MD5 Help
 

Hi, i`ve noticed as i browse through some Linux distro sites that some of them mention about a MD5 / MD5 Checksum hash value or something and all i`ve seemed to really learn about it is that it`s got something to do with Cryptography with a 128bit something or other, apart from that i don`t really understand.
Could anyone help me with this please?

Thanks :

Hi,

If you are asking for a quick howto on how to use MD5 hash that is shown at the site:

After downloading your file, use md5sum <file> to create the MD5 hash.

The output should be the same as the hash mentioned on the site. If it is not, a few things could have happened: The download itself corrupted the file (most probable) or someone tempered with the file (virus, malware etc). Guess I don't need to tell you that the file should not be used if this is the case.

If you want to know more about md5:
unofficial home of md5
wikipedia

Hope this helps.

It only sort of has to do with cryptography. A hash is the output of a one way function on some input. One way means that given the output, there is NO WAY to determine the input. For example, the function "input * 3" is a 2 way function. If I am given the output 6, I know the input was 2. However, the function "input mod 7" is one way. If I'm given the output 2, there is no way to know if the input was 2, 9, 16, etc. The problem with hashes is that they have what are known as collisions (the 2, 9, and 16 in this example all collide with an output of 2). ALL hashes will have collisions (otherwise they would be 2 way). The trick is to have as few collisions as possible. MD5 is a VERY complicated function that has a very limited number of collisions. This means it is almost impossible to come up with two inputs that will collide with the same output. This means that if you have a file and get an MD5 hash of that file, any other file with the same MD5 hash is almost certainly a copy of that file.

HTH

Forrest