161

Modern SSDs use a technology called SED which allows instant erasure. It works by transparently encrypting the entire drive and keeping the key on the drive. ATA Secure Erase is then implemented by wiping the key alone, which renders the rest of the data immediately unreadable (assuming of course that it has been correctly implemented on that particular ...


70

Yes that is a good idea to overwrite then delete/release the value. Do not assume that all you have to do is "overwrite the data" or let it fall out of scope for the GC to handle, because each language interacts with the hardware differently. When securing a variable you might need to think about: encryption (in case of memory dumps or page caching) ...


51

Very good question. Yes, by default, WinRAR leaves traces of temporarily extracted files. WinRAR does indeed create temporary files when opening them directly from the archive. It also performs a normal deletion once WinRAR is closed. However, deleted files do physically stay on the disk after you delete them. Normal delete operations only delete the file ...


34

Storing a value that isn't used again? Seems like something that would be optimized out, regardless of any benefit it might provide. Also, you may not actually overwrite the data in memory depending upon how the language itself works. For example, in a language using a garbage collector, it wouldn't be removed immediately (and this is assuming you didn't ...


18

You need a threat model You should not even begin to think about overwriting security variables until you have a threat model describing what sorts of hacks you are trying to prevent. Security always comes at a cost. In this case, the cost is the development cost of teaching developers to maintain all of this extra code to secure the data. This cost ...


15

The best citation I can give is from Overwriting Hard Drive Data: The Great Wiping Controversy, which was published as part of the 4th International Conference on Information Systems Security, ICISS 2008. You can view the full text of the paper by viewing the book on Google Books, and jumping to page 243. The following excerpt is from their conclusion: ...


14

Yes, it is good practice security-wise to overwrite data that is particularly sensitive when the data is no longer necessary, i.e. as part of an object destructor (either an explicit destructor provided by the language or an action that the program takes before deallocating the object). It is even good practice to overwrite data that isn't in itself ...


11

Given that the device is not a solid state drive, should a secure ATA erase still be performed? If you want to erase the data, you can use ATA Secure Erase. It is not meant only for solid state drives and works fine on spinning rust. It takes a lot longer than on SSDs because hard drives are less likely to support SED, which allows instant erasure by ...


11

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 ...


8

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.


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 ...


5

Destroying data properly without physically damaging the media is quite a difficult task, especially since HDDs have started coming with block reallocations. This is orders of magnitude more difficult (if not impossible) with SSDs, since there the firmware does literally magic with what is really stored in the flash. As my comment asking for more detailed ...


5

It is almost certain that whatever you do, your data will not be irrevocably destroyed. Even if the organisation you trusted with your personal data had the best of intentions it would be an enormous effort to really physically delete all of your data from all the places it will have been duplicated to, including backups and SSD spare sectors. No ...


4

Normally when you wipe a drive there are still ghost remains of the data even after overwriting the disk multiple times. I'll save you some work. This isn't true, and hasn't ever been true as far as anyone can tell. The technique often referred to here is called Magnetic Force Microscopy (MFM) and was referenced in an old DoD standard for disk erasure. ...


4

It is important to overwrite sensitive data immediately after it is needed because, otherwise: The data stays on the stack until overwritten, and might be viewable with a frame overflow from a different procedure. The data is subject to memory scraping. Indeed, if you look at the source code for security-sensitive applications (e.g. openssh), you will find ...


4

The aluminium coating of the CD reacts and creates plasma. So it burns the CD effectively. Below you can see the image of a microwaved CD. It's safe to say it's been destroyed.


4

As usual, the Wikipedia page contains useful links (Wikipedia is not "The Truth" but it is a great starting point for investigating technical issues and making one's own mind). In particular, it says that: As of November 2007, the United States Department of Defense considers overwriting acceptable for clearing magnetic media within the same security area/...


3

It depends. If you want to delete every trace of the file, it is more complex than overwriting sectors. Depending on which file system you are using, but if e.g. NTFS: even if you fill all free space, there can be things left behind in the MFT, journaling areas, etc. If it is a very small file, the entire file can be contained in the MFT, etc Also, ...


3

The original example shows a stack variable because it's a native int type. Overwriting it is a good idea otherwise it lingers on the stack until overwritten by something else. I suspect if you are in C++ with heap objects or C native types allocated via pointers and malloc that it would be a good idea to Use volatile Use pragmas to surround the code ...


2

It is possible that the chunk of memory was paged out before you went and deleted it, depending on how the usage distribution in the page file plays out the data may live there forever. So to successfully remove the secret from the computer you must first ensure the data never reaches persistent memory by pinning the pages. Then ensure the compiler doesn't ...


2

Windows have a tool called cipher which can be use to fully overwrite empty disk space with 0x00 and 0xFF Just simply run in cmd: cipher /w:c: (c: is the drive letter you wanted to run on)


2

You can't be guaranteed that your file will be deleted successfully just by trying to overwrite it with other files. You don't have any say over what sectors get written with data. Your deleted file will stay on the hard drive until the OS determines that it needs to write over those sectors. So the short answer is no. Sdelete is a sysinternals tool that ...


2

I'm not 100% sure what the EU laws and guidelines would be however; I suspect it's left to the member states to decide what to issue in regards to deletion of personal information. with that said I found a PDF from the UKs Information commissioner’s Office (ICO) and they state in this document that... ...the ICO will adopt a realistic approach in terms of ...


2

Stealing data living on one VM directly from another VM is not a realistic attack scenario currently. While there are side channels which allow a small information leakage it is currently more a theoretical and expensive thing to exfiltrate data that way. Much more likely are attacks directly against the VM containing the data (i.e. SQL injection, SSH brute ...


2

Regarding the reuse of recycled tape; the business may appear sound but the technical parts are not. Even apart from the issue of securely wiping data, it is hard to determine if tapes were properly stored before they were sent to you for recycling. Magnetic tape is susceptible to mold damage if stored in high humidity conditions. Unless it is used for ...


1

ENISA is probably your friend here, taking a look at the ENISA report on Securing personal data in the context of data retention, there is a specific quote: there are no norms and standards in place regulating how the destruction of data should take place. along with the recommendation: Provide clear instructions on the procedures that have to be ...


1

Actually the answer is yes, you probably should overwrite it before deleting it. It you are a web-application developer then you should probably overwrite all data before using delete or free functions. Example of how this bug can be exploited: The user can insert some malicious data into input field. You proceed the data and then call free function of ...


1

The best solution is really the simplest. Don't save the information you don't want to end up in someone else's hands in the first place. Don't want your logs to be recoverable after deletion? Don't log. Don't want your cookies to be used to track you? Don't use cookies. Don't want deleted messages to be recoverable later? Well, that's a tough one, because ...


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