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Do you have any sources for the assertion that resetting an iOS device doesn’t remove data?

wrboyce 5y ago
Do iOS devices not leverage full disk encryption? In which case I’d assume simply wiping the encryption keys/fde headers would be sufficient? (Which it almost certainly does.)
croon 5y ago
https://www.apple.com/ca/business-docs/iOS_Security_Guide.pdf https://www.apple.com/ca/business-docs/iOS_Security_Guide.pd... > The “Erase all content and settings” option in Settings obliterates all the keys in Effaceable Storage, rendering all user data on the device cryptographically inaccessible. Semantics debate around whether leaving data practically inaccessible is the same as removing it, but considering where we are, I'd say it isn't. Granted, this is from 2018, but I doubt the defaults and concept have changed.
- Retric 5y ago
  Securely deleting the keys is safer than simply practically inaccessible. That suggests their is some impractical way to access the data, care to suggest what that might be?
  - emsy 5y ago
    Overwriting flash with 0s. To be fair I think the iPhone should grant you that option (MacOs does). But to suggesting that leaving an encrypted block of data on the device is on the same level as leaving unencrypted blocks of data lying around is foolish.
    - deleted 5y ago
      [deleted]
    - Retric 5y ago
      Overwriting flash data isn’t going to give you access to the data. It might in theory be more secure, but I would favor encryption at rest rather than simply overwriting plain text.
  - jfrunyon 5y ago
    Encryption can be (and in fact certainly will be, given enough time) broken.
    - Retric 5y ago
      It is possible in theory to recover some information from overwriting flash data with zeros, it’s also possible in theory for well designed modern encryption to be broken but neither of those are guaranteed at this point.
      - jfrunyon 5y ago
        Essentially every encryption scheme in history has been broken. It's a bit silly to think that "well designed modern" makes it safe. The others were all well designed and modern at one time, too. The only scheme that's truly unbreakable is a one-time pad and that's... well... not really practically useable. Personally, that's not a risk that I would care about (especially in the context of an Echo Dot or even an iPhone), but deleting the keys will not be better than inaccessible forever.
vlovich123 5y ago
Even if you didn’t have the public docs explaining this, you could make an educated guess because resetting the iOS device takes the same amount of time regardless of how much data you put on it and that time is on the order of 10s of seconds. iPhones don’t have erase speeds of 12gigabit/s - I don’t think there’s any storage technology that could do that. Also remember that Apple takes seriously the concern about the data leaking because the OS decided* to blacklist a bad block. Once a block has gone bad you probably shouldn’t rely on attempts to erase it working out. * if I recall correctly iOS devices don’t use a traditional flash controller and Apple does that mapping themselves (it’s also largely why Apple devices have better flash performance than competitors)
- ashtonkem 5y ago
  > you could make an educated guess because resetting the iOS device takes the same amount of time regardless of how much data you put on it This is incorrect. Secure deletion should cover the entire disk no matter how much data was used before, in order to deny an attacker any information or to guide their recovery efforts. I would absolutely expect a secure deletion process to take the exact same amount of time regardless of how much data is used. A better tell is the difference between the same model of phone with different storage sizes. A 512GB iPhone should take 2x as long to securely wipe compared to a 256GB one, assuming they’re actually overwriting the encrypted data with random noise. > iPhones don’t have erase speeds of 12gigabit/s It’s worth pointing out that a true secure delete is actually a write not a delete. But it’s true that your typical iPhone could not possibly overwrite its entire disk in 10s or so, although last time I did a reset it took much longer than that.
  - vlovich123 5y ago
    > This is incorrect. Secure deletion should cover the entire disk no matter how much data was used before, in order to deny an attacker any information or to guide their recovery efforts. I would absolutely expect a secure deletion process to take the exact same amount of time regardless of how much data is used. That's a fair point. Still, mobile devices typically employ FDE to avoid the need for scribbling over the entire flash (also improves the lifetime of the flash in that way). > It’s worth pointing out that a true secure delete is actually a write not a delete Flash storage doesn't work that way unless you're referring to something else. To write a block you have to erase it first (makes the block all 1s or all 0s depending on the chip). An update of a block is technically then a read/erase/modify/write (although flash translation layers will elide the first 3 steps by writing to a free block & marking the old one as GC'able). Writing random patterns into flash to my knowledge generally isn't needed anyway as it was with magnetic storage. The only purpose of writing in a secure erase scenario is to try to overwhelm the flash translation layer to force every block to be touched. > although last time I did a reset it took much longer than that. I haven't profiled it, but any slowness erasing an iOS device is probably because the flash storage backing the secure element is optimized for reads rather than writes. Additionally, it may be erasing various metadata/caches in the OS storage that aren't covered by the encryption key.

Do iOS devices not leverage full disk encryption? In which case I’d assume simply wiping the encryption keys/fde headers would be sufficient? (Which it almost certainly does.)

croon 5y ago

https://www.apple.com/ca/business-docs/iOS_Security_Guide.pdf https://www.apple.com/ca/business-docs/iOS_Security_Guide.pd... > The “Erase all content and settings” option in Settings obliterates all the keys in Effaceable Storage, rendering all user data on the device cryptographically inaccessible. Semantics debate around whether leaving data practically inaccessible is the same as removing it, but considering where we are, I'd say it isn't. Granted, this is from 2018, but I doubt the defaults and concept have changed.

Retric 5y ago
Securely deleting the keys is safer than simply practically inaccessible. That suggests their is some impractical way to access the data, care to suggest what that might be?
- emsy 5y ago
  Overwriting flash with 0s. To be fair I think the iPhone should grant you that option (MacOs does). But to suggesting that leaving an encrypted block of data on the device is on the same level as leaving unencrypted blocks of data lying around is foolish.
  - deleted 5y ago
    [deleted]
  - Retric 5y ago
    Overwriting flash data isn’t going to give you access to the data. It might in theory be more secure, but I would favor encryption at rest rather than simply overwriting plain text.
- jfrunyon 5y ago
  Encryption can be (and in fact certainly will be, given enough time) broken.
  - Retric 5y ago
    It is possible in theory to recover some information from overwriting flash data with zeros, it’s also possible in theory for well designed modern encryption to be broken but neither of those are guaranteed at this point.
    - jfrunyon 5y ago
      Essentially every encryption scheme in history has been broken. It's a bit silly to think that "well designed modern" makes it safe. The others were all well designed and modern at one time, too. The only scheme that's truly unbreakable is a one-time pad and that's... well... not really practically useable. Personally, that's not a risk that I would care about (especially in the context of an Echo Dot or even an iPhone), but deleting the keys will not be better than inaccessible forever.

vlovich123 5y ago

Even if you didn’t have the public docs explaining this, you could make an educated guess because resetting the iOS device takes the same amount of time regardless of how much data you put on it and that time is on the order of 10s of seconds. iPhones don’t have erase speeds of 12gigabit/s - I don’t think there’s any storage technology that could do that. Also remember that Apple takes seriously the concern about the data leaking because the OS decided* to blacklist a bad block. Once a block has gone bad you probably shouldn’t rely on attempts to erase it working out. * if I recall correctly iOS devices don’t use a traditional flash controller and Apple does that mapping themselves (it’s also largely why Apple devices have better flash performance than competitors)

ashtonkem 5y ago
> you could make an educated guess because resetting the iOS device takes the same amount of time regardless of how much data you put on it This is incorrect. Secure deletion should cover the entire disk no matter how much data was used before, in order to deny an attacker any information or to guide their recovery efforts. I would absolutely expect a secure deletion process to take the exact same amount of time regardless of how much data is used. A better tell is the difference between the same model of phone with different storage sizes. A 512GB iPhone should take 2x as long to securely wipe compared to a 256GB one, assuming they’re actually overwriting the encrypted data with random noise. > iPhones don’t have erase speeds of 12gigabit/s It’s worth pointing out that a true secure delete is actually a write not a delete. But it’s true that your typical iPhone could not possibly overwrite its entire disk in 10s or so, although last time I did a reset it took much longer than that.
- vlovich123 5y ago
  > This is incorrect. Secure deletion should cover the entire disk no matter how much data was used before, in order to deny an attacker any information or to guide their recovery efforts. I would absolutely expect a secure deletion process to take the exact same amount of time regardless of how much data is used. That's a fair point. Still, mobile devices typically employ FDE to avoid the need for scribbling over the entire flash (also improves the lifetime of the flash in that way). > It’s worth pointing out that a true secure delete is actually a write not a delete Flash storage doesn't work that way unless you're referring to something else. To write a block you have to erase it first (makes the block all 1s or all 0s depending on the chip). An update of a block is technically then a read/erase/modify/write (although flash translation layers will elide the first 3 steps by writing to a free block & marking the old one as GC'able). Writing random patterns into flash to my knowledge generally isn't needed anyway as it was with magnetic storage. The only purpose of writing in a secure erase scenario is to try to overwhelm the flash translation layer to force every block to be touched. > although last time I did a reset it took much longer than that. I haven't profiled it, but any slowness erasing an iOS device is probably because the flash storage backing the secure element is optimized for reads rather than writes. Additionally, it may be erasing various metadata/caches in the OS storage that aren't covered by the encryption key.