CFUUID stored in SSKeychain is null in some devices

Question

My published application makes use of the CFUUID and SSKeychain in order to identify the device (and to keep that ID unchanged even if the app is uninstalled and reinstalled)

I save those device ID in the server, and I recently noticed that some users have several of those IDs for the same real device. The only explanation I see is that the ID is not being saved or loaded from the Keychain and thus the device generates a new one. The strange thing is that it works fine on some other devices running the same iOS version.

Any ideas on what could be going on?

This is my related code in (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

NSString* identifier = @"appName";
NSString* serviceName = @"com.company.appName";
NSString *retrieveuuid = [SSKeychain passwordForService:serviceName account:identifier];
if (retrieveuuid == nil) {
    CFUUIDRef theUUID = CFUUIDCreate(NULL);
    CFStringRef string = CFUUIDCreateString(NULL, theUUID);
    CFRelease(theUUID);
    NSString *uuid  = (NSString*) string;
    [SSKeychain setPassword:uuid forService:serviceName account:identifier];
}

EDIT: My guess is that retrieveuuid == nil is not working as expected for some reason. Later in the app I register for push notifications and send the push token to the server together with this CFUUID that I read with the same exact line [SSKeychain passwordForService:serviceName account:identifier] but when it is sent to the server it is not nil (So I can see several CFUUIDs with the same push token).

EDIT 2 to attach more actual code.

AppDelegate.m

NSString* identifier = @"appName";
NSString* serviceName = @"com.company.appName";
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    //Creating UUID
    NSString *retrieveuuid = [AppDelegate getDeviceId];
    if (retrieveuuid == nil) {
        CFUUIDRef theUUID = CFUUIDCreate(NULL);
        CFStringRef string = CFUUIDCreateString(NULL, theUUID);
        CFRelease(theUUID);
        NSString *uuid  = (NSString*) string;
        [SSKeychain setPassword:uuid forService:serviceName account:identifier];
    }

    [[UIApplication sharedApplication] registerForRemoteNotificationTypes:
     (UIRemoteNotificationTypeBadge | UIRemoteNotificationTypeSound | UIRemoteNotificationTypeAlert)];
}

+ (NSString*) getDeviceId {
    return [SSKeychain passwordForService:serviceName account:identifier];
}

- (void)application:(UIApplication*)application didRegisterForRemoteNotificationsWithDeviceToken:(NSData*)deviceToken
{
    NSString *newToken = [deviceToken description];
    newToken = [newToken stringByTrimmingCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:@"<>"]];
    newToken = [newToken stringByReplacingOccurrencesOfString:@" " withString:@""];

    _deviceToken = [[NSString alloc] initWithString:newToken];

    NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
    NSString *user = [prefs objectForKey:@"appNameUsername"];

    if(user && ![user isEqualToString:@""]){
        RestClient *rest = [[RestClient alloc] init];
        rest.delegate = self;
        rest.tag = 2;
        [rest updateToken:newToken ForUsername:user];
        [rest release];
    }
}

RestClient.m

-(void) updateToken:(NSString *)token ForUsername:(NSString *)userName{
    NSArray* info = [NSArray arrayWithObject: [NSMutableDictionary dictionaryWithObjectsAndKeys:
                                               userName, @"Username",
                                               token, @"TokenNo",
                                               [[UIDevice currentDevice].model hasPrefix:@"iPad"] ? @"iPad" : @"iPhone", @"Device",
                                               [UIDevice currentDevice].systemVersion, @"OSVersion",
                                               [AppDelegate getDeviceId], @"DeviceID",
                                               @"updateToken", @"CMD",
                                               nil]];
    [self doAction:info];
}

The doAction method just sends the data to the server and then callback the delegate, that part works fine. I can see on the server the logs of receiving this command:

"JSONCMD":"[
{   "TokenNo" : "f0d3aa21758350333b7e6315c38_EDIT_257c1838f49c43049f8380ec1ff63", 
    "AppVersion" : "1.0.4",
    "Username" : "user@server.com", 
    "CMD" : "updateToken", 
    "OSVersion" : "7.0.4", 
    "DeviceID" : "9B794E11-6EF7-470C-B319-5A9FCCDAFD2B", 
    "Device" : "iPhone"
}
]  

I see 2 possible candidates causing the strange behaviour, the NSStrings in the controller body and the static getDevice method. However, I don't see how this could work in many devices but fail in others.

Answer 1

I've had the same problem and I've found the solution. The Problem occurs with devices where user has the passcode set to unlock the phone. On iOS7 some code can run in the background (push notifications, background fetch) and if you save something in the keychain with standard accessibility type, you cannot read it when the device is locked (and the app is running in the background). Try to set this:

[SSKeychain setAccessibilityType:kSecAttrAccessibleAlways];

before you read/write the keychain. Hope it helps.

Answer 2

NSString *retrieveuuid = [SSKeychain passwordForService:serviceName account:identifier];

The retrieveuuid depends with the service, witch is always the same thing, but it depends also with the account. I think your problem is that one user can have multiple accounts in the same device, then your code are generating a UUID for each account.