MD5Sums

Now, it's a long time i use computers, and 2 years i use Linux, and i know i'm supposed to know this, but...
What are MD5Sums? and how do i check them?
(I know they are used to verify the sizes of files (useful when checking large downloads) But i wouls like a more technical explanation.
Thank you very much in advance.
-NSKL

An MD5Sum is a type of check sum. How it works is that a special program (called md5sum on linux) is used at the end distributing the file (where you download the thing from) to create a series of alpha-numeric characters. This series is unique to this file and is created from the file's innards using the MD5 hashing algorithm.

If a file is changed even slightly then it will show up. So if one bit has been switched (either through someone altering the file [possibly maliciously] or corruption) the check sum of the file will be different from the original check sum.

To use these things you use the linux program md5sum. type md5sum filename to create a checksum. You can channel the output to a different file if you want with the > operator. To check a file use md5sum --check checksumfile.md5.

Someone has actually found a flaw in it by finding two inputs that create the same output. Bit of a bugger but never mind.

Hope that answers your queries. Anything more just ask.