There is a slight difference.

Keychain and NSFileManager have possible modes of "kSecAttrAccessibleAfterFirstUnlock" [0] and "NSFileProtectionCompleteUntilFirstUserAuthentication" [1] respectively that are (fittingly) in an open state within your app after you've unlocked the device.

[0]: https://developer.apple.com/reference/security/ksecattracces...

[1]: https://developer.apple.com/reference/foundation/nsfilemanag...