[heise online UK] Secure deletion: a single overwrite will do it

Dave Kleiman dave at davekleiman.com
Tue Jan 20 19:18:39 EST 2009

On Mon, 19 Jan 2009, Stefan Kelm wrote:
> ...it has to be overwritten completely, sector
> by sector. Although this takes time, it costs nothing: the dd command in
> any Linux distribution will do the job perfectly.

Note quite perfectly, and not nearly as fast as the built-in option (see below).

On Mon, 20 Jan 2009, Jason wrote:
>I agree in general, although you still have to watch out for "reserve tracks" 
>(search on this page)....."All hard disks have reserved sectors, which are used automatically by the 
>drive logic if there is a defect in the media.":

Yes the main areas you are referring to are known as the P-List (Primary Defects List – manufacture defect info that does not change) G-List (Grown Defects Lists – sector relocation table). You can only access the P-List with special commands and tools. 

However, you can wipe the G-List are if you do it outside of an OS (or a tool that can access the system area), since the OS knows nothing of these sectors. The easiest (possible the best because of speed) way to accomplish this in modern ATA hard drives (2001 forward) is with the built-in Secure Erase program. Conveniently placed there for us by Recording Research (CMRR) headed by Gordon Hughes, Associate Director of CMRR, USSD on the Secure Erase Initiative.

""At the ANSI T-13 Committee meeting in 2004, Gordon described the differences between block erase as described in government document DoD2550 and Secure Erase. Unlike block level erase Secure Erase also overwrites reassigned blocks and can be up to eight times faster (per CMRR tests).
In addition the enhanced SE command qualifies for Federal Government secret data classification erasure."" 

You can download a DOS-based utility HDDerase that securely erases all data on ATA hard disk drives via the internal secure erase command. http://cmrr.ucsd.edu/people/Hughes/SecureErase.shtml

And yes, I am the same Dave Kleiman from the paper.

The Cryptography Mailing List
Unsubscribe by sending "unsubscribe cryptography" to majordomo at metzdowd.com

More information about the cryptography mailing list