CDS523 Principle of Data Analytics

CDS523 Principle of Data Analytics and Programming

Programming Assignment 3

(Due: 20

th November 2024, 23:59)

1. (5 marks) In the past, the frequency analysis of letters was an important step in breaking cipher. Write a 

Python program that prompt the user to input the path of a text file and output the occurrence count of 

all 26 English alphabet (ignoring case) in the text file specified by the user.

Sample input and output:

Terminal

Please enter the path of the text file: asg3_q1_sample.txt

The frequency of English alphabet:

a: 1

b: 1

c: 1

… 

z: 1

You should output the count of every English alphabet one by one in alphabetical order. Each line should 

contain an English alphabet followed by its count. The counts of some English alphabets in the sample 

input and output are omitted to save space in this assignment specification but your program should 

output the count of all English alphabets.

2. (15 marks in total) In cryptography, a Caesar cipher is one of the simplest forms of substitution cipher. 

The encryption is performed through shifting each letter in the plaintext forward by a number of posi tions defined by the user along the alphabetical order. For example, if the user has defined the number 

of forward position shift to be 4, every letter E in the plaintext will be replaced by A in the ciphertext 

because character A is 4 positions in front of letter E in alphabetical order.

Consider the following mapping between each alphabet in plaintext and its corresponding alphabet in 

ciphertext where the encryption is performed by shifting 4 alphabets forward.

Plain A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Cipher W X Y Z A B C D E F G H I J K L M N O P Q R S T U V

Process of Encryption:

Input plaintext:

The quick brown fox jumps over the lazy dog.

Encryption Process

Plain T h e q u i c k b r o w n f o x j u m p s o v e r t h e l a z y d o g .

↓↓↓ ↓↓↓↓↓ ↓↓↓↓↓ ↓↓↓ ↓↓↓↓↓ ↓↓↓↓ ↓↓↓ ↓↓↓↓ ↓↓↓

Cipher P d a m q e y g x n k s j b k t f q i l o k r a n p d a h w v u z k c .

Output ciphertext:

Pda mqeyg xnksj bkt fqilo kran pda hwvu zkc.

Process of Decryption:

The decryption of a ciphertext encrypted with Caesar cipher can be achieved by reversing the encryption 

process (i.e. shifting the letters backward).

Input ciphertext:

Pda mqeyg xnksj bkt fqilo kran pda hwvu zkc.

Decryption Process

Cipher P d a m q e y g x n k s j b k t f q i l o k r a n p d a h w v u z k c .

↓↓↓ ↓↓↓↓↓ ↓↓↓↓↓ ↓↓↓ ↓↓↓↓↓ ↓↓↓↓ ↓↓↓ ↓↓↓↓ ↓↓↓

Plain T h e q u i c k b r o w n f o x j u m p s o v e r t h e l a z y d o g .

Output plaintext:

The quick brown fox jumps over the lazy dog.

a) (6 marks) Write a program that prompt the user to input (1) the number of forward position shift and

(2) the plaintext message that they want to encrypt into the console. The program then output the 

encrypted message to the console.

Sample input and output:

Terminal

Please enter the number of position shift: 4

Please enter the plaintext message: The quick brown fox jumps over the 

lazy dog.

The encrypted message is: Pda mqeyg xnksj bkt fqilo kran pda hwvu zkc.

b) (5 marks) Modify the program in (a) such that it will prompt the user to input (1) the number of for ward position shift, (2) the path of the plaintext text file and (3) the path of the ciphertext text file.

The program then encrypts the content of the plaintext text file and output the result ciphertext to 

the ciphertext text file.

Sample input and output:

Terminal

Please enter the number of position shift: 4

Please enter the path of the input plaintext file: plaintext.txt

Please enter the path of the output encrypted file: encrypted.txt

c) (2 marks) Modify the program in (a) such that it will prompt the user to input (1) the number of for ward position shift and (2) the encrypted message that they want to decrypt into the console. The 

program then output the decrypted plaintext message to the console.

Sample input and output:

Terminal

Please enter the number of position shift: 4

Please enter the encrypted message: Pda mqeyg xnksj bkt fqilo kran pda 

hwvu zkc.

The decrypted message is: The quick brown fox jumps over the lazy dog.

d) (2 marks) Modify the program in (c) such that it will prompt the user to input (1) the number of for ward position for shifting, (2) the path of the ciphertext text file and (3) the path of the decrypted

plaintext text file. The program then decrypts the content of the ciphertext text file and output the 

result plaintext to the plaintext text file.

Sample input and output:

Terminal

Please enter the number of position shift: 4

Please enter the path of the input encrypted file: encrypted.txt

Please enter the path of the output decrypted file: decrypted.txt

Assumption:

• Only English alphabet (upper case or lower case) characters have to be encrypted and decrypted. 

• Characters other than English alphabet are preserve during the encryption and decryption.

• Case of every English alphabet is preserved during the encryption and decryption process.

Assumptions

You may assume that every input of the program is valid in format.

Submission

Students should submit their source code as (1) a single Jupiter Notebook file (i.e. .ipynb file) OR (2) a zip file 

that contains standalone Python script files (i.e. .py files) for answering the programing questions to the 

submission box on the Moodle elearning platform on or before 20

th November 2024, 23:59. Students are 

expected to name their file submission in the name of <your_student_ID>_asg3.ipynb OR

<your_student_ID>_asg3.zip and their source code should follow the following format: