Disk Cleaner?

Hi all, I just wanted to know if I was practical to create a program that will search a disk for free space then overwrite it with random data.

Also how would I go about writing such a program? Could someone give me some advice? Or point me in the right direction to some info???

If you are asking such a question, I don't think you are up for it. It is a lot more complex than it sounds. Due to the way modern file-systems work, it is very difficult to find free space. I would say it's right next to impossible if you don't know how your target filesystem works. If it's something proprietary and complex like NTFS, I would say just forget about it.

Short answer: it is not practical.

Well someone does it... do they not?

Just do some research on your filesystem.

Yes, there is a handful of people in the programming world that can do this. But that doesn't mean everyone can do it.

I hate to argue, but it is far from impossible.

I would recommend finding an open-source project that does something similar, and go from there.

That’s what I thought, there a quite a few programs that do it well something similar. I was looking around on sourceforge.net. see if i can find some code to go over.

And I also found a vb script that sorta dose the same thing http://www.codeproject.com/KB/vbscri...te_script.aspx but isn't really what i am looking for.. & its in vb.

Writing random bits to a File System is easy: open a file -> write random bits. Ten lines of C++ and you'll have it. The underlying file system should figure out where to create new files in available--empty/free--space. That's all the script does. This isn't the same thing as writing random bits to any unused blocks on a disk. It isn't even conceptually similar to completely trashing old data on a disk. It's not at all secure. You'll need to know virtually everything about the File System in question to actually make anything that would be secure. (NTFS for example can store small files directly in the file table. If you deleted such a small file and ran that script it would not even touch the actual data you wanted to garbage.)

So, what are you actually wanting to do?

Soma

You'll need to know virtually everything about the File System in question to actually make anything that would be secure.

which, for something like NTFS is impossible, even if not for the complexity. The specifications of the FS is not even open to the public. You will have to reverse engineer it, and that is by no means an easy task (it took Linux kernel developers many years of work to get NTFS support into the Linux kernel, for example, and it is still read-only as of now IIRC).

I would recommend finding an open-source project that does something similar, and go from there.

It has to be one that works for NTFS, too, as what you are trying to do is very filesystem-dependent. I doubt anything like that exists. Feel free to prove me wrong.

... overwrite it with random data...

wouldn't 0's work equally well?

Originally Posted by Loic

Hi all, I just wanted to know if I was practical to create a program that will search a disk for free space then overwrite it with random data.

Also how would I go about writing such a program? Could someone give me some advice? Or point me in the right direction to some info???

Open a file. Start writing random data to the file. Keep going until the OS gives you an error because you ran out of disk space. You have now overwritten all free space on the drive, with random data. Now delete the file you just created.

EDIT: If you're looking for security from the cops -- good luck. Not only will they find the little bits you didn't catch, but there is technology which can read old bit states to a reasonable degree of precision -- i.e., they can read data you've overwritten with something else. That's why industrial strength data erasure tools make multiple passes with different bit sequences. And if you want real security, smash the drive and then burn it.

EDIT EDIT: For instance, did you clear your browser cache? If not, the free block eraser won't erase those sectors, and you might get "busted." I really question the legitimate need for pure data erasure. The big boys just destroy the drives when they need data to go away.

Ok well i found this program on sourceforge.net http://sourceforge.net/projects/eraser

seems to be what i need to look into.

Originally Posted by brewbuck

Open a file. Start writing random data to the file. Keep going until the OS gives you an error because you ran out of disk space. You have now overwritten all free space on the drive, with random data. Now delete the file you just created.

EDIT: If you're looking for security from the cops -- good luck. Not only will they find the little bits you didn't catch, but there is technology which can read old bit states to a reasonable degree of precision -- i.e., they can read data you've overwritten with something else. That's why industrial strength data erasure tools make multiple passes with different bit sequences. And if you want real security, smash the drive and then burn it.

EDIT EDIT: For instance, did you clear your browser cache? If not, the free block eraser won't erase those sectors, and you might get "busted." I really question the legitimate need for pure data erasure. The big boys just destroy the drives when they need data to go away.

well, i think i am going to start looking over the source of that eraser program. just need to find the source now :S but it seems to be what i am looking for...

and, as for what you said about someone trying to hide something from the cops... 99.9% of programs i found all make multiple passes with different data. "eraser" dose up to 35 i think... and if i am not mistaken. i read somewhere that an Department of defensive method only makes 7 passes?

but i am sure there is still much to be learnt...