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I believe iOS handles this by ensuring all flash-written data is encrypted with an on-device key. A 'wipe' then definitively erases that key - making further o
by gojomo 5y ago
I believe iOS handles this by ensuring all flash-written data is encrypted with an on-device key.
A 'wipe' then definitively erases that key - making further overwrites of the freed data unnecessary.
If the crypto is strong, and the key never exfiltrated, then this may be even better than an explicit overwrite, which on some media (like magnetic drives) may still leave trace hints of the old data that advanced techniques could recover.
- lolthishuman 5y agoI’ve read opsec material that no matter how many passes you do it can still be read. Hard to know for sure unless you know the stack in and out like the back of your hand.
- tailspin2019 5y agoThat’s probably true but the GP is likely drawing the distinction that iOS tries to do an “unrecoverable” delete as best it can whereas presumably the Echo is not doing this (encrypting the data and then deleting the key as part of the reset).
- vlovich123 5y agoA lot of that opsec material is very dated back from when density was lower and you had a spinning disk. Do you have any that’s evidence-based that such techniques are needed for flash storage? If anything the opsec concerns are different. There’s very little that would force the controller to actually perform erase of specific blocks (eg the flash could blacklist blocks due to errors). To my knowledge that’s the primary concern, not that the data is still somehow recoverable once erased (which used to be true but I’m not sure holds for modern storage).
- nyolfen 5y agothis does not apply to cryptoshredding or any modern storage media. even a single pass on magnetic media renders data unrecoverable.
- jcrawfordor 5y ago1) Modern research suggests that recovering data which has been overwritten once on magnetic media is probably not feasible due to the high density of modern magnetic storage devices and the use of dynamically aligning heads (e.g. that follow track geometry as they read) instead of absolutely positioned heads (stepper motors) that allow for more error in alignment. 2) Nonetheless, there is an appreciable risk of data remaining on the device due to non-volatile caches, remapped disk areas, and other factors that are not always well understood or disclosed by the manufacturer. Manufacturers have also been found to be unreliable in their implementation of ATA security features (e.g. embedded secure erase). As a result, with few exceptions it is U. S. government policy to permanently destroy all storage devices rather than trusting any kind of secure erasure. The typical NSA-approved method is either to degauss (surprisingly tricky to do right) and then crush, or reduce to 2mm particles with a device resembling a large, terrifying blender.
- jfrunyon 5y ago> As a result, with few exceptions it is U. S. government policy to permanently destroy And as a result, (probably) Iron Mountain makes bucketloads because we don't just encrypt the drives (let's face it, that would be perfectly acceptable for 99% of US government computers - maybe Top Secret stuff deserves proper destruction).
- kps 5y ago> I’ve read opsec material that no matter how many passes you do it can still be read. If that were true, we'd have infinite storage capacity.
- taeric 5y agoGiving some charity to the claim, I'm assuming it meant on devices you plan to dispose of.
- neolog 5y agoI don't see how throwing it away improves storage capacity in a way that would invalidate GP's comment
- taeric 5y agoThe assumption isn't infinite capacity. It is recovery of the last data.
- DSMan195276 5y agoIs that fundamentally different from the question of whether overwriting data can make it unreadable? If yes then you can eventually make the "last data" unrecoverable by overwriting it. And if no then presumably you can recover anything previously written to the disk, ergo infinite capacity.
- tempestn 5y agoPresumably the original comment meant that you can't guarantee the original data is unreadable with any finite number of overwrites, not that you can always read the original data after overwriting. I'm not saying that's true, but it's a logical interpretation that doesn't imply infinite storage.
- Gigachad 5y agoEven if you could find the original crypto header, You still need to know the password to unlock it. On iphones, the secure enclave will hold the decrypted key while its running but you need to enter the password after a reboot.
- Gigachad 5y agoAlso if someone had the technical capability to do this. I would be infinitely more concerned about them having an exploit which allows them to hack my next phone and grab all the data while its running.
- fpgaminer 5y ago> If the crypto is strong, and the key never exfiltrated, then this may be even better than an explicit overwrite, which on some media (like magnetic drives) may still leave trace hints of the old data that advanced techniques could recover. The idea that magnetic drives left readable traces behind after an overwrite is a myth (especially of modern drives; if I recall the article I'm thinking of correctly the myth may have had a _slim_ chance of being true with old drives [like 100MB days]).
- rootw0rm 5y agoI'm fairly certain you're correct, but the fact that various secure delete tools overwrite data multiple times probably helps propagate this myth.
- quaintdev 5y agoI wonder how it is even possible in those 100MB disks.
- thefurrysquid 5y agoLow density data, paired with not very accurate head tracking.
- rebuilder 5y agoThe idea was that, since the drive head doesn’t pass over precisely the same area on the track every time it writes to the disk, the track has to be wide enough to account for this lack of precision. Thus, a single overwrite pass could leave a portion of the track’s edge unchanged and readable with an electron microscope or something.
- Doxin 5y agoI always figured that a write wouldn't change the magnetic field 100%. Say it's 90% effective at changing the magnetic field. There's now four options: 1 overwritten by 0: 10% field strength 0 overwritten by 0: 0% field strength 1 overwritten by 1: 100% field strength 0 overwritten by 1: 90% field strength But I guess that's not quite true.
- infogulch 5y agoI agree, there is only one reasonable method to consider a drive "wiped": encrypt all data written to it with a key; wipe == destroy the key. Drives are basically little computers now, they have full-featured CPUs, OSes, memory, write caches and persistent buffers, they compress data before writing it, lie to you about where the data is (ok fine, it's a legitimate abstraction), and who knows what else. My point is that drives have become way too complex for wiping by "overwriting" "every" "block" to ever be an option again (and yes all three of those words deserve scare-quotes). The answer to this problem has become: always encrypt, lose the key to wipe. Period.
- flavius29663 5y agowhat if you just fill the whole disk with random bytes? Wouldn't that take care of it ?
- thelopa 5y agoThere could be bits of plain text data left over in over-provisioned storage set up in case a block goes bad (e.g. a flash cell that can no longer erase).
- flavius29663 5y agoWould that extra cell be used unless there is a need for it? If there is a need for it, then I assume it will be a need for it when you fill the drive too. But yeah, it depends on the manufacturer of the drive, so you don't want to take the chance, Full encryption is unbeatable.
- dan000892 5y agoFlash devices maximize the longevity of the cells by wear leveling. The on-board controller maintains a map between the physical cell layout and the logical layout that's changing with every single write operation. Extra cells are used both reactively and proactively. Reactively: Error when erasing or write/verifying a cell? Copy contents to spare cell, flag old cell as bad, update the map, maybe complain if running low on spare cells but otherwise call it a day. Proactively: Cells are only rated for so many erase operations which directly informs the longevity (total bytes written) of a drive. MLC cells can be written to 3,000 times and SLC 20,000 but the latter is much more expensive. For use cases where greater longevity is required (without spending SLC money), why not put a disk together that has twice as many cells as it needs and wear level across all of them? If you `dd if=/dev/zero of=/dev/sdX bs=64k status=progress` your 32GB drive and it'll complete after 32GB but you have no way of knowing how many more cells that drive has that you didn't touch. (Also as one of the parents pointed out, disk controllers are getting smart. You don't know if it was transparently compressing data too causing you to touch even fewer cells. ATA Secure Erase is the way to go.)
- emodendroket 5y agoNot true of older Android phones, however.
- deleted 5y ago[deleted]
- 8note 5y agoIf the crypto is strong, wouldnt the leftovers be equivalent to not overwriting? The only better is less wear on the disk
- sizzle 5y agoI’ve always wondered this, instead of writing many passes of gibberish data that takes many hours, could I simply format the drive in seconds, encrypt the whole blank drive with a long generated password, then format and encrypt a second time in seconds and be done? Or if I’m feeling spicy, do all this then hit it with a hammer until it’s shattered in a million pieces like my dreams of working in tech.
- Kwpolska 5y agoIf the first encrption would encrypt the entire drive, then you’ve effectively done a 1-pass erase. It might work, but I would still prefer specialized software — perhaps the encryption method of choice would still leave some data unencrypted or untouched. The hammer method also sounds fine to me.