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« on: January 03, 2013, 03:29 am »
The Secure Erase (SE) command was added to the open ANSI standards that control disk drives, at the request of CMRR at UCSD. The ANSI T13.org committee oversees the ATA interface specification (also called IDE) and the ANSI T10.org committee governs the SCSI interface specification.
Secure erase is built into the hard disk drive itself and thus is far less susceptible to malicious software attack than external software utilities. The SE command is implemented in all ATA interface drives manufactured after 2001 (drives with capacities greater than 15 GB), according to testing by CMRR. A standardized internal secure erase command also exists for SCSI drives, but is optional and not currently implemented in SCSI drives tested.
Secure erase is a positive easy-to-use data destroy command, amounting to "electronic data shredding." Executing the command causes a drive to internally completely erase all possible user data record areas by overwriting, including g-list records that could contain readable data in reallocated disk sectors (sectors that the drive no longer uses because they have hard errors). SE is a simple addition to the existing "format drive" command present in computer operating systems and storage system software, and adds no cost to hard disk drives. Because the Secure Erase command is carried out within hard disk drives, no additional software is required either.
Secure erase does a single on-track erasure of the data on the disk drive. The U.S. NATIONAL SECURITY AGENCY PUBLISHED AN INFORMATION ASSURANCE APPROVAL OF SINGLE PASS OVERWRITE, AFTER TECHNICAL TESTING AT CMRR SHOWED THAT MULTIPLE ON-TRACK OVERWRITE PASSES GAVE NO ADDITIONAL ERASURE. Secure erase has been approved by the U.S. National Institute for Standards and Technology (NIST), Computer Security Resource Center. NIST document 800-88 approves SE at a higher security level than external software block overwrite utilities like as Norton Government Wipe, and it meets the legal requirements of HIPAA, PIPEDA, GLBA, and Sarbanes-Oxley.
Software overwrite utilities running in protected execution environments (e.g. running inside file system hardware like RAID arrays or inside secure computers) could be verified secure under NIST 800-88. For the most sensitive data, the government requires physical destruction of drives. Drive manufacturers today are pursuing higher security secure erase (including secret data), via in-drive data encryption (see below).
Data Encryption Secure Erase
Recently, 2.5-inch hard disk drives for laptop computers have been introduced which encrypt user data before recording -- internal full data encryption. Such drives provide protection of data should the laptop or drive be lost or stolen, and even provide high protection from forensic data recovery. These drives also offer a new, instantaneous way to sanitize data on a hard disk drive -- by securely discarding the encryption key.
Why encrypt data at rest in drives instead of in computers, such as by user application programs that access the data? Because computer level data encryption defeats the purpose of many important data management functions, such as incremental backup, continuous data protection, data compression, de-duplication, virtualization, archiving, content addressable storage, advanced routing, and thin provisioning. Defeating these operations causes significant penalties to enterprise storage companies in data access speed and cost. Each of these operations exploits the structure of user data, and needs to inspect the data. They become inefficient or nonfunctional if the data has been randomized by encryption. For example, data compression ratios may fall from more than 2:1 to less than 1:1, because compressing random data can expand it instead. De-duplication won't find identical data sets if they are encrypted by different users.
Computer level encryption could be employed with in-drive encryption as well, the double encryption does no harm and provides additional security. In-drive encryption can relieve encryption key management problems inherent in removable storage, like laptop disk drives or tape backups. In fact, hardware-based tape drive encryption may become widespread 11 by 2007 due to widely publicized losses of backup tape reels containing identity theft data on millions of people.
Full Disk Encryption (FDE) Enhanced Secure Erase (FDE-SE), securely changes the internal drive encryption key, to render encrypted user data on disk indecipherable. This is enabled via the Enhanced SE command in the present ATA ANSI specs. FDE SE encryption needs to be tested for protection against advanced forensic analysis. The results will determine the erasure security data level -- Confidential, Secret, Top Secret, or higher. The US Commerce Department prohibits most 256-bit and higher encryption export overseas, limiting FDE E-SE to AES-128-bit encryption (since disk
drives are a global industry).
AES-256 bit encryption in FDE drives could allow FDE SE at a somewhat higher security level. Note that a FDE E-SE operation amounts to double AES-128, because the data encrypted by the discarded key is decrypted by the new key, and AES is a symmetric encryption scheme. It would appear that a brute force attack on double AES-128 requires
the same computational effort as single AES-256. For paranoid-level security, the cypt-text in an FDE disk drive could be eliminated by a Normal OW SE done after the FDE E-SE.
An open industry standard for FDE is being worked on by the Trusted Computing Group overall specification (the Storage Working Group in trustedcomputinggroup.org). Drive members of the TCG include Seagate, HGST, Fujitsu and WD. SE via encryption may be included, consistent with the ANSI open standards for ATA drives (t13.org). CMRR has begun testing FDE-SE drives. They take less than 15 milliseconds to complete an Enhanced SE; while a 750 GB ATA-interface HDD can take over an hour to erase using conventional Secure Erase (or many hours using external overwrite software).
Computer Forensics Data Recovery
Forensics recovery uses exotic data recovery techniques by experts with advanced equipment. Its normal purpose is to recover data from failed hard disk drives, and for legal discovery. Forensic companies can successfully recover unerased but protected data in a disk drive using electronic instrumentation. However, the secure erase commands discussed above erase all user data on the disk drive beyond physical disk drive forensic recovery. Drives old enough to permit such attack are too old to have the Secure Erase built-in command.
Paranoid-level recovery concerns based on hypothetical schemes are sometimes proposed by people not experienced in actual magnetic disk recording, claiming the possibility of data recovery even after physical destruction. One computer forensics data recovery company claims to be able to read user data from a magnetic image of recorded bits on a disc, without using normal drive electronics. Reading back tracks from a disk taken out of a drive and tested on a spin stand was practical decades ago, but no longer with today's microinch-size tracks.
The time required by exotic technologies is itself a barrier to data recovery and increases data security. Also, accessing data from magnetic images requires overcoming almost a dozen successive magnetic recording technology hurdles. Even if these hurdles were overcome, about an hour would be required to recover a single user data block out of millions on a disk. Recovering substantial amounts of data in less than months requires that the disk be intact and undamaged, so that heads can be flown over it to obtain data playback signals; then overcoming these technology hurdles. Simply bending a disk makes this nearly impossible, so physical damaging drives to warp their disks makes recovery practically impossible.
Other "experts" claim that limited information can be recovered from unerased track edges. But this has been shown to be false by tests at CMRR. Such recovery also presumes detailed technical knowledge of the drive's magnetic recording design. Charles Sobey at ChannelScience.com wrote an illuminating article on drive-independent data recovery, showing how difficult these hurdles are.
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