If you have enabled iCloud, then your data is stored in your personal iCloud Account which is encrypted by default by Apple using your Apple ID credentials. We don’t perform additional encryption on top.
As an additional security precaution, you can add passcode protection to safeguard your data. Please also go through Apple’s Security guidelines for best practices such as adding two factor authentication to your Apple ID.
Note: Passcode protection is currently saved local to the device and therefore not synced to other devices. Therefore passcode protection will currently not protect again delete and reinstall of the app from the App Store.