MD5的全称是Message-digest Algorithm 5（信息-摘要算法），用于确保信息传输完整一致。在90年代初由MIT Laboratory for Computer Science和RSA Data Security Inc,的Ronald L. Rivest开发出来，经MD2、MD3和MD4发展而来。它的作用是让大容量信息在用数字签名软件签署私人密钥前被"压缩"成一种保密的格式（就是把一个任意长度的字节串变换成一定长的大整数）。-The full name of MD5 is Message-digest Algorithm 5 (Information- Summary of algorithm), to ensure consistent messaging integrity. In the early 90s by the MIT Laboratory for Computer Science and RSA Data Security Inc, the Ronald L. Rivest developed by the MD2, MD3 and MD4 evolved. Its role is to enable large-capacity information signed with a digital signature private key before the software was "compressed" into a confidential format (is an arbitrary length string of bytes must transform into a big long integer).