CE235 Transposition Cipher

 Assignment One: Implementation of Autokey Cipher and Row Transposition Cipher CE235 Assignment One

2024-2025

University of Essex

1. Task of Assignment One

The aim of Assignment One is to write a Python program, which will implement the Autokey cipher and the Row transposition cipher. The introduction of the two ciphers can be found from the lecture notes.

Specifically, this assignment task is expected to do the following:

§ Design (with flowcharts) and develop a Python program with encryption and decryption functions for Autokey

cipher and the Row transposition cipher.

§ For the Row transposition cipher, if the length of the plaintext message (number of letters in message) is not

multiple times of the key length, you can add several letters to the end of the message before encryption, and delete these added letters after decryption to recover the original message.

A sample Python program caesar.py for Caesar cipher is provided for reference. The sample Python program can be run with default demo message and key from the command line in Terminal window like this:

python caesar_ciphyer.py

This reference program caesar_ciphyer.py encrypts a given message and then performs decryption. After the caesar_ciphyer.py program is run, it will display the plaintext, ciphertext, and the decrypted plaintext. If the cipher works correctly, the plain text and decrypted text should be the same.

Your program for these two ciphers should have a name like ak_registrationnumber.py (replace registrationnumber with your own registration number). Your program must run from command line like this (with a registration number 123456) :

python ak_123456.py

The outputs of ak_registrationnumber.py (including the key, plaintext, ciphertext and decrypted text) are required to be

displayed, following the display format given in the reference program caesar_ciphyer.py. 2. How to submit

Submit one python program file to Faser with the following filename (replace registration number by your own one):

ak_registrationnumber.py

Submission deadline is Wednesday, 04/12/2024 (UK time: 23:59); Beijing time: Thursday, 7:59, 05/12/2024.

3. Marking Scheme

There are 12 marks for this assignment (out of 100 marks for the overall module marks).

1) Flowcharts for the Autokey cipher and the Row transposition cipher take 1 mark each. The functions for the Autokey

cipher and the Row transposition cipher take 5 marks and 5 marks, respectively.

2) You will be asked by Professor He or the teaching assistants at NWU to demonstrate your work (including flowcharts

and program) and answer some questions to ensure it is your own work. Marks will be given according to the quality of your work and the demonstration. If you are asked to but you don’t demonstrate your work, no mark will be given to your assignment work.

3) Apart from demonstration of your work to the teaching staff members, it is mandatory for you to submit your program file to Faser (flowcharts are not to be submitted to Faser). You will not get mark for your work on the assignment if your program is not submitted to Faser. If your submission is late, there will penalty on your mark according to the university policy.

4) Extra check of your submitted program may be conducted by Professor He. If any programming or plagiarism problems are found from the check, your marks will be deducted.

4. Plagiarism

You should work individually on this assignment. Anything you submit is assumed to be entirely your own work. The usual Essex policy on plagiarism applies: http://www.essex.ac.uk/plagiarism/.

Appendix A. Sample Python Program for Caesar Cipher

 import sys #------------------------------------------------------------------------------ ### Note: Allow the program to be run from the command line:

## You can simply use the default message and key given in the program # python caesar_cipher.py

## You can also use message and key given in command line in Terminal (not required), ## where, atestmessage is the message (no space!)