railfence in python

Rail Fence Cipher（栅栏密码）是一种简单的加密方法，它通过将明文沿着一个"栅栏"进行排列，然后读取加密后的密文来实现加密。在Python中可以使用以下代码实现rail fence cipher:

def rail_fence_encrypt(plain_text, key):
    fence = [[] for _ in range(key)]
    rail = 0
    direction = 1
    for char in plain_text:
        fence[rail].append(char)
        rail += direction
        if rail == key-1 or rail == 0:
            direction = -direction
    cipher_text = ''.join([c for rail in fence for c in rail])
    return cipher_text

def rail_fence_decrypt(cipher_text, key):
    fence = [[] for _ in range(key)]
    rail = 0
    direction = 1
    for char in cipher_text:
        fence[rail].append(None)
        rail += direction
        if rail == key-1 or rail == 0:
            direction = -direction
    index = 0
    for i in range(key):
        for j in range(len(fence[i])):
            fence[i][j] = cipher_text[index]
            index += 1
    plain_text = ''.join([c for rail in fence for c in rail if c is not None])
    return plain_text

使用上述代码，您可以将明文进行加密并将其解密回原始明文。要加密或解密，您只需要调用相应的函数，并将原始明文或密文以及密钥作为输入参数传递给它们。例如，以下是使用上述代码进行加密和解密的示例：

plain_text = "HELLO WORLD"
key = 3
cipher_text = rail_fence_encrypt(plain_text, key)
print(cipher_text) # HOLELWRDLO
decrypted_plain_text = rail_fence_decrypt(cipher_text, key)
print(decrypted_plain_text) # HELLO WORLD