[wpietri]

Probably not. Erasing leaves marks.

The only marketable purpose for an instant erasure system like that is protection of information (personal or commercial). To build that, you'd make something that zeros all the files and deletes them, deletes and overwrites all the contacts, and such.

But the structures left after that don't look like a brand new device. They look like you had a bunch of things and then erased them. Cops won't know what you erased, but they'll know you handed them a phone that was recently erased.

Now maybe somebody will build an app tuned for obstruction of justice, so it tries to make the phone look brand new. And maybe you'll be very lucky and they'll get it working perfectly on your specific phone. But then you have to explain how you have a brand new phone that was actually purchased a year ago. And how it has no record of any of the calls that your phone carrier will have records of. The obvious conclusion is that you wiped it sometime after your last call and with special software that only appeals to people planning on hindering an investigation.

Is that enough to convict you for obstruction of justice? I have no idea; it probably depends on how much a prosecutor cares. But is it enough to convince cops you are vigorously hiding something? You bet.

[PhantomGremlin]

make something that zeros all the files and deletes them, deletes and overwrites all the contacts

No, there's no need for anything that complicated.

In principle, encrypting all data on a phone is really simple to implement. In practice, it's carefully thought out to avoid edge cases. The general idea is something like this:

   when first activated, the
   phone generates a random 256-bit AES key

   phone uses this random AES key to encrypt
   all data stored on the phone

   phone retains this random key in a special
   location, and encrypts this key by using
   the user-provided PIN

To quickly erase all data on the phone, all that's necessary is to overwrite the key in the special location with random data. From that point on, there is no feasible way to recover anything on the phone. Period.

It isn't necessary to erase an entire device. It's merely necessary to replace a 32-byte field (that contains the true AES key) with 32-bytes of random data.

From then on, it doesn't matter what the PIN is. Data on the phone is jibberish unless and until the proper 256-bit AES key is produced. That key no long exists, so from that point on the only way to recover the data is by brute forcing AES, by trying all possible 2^256 combinations.

They look like you had a bunch of things and then erased them

No, what remains is indistinguishable from the case where the correct PIN hasn't been provided. Having "things" on the phone is no evidence of guilt. There is absolutely no evidence that the phone was erased. All that is known is that the provided PIN isn't able to decrypt the data.

[wpietri]

Good point. If the phone OS supports encryption and allows this sort of auto-destruction of keys, then that's a lot better.

What we were discussing is abakker's proposal for something that "wipes the phone", and I think my comments are still relevant to that approach.

Of course, a suddenly unreadable phone is still suspicious, but if your plan were perfectly implemented, it might be impossible to prove obstruction of justice.

[realusername]

It depends, is there any legal requirement that the device actually has to record a call log normally ?

[wpietri]

Not sure how that matters. Is there any legal requirement to keep your receipts? No, but if you suddenly throw them out because you think the police might find them useful, that's still obstruction of justice.