Surprising Facts About Shred Size and Security

I have supplied many customers with conventional hard disk drive (HDD) shredders that offered either the standard 1.5" shred width or the high-security 0.75" shred width. But the fact is that the difference in actual data protection between those two shred sizes is small.  In fact, 1.5" vs. 0.75" doesn't really affect who can potentially recover data from the media: Either particle size will require a forensic lab with millions of dollars in equipment and resources to recover data. A smaller size merely adds time and cost to the recovery process.  

However, physical destruction of Solid State Drives (SSD) is a completely different challenge - and particle size is far more critical. Please note that I am not making a blanket “the smaller the better” statement (in other words, a linear progression of smaller sizes is not necessarily better). Rather, the unique architecture of an SSD means there are security “breaks” as particle size decreases, which establishes a stepped series of security thresholds. In between these breaks, all data destruction processes and particle sizes offer similar security results. The measurements of these breaks are averages based NAND chip dimensions expected over the next few years. 

Let’s look at some scenarios: 

A.      Bending, Crushing, Punching or Shredding to > 3/8"

Each of these approaches is likely to allow some NAND chips to remain completely intact after the process.  In this scenario, anyone with some fairly basic hardware and a good deal of knowledge can attempt data recovery on any one of the multiple NAND chips that may have survived destruction of the media. While on the one hand there is a high degree of complexity involved in extracting the chips and interpreting recovered data, on the other hand we know that the population of individuals qualified to attempt recovery is also extensive. This state of affairs constitutes a potentially unacceptable degree of risk for many organizations. 

B.      Strip cut shredding to < 3/8", or crushing using SSD-specific crushing systems

NAND chips generally measure a couple millimeters or less in thickness; in other words, tiny.  As storage media circuit boards containing the NAND chips pass through strip-cut shredder cutters, they bend and contort.  This process usually destroys NAND chips because, unlike PCB, NAND chips tend to shatter as they are subject to torsional pressure, or when cutters engage the chips directly.  There are circumstances, however, where the chips can pop off the boards, and slide freely in between the cutters.  In this case, the chips may escape destruction. Nevertheless, this process is clearly more secure than those described in Scenario A, because the likelihood (or frequency) of intact chips is much lower. 

As for crushing using SSD-specific equipment, if everything with the process is working correctly, all chips should always be destroyed.  That said, a broken pin or two on an SSD-adapter for your crusher, or a deformed pressure plate could easily result in ineffective destruction.  Furthermore, this process does not displace and scramble destroyed drive components (as shredding does), so anyone looking to recover data would be able to locate intact chips more easily. 

C.      Disintegration or cross cut shredding < 100mm²

Now we're really stepping up in class due to the simple fact that if you're cross-cut shredding or disintegrating down to particle sizes below 100 sq mm, zero NAND chips will escape the destruction process.  As a result, this method precludes data recovery attempts using commonly available hardware or methods, and only professionals with extremely expensive, specialized equipment can make even a reasonable attempt at recovering data from such drive particles.  Fifteen year-old Anonymous wannabes need not apply: go back to "Catchin' em all." 

Above and beyond

There are NSA-approved disintegrators for physically reducing flash media and solid state devices down to particles sizes around 2mm in length... Think gritty beach sand.  It would be reasonable to think that this level of destruction renders the data unrecoverable by any means; I don't really know if that's true or not.  I do know that if it's not true, the exact same folks who might be able to attempt data recovery on < 100mm² destroyed media are the only ones who could perform successful recovery on media subjected to any of the other, "lesser" methods of destruction.

My conclusion is this: any process that assures destruction of 100% of the NAND chips 100% of the time will make data recovery impossible without loads of equipment and training. Almost without exception, these resources are to be found only at government or government-contracted facilities.  If this level of data protection is still inadequate for the type and value of information that is being protected, than yes: smaller is better.  One thing that won’t change is that the smaller particles of shredded material can be reduced, the more difficult, time consuming and expensive it is to recover data from them.