Encrypt Realm database

[niqdev]

Implement a migration strategy to encrypt Realm database (version 0.87.5) and decide where and how to store the secure Key.

KeyStore is available only for API > 18 and currently minSdkVersion is 16, moreover KeyGenParameterSpec is available only on API > 23.

Below few useful links

http://stackoverflow.com/questions/34174113/updating-changing-realm-encryption-key
https://github.com/android/platform_development/tree/master/samples/Vault
http://android-developers.blogspot.it/2013/02/using-cryptography-to-store-credentials.html
https://medium.com/@vashisthg/android-secure-shared-preferences-10f8356a4c2b#.dw176v2cl

Example
https://github.com/googlesamples/android-BasicAndroidKeyStore

[niqdev]

... AndroidKeyStore deleted after changing screen lock type 😥

[niqdev]

Unfortunately also other libraries like ophio/secure-preferences and Qlassified-Android are affected by this well known issue.
So also if for an attacker who has physical access to the device would be harder (not impossible) to retrieve the keystore, the app would crash and the user will lose all its configuration just changing for example screen lock from pattern to PIN.
For this reason I will use scottyab/secure-preferences to store the database encryption key.

[niqdev]

App v2.2.0 has encrypted database