How to detect a cracked iPhone App and a jailbroken device (different methods)

Question

I'm building a blacklisting service for cracked iPhone apps and I am curious if I missed a method for detecting cracked apps.

In the moment following app crack detection methods are available for the service:

1. checking plist size
2. checking signer identity
3. checking if binary is crypted (not sure if this is working correctly since no cracked app got detected this way)
4. checking modified date of info.plist against modified date of package (not sure if this is working - used code like: http://snippie.net/snip/f7530ff2 to do that)

I also wonder if it is possible to check if the device is jailbroken? This would help, too, because the service will work much like a spam blacklist and jailbreak could be used to increase the score.

I have also included a honeypot, which shows me that the tools used by the crackers eliminate some of the checks I do. For instance the plist check for size or signer identity.

My question is now:

• Are there more "good" checks I should use?

and

• Is there a way to detect Jailbreak?

Thanks for any help!

Answer 1

NEVER try and block jailbroken devices from using your app, just cracked ones. If you block jailbroken devices they'll be forced to use a patched version with all the checks removed.
Also ALL my devices are jailbroken so if a developer blocks jailbroken devices I would have to ignore their apps. Over 10% of all iDevices are jailbroken so this is a very bad idea.

EDIT: As I'm getting lots of down votes for this I'll post some methods to detect a jailbreak.

- (BOOL)fileExistsAtPath:(NSString *)path{
    NSLog(@"Check if file '%@' exists", path);

    struct stat buffer;   
    return stat([path UTF8String], &buffer) == 0;
}

- (BOOL)jailbroken{
    return ([self fileExistsAtPath:@"/Applications/Cydia.app"]);
}