本次美国代写主要为MAT 331 的project

Summary: In Part 1 you will design and implement a symmetric-key cryptosystem. You can

combine and modify the systems we have used in class, or you may do something completely

different. You will use your cryptosystem to encrypt several messages with secret keys.

In Part 2, we will randomly assign each student a different target cryptosystem designed by

a classmate; your goal will be to break the one assigned to you. You will have access to the

encryption and decryption algorithms that your classmate designed, but you will not be given the

secret keys. You will receive (small amounts of) bonus points if (i) you exploit weaknesses in the

target cryptosystem, or (ii) your own cryptosystem resists attacks from the classmate assigned to

attack it. In this way you will be incentivized to make your cryptosystem strong and to try hard to

attack the one you’ve been assigned. However, you will still be able to achieve a high grade without

these extra points.

This back and forth between the cryptographer designing a cryptosystem and the cryptanalyst

attacking it is meant to mimic how cryptology develops in the real world. You will get to play both

roles – cryptographer and cryptanalyst.

Collaboration Policy: You can discuss topics related to programming or cryptographic algo-

rithm design with your classmates or others. You may also research cryptography on the internet

or from books (this is certainly not required). But you must design and write your own algorithm

and report. In particular, you should understand how your code works, and be able to justify your

design choices.

For this part, you will submit four files on Blackboard as Project 1, Part 1. The files are described

below.

A “symmetric-key” cryptosystem is a system for two people, Alice and Bob, who have agreed on

a single secret key before-hand, to encrypt and decrypt messages sent over an insecure channel. The

shift cipher, Vigenere cipher, and one-time pad are all examples of symmetric-key cryptosystems.

There are various notions of security, but essentially what we desire is that an eavesdropper Eve

who sees the ciphertexts cannot gain much useful information about the plaintexts.

Your task is to design, implement, and describe a symmetric-key cryptosystem with the following

specifications:

A plaintext to be encrypted consists of a string containing only the characters A,B,. . . ,Z. A