How can I locally detect iPhone clock advancement by a user between app runs?

Question

A common exploit in casual games is to artificially advance the system clock to jump ahead in gameplay. How can such user clock advancement be detected by an app on an iOS device?

• Must not involve network communication
• Must not assume app is open (running or suspended) while clock is advanced
• Must detect clock advancement, detecting clock rollback is not sufficient

Ideally, the solution would be robust against reboots, but that is not a requirement.

Answer 1

CACurrentMediaTime & mach_absolute_time

Take a look at this questions:

iOS: How to measure passed time, independent of clock and time zone changes?

Calculating number of seconds between two points in time, in Cocoa, even when system clock has changed mid-way

CACurrentMediaTime uses mach_absolute_time: http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/CoreAnimation_functions/Reference/reference.html

Here you have an example on how to use CACurrentMediaTime: http://www.informit.com/blogs/blog.aspx?b=02b4e309-308c-468a-bab1-cebb1404be6a

Here you have a more information on mach_absolute_time: http://developer.apple.com/library/mac/#qa/qa1398/_index.html http://shiftedbits.org/2008/10/01/mach_absolute_time-on-the-iphone/