I am finally getting around to cleaning up my office. It’s been a few years and there are a lot of electronic gadgets including computers, KVMs and so forth that were for projects long past and I need to make room for more current projects and their associated stuff. One thing I had to deal with was a pile of old IDE disks. Some were for notebooks (most of those were dead), while some were drives for desktop or rack-mount computers. Part of my task was to see if there was any useful info on the drives, extract that info, and the wipe the drives.
Over about ten hours of looking at drives, I think I saved a handful of files. But some of the data on the drives may have had personal or otherwise sensitive information and I wanted to be sure to wipe it out. As most people know, just deleting the file isn’t enough as that process just marks the part of the disk where the data as stored as “free to be used again”, and doesn’t actually destroy the data. What’s necessary is to “wipe” the data. That is, write over it a few times so it cannot be recovered. While a few writes will stop most people, some government agencies (and maybe some private labs) can extract data that has been overwritten – I’m not too worried about anyone with that level of capability trying to extract some old data of mine.
Wiping the data in a disk file is a simple task: one just writes a few different patterns onto the file and it’s done. The patterns are often a combination of all 1’s, all 0’s and some random data. Some tools write over data two or three times, some many more based on a configuration. In Learning Tree Course 468, System and Network Security Introduction we talk about the necessity of wiping files, how it works, and how to do it.
I wanted to write over all the unused (“free”) blocks on the disk and I couldn’t find a tool on my laptop to do that. After a short search I found that Microsoft Windows actually comes with a tool to do this. It’s called “cipher”. Cipher does many other things I’ll mention shortly regarding encrypting disks and files, but I was concerned with its ability to clean the free list. To do that, use
cipher /w:X Where
X is the drive whose free list is to be wiped.
That’s it. It may take some time as it writes over the list three times. A large drive with a lot of free blocks can take several minutes or hours.
Cipher also manipulates the keys used for encrypting files, creates a recovery agent and otherwise configures the Windows filesystem encryption features. I’m glad I found about this tool as it made my work much easier. I hope you get the opportunity to check it out.
To your safe computing,