说明：  遇到带密码的文档，感觉很烦恼吧，虽然这本书不能完全教会你如何破解密码~~，但是它可以教会你加密解密的原理
(Encountered with password files, you feel a great deal, although this book can not teach you how to crack the password ~ ~, but it can teach you the principles of encryption and decryption)