# Data Erasure Algorithms

There exists an assumption that even when the storage medium is overwritten, physical properties (data remanence) of the medium may make it possible to recover the previous contents by using laboratory techniques.

To counteract this developed various data erasure algorithms. They indicate the number and sequence of write passes specific or random data.

It should be borne in mind that the more passes algorithm includes, the longer it takes to execute it.

Some of these algorithms are the national standards, and some offered by independent experts.

Note that the need for complex and lengthy algorithms is questionable. And there exists an assumption that in the real world, at least in many cases, a single overwrite by any data is enough that erased data can not be recovered.

**Data erasure algorithms used by Red Button**

Algorithm |
Passes |
Description |

Overwrite with Zeros | 1 | Logical zeros (0x00 numbers) to each byte of each sector. |

Overwrite with Random Data | 1 | You data is overwritten with random data. |

NAVSO P-5239-26 (RLL) | 3 | First pass - 0x01 to all sectors, 2 вЂ” 0x27FFFFFF, 3 вЂ” random symbol sequences, 4 - verification.
Red Buton performs only the first three passes. Navy Remanence Regulation, U.S. Navy Publication NAVSO P-5239-26 |

VSITR | 7 | The German national standard. 1 - 6 passes - alternate sequences of: 0x00 and 0xFF; seventh - 0xAA; i.e. 0x00, 0xFF, 0x00, 0xFF, 0x00, 0xFF, 0xAA. |

Complex Overwrite (Bruce Schneier's Algorithm) | 7 | Bruce Schneier offers seven pass overwriting algorithm in his Applied Cryptography book. First pass - 0xFF, second pass - 0x00, and then five times with a random sequence. |

Very Complex Overwrite (Peter Gutmann's Algorithm) | 35 | The method was presented in the paper Secure Deletion of Data from Magnetic and Solid-State Memory.
The article "Gutmann method" on Wikipedia |