
Key-based device unlocking - samstokes
http://continuations.com/post/139510663785/key-based-device-unlocking-questionidea-re-apple
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BinaryIdiot
This simply isn't feasible.

Yes you can do key escrow via PGP (so you could, in theory, have a sound
encryption algorithm at work) but you have multiple sets of issues with this
idea.

First the way this escrow works is you encrypt the file system with a randomly
generated key. This key is then encrypted by using this escrow key the
manufacturer keeps along with another copy of the key being encrypted by some
random, initial password which is kept in plaintext or somehow already known
to the user (gotta be able to decrypt the encrypted filesystem when the user
first gets the phone). At that point the default password is used, the user
re-encrypted the key for the data using their own passcode. Now you have two
keys that can unlock the phone. This ignores the whole issue of being able to
access that data's initial key the entire time during transport but how else
are you going to give the user the ability to decrypt the data key so they can
even access the device?

Then what do you do with the keys? Phones are made in China so there would be
zero stopping China from forcing all companies to provide this escrow key. But
let's say you got around that, how do you respond to lawful requests for these
keys? You either need to move them all to the United States or keep them in
China; either way they're sitting somewhere, at least, where attackers could
attempt to gain access to.

Second, and honestly the biggest issue here, is the UX of this flat out sucks.
So now if you forget your password you either have to format the phone (thusly
destroying the original escrow key) or the phone is simply bricked and there
is no way to recover.

There is simply not a mathamatically way to provide multiple parties access to
an encrypted piece of data / volume without decreasing its security.

