SSD data-erasure challenges surprise expert

A Study finds that erasing data stored on SSDs can be difficult, and at times nearly impossible.

Computerworld - Until the results of a study emerged late last month, few storage experts suspected that it would be more difficult to erase data stored on solid-state drives than it would be to erase data from hard disk drives. "I don't think anyone ever knew about this," said Bruce Schneier, chief security technology officer at BT Group and author of multiple books on data security issues.

Other industry experts acknowledged that they were also taken aback by the findings of researchers at the University of California, San Diego. However, they mostly agreed that some SSD sanitation methods can be more successful than others.

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Computerworld - Until the results of a study emerged late last month, few storage experts suspected that it would be more difficult to erase data stored on solid-state drives than it would be to erase data from hard disk drives.  "I don't think anyone ever knew about this," said Bruce Schneier, chief security technology officer at BT Group and author of multiple books on data security issues. Other industry experts acknowledged that they were also taken aback by the findings of researchers at the University of California, San Diego.  However, they mostly agreed that some SSD sanitation methods can be more successful than others.  For example, some noted that SSDs with native encryption capabilities can generally prevent data from being accessed, even after a drive's end of life.

The study found that fully erasing data stored on SSDs is at best a difficult task and at worst nearly impossible.  While overwriting data several times can ensure data erasure on many SSDs, the researchers found that they were still able to recover data on some overwritten drives.  The UCSD researchers tested 12 SSDs and found that none of the available software techniques for erasing individual files was fully effective.  The researchers did not identify the products used in the test. In a paper titled "Reliably Erasing Data from Flash-Based Solid State Drives," the researchers wrote that "all single-file overwrite sanitization protocols failed" and reported that "between 4% and 75% of the files' contents remained on the SATA SSDs."  USB flash drives didn't fare much better.  Between 0.57% and 84.9% of data remained on the drives after researchers attempted an overwrite.  The researchers even tried overwriting free space on the SSDs and defragmenting them to redistribute data and encourage the flash translation layer to reuse more physical storage locations.  That process also proved mostly ineffective, they said.  Data on only four of the 12 SSDs tested was erased when researchers used the native "Erase Unit" command in the drives.  In that test, one SSD had reported itself to be fully sanitized, yet researchers were able to recover data on the drive.

Kent Smith, senior director of product marketing at SSD controller maker SandForce Inc., said most data stored on an SSD should be safe when cryptographic erasure processes are used.  The technique calls for first encrypting an SSD, which would allow access only to users with passwords.  When the SSD reaches its end of life, the user can delete the encryption keys, which Smith said would eliminate the possibility of unencrypting and accessing the data.  "Unless you can break the 128-bit AES encryption algorithm, there's just no way to get to the data," Smith said.

The UCSD researchers agreed that crypto-erasure is a good way to ensure that an SSD can be sanitized at its end of life or when it's slated for reuse.  Schneier is a proponent of using inexpensive SSDs and encrypting their data with freeware, such as TrueCrypt, or with relatively low-cost products, like PGPdisk. SSD makers are pushing the National Institute of Standards and Technology to redefine some of the military erase overwrite protocols to recognize that encrypted drives can be cryptographically erased without the need to overwrite the flash.  "But that's not happening tomorrow," Smith said.  "Government agencies take a long time to embrace standards."