we are creating a location-enabled app where users use this app to record certain events in the field.
The important part of the event data is when an event happened. This is no issue when user is online, but we also support situations when user is offline (by remembering & later syncing events).
There could be situations when users are offline and they change the time on the phone, so that event times are wrongly recorded.
So, what would be the best way to ensure we get a correct time, independent of user actions, given that device could be offline. Some ideas:
GPS time. Is it possible to acquire it?
Tracking system time changes made by user?
Any other idea?
Note: time does need second accuracy, approximately minute accuracy would be ok.
Note2: we are creating mobile apps for Android and iPhone, so I'm interested for generic solutions and also solutions that are specific to any of those two platforms.
I, personally, wouldn't worry so much about this scenario. The liklihood of someone intentionally changing the time on their Android (which periodically throughout the day syncs to a time server automatically) while offline seems low to me. That being said, the only way I could see compensating for this is to keep a service running in the background that keeps a running tally of the seconds passed since recording the location data offline. Once uploaded to your servers you could use the elapsed seconds to calculate a time offset from current UTC time. It's an awful lot to go through, but it would work.
GPS time is an interesting idea, but Android allows users of the SDK to send mock locations to their devices. I'm not sure you could reliably track changes to system time either, and even if you could you'd be capturing them after the fact without the current real time as context.
We use GPS times in our app for very similar reasons. Since our users are in different time zones and we want local times, we define from our server what time zone they are in at installation time (they don't move very far). Hadn't thought of the mock GPS locations, but you would need to be a fairly advanced user to do that.
Related
I need to make an application that will start playing same media on two (or more) iPhones simultaneously, the problem is that it has to be perfect, no second delays and such. Is it possible that iPhone has some universal time stamp that is perfectly (or near-perfect) on every device. Or maybe I have some other options?
2 rules:
Find a way to have the same time on each devices
Use a "startAtTime" function using this shared uniform time. No "startNow" function.
the iPhones are supposed to be able to sync their date and time using a remote server, if this is not accurate enough (who knows), a way to achieve this (assuming you iPhone are able to communicate between them already):
The master send its time to a slave 10 (or more) times.
Each time the slave compare it's time with the one received and make a delta
After 10 tries, make a mean of the deltas and use this mean to adjust the slave time accordingly
There's no internal clock that is different to the system clock - so this means that each of the devices could have completely different time settings (in fact, it's highly likely that they will have different time settings even if only by a second or two).
Using a network/internet connection to synchronise against a central time server may be an approach that could be taken, but that would then require the network/internet connection and you would have to set the clocks taking into account lags on the connection to/from the time server.
You could have to have some kind of local synchronising system. If they are in close proximity, one approach may be to create an ad-hoc bluetooth connection between the devices in your app and then use some synchronisation code in you app to get the internal timers the same. You could, for example, have the first app to launch be the "controller" and then all the other apps would seek this controller and synchronise against it. The synchronisation could just be the controller sending out timestamp messages which the other devices can get and set an internal counter to match.
Without knowing much more about the requirements, it's hard to say how best to approach this as there may be limitations regarding time between running the app and it making the sound, or if you have to have a triggering signal, or if it is just at time x they need to make the sound.
If they are in same time zone and same time set ,you can schedule it to start your function in the paticular point of time using NSTimer's
- (id)initWithFireDate:(NSDate *)date interval:(NSTimeInterval)ti target:(id)t selector:(SEL)s userInfo:(id)ui repeats:(BOOL)rep;.
One option you have is to access the time from a common server and then start a timer on both devices accordingly (calculating depending on the time you got from the service)so you have exact time on both the devices and then play it ...
Even this has a catch as internet speed may vary and there might be a slight in delay on one of the two devices in getting the response from the server as compared to the other device and looking at your requirement they might go out of sync by a milisecond or so which will be visible.. :/ any other ideas anyone.. ?
In my application i want to run an internal clock in background mode [while application is not running in foreground].
The whole functionality will be like this:
The objective is to get the server time to use in the application, because using device time may sometimes cause issues. The issues may be in situations like somebody has changed the user's iPhone time etc. So i am following the below method.
-Running an internal clock in my application background even if the application is not running.
-Communicate with server every 15 minutes to get the real time and run a timer.
-If net is disconnected in between,timer will continue and take the timer time.
My application is heavily depended on this time factor as this is a ticket booking system.Kindly help me to implement this or please confirm whether this is possible or not?
I am developing an iPhone application which involves Ticket Booking System. I registered my application as location based beacuse it is using user's location taken in background for a purpose.
My problem is that i need to run an internal clock in my application in background mode. I need to write the codes for internal clock in core location delegate methods, so that internal clock will also run along with the location bsed services. Will my app get rejected? Is anything wrong in doing like this?
I need to get the correct time to use in my app, so that i am running this internal clock. I can use NSDate, but that will return the device time. Anyone can change the device time. So once somebody chaged, wrong time will affect the smooth functioning of the app. Kindly some body suggest to get the correct time with out running the internal clock ?
Update: Sorry to say my original answer isn't correct. When the device goes to sleep (can happen sometime after it's locked) the internal CPU clock stops ticking, and mach_absolute_time won't update either. Theoretically it will return the exact same value if you call it right before the device went to sleep, and after it awakes.
The best available way I know of to check for date changes is kern.boottime, it holds the boot time, and is modified whenever the system time changes. Among other things, kern.boottime will be updated if the user changes the time, or if the OS changes the time itself according to info from cell towers.
So, in your case, you can take the original time you calculated and modify it according to the modifications in kern.boottime. If you see kern.boottime changed significantly, it may mean that the device was turned off, and in this case you will need to contact the server to ask it for the time until the flight.
Relevant code:
time_t getBootTimeSecs(void)
{
struct timeval boottime;
size_t size = sizeof(boottime);
int ret = sysctlbyname("kern.boottime", &boottime, &size, NULL, 0);
assert(ret == 0);
return boottime.tv_sec;
}
Original (incorrect) answer: You can use mach_absolute_time which isn't affected by date changes made by the user.
When you book the ticket, get the correct date from the server and record mach_absolute_time. Now you will always be able to call mach_absolute_time whenever you want, calculate the difference from the one you recorded initially, and display the correct date.
This will only work as long as the device wasn't shut down, in that case it makes sense for the app to re-connect to the server to get the correct date.
You can also either Local or Push Notifications to alert the user when the target date is getting closer, even if the app isn't running.
apple is support small task for background mode which will work for approximate 10 sec only.
so you can do one thing when app is active then get time form server and update your local time according that.
I think that you can only detect that the date of the iOs device has been changed (using NSSystemClockDidChangeNotification).
I guess you to use this notification and force reload the real date of your application from your server (With a WebService).
EDIT: You can use the systemUptime in NSProcessInfo:
NSLog(#"ProcessInfo System uptime: %f",[NSProcessInfo processInfo].systemUptime);
but it will not solve your problem if the Device is restarted.
I think there are 2 ways you can go about solving your problem.
Never use system time. In other words, never call [NSDate date] in your code. When you need the current time, call an NTP server. This will of course cause latency in your app, but will guarantee accuracy.
When the app launches, or enters foreground, verify that the system time is reasonably accurate against an NTP server. If the system time is off by more than your tolerance level, then do not let them continue running the app until they address it. If the system time is okay, then start monitoring to ensure they don't change the system time while running the app (NSSystemClockDidChangeNotification). If they pass the initial check, but the move the clock forward, you can catch that and disable the app til they change it back to being accurate.
Here is an iOS NTP implementation which could be helpful in implementing either solution above. http://code.google.com/p/ios-ntp/
EDIT: The Ticketmaster app uses technique #2, so this seems like a reasonable solution for a ticketing app that requires your system time to be correct.
timezone settings should not affect time as in UTC
your app cannot run in the background. Abusing the location requirement for this will cause your app to be rejected by Apple
so my suggestion: do the logic server side with push notification
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.
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/
I was thinking about the fact that the CoreLocation stuff could do this if that part of the GPS data was exposed to you. However that got me thinking.
My only (far fetched) suggestion is to put something into background processing - which has to be for one of a small specific set of reasons, for example to track location in the background. As a side effect of that, try to detect a clock change on a regular timer. Apple might reject it as it may be clear that its not using the location information and its just a reason to exploit background processing.
Any solution not involving networking is so much harder to implement, I wonder why you're not using it.
Whilst I don't think it's possible to reliably determine whether or not a user has manually turned their clock forward without network access, you can of course reliably determine if they've travelled back in time. And since we know this to be physically impossible it can therefore be assumed they have manipulated their clock to cheat.
What I mean by this is, isn't the usual process to trigger some action in-app that requires a period of waiting, exit the app and turn the clock forward, re-launch the app to gain whatever they were waiting for and then reset the clock back to the actual time?
If this is indeed the case, then to build on the suggestion by #smgambel, you could store the physical time and current time-zone on each launch and compare with the previously stored time and time-zone. If the time is behind the previously stored time, and the time-zone of the device hasn't changed then you can safely assume the user has manipulated the clock.
I have an app that requires me to take an action after some period of time. For example, if an user hasn't been inside the app in few weeks, when the user eventually starts the app, I have to ask them to put in a special code that was given to them when they installed this app. (this is an in-house app and i am being required to do this due to security concerns)
I am using the [NSDate date] method to retrieve the date when the user logs in and save it into a database. I compare this saved date next time they open up the app and see how long its been since their last login. The problem is that [NSDate date] gives the time that is effected by the time settings that can be changed manually by the user in the native settings app. As you can probably tell, this causes lots of problems to my situation. If the user is suppose to be put the special code after 3 weeks of inactivity, he can cause the app to show this screen by modifying the time in the native settings app or worse, get away from it by setting the time to a previous date that will be within 3 weeks of his activity.
Is there a way to get the "system time" instead of the "user time"? I have looked into mach_absolute_time() but this gets reset after restart of the device. Since the time of inactivity I will be comparing against is pretty large, chances are device would have been restarted by then. I also thought of using network connection to get the time from servers outside the app, but lots of users won't have access to wifi where they use their iPads. That will be my last resort solution if i can't find anything else. Because of their location during usage, I am trying to use everything on the device itself.
Am I overlooking something simple here? this seems too simple of a problem to not have an answer. Please guide me toward the right direction. Thank you in advance.
Why not query a remote server for the time - lots of NTP servers about or just make a simple HTTP request to a php script on your own server. Of course if your app is likely never to be connected to the internet that could be a problem, but once you have a 3rd party time its quite easy to guess if the user has been playing with the clock.
If this is an inhouse app (so you aren't constrained by Apples approval process), you could mark your app as doing some background stuff (voip or receiving location updates), so that the app will always be active and you'd be able to update some sort of an "unused" counter. Voip app will even be restarted by the OS after device reboot.
But of course it'll drain the battery somewhat.
Either: make having the actual time an essential feature of your app. This way the users will have a need to keep the time of the device current and can't go back three weeks
Or: mark the code as expired and save this information before the app informs the user. This will stop most user from setting the time back. Most will try once or twice, see that the app stays disabled and will give up.
You can also save the timestamp of the last successful execution and if that is more than a reasonable time frame in the future (remember summer/winter time) then consider it a "hack attempt". Put a CRC check (or whatever obscure idea you come up with) on that timestamp and save it too and you will stop a large number of script kiddies.
You can never stop the diehard hacker who search actively for every trick you might have put into the app. Just focus on the "average" user.
I'm thinking about building an iphone app that would use the GPS feature to track where someone is and for how long. I realize I could probably get the current location from the iphone from a website but the only way I'm familiar with is using ajax calls, etc (Sorry if this is a rather newbie concept) but I fear that would bog down my servers with constant calls to track time. Is there a better way to do this? Any resources I could consult on this idea/concept? Is it even plausible at this point?
I'm more versed in php/mysql but trying to branch out on some new ideas I've had. Any help would be greatly appreciated!
You could keep a local datastore then only send updates to the server when the app detects that the user has moved. I'm pretty sure that would work and on the server side you just work out the last time a user checked in and then compare that against the current time to see how long they have been somewhere. The only technical issue I can see with this is that this requires the user to have the iphone on and the app open the ENTIRE time they are somewhere, which would mean the iphone is now just a rather expensive GPS tracker with a built in phone!
you could store user locations on a local list on the iphone and once an hour you send the list with location/timesptamp pairs to server.
As James Raybould says, you can compute on server how long a user stayed inside a range for a given position. And also by sending data once an hour... not each time the iphone detects that user moved, then you save your server for continuously pings.