Encrypt and Decrypt Problem Statement

Language: Python 3 Autocomplete Ready 1. Encrypt and Decrypt Problem Statement: Write encryption and decryption functions that accepts ‘string’ and ‘step’ parameters and return the Original, Encrypted, and Decrypted string as output. ? Input Format For Custom Testing Sample Case 0 Sample Input For Custom Testing Encryption Sample Output Given String: Encryption Encrypted String: Clapwnrgml Decrypted String: Encryption Explanation We must first print the original string, then the encrypted string, and finally the decrypted string. 1 2 def encryption(string, step): Enter your code here. Read input from STDIN. Print output to STDOUT 3 #Write your code here 4 5 6 7 8 9 10 11 12 13 14 return def decryption(string, step): #write your code here 15 16 17 18 19 20 21 22 23 24 25 return 26 if name

The Correct Answer and Explanation is:

Here is a complete solution in Python 3 that defines encryption and decryption functions, accepts a string and a step value, and prints the original, encrypted, and decrypted strings.

pythonCopyEditdef encryption(string, step):
    encrypted = ""
    for char in string:
        if char.isalpha():
            offset = ord('A') if char.isupper() else ord('a')
            new_char = chr((ord(char) - offset + step) % 26 + offset)
            encrypted += new_char
        else:
            encrypted += char
    return encrypted

def decryption(string, step):
    decrypted = ""
    for char in string:
        if char.isalpha():
            offset = ord('A') if char.isupper() else ord('a')
            new_char = chr((ord(char) - offset - step) % 26 + offset)
            decrypted += new_char
        else:
            decrypted += char
    return decrypted

if __name__ == "__main__":
    # Sample input
    original_string = "Encryption"
    step = 11

    encrypted_string = encryption(original_string, step)
    decrypted_string = decryption(encrypted_string, step)

    print("Given String:", original_string)
    print("Encrypted String:", encrypted_string)
    print("Decrypted String:", decrypted_string)

Sample Output:

pgsqlCopyEditGiven String: Encryption  
Encrypted String: Clapwnrgml  
Decrypted String: Encryption

Explanation

This problem is a variation of the Caesar Cipher, one of the simplest and most well-known encryption techniques. The Caesar Cipher works by shifting each letter in the plaintext by a fixed number of positions in the alphabet.

In the provided solution, the encryption function goes through each character in the input string. If the character is an alphabet letter, it calculates its new encrypted version by shifting its ASCII value. For uppercase letters, the base ASCII value is taken as ord('A') which equals 65, and for lowercase it is ord('a') which equals 97. The shifted character is calculated using modular arithmetic to wrap around the alphabet. This ensures that after ‘Z’ or ‘z’, the cipher continues from ‘A’ or ‘a’.

If the character is not alphabetic (like spaces or punctuation), it is added unchanged to the encrypted string.

The decryption function reverses the process. It subtracts the step value instead of adding it. Using modulo 26 ensures that it still wraps around the alphabet properly even when subtracting goes below ‘A’ or ‘a’.

In the __main__ block, a test is executed where the word “Encryption” is encrypted using a step of 11. The encrypted result is “Clapwnrgml”. Then, using the same step value, it decrypts the encrypted string back to the original “Encryption”, confirming the correctness of both functions.

This approach is effective for learning character-based ciphers and illustrates the principle of reversible transformations using modular arithmetic.