MD5

MD5 means Message-Digest Algorithm 5, invented by Ronald L. Rivest. It develops from MD4、MD3、MD2. MD5 is not used for compiling the cipher and making cipher enigmatical.It is a hash arithmetic and is used for prevent to alter the original text by comparing information summary. MD5 ciphered the byte string of any length to a fixed length interger (usually length in 16 to 32 digits). During the cipher process, some data information will be filtrated. Therefore, it is impossible to draw original text by inversely calculate the ciphered text.

For example, if you sign up to a bbs, set the password "qiuyu21". Through the MD5 process, this password will change to"287F1E255D930496EE01037339CS978D". When you click "submit", the server's database will record the calculation result "287F1E255D930496EE01037339CS978D" rather than your original password "qiuyu21". As a result, when you log in the bbs next time, server will still translate your password typed " qiuyu21" to the MD5 calculation result. After checkout, if the result matches the data in database, you can successfully log in.

What is the advantage of MD5? Well, If a hacker breaks the database, he can not use the MD5 result to log in. However, if database record the original password, once a hacker break the database, he or she could get all passwords and log in sucessfully in any other's user name.

MD5 is still in high level of security in nowadays society.