Sanitizing SSD

Sanitizing a drive is the action to fully and securely erase the information on a drive so that there is no mean, logical through commands, or analog through examination of stored analog information, to recover any erased data. This action is well-known and mastered for magnetic drives. There are clear documented software methods and even ATA or SCSI dedicated commands.

What about Solid State Drives (SSD)? SSD are becoming mainstream. They offer the benefits of speed and low consumption. Can they be securely erased? WEI, GRUP, SPADA and SWANSON presented at Usenix FAST a study. Their paper, entitled “Reliably Erasing Data From Flash-Based Solid State Drives”, checks whether the methods used for magnetic drives are still valid, and if the ATA and SCSI commands are efficient.

The conclusions are worrying.

For sanitizing entire disks, built-in sanitize commands are effective when implemented correctly, and software techniques work most, but not all, of the time. We found that none of the available software techniques for sanitizing individual files were effective.

In other words, if nobody has done the test before and published it, you cannot be sure. You have to either trust the manufacturer or do the test (which is destructive) yourself.

Funnily, BELL and BODDINGTON published in the The Journal of Digital Forensics, Security and Law, a paper entitled “Solid State Drives: The Beginning of the End for Current Practice in Digital Forensic Recovery?”. Their conclusion was that because SSD implemented automatic garbage collection that erased unused sectors, remnant data would be erased.

Who is right? I would believe the conclusions of the first team. The second team assumes that the forensics team accesses the data through logical commands or means. In that case, yes, data may be erased. On the other hand, the first team directly accesses the physical flash chips. Thus, they bypass the garbage collection. We may assume, that a serious forensics team, being aware of this problem, would rather directly work on the physical components. By the way, forensics teams are already doing this same type of examination when the hard disk has been voluntarily smashed.

Conclusion: Be aware of this risk at least until SSD manufacturers will have agreed on a certification that would prove the efficiency of the implementation of their sanitizing commands.

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