Vernam密码KeyError: 0 Python

import random
import string

def generate_key(length):
    return ''.join(random.choice(string.ascii_letters + string.digits) for _ in range(length))

def vernam_encrypt(plaintext, key):
    if len(plaintext) != len(key):
        raise ValueError("Key length must match plaintext length")
    return ''.join(chr(ord(p) ^ ord(k)) for p, k in zip(plaintext, key))

def vernam_decrypt(ciphertext, key):
    return vernam_encrypt(ciphertext, key)  # XOR is symmetric

# 示例使用
plaintext = "Hello, World!"
key = generate_key(len(plaintext))

try:
    ciphertext = vernam_encrypt(plaintext, key)
    print(f"Ciphertext: {ciphertext}")
    decrypted_text = vernam_decrypt(ciphertext, key)
    print(f"Decrypted text: {decrypted_text}")
except ValueError as e:
    print(e)