Checksum - help me understand it please

[MichaelD]

I know a checksum is there so you can ensure you got all the bits and bytes of the download. But how do I "use" it?

I'm downloading a Mandrake Linux Distro (won't be done for hours...it's 2GB+) and it has a checksum listed for it.

Once the DL is complete, what am I supposed to do w/the checksum? I know how to burn an .iso to a CD/DVD.

Here's what the checksums says:

5f09b941c03d0511862fcdf60f1526c4 Mandrakelinux-10.1-Official-Download-DVD.i586.iso

 

[drag]

Well all a checksum is is the result of a mathmatical formula that uses the file as a number.

So basicly it takes the entire file, runs it thru the formula, and poops out a number at the end. They way the formula is suppose to work is that no 2 files will have the same checksum... even if only one bit was changed it would pop out a entirely different result.

There are 2 commonly used checksums... md5sum and sha1sum... I beleive. Md5sum is more common, but I think that somebody found a weakness in it that if you purposely modify a file in a very specific manner you may get it to pop out 2 of the same numbers. Not sure.

But it's probably md5sum. It'll say somewere in the file or in the file name. There is a command line program you can use for doing this. In Linux it's called md5sum and is usually aviable by default, but for windows you'd have to find and install a md5sum.exe program. Also there are a lot of other programs aviable that will also do it for you.

 

[MichaelD]

Thanks, Drag.

So, being that I'm DLing a Linux distro, there's a chance that once I un-rar the file, they'll be a checksum checker program called "md5sum" or similar in there somewhere?

Cool.

Thanks for your help.

 

[drag]

Nope. I've never seen it bundled with something like that. It's standard for Linux people to have that by default, but a quick google will find it for you in Windows.

Generally for downloading big stuff I like using bittorrent better. With that it has it's own checksums that double check everything automaticly.. I beleive. You pretty much never have to worry about getting a corrupted download. (just as long as the original that started the torrent was fine). Plus it's faster.

 

[MichaelD]

Thanks Drag.

 

[sybille]

I've used digestIT, a small program for Windows that adds an entry to the context menu in Windows Explorer (the right-click menu) with options to calculate and compare hashes:
http://digestit.kennethballard.com/index.html

 

[MichaelD]

Thank you, sybille.

After some figuring it out, I got the Windows version of md5summer to work.

I'm still a GUI guy...trying to learn Linux.

Thanks again.