MD5算法具有以下特点：
1、压缩性：任意长度的数据，算出的MD5值长度都是固定的。
2、容易计算：从原数据计算出MD5值很容易。
3、抗修改性：对原数据进行任何改动，哪怕只修改1个字节，所得到的MD5值都有很大区别。
4、强抗碰撞：已知原数据和其MD5值，想找到一个具有相同MD5值的数据（即伪造数据）是非常困难的。
MD5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十六进制数字串）。除了MD5以外，其中比较有名的还有sha-1、RIPEMD以及Haval等。(The MD5 algorithm has the following characteristics:
1: compression of arbitrary length data, calculate the MD5 value of the length is fixed.
2, easy to calculate: from raw data to calculate the value of MD5 is very easy.
3, anti modification: any modifications to the original data, even if only to modify 1 bytes, the MD5 values are very different.
4, strong anti collision: known as original data and its MD5 value, want to find someone with the same MD5 value of the data (i.e. data falsification) is very difficult.
The role of MD5 is to make the large capacity information in the private key is signed with a digital signature software are compressed into a confidential format (is an arbitrary length byte string transform into a long string of sixteen hexadecimal numbers). In addition to MD5, one of the more famous are SHA-1, RIPEMD and Haval.)