加密工具

# Caesar Cipher — encode and decode with any shift (ROT13 = shift 13)

def caesar_encode(text: str, shift: int) -> str:
    result = []
    for ch in text:
        if ch.isalpha():
            base = ord('A') if ch.isupper() else ord('a')
            result.append(chr((ord(ch) - base + shift) % 26 + base))
        else:
            result.append(ch)
    return ''.join(result)

def caesar_decode(text: str, shift: int) -> str:
    return caesar_encode(text, -shift)

# ROT13 is simply shift=13
rot13 = lambda s: caesar_encode(s, 13)

print(caesar_encode("Hello, World!", 3))   # Khoor, Zruog!
print(caesar_decode("Khoor, Zruog!", 3))   # Hello, World!
print(rot13("Hello"))                       # Uryyb
print(rot13("Uryyb"))                       # Hello  (self-inverse)

# Brute-force all 25 shifts to crack a Caesar cipher
ciphertext = "Khoor, Zruog!"
for shift in range(1, 26):
    print(f"Shift {shift:2d}: {caesar_decode(ciphertext, shift)}")