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| 1 | +# Import sys for system operations and colorama for colored output. |
| 2 | +import sys |
| 3 | +from colorama import init, Fore |
| 4 | + |
| 5 | +# Initialise colorama |
| 6 | +init() |
| 7 | + |
| 8 | + |
| 9 | +# Function to Encrypt using the Vigenère cipher. |
| 10 | +def vigenere_encrypt(plain_text, key): |
| 11 | + encrypted_text = '' |
| 12 | + |
| 13 | + # Repeat the key to match the length of the plaintext. |
| 14 | + key_repeated = (key * (len(plain_text) // len(key))) + key[:len(plain_text) % len(key)] |
| 15 | + |
| 16 | + # Iterate through each character in the plaintext. |
| 17 | + for i in range(len(plain_text)): |
| 18 | + # Check if the character is an alphabet letter. |
| 19 | + if plain_text[i].isalpha(): |
| 20 | + # Calculate the shift based on the corresponding key letter. |
| 21 | + shift = ord(key_repeated[i].upper()) - ord('A') |
| 22 | + |
| 23 | + # Encrypt uppercase and lowercase letters separately. |
| 24 | + if plain_text[i].isupper(): |
| 25 | + encrypted_text += chr((ord(plain_text[i]) + shift - ord('A')) % 26 + ord('A')) |
| 26 | + else: |
| 27 | + encrypted_text += chr((ord(plain_text[i]) + shift - ord('a')) % 26 + ord('a')) |
| 28 | + else: |
| 29 | + # If the character is not an alphabet letter, keep it unchanged. |
| 30 | + encrypted_text += plain_text[i] |
| 31 | + |
| 32 | + # Return the final encrypted text |
| 33 | + return encrypted_text |
| 34 | + |
| 35 | + |
| 36 | +# Decryption function for the Vigenère cipher |
| 37 | +def vigenere_decrypt(cipher_text, key): |
| 38 | + decrypted_text = '' |
| 39 | + |
| 40 | + # Repeat the key to match the length of the ciphertext |
| 41 | + key_repeated = (key * (len(cipher_text) // len(key))) + key[:len(cipher_text) % len(key)] |
| 42 | + |
| 43 | + # Iterate through each character in the ciphertext |
| 44 | + for i in range(len(cipher_text)): |
| 45 | + # Check if the character is an alphabet letter |
| 46 | + if cipher_text[i].isalpha(): |
| 47 | + # Calculate the shift based on the corresponding key letter |
| 48 | + shift = ord(key_repeated[i].upper()) - ord('A') |
| 49 | + |
| 50 | + # Decrypt uppercase and lowercase letters separately |
| 51 | + if cipher_text[i].isupper(): |
| 52 | + decrypted_text += chr((ord(cipher_text[i]) - shift - ord('A')) % 26 + ord('A')) |
| 53 | + else: |
| 54 | + decrypted_text += chr((ord(cipher_text[i]) - shift - ord('a')) % 26 + ord('a')) |
| 55 | + else: |
| 56 | + # If the character is not an alphabet letter, keep it unchanged |
| 57 | + decrypted_text += cipher_text[i] |
| 58 | + |
| 59 | + # Return the final decrypted text |
| 60 | + return decrypted_text |
| 61 | + |
| 62 | + |
| 63 | +key = "KEY" |
| 64 | +# Get user input (Message to encrypt). |
| 65 | +plaintext = input('[!] Enter your message: ') |
| 66 | + |
| 67 | +# Encrypt the plaintext using the Vigenère cipher |
| 68 | +cipher_text = vigenere_encrypt(plaintext, key) |
| 69 | + |
| 70 | +# Print the results |
| 71 | +print(f"[+] Plaintext: {plaintext}") |
| 72 | +print(f"{Fore.GREEN}[+] Ciphertext: {cipher_text}") |
| 73 | + |
| 74 | +# Ask if user wants to decrypt the message (just to see the functionality.) |
| 75 | +ask_to_decrypt = input('\n\n[?] Do you want to decrypt the message?\n[?] Y or N: ').lower() |
| 76 | + |
| 77 | +# If user wants to. |
| 78 | +if ask_to_decrypt == 'y': |
| 79 | + # Decrypt the ciphertext back to the original plaintext. |
| 80 | + decrypted_text = vigenere_decrypt(cipher_text, key) |
| 81 | + print(f"{Fore.GREEN}[+] Decrypted text: {decrypted_text}") |
| 82 | + |
| 83 | +# If user does not want to. |
| 84 | +elif ask_to_decrypt == 'n': |
| 85 | + sys.exit() |
| 86 | +# When an invalid input is entered. |
| 87 | +else: |
| 88 | + print(f"{Fore.RED}[-] Invalid input.") |
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