实现数字签名，首先用MD5对要发送的文件进行摘要，产生MD5码，然后将文件和摘要一同发送给对方进行验证，若两次的摘要相同，则说明文件在发送过程中没有被篡改，反之，篡改了。-Realize digital signature, first for sending in MD5 documents are the, produce the MD5 yards, then will file and the send to each other together for verification, if two of the same, show file in the course of transmission is not tamper with the, conversely, tampering.