encrypt data in SharedPreferences

Im currently developing a framework for oAuth 1 and 2 access to webservices and my question is, how do i store sensitive data like an oAuth access key in a secure way? the problem with this keys is that some platforms like twitter use a permanent key and if someone would get access to this key he could do whatever he wants with the users twitter account..

so is it possible to automatically encrypt the data before it is stored in the shared preferences? Or is there a better way/place to store very important data?

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