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Hardware-based full disk encryption (FDE) is available from manyhard disk drive (HDD/SSD) vendors, including:Hitachi, Integral Memory, iStorage Limited,Micron,Seagate Technology,Samsung,Toshiba,Viasat UK, andWestern Digital. Thesymmetric encryption key is maintained independently from the computer'sCPU, thus allowing the complete data store to be encrypted and removing computer memory as a potentialattack vector.
Hardware-FDE has two major components: the hardware encryptor and the data store.There are currently four varieties of hardware-FDE in common use:
Hardware designed for a particular purpose can often achieve better performance thandisk encryption software, and disk encryption hardware can be made more transparent to software than encryption done in software. As soon as the key has been initialised, the hardware should in principle be completely transparent to the OS and thus work with any OS. If the disk encryption hardware is integrated with the media itself the media may be designed for better integration. One example of such design would be through the use of physical sectors slightly larger than the logical sectors.
Usually referred to asself-encrypting drive (SED).HDD FDE is made by HDD vendors using theOPAL and Enterprise standards developed by theTrusted Computing Group.[1]Key management takes place within the harddisk controller and encryption keys are 128 or 256bitAdvanced Encryption Standard (AES) keys.Authentication on power up of the drive must still take place within theCPU via either asoftwarepre-boot authentication environment (i.e., with asoftware-based full disk encryption component - hybrid full disk encryption) or with aBIOS password. In additions, some SEDs supportIEEE 1667 standard.[2]
Hitachi,Micron,Seagate,Samsung, andToshiba are the disk drive manufacturers offeringTrusted Computing GroupOpal Storage SpecificationSerial ATA drives. HDDs have become a commodity so SED allow drive manufacturers to maintain revenue.[3] Older technologies include the proprietary Seagate DriveTrust, and the older, and less secure,PATA Security command standard shipped by all drive makers includingWestern Digital. Enterprise SAS versions of the TCG standard are called "TCG Enterprise" drives.
Within a standardhard drive form factor case the encryptor (BC),key store and a smaller form factor, commercially available, hard disk drive is enclosed.
Examples includeViasat UK (formerly Stonewood Electronics) with their FlagStone, Eclypt[4] and DARC-ssd[5] drives or GuardDisk[6] with anRFID token.
The insertedhard drive FDE allows a standardform factorhard disk drive to be inserted into it. The concept can be seen on[7]
The encryptor bridge and chipset (BC) is placed between the computer and the standard hard disk drive, encrypting every sector written to it.
Intel announced the release of the Danbury chipset[9] but has since abandoned this approach.[citation needed]
Hardware-based encryption when built into the drive or within the drive enclosure is notably transparent to the user. The drive, except for bootup authentication, operates just like any drive, with no degradation in performance. There is no complication or performance overhead, unlikedisk encryption software, since all the encryption is invisible to theoperating system and the hostcomputer's processor.
The two main use cases areData at rest protection, and Cryptographic Disk Erasure.
For Data at rest protection a computer or laptop is simply powered off. The disk now self-protects all the data on it. The data is safe because all of it, even the OS, is now encrypted, with a secure mode ofAES, and locked from reading and writing. The drive requires an authentication code which can be as strong as 32 bytes (256 bits) to unlock.
Crypto-shredding is the practice of 'deleting' data by (only) deleting or overwriting the encryption keys.When a cryptographic disk erasure (or crypto erase) command is given (with proper authentication credentials), the drive self-generates a new media encryption key and goes into a 'new drive' state.[10] Without the old key, the old data becomes irretrievable and therefore an efficient means of providingdisk sanitisation which can be a lengthy (and costly) process. For example, an unencrypted and unclassified computer hard drive that requires sanitising to conform withDepartment of Defense Standards must be overwritten 3+ times;[11] a one Terabyte Enterprise SATA3 disk would take many hours to complete this process. Although the use of fastersolid-state drives (SSD) technologies improves this situation, the take up by enterprise has so far been slow.[12] The problem will worsen as disk sizes increase every year. With encrypted drives a complete and secure data erasure action takes just a few milliseconds with a simple key change, so a drive can be safely repurposed very quickly. This sanitisation activity is protected in SEDs by the drive's own key management system built into the firmware in order to prevent accidental data erasure with confirmation passwords and secure authentications related to the original key required.
Whenkeys are self-generated randomly, generally there is no method to store a copy to allowdata recovery. In this case protecting this data from accidental loss or theft is achieved through a consistent and comprehensive data backup policy. The other method is for user-defined keys, for some Enclosed hard disk drive FDE,[13] to be generated externally and then loaded into the FDE.
Recent hardware models circumventsbooting from other devices and allowing access by using a dualMaster Boot Record (MBR) system whereby the MBR for the operating system and data files is all encrypted along with a special MBR which is required to boot theoperating system. In SEDs, all data requests are intercepted by theirfirmware, that does not allow decryption to take place unless the system has beenbooted from the special SEDoperating system which then loads theMBR of the encrypted part of the drive. This works by having a separatepartition, hidden from view, which contains the proprietaryoperating system for the encryption management system. This means no other boot methods will allow access to the drive.[citation needed]
Typically FDE, once unlocked, will remain unlocked as long as power is provided.[14] Researchers atUniversität Erlangen-Nürnberg have demonstrated a number of attacks based on moving the drive to another computer without cutting power.[14] Additionally, it may be possible to reboot the computer into an attacker-controlled operating system without cutting power to the drive.
When a computer with a self-encrypting drive is put intosleep mode, the drive is powered down, but the encryption password is retained in memory so that the drive can be quickly resumed without requesting the password. An attacker can take advantage of this to gain easier physical access to the drive, for instance, by inserting extension cables.[14]
The firmware of the drive may be compromised[15][16] and so any data that is sent to it may be at risk. Even if the data is encrypted on the physical medium of the drive, the fact that the firmware is controlled by a malicious third-party means that it can be decrypted by that third-party. If data is encrypted by the operating system, and it is sent in a scrambled form to the drive, then it would not matter if the firmware is malicious or not.
Hardware solutions have gained criticism for being poorly documented. Many aspects of how the encryption is done are not published by the vendor. This leaves the user with little possibility to judge the security of the product and potential attack methods. It also increases the risk of avendor lock-in.
In addition, implementing system wide hardware-based full disk encryption is prohibitive for many companies due to the high cost of replacing existing hardware. This makes migrating to hardware encryption technologies more difficult and would generally require a clear migration and central management solution for both hardware- and software-basedfull disk encryption solutions.[17] however Enclosed hard disk drive FDE and Removable Hard Drive FDE are often installed on a single drive basis.