IOS Developer Cheat Sheet – OWASP

In general, an app should store locally only the data that is required to perform its functional tasks. This includes side channel data such as system logging (see M8 below). For any form of sensitive data, storing plaintext data storage in an app’s sandbox (e.g., ~/Documents/* ) should always be avoided. Consumer-grade sensitive data should be stored in secure containers using Apple-provided APIs.

via IOS Developer Cheat Sheet – OWASP.