Ask HN: What's the best way encrypt data for a journal app I'm releasing?

I've been working on a journaling app for iOS for a little while.

One of the last pieces is to encrypt the data. Since there will be alot of sensitive information in here, I want to know the best way to do that.

I've found some libraries that will help me do this. But I have questions around implementation.

1) Is it necessary for me to ask each user for a password & use that as the key? Because if they lose it, I have no way to recover their data 2) Should I just create a global key to encrypt the whole app and use that?