword
4. at the end of the codeword continue with the next unused letter of the alphabet that follows the last
letter in the codeword
5. continue filling in letters in alphabetical order leaving out those letters already used; if necessary,
start from the beginning of the alphabet again similar to a shift cipher

Q3- Feistel Ciphers

Q4: one time is not correct but tow time is correct. how?

 

"Our Prices Start at $11.99. As Our First Client, Use Coupon Code GET15 to claim 15% Discount This Month!!":

Get started

0 replies

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply