Implement modified vigenere cipher for all printable ASCII

DIRECTORY.md

@@ -109,6 +109,7 @@
  * [Morse Code](ciphers/morse_code.py)
  * [Onepad Cipher](ciphers/onepad_cipher.py)
  * [Permutation Cipher](ciphers/permutation_cipher.py)
+ * [Printable ASCII Vigenere Cipher](ciphers/printable_ascii_vigenere_cipher.py)
  * [Playfair Cipher](ciphers/playfair_cipher.py)
  * [Polybius](ciphers/polybius.py)
  * [Porta Cipher](ciphers/porta_cipher.py)

ciphers/printable_ascii_vigenere_cipher.py

@@ -0,0 +1,103 @@
+"""
+This program encrypts or decrypts messages using a modified Vigenere cipher
+that operates on all printable ASCII characters (from 32-126) instead of just letters.
+Each character in the message is shifted by a value derived from the corresponding
+character in the key. When the end of the key is reached, it repeats cyclically.
+
+Algorithm summary:
+- For each printable character:
+ * Convert both the message and key characters to their ASCII codes.
+ * During encryption: add the key's ASCII value to the message character.
+ * During decryption: subtract the key's ASCII value from the message character.
+ * Wrap the result within the printable ASCII range using modulo arithmetic.
+- Non-printable characters are left unchanged.
+- The key repeats automatically to match the message length.
+
+Reference: https://stackoverflow.com/questions/28182091/ascii-vigenere-cipher-implementation-in-java
+"""
+
+PRINTABLE_START = 32
+PRINTABLE_END = 126
+PRINTABLE_RANGE = PRINTABLE_END - PRINTABLE_START + 1
+
+
+def encrypt_message(key: str, message: str) -> str:
+ """
+ Encrypts a message using printable ASCII Vigenere cipher.
+
+ >>> encrypt_message('key', 'Hello!')
+ "Tk'xu;"
+ >>> encrypt_message('SUpeR$eCR3t_KEY', 'This is a message to encrypt.')
+ 'H^zyr.ycTS#e_Y[[[1zbDkRVF/p`s'
+ """
+ return translate_message(key, message, "encrypt")
+
+
+def decrypt_message(key: str, message: str) -> str:
+ """
+ Decrypts a message using printable ASCII Vigenere cipher.
+
+ >>> decrypt_message('key', "Tk'xu;")
+ 'Hello!'
+ >>> decrypt_message('SUpeR$eCR3t_KEY', 'H^zyr.ycTS#e_Y[[[1zbDkRVF/p`s')
+ 'This is a message to encrypt.'
+ """
+ return translate_message(key, message, "decrypt")
+
+
+def translate_message(key: str, message: str, mode: str) -> str:
+ """
+ Translates (encrypts or decrypts) a message using the given key.
+
+ >>> translate_message('key', 'Hello!', 'encrypt')
+ "Tk'xu;"
+ >>> translate_message('key', "Tk'xu;", 'decrypt')
+ 'Hello!'
+ """
+ translated = []
+ key_index = 0
+ key_bytes = [ord(ch) for ch in key]
+
+ for symbol in message:
+ sym_val = ord(symbol)
+
+ if PRINTABLE_START <= sym_val <= PRINTABLE_END:
+ key_val = key_bytes[key_index]
+
+ if mode == "encrypt":
+ new_val = (
+ sym_val - PRINTABLE_START + key_val
+ ) % PRINTABLE_RANGE + PRINTABLE_START
+ elif mode == "decrypt":
+ new_val = (
+ sym_val - PRINTABLE_START - key_val
+ ) % PRINTABLE_RANGE + PRINTABLE_START
+ else:
+ raise ValueError("Mode must be 'encrypt' or 'decrypt'")
+
+ translated.append(chr(new_val))
+
+ key_index = (key_index + 1) % len(key_bytes)
+ else:
+ translated.append(symbol)
+
+ return "".join(translated)
+
+
+if __name__ == "__main__":
+ message = input("Enter message: ")
+ key = input("Enter secret key: ")
+ mode = input("Encrypt/Decrypt [e/d]: ")
+
+ if mode.lower().startswith("e"):
+ mode = "encrypt"
+ translated = encrypt_message(key, message)
+
+ print(f"Encrypted message: {translated}")
+ elif mode.lower().startswith("d"):
+ mode = "decrypt"
+ translated = decrypt_message(key, message)
+
+ print(f"Decrypted message: {translated}")
+ else:
+ print("Invalid mode. Use 'e' or 'd'.")