Sandboxing and App data storage

As we mentioned in the beginning of the chapter, a code signature is placed on the app bundle itself with additional protection, so that the signature is verified not only when the app is installed, but also at runtime when the app is launched, to make sure that it has not been modified in the meantime. This is for stability as much as it is for security, since code that has been modified or allowed to run roughshod on the system can cause the device, which we might just want to be able to use to call 911 in an emergency, to crash.

We spoke about a mobile user which would have a home folder. Unlike the common consumer computer OS, the data storage location of an app is randomly generated and kept separate from the user (besides the containerization of specific preferences that help sharing among a developer's apps, so those settings persist even if an app is deleted). There are frameworks, which are shipped by Apple in its SDK, that encourage storing...