周期为3，第一张表由密钥字产生（密钥字自拟），第二张表由洗牌法产生（字母a~z与数字0~25一一对应），第三张表由公式法产生（Z26上的一一变换）。-Period 3, the first table generated by the key words (key words self), the second table generated by the shuffling method (the letters a ~ z-one correspondence with the numbers 0 to 25), the third table from the formula generation (Z26 on one by one transformation).