this post was submitted on 15 May 2024
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I suspect that it doesn't actually work. I mean, they can overwrite the logical positions in the file file if they want, but that doesn't entail that it actually overwrites the underlying physical blocks, for a number of reasons, starting with some of the stuff at the drive level, but also because of higher-level issues. What filesystem does Android use?
googles
Looks like yaffs2, at least on this system.
https://stackoverflow.com/questions/2421826/what-is-androids-file-system
https://en.wikipedia.org/wiki/YAFFS
Yeah, note the "log-structured" bit there.
https://en.wikipedia.org/wiki/Log-structured_file_system
So, what happens is that when you write, it's going to the log, and then there's a metadata update once the write is complete saying "I wrote to the log". The app probably isn't writing to the previous location of the data on the disk, because writing to byte offset 32,000 the second time in a file will go to a different logical location on the storage device than the first time you wrote it, causing the thing to not actually be overwritten.
googles
https://arxiv.org/pdf/1106.0917
I'd also note that this is a lead-up to proposed solutions, but that's only handling things down to the level that the OS sees, not what the flash device sees; they don't mention things like wear leveling, so they probably aren't taking that into consideration.
EDIT: Oh, they do mention it, but just to say that some of their approach might work (like, what they mean is that if it writes enough data in the background, it might eventually overwrite whatever, even if the OS has no control as to what's being written):
So if I am reading this right thermite is the safest way to permanently delete my data right?
Well, physical destruction. Thermite maybe isn't the best route.
Really, it depends on your definition of best.
Nope regardless of the situation. Thermite is always the best solution
It will be effective as fuck though.