Data erasure

Eraser (English eraser ), Wiper or shredder means software that help can be irretrievably delete data from a specific computer storage medium. The functioning of the data carrier is not affected.

Basis

The recovery of all deleted data is normally possible because simply notes when you delete a file in the file system that the corresponding data area is now free again. The data itself, however, remain physically on the disk until the appropriate field is overwritten with new data.

So-called Eraser to by a " Secure Erase " protect against that deleted, sensitive data can be recovered by special procedures.

More detailed information is provided in the article hard drive.

Operation

Eraser to overwrite the file to delete one or more times with random or selected characters. Partial change Eraser additionally the corresponding directory entry in the file system.

Depending on the software and setting this is done by one or more of the various algorithms and recommendations of state regulators:

• The Federal Office for Security in Information Technology recommends in its "Guidelines for the BSI confidentiality of VS in the use of IT " is a six-time override of data. In each case the bit pattern of the previous passage can be reversed. In the final deletion run is again overwritten with " 01010101 ".
• Similar methods are "P- 5239-26 (RLL ) U.S. NAVSO " and "U.S. NAVSO P 5239-26 ( MFM) " described in the U.S. Navy regulations.
• A recommended by the U.S. Department of Defense algorithm overwrites the data first in two runs three times each in order to overwrite it again with pseudo - data.
• After introduced in 1996 Gutmann method data should be overwritten 35 times.
• Two other well-known methods of deletion are "Russian GOST P50739 -95 " and " Bruce Schneier 's Algorithm"

The above-mentioned algorithms, for example, in the Unix programs Wipe and shred (Unix) used. Darik 's Boot and Nuke is a Linux-based live system for zeroing data. Even by means of the executable under Windows AxCrypt encryption software can be deleted safely to the algorithms files mentioned above.

Need

Programs for Data Recovery can easily recover files noted as deleted in the system under certain circumstances. In addition, various specialized companies offer as part of the data recovery or computer forensics to their services to restore seemingly lost files.

In order to prevent such recovery, overwriting the free given again by the previous deletion region on the data storage is necessary. How often and in what form the corresponding areas need to be overridden, is highly controversial.

In an imagined end of 2008 scientific study of this question was investigated in terms of hard drives. Data were " overwritten controlled conditions and the magnetic surfaces then examined with a magnetic force microscope " under. In the study, it was found that regardless of age and the memory size of the checked storage medium, the probability of recovering the data already after a single overwrite " virtually zero " was. Only with clarity on the position of the requested data, it was possible in 0.97 percent of all cases, to reconstruct a single byte correctly.