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Data remanence is the residual representation of that remains even after attempts have been made to remove or erase the data. This residue may result from data being left intact by a nominal operation, by reformatting of storage media that does not remove data previously written to the media, or through physical properties of the that allow previously written data to be recovered. Data remanence may make inadvertent disclosure of possible should the storage media be released into an uncontrolled environment ( e.g., thrown in the trash or lost).Various techniques have been developed to counter data remanence. These techniques are classified as,. Specific methods include, and.Effective application of countermeasures can be complicated by several factors, including media that are inaccessible, media that cannot effectively be erased, advanced storage systems that maintain histories of data throughout the data's life cycle, and persistence of data in memory that is typically considered volatile.Several exist for the secure removal of data and the elimination of data remanence. Contents.Causes Many, and other software provide a facility where a is not immediately when the user requests that action. Instead, the file is moved to a, making it easy for the user to undo a mistake.

Similarly, many software products automatically create backup copies of files that are being edited, to allow the user to restore the original version, or to recover from a possible crash ( feature).Even when an explicit deleted file retention facility is not provided or when the user does not use it, operating systems do not actually remove the contents of a file when it is deleted unless they are aware that explicit erasure commands are required, like on a. (In such cases, the operating system will issue the command or the UNMAP command to let the drive know to no longer maintain the deleted data.) Instead, they simply remove the file's entry from the, because this requires less work and is therefore faster, and the contents of the file—the actual data—remain on the. The data will remain there until the reuses the space for new data. In some systems, enough filesystem are also left behind to enable easy by commonly available. Even when undelete has become impossible, the data, until it has been overwritten, can be read by software that reads directly. Often employs such software.Likewise, or a system is unlikely to write to every area of the disk, though all will cause the disk to appear empty or, in the case of reimaging, empty except for the files present in the image, to most software.Finally, even when the storage media is overwritten, physical properties of the media may permit recovery of the previous contents.

In most cases however, this recovery is not possible by just reading from the storage device in the usual way, but requires using laboratory techniques such as disassembling the device and directly accessing/reading from its components. The gives further explanations for causes of data remanence.Countermeasures. Main article:There are three levels commonly recognized for eliminating remnant data:Clearing Clearing is the removal of sensitive data from storage devices in such a way that there is assurance that the data may not be reconstructed using normal system functions or software file/data recovery utilities. The data may still be recoverable, but not without special laboratory techniques.Clearing is typically an administrative protection against accidental disclosure within an organization. For example, before a is re-used within an organization, its contents may be cleared to prevent their accidental disclosure to the next user.Purging Purging or is the removal of sensitive data from a system or storage device with the intent that the data cannot be reconstructed by any known technique. Purging, proportional to the sensitivity of the data, is generally done before releasing media beyond control, such as before discarding old media, or moving media to a computer with different security requirements.Destruction The storage media is made unusable for conventional equipment. Effectiveness of destroying the media varies by medium and method.

Depending on recording density of the media, and/or the destruction technique, this may leave data recoverable by laboratory methods. Conversely, destruction using appropriate techniques is the most secure method of preventing retrieval.Specific methods Overwriting A common method used to counter data remanence is to overwrite the storage media with new data. This is often called wiping or shredding a file or disk, by analogy to common methods of, although the mechanism bears no similarity to these.

Because such a method can often be implemented in alone, and may be able to selectively target only part of the media, it is a popular, low-cost option for some applications. Overwriting is generally an acceptable method of clearing, as long as the media is writable and not damaged.The simplest overwrite technique writes the same data everywhere—often just a pattern of all zeros.

At a minimum, this will prevent the data from being retrieved simply by reading from the media again using standard system functions.In an attempt to counter more advanced data recovery techniques, specific overwrite patterns and multiple passes have often been prescribed. These may be generic patterns intended to eradicate any trace signatures, for example, the seven-pass pattern: 0xF6, 0x00, 0xFF, random, 0x00, 0xFF, random; sometimes erroneously attributed to the US standard.One challenge with an overwrite is that some areas of the disk may be, due to media degradation or other errors. Software overwrite may also be problematic in high-security environments which require stronger controls on data commingling than can be provided by the software in use. The use of may also make file-based overwrite ineffective (see the discussion below under ).There are specialized machines and software that are capable of doing overwriting.

The software can sometimes be a standalone operating system specifically designed for data destruction. There are also machines specifically designed to wipe hard drives to the department of defense specifications DOD 5220.22-M. Feasibility of recovering overwritten data investigated data recovery from nominally overwritten media in the mid-1990s. He suggested may be able to recover such data, and developed specific patterns, for specific drive technologies, designed to counter such. These patterns have come to be known as the.Daniel Feenberg, an economist at the private, claims that the chances of overwritten data being recovered from a modern hard drive amount to 'urban legend'. He also points to the ' created on a tape of discussing the. Erased information in the gap has not been recovered, and Feenberg claims doing so would be an easy task compared to recovery of a modern high density digital signal.As of November 2007, the considers overwriting acceptable for clearing magnetic media within the same security area/zone, but not as a sanitization method.

Only or is acceptable for the latter.On the other hand, according to the 2014 Special Publication 800-88 Rev. 1 (p. 7): 'For storage devices containing magnetic media, a single overwrite pass with a fixed pattern such as binary zeros typically hinders recovery of data even if state of the art laboratory techniques are applied to attempt to retrieve the data.' An analysis by Wright et al.

Of recovery techniques, including magnetic force microscopy, also concludes that a single wipe is all that is required for modern drives. They point out that the long time required for multiple wipes 'has created a situationwhere many organisations ignore the issue all together – resulting in data leaks andloss.' Degaussing is the removal or reduction of a magnetic field of a disk or drive, using a device called a degausser that has been designed for the media being erased. Applied to, degaussing may purge an entire media element quickly and effectively.Degaussing often renders inoperable, as it erases low-level that is only done at the factory during manufacturing.

In some cases, it is possible to return the drive to a functional state by having it serviced at the manufacturer. However, some modern degaussers use such a strong magnetic pulse that the motor that spins the platters may be destroyed in the degaussing process, and servicing may not be cost-effective. Degaussed computer tape such as can generally be reformatted and reused with standard consumer hardware.In some high-security environments, one may be required to use a degausser that has been approved for the task. For example, in government and military jurisdictions, one may be required to use a degausser from the 's 'Evaluated Products List'. Encryption data before it is stored on the media may mitigate concerns about data remanence.

If the is strong and carefully controlled, it may effectively make any data on the media unrecoverable. Even if the key is stored on the media, it may prove easier or quicker to just the key, vs the entire disk. This process is called.Encryption may be done on a basis, or on the. Are one of the few possible methods for subverting a method, as there is no possibility of storing the plain text key in an unencrypted section of the medium. See the section for further discussion.Other (such as, acquisition of a written note containing the decryption key, or ) may offer a greater chance to success, but do not rely on weaknesses in the cryptographic method employed. As such, their relevance for this article is minor.Media destruction. The pieces of a physically destroyed hard disk drive.Thorough destruction of the underlying storage media is the most certain way to counter data remanence.

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Tolerance Data 2017 Download

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Tolerance Data 2019

Ben Rothke, CISSP, British Telecom.

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