[melito]

In iOS you can specify that files in an app's sandbox are "encrypted" when the device is locked.

https://developer.apple.com/library/mac/documentation/FileMa... (See "Files Can Be Encrypted On Disk")

Implementing the feature is pretty trivial and works on a file by file basis

https://developer.apple.com/library/ios/documentation/iPhone... (See "Protecting Data Using On-Disk Encryption")

More details about the options here: https://developer.apple.com/library/ios/documentation/Cocoa/...

https://developer.apple.com/library/ios/documentation/Cocoa/...