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63

Best stop doing that. Never overwrite an SSD/flash storage device completely in order to erase it, except as a last resort. NVRAM has a limited amount of write cycles available. At some point, after enough writes to an NVRAM cell, it will completely stop working. For modern versions, we're in the ballpark of an estimated lifespan of 3,000 write cycles. ...


53

Summary: it was marginally better on older drives, but doesn't matter now. Multiple passes erase a tree with overkill but miss the rest of the forest. Use encryption. The origin lies in work by Peter Gutmann, who showed that there is some memory in a disk bit: a zero that's been overwritten with a zero can be distinguished from a one that's been overwritten ...


38

Yes. If you do a normal format, the old data can be recovered. A normal format only deletes/overwrites a tiny bit of filesystem metadata, but does not overwrite all of the data itself. The data is still there. This is especially true on SSDs, due to wear levelling and other features of SSDs. The following research paper studies erasure of data on SSDs: ...


26

The only NIST approved method to securely erase a hard drive is by utilizing the secure erase internal command - documented at the Center for Magnetic Recording Research (CMRR) - and that is what everyone should be doing. It is an ATA command, and covers (S)ATA interfaces. After that, you can optionally degauss the drive to erase the firmware itself. Lots ...


20

The proper answer for this question is very situational, and dependent upon the policies and procedures in place at your company. Many companies have in place methods of backing up portions of the drive meant for user data, or even the entire drive, across the corporate network. If they've performed such backups on your system, there's nothing you can do ...


18

Overwriting the data is either insufficient or useless, depending on how things are done internally by the device itself. Flash memory has a limited life, expressed in terms of read/write cycles. To sum it up, you can have one block of data full of zeros; bits can be changed from zero to one individually, but the reset to zero can be done only for a complete ...


18

The reason you write '0' instead of '1' has to do with the way magnetic storage encodes the 0 and the 1. a long explanation of it can be found on Wikipedia under Run-length_limited. In short RLL is the methodology used to store the '1' and '0' and it is more complex than just to store the bit values themselves. On a side note to make the drive more like it ...


15

From a theoretical standpoint the idea of total drive destruction may be the only way of destroying data on a hard drive fully. From a practical standpoint, I've not seen any evidence that it's possible to recover meaningful data from a standard hard drive (ie, not taking SSDs or other devices that use wear levelling or similar technologies) after a once ...


11

As storage technologies change over time, using different encodings and remappings to deal with sector errors, the best way to permanently erase data changes also. Very smart people have expended enormous amounts of time and effort arguing over this problem. Most of them end up at the same bottom line, which is: the only method you can truly trust is ...


11

A paper from 2011 by four people from the University of California, San Diego writes in section "3.2.1 Built-in sanitize commands": Of the 12 drives we tested, [...] Eight of the drives reported that they supported the ATA SECURITY feature set. One of these encrypts data, so we could not verify if the sanitization was successful. Of the remaining ...


11

You are seeing a consequence of the ongoing war between binary and decimal systems. Namely, 210 = 1024, which is close to 1000. Hence a widespread habit of saying "kilobyte" (as in "1000 byte") for a quantity of 1024 bytes. When we go to megabytes and gigabytes, the deviation increases: 220 = 1048576, and 230 = 1073741824. Therefore, if tool A displays a ...


10

Do you need to erase the data, or do you need to persuade other people that the data has been erased? (I will only talk about 'entire disk' wiping; I'm not talking about wiping single files or slack space.) As far as I am aware there is no software package that claims to be able to recover data that has had a single overwrite. There are no companies that ...


10

You've described the principles behind a live CD boot. This can be most strongly ensured by having no permanent media within the machine. I'm going to gear my answer towards Linux as that's what I'm most familiar with in this context. Having a hard drive with all disk partitions mounted as read-only and all read-write partitions mounted in memory would also ...


10

It can be. Generally speaking, programs while running don't tend to wipe out their data (they do, after all, tend to need it), and any process with the ability to access other programs' allocated RAM can, in fact, read it. This is how, for example, the recent spate of big box store hacks were able to leak so much credit card data -- the attacks were carried ...


9

I'll put my proper IT hat on - still just about fits - and suggest you could try asking your IT team what their process is - the answer might reassure you. Typically, IT are going to make a "just-in-case" backup of your drive and put it on a shelf ("just-in-case" management realises a year after you've gone that you had a file on your drive that is ...


9

Logically deleting is very common in many application that handle huge amounts of data for performance reasons. This includes other email programs for example Microsoft Outlook and even database servers for example MySQL. Even files, that you delete from your hard disk, are not actually destroyed. The space is just flagged as empty and may be override in ...


9

There is a well-known reference article by Peter Gutmann on the subject. However, that article is a bit old (15 years) and newer harddisks might not operate as is described. Some data may fail to be totally obliterated by a single write due to two phenomena: We want to write a bit (0 or 1) but the physical signal is analog. Data is stored by manipulating ...


8

You are correct, in order for a file to be deleted the actual disk blocks it previously inhabited must be overwritten. This is generally done with random data; for example, the Windows tool 'cipher' overwrites unused (e.g., formerly used) disk space with 0s, then 1s, and then random data. If a forensic investigator were to look at your computer's disk, and ...


8

The problem with deleting files is that the file data is just one small part of what really gets saved onto your disk. On a modern filesystem there will be lots of metadata and other artefacts scattered around the disk: Journal entries on journalling filesystems, e.g. NTFS, ext3, ext4. Search index entries. Prefetch / superfetch cache entries. Shadow ...


8

No on both counts, assuming the implementation is within spec. Secure erase works through encryption, usually AES. Essentially, everything that is written to the SSD is first encrypted with a master key. This happens all the time, is entirely managed by the device's on-board firmware, and is completely transparent. The master key is randomly generated on ...


8

No, it isn't necessary. With modern (less than 10 year old) hard drives, it is not required to overwrite a disk more than once. There is an often cited paper which says that you need to overwrite data at least 10 times to be sure, but that paper is over 20 years old and thus applies to outdated hard drives. Modern hard drives use much weaker magnetic ...


8

NTFS sort of does if you include The Encrypting File System as part of it. The Encrypting File System (EFS) on Microsoft Windows is a feature introduced in version 3.0 of NTFS Secure deletion is supported by cipher.exe: You can use the Windows Cipher utility (with the /W option) to wipe free space including that which still contains deleted ...


7

SSD's and Flash drives are an interesting problem... As @Bell pointed out as a response to this question: Yes, the effectiveness of the shredding operation is dependent on a fixed or physical mapping between a block number and piece of non-volatile storage. This works for spinning media but not for SSDs which virtaulise their blocks for performance ...


7

1) With modern filesystems, there is no more concept of securely deleting an individual file. It might have been copied around, snapshotted, written to a different location upon editing, etc. 2) With modern drives, there is no deletion / wipe without confirming it. Some drives have had a Secure Wipe command flat-out lies to you, returning immediately while ...


7

If you use sdelete from Microsoft (http://technet.microsoft.com/en-us/sysinternals/bb897443.aspx) you don't have to install anything. It has an option to fill the unused disk space with zeroes too. If you already deleted the files this is what I'd just to make sure that nothing remains of the original file.


6

EEPROMs work by storing charge in floating-gate transistors. Think of these transistors like tiny capacitors that leak extremely slowly (typically with retention lifetimes of 10+ years), except with the added provision that you can tell whether it's charged or uncharged. Programming one simply involves feeding it a power source and pulling the gate to high ...


6

Sounds like a fun project. I know you said "simple," but here are my thoughts anyway. The data you're writing the file over with isn't random, and one pass will still leave traces of the original data. It depends on the storage medium. For example, with magnetic devices, there's magnetic force microscopy. Even after ten rounds of the same thing, I'm not ...


6

If ATA Secure Erase is not an option or not supported on your hard drive, I'd recommend DBAN. DBAN is a well-engineered piece of software for wiping a hard drive, by performing multiple overwrite passes at a very low level. As a result, it is time-consuming but very thorough. It includes methods based upon Gutmann's research, DOD standards, and other ...


6

When you delete a file, the information is not immediately removed from the disk. Instead, the OS/file system simply updates a database keeping track of files on the disk to acknowledge that the file is no longer needed and hides the file from being visible. The information is only removed when, at some point in the future, the OS decides to use the space ...


5

First of all, a single overwrite is adequate for all current magnetic hard drives. It has never been as easy to recover information from drives as people have claimed. Second of all, you can't erase flash drives simply by overwriting them. You'll wear them out with overwrites long before you actually overwrite all the data. The only way you can be ...



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