implement android keystore to prevent unwarranted access to private key

[harlo]

(harlo#3)

While access to the internal data is protected on non-rooted devices, a rooted device could potentially access the contents of the iocipher storage and abuse the private key.

Proposed fixes:

1. use android keystore to further protect access to private key's credentials, that way it can only be accessed in-app

We should further discuss properly using Android Keystore, especially in relation to rooted devices.

[n8fr8]

How does this interact with Cacheword? That is controlling the key used to unlock IOCipher. Shouldn't we implement this capability in Cacheword itself, and not just in CameraV?

[eighthave]

yes it would be great if cacheword used the Android Keystore, as long as it provides a real security improvement and doesn't harm usability. I haven't looked too deeply into the Android KeyStore stuff, so I can't say too much about it.

Here's what Abel has to say on the topic:
https://dev.guardianproject.info/issues/3119

[harlo]

Agree, but I didn't want to touch Cacheword because I am not as familiar with the codebase. Also worth noting, it appears that my upgrade to Marshmallow borked this feature as I implemented it (although working fine on pre-6 devices). Will follow up in coming days...