srm (Secure rm)

You've probably noticed the "Secure Empty Trash" under the Finder's file menu. What you may not know is that this came from an open source project called srm (secure rm) and that you have a command line "srm" also.

As srm works like rm, but with extra options, it's easy to substitute this for rm. You can't quite alias it, because rm has some options that are obviously incompatible (like -P, which attempts its own forensic scrubbing), but for command line use, it's mostly the same. There are some additional "srm" options, such as being able to overwrite without unlinking and cutting back on the degree of overwriting (by default a file is overwritten 35 times).

The algorithm used by default bears the name of the author of Secure Deletion of Data from Magnetic and Solid-State Memory (Peter Gutmann). Why is all this necessary? Because disks are mechanical devices and storage is is quite fuzzy, so weak images of previous data are still present after a simple overwrite. Also, disk heads may move slightly out of track over time, leaving a magnetic trail "off to the side".

If you really, really need to protect data, the only absolute method is physical destruction of the media, but "srm" is probably good enough for most of us.

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