iOS - Protecting files with a custom encryption key?

Question

Yesterday I posted this question about protecting files: Protecting the app sandbox

As mentioned, it appears that this is effective for protecting a file if the user has a passcode on the iPad. Naturally this raises the question of how to handle the encryption if the user does not. Now I have an idea, but am not sure if it's feasible or not.

Is there any way to override the encryption key to use a custom one? My gut instinct is no, but I figured there may be a way. (Btw, this is just an experiment for fun, I don't plan on submitting this to the app store...) My application has a login, and it would be very handy if this could be handled at the application level to accommodate users that do not have a lock.

However, I suppose it wouldn't be unreasonable to disable the saving feature if there is no device passcode... Any thoughts?

score -1 · Accepted Answer · answered Jan 05 '11 at 14:47

-1

You can generate encryption key, based on login/password, this allowing user to open his files only if he know password. However, you'll need provide ability to restore data in some way if user will forget his password.

answered Jan 05 '11 at 14:47

Nickolay Olshevsky

13,706
1
34
48

Yeah, well I wanted to explore the options available before I go implementing my own encryption scheme. I will ultimately do something like this if all else fails... – gabaum10 Jan 05 '11 at 14:52
You can use OpenSSL, it contains all needed functionality. – Nickolay Olshevsky Jan 05 '11 at 14:53
Will this play nice while writing NSData to the disk? – gabaum10 Jan 05 '11 at 14:58
openSSL should work with char*, however NSData can be easily converted to this type. – Nickolay Olshevsky Jan 05 '11 at 14:59
This is true, interesting approach. Have you ever done this? I am going to dig around some more (and wait to see if anyone else has anything to add), before I mark this... – gabaum10 Jan 05 '11 at 15:05
Unfortunately, I only looked over OpenSSL sources some time ago, and know what it should be able to do. – Nickolay Olshevsky Jan 05 '11 at 15:35

iOS - Protecting files with a custom encryption key?

1 Answers1

Linked