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I have a small issue with this post.
While the information contained therein is technically sound and correct, it is not "sanitizing" per se, as recovery is still possible by an adversary. At the very least, dd if=/dev/random should be used, as opposed to /dev/zero. There has been a lot of publicized research on that subject, proving that overwriting with zeroes is not going to stop "the bad guys".

The reason the data is overwritten with all zeros instead of with random characters is so the wipe can be verified. Although we know using all random characters has the same result, it can not be proven in court to be wiped. Perhaps over writing with random then a second pass with all zeros for verification...

I have been using the method in this post for three years to wipe media without any problems.

Thanks for the link, looks like my point was not valid for the case when you try to recover data from today's drive using the technology referenced in Guttmann's paper.

Err... Craig Wright's research was in regards to magnetic storage, not solid state. I completely agree with the first poster (although maybe for a different reason) - urandom is a much better choice. You have absolutely no idea what the storage controller on a flash drive will do with an instruction to write all zeros. Maybe "to save a write cycle on my solid state memory, I'll just mark this whole section as being zeros". Much better to use urandom, since there is so much entropy, the controller will have no choice but to actually commit the data. There are still other issues related to wear levelling that mean you probably aren't really sanitising it.

The reason for wiping with all zeros is so the wipe can be verified. If all random characters are used there us no way to prove in court the media was sterilized. Maybe using all random characters followed by a pass with all zeros...

I have been using the posted method for three years now and have not had any issue.

"[...] as recovery is still possible by an adversary."
If you referer to the now-dating "Secure Deletion of Data from Magnetic and Solid-State Memory" by Peter Gutmann, you may want to read the "Epilogue" and "Further Epilogue" section of the updated paper. It is state that the "[...] paper is now more than fifteen years old, and discusses disk storage technology that was current 15-20 years ago.", that "with the ever-increasing data density on disk platters and a corresponding reduction in feature size and use of exotic techniques to record data on the medium, it's unlikely that anything can be recovered from any recent drive" and finally that "with ultra-high densities and use of perpendicular recording I don't see how MFM would even get a usable image". Like Gutman said, unless you deal with mid-90s technologies or older, "even if you've got 10KB of sensitive data on a drive and can't erase it with 100% certainty, the chances of an adversary being able to find the erased traces of that 10KB in 80GB of other erased traces are close to zero."
So unless you need to erease "top secret for national security" kind of data, I don't see the benifit of doing more than one passes. The technology needed to maybe recover some data that maybe useful are quite expensive and way to much time consuming.

Now, between /dev/random VS /dev/zero, set apart the sense of more security that may provide the use of /dev/random, both give the same level of security (for 1 passe at least).

My 2 cents.

My understanding of this technique is that it works great for standard hard drives but for flash drives it might or might not work properly because write levelling techniques distribute the write operations to non-contiguous blocks. How do you know you've hit the entire surface of the drive unless you fill up the entire capacity of the drive? I've just been deleting my junk, using Sdelete to clean the free space and then using Recuva to verify theres nothing there. Possibly more steps than I really need, but it seems to be working out ok. If someone has verified the DD method works for flash drives as well I'd love to start using that as thats how I handle standard hard drives now and I'd love to standardize my process.

Two quick comments:

1) It's easy to verify the write:

dd if=/dev/urandom | tee /dev/sdb | md5sum ; md5sum /dev/sdb
But I agree - you are probably better off with a final all zero pass.

2) Hal - That is exactly what I'd expect. What I mean was without using enough entropy, how do you know the controller doesn't just record a bitmap of zeroed blocks or similar? When you ask what's on the device, it can still say "why, it's full of zeros!" and pass your test. It then saves a write over the whole physical device. I have absolutely no idea if any controller does this, but if I was trying to sanitise media, I wouldn't assume they didn't.... While some like JG might be prepared to assert categorically that no device on the market does it, I wouldn't be so bold :)

Al

Does anyone have an opinion on using the hdparm -security-erase commands to wipe hard drives?

@Hal, @JG

Not sure if you saw this:
http://www.usenix.org/events/fast11/tech/full_papers/Wei.pdf

From the article:
"Since some SSDs compress
data before storing, they will write fewer bits to the flash
if the data is highly compressible. This suggests that
for maximum effectiveness, SSD overwrite procedures
should use random data."

Even if there weren't specific examples, I still think random data is better, since the above becomes a non issue.

Cheers,
Alan