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def double_encrypt(msg, key1, key2):
    ciphertext1 = encrypt(msg.encode(), key1)
    ciphertext2 = encrypt(ciphertext1, key2)
    return ciphertext2

def double_decrypt(ciphertext, key1, key2):
    plaintext1 = decrypt(ciphertext, key1)
    plaintext2 = decrypt(plaintext1, key2)
    return plaintext2.decode()

def encrypt(msg, key):
    key = key.encode()
    ciphertext = bytearray()
    for i, b in enumerate(msg):
        ciphertext.append((b + key[i % len(key)]) % 256)
    return bytes(ciphertext)

def decrypt(ciphertext, key):
    key = key.encode()
    plaintext = bytearray()
    for i, b in enumerate(ciphertext):
        plaintext.append((b - key[i % len(key)]) % 256)
    return bytes(plaintext)

msg = '你好，世界！'
key1 = '密码1'
key2 = '99密码999'

ciphertext = double_encrypt(msg, key1, key2)
# print('Ciphertext:', ciphertext)

plaintext1 = double_decrypt(ciphertext, key1, key2)
print('Plaintext1:', plaintext1)
plaintext2 = double_decrypt(ciphertext, key2, key1)
print('Plaintext2:', plaintext2)

#>>> Plaintext1: 你好，世界！
#>>> Plaintext2: 你好，世界！