CS6630 Assignment 1 Cryptography 101 Solved




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Question 1)

A cipher can be implemented in multiple ways depending on the underlying
hardware. We have seen details about the different implementations of AES in class.
One such implementation is the AES T-Table Implementation.
This question is on a lightweight cipher called CLEFIA. The details about CLEFIA are present
here along with a reference implementation.
1. The first part of the assignment is to implement a CLEFIA-128 (T-Table based) cipher (
using C programming language).
2. Provide a write-up that includes the details of the cipher implementation and a Makefile.
Note: The code will be used in most of the upcoming assignments. Implementations available
on google may not be a good choice. ( Marks : 50 )

Question 2)

In class we saw an example of a timing side channel attack on a password checker
where the password is provided by the user and the stored password is compared character by
character. The password checker returns when it finds a mismatch between the two.
To prevent the attackers from obtaining the password in such a way, in practice, we compute the
hash of the password provided by the user and the hash of the stored password.
Can you extract the stored password with this countermeasure in place?

Use nc 5555 to access the binary for this question.
a) Submit the stored password. (10 marks)
b) Hash functions are subjected to collision attacks where multiple passwords end up
having the same hash. Submit a set of 5 passwords which would also have the same
hash as the stored password. (10 marks)
c) Submit a write up on your method used to extract the password. The write up should
contain references like websites/tools used (if any) and the methods adopted should be
explained in detail using code snippets. (30 marks)