Assignment 2

Due on 14/03/2023

Problem(s)

Part-1:

Implement one of the following two algorithms (for Base64 characters except [+, /], i.e.,A to Z, a to z, and 0 to 9) as per the instructions:

• Vernam-Vigenère Cipher: (i.e. a Vigenere Cipher with Key Length equal to message length) (odd roll numbers)
• Vigenère Cipher: (even roll numbers)

Part-2:

Implement a code for launching the Padding Oracle Attack on a Cipher Block Chaining (CBC) algorithm with the following steps:

1. Design CBC cipher

   • block size = key size = IV size = 3
   • Keep it specific to to the char. [0 to 9] (here, the datatype is ‘character,’ NOT int)
   • Use ‘0’ in case of padding

2. Write a function to generate all possible sets of keys

   • Remember the key size
   • Write a function to automatically call decryption() for a given ciphertext bruteforcing the keys

3. Write a function to generate all possible sets of IVs

   • Remember the IV size
   • Write a function to automatically call decryption() for a given ciphertext bruteforcing the IVs

4. Implement the Padding Oracle Attack for ciphertext (given as input)

* Part 2 is a CHALLENGE question and stepwise marking will be done for the same!

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