Data Remanence - Complications - Data On Solid-state Drives

Data On Solid-state Drives

Research from the Center for Magnetic Recording and Research, University of California, San Diego has uncovered problems inherent in erasing data stored on solid-state drives (SSDs). Researchers discovered three problems with file storage on SSDs:

First, built-in commands are effective, but manufacturers sometimes implement them incorrectly. Second, overwriting the entire visible address space of an SSD twice is usually, but not always, sufficient to sanitize the drive. Third, none of the existing hard drive-oriented techniques for individual file sanitization are effective on SSDs.

Flash-based solid-state drives differ from hard drives in two ways: first, in the way data is stored and second, in the way the algorithms are used to manage and access that data. These differences can be exploited to recover previously erased data. SSDs maintain a layer of indirection between the logical addresses used by computer systems to access data and the internal addresses that identify physical storage. This layer of indirection enhances SSD performance and reliability by hiding idiosyncratic interfaces and managing flash memory's limited lifetime. But it can also produce copies of the data that are invisible to the user and that a sophisticated attacker could recover. For sanitizing entire disks, sanitize commands built into the SSD hardware have been found to be effective when implemented correctly, and software-only techniques for sanitizing entire disks have been found to work most, but not all, of the time. In testing, none of the software techniques were effective for sanitizing individual files. These included well-known algorithms such as the Gutmann method, US DoD 5220.22-M, RCMP TSSIT OPS-II, Schneier 7 Pass, and Mac OS X Secure Erase Trash.