"""
ROT13 Cipher Implementation in Python.
"""
'''
ROT13 is a simple substitution cipher that replaces a letter with the 13th letter
after it in the alphabet. Because the English alphabet has 26 letters (13 * 2),
applying ROT13 twice restores the original text (it is its own inverse).
'''
import string
def rot13(text: str) -> str:
"""
Transforms a string using the ROT13 substitution cipher.
Args:
text (str): The input string to transform.
Returns:
str: The transformed ROT13 string.
"""
# Define lowercase and uppercase alphabets
lower = string.ascii_lowercase
upper = string.ascii_uppercase
# Create a translation table that maps each letter 13 positions ahead, wrapping around
trans_table = str.maketrans(
lower + upper,
lower[13:] + lower[:13] + upper[13:] + upper[:13]
)
# .translate() applies the character mapping efficiently in C under the hood
return text.translate(trans_table)
def main() -> None:
# Input string specified
message = "Hello, World! 123"
print(f"Original: {message}")
# Apply ROT13 encryption
encrypted = rot13(message)
print(f"ROT13: {encrypted}")
# ROT13 is its own inverse; applying it again decrypts the message
decrypted = rot13(encrypted)
print(f"Decrypted: {decrypted}")
if __name__ == "__main__":
main()
'''
run:
Original: Hello, World! 123
ROT13: Uryyb, Jbeyq! 123
Decrypted: Hello, World! 123
'''
