How to check user's device in iOS SDK

Question

I am trying to fix Sim Swap issue in my app. I want a unique way to identify user's phone. So tried for following cases

• I know that we can't get phone IMEI & other information from user device as per below links

Link1 Link2

• I can use identifierForVendor but it also changes on every installation of the app.

• The third option is to use DeviceCheck API to identify the device but it comes in only iOS 11.

Please let me know how to identify a users device & temporary disabled user's account in case of Sim Swap.

Answer 1

An acceptable solution is to generate a unique UUID and save it to Keychain, Keychain items persists even after application deletion,

/* DeviceUID.h
#import <Foundation/Foundation.h>

@interface DeviceUID : NSObject
+ (NSString *)uid;
@end
*/


// Device.m
#import "DeviceUID.h"

@import UIKit;

@interface DeviceUID ()

@property(nonatomic, strong, readonly) NSString *uidKey;
@property(nonatomic, strong, readonly) NSString *uid;

@end

@implementation DeviceUID

@synthesize uid = _uid;

#pragma mark - Public methods

+ (NSString *)uid {
    return [[[DeviceUID alloc] initWithKey:@"deviceUID"] uid];
}

#pragma mark - Instance methods

- (id)initWithKey:(NSString *)key {
    self = [super init];
    if (self) {
        _uidKey = key;
        _uid = nil;
    }
    return self;
}

/*! Returns the Device UID.
    The UID is obtained in a chain of fallbacks:
      - Keychain
      - NSUserDefaults
      - Apple IFV (Identifier for Vendor)
      - Generate a random UUID if everything else is unavailable
    At last, the UID is persisted if needed to.
 */
- (NSString *)uid {
    if (!_uid) _uid = [[self class] valueForKeychainKey:_uidKey service:_uidKey];
    if (!_uid) _uid = [[self class] valueForUserDefaultsKey:_uidKey];
    if (!_uid) _uid = [[self class] appleIFV];
    if (!_uid) _uid = [[self class] randomUUID];
    [self save];
    return _uid;
}

/*! Persist UID to NSUserDefaults and Keychain, if not yet saved
 */
- (void)save {
    if (![DeviceUID valueForUserDefaultsKey:_uidKey]) {
        [DeviceUID setValue:self.uid forUserDefaultsKey:_uidKey];
    }
    if (![DeviceUID valueForKeychainKey:_uidKey service:_uidKey]) {
        [DeviceUID setValue:self.uid forKeychainKey:_uidKey inService:_uidKey];
    }
}

#pragma mark - Keychain methods

/*! Create as generic NSDictionary to be used to query and update Keychain items.
 *  param1
 *  param2
 */
+ (NSMutableDictionary *)keychainItemForKey:(NSString *)key service:(NSString *)service {
    NSMutableDictionary *keychainItem = [[NSMutableDictionary alloc] init];
    keychainItem[(__bridge id)kSecClass] = (__bridge id)kSecClassGenericPassword;
    keychainItem[(__bridge id)kSecAttrAccessible] = (__bridge id)kSecAttrAccessibleAlways;
    keychainItem[(__bridge id)kSecAttrAccount] = key;
    keychainItem[(__bridge id)kSecAttrService] = service;
    return keychainItem;
}

/*! Sets
 *  param1
 *  param2
 */
+ (OSStatus)setValue:(NSString *)value forKeychainKey:(NSString *)key inService:(NSString *)service {
    NSMutableDictionary *keychainItem = [[self class] keychainItemForKey:key service:service];
    keychainItem[(__bridge id)kSecValueData] = [value dataUsingEncoding:NSUTF8StringEncoding];
    return SecItemAdd((__bridge CFDictionaryRef)keychainItem, NULL);
}

+ (NSString *)valueForKeychainKey:(NSString *)key service:(NSString *)service {
    OSStatus status;
    NSMutableDictionary *keychainItem = [[self class] keychainItemForKey:key service:service];
    keychainItem[(__bridge id)kSecReturnData] = (__bridge id)kCFBooleanTrue;
    keychainItem[(__bridge id)kSecReturnAttributes] = (__bridge id)kCFBooleanTrue;
    CFDictionaryRef result = nil;
    status = SecItemCopyMatching((__bridge CFDictionaryRef)keychainItem, (CFTypeRef *)&result);
    if (status != noErr) {
        return nil;
    }
    NSDictionary *resultDict = (__bridge_transfer NSDictionary *)result;
    NSData *data = resultDict[(__bridge id)kSecValueData];
    if (!data) {
        return nil;
    }
    return [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
}

#pragma mark - NSUserDefaults methods

+ (BOOL)setValue:(NSString *)value forUserDefaultsKey:(NSString *)key {
    [[NSUserDefaults standardUserDefaults] setObject:value forKey:key];
    return [[NSUserDefaults standardUserDefaults] synchronize];
}

+ (NSString *)valueForUserDefaultsKey:(NSString *)key {
    return [[NSUserDefaults standardUserDefaults] objectForKey:key];
}

#pragma mark - UID Generation methods

+ (NSString *)appleIFA {
    NSString *ifa = nil;
    Class ASIdentifierManagerClass = NSClassFromString(@"ASIdentifierManager");
    if (ASIdentifierManagerClass) { // a dynamic way of checking if AdSupport.framework is available
        SEL sharedManagerSelector = NSSelectorFromString(@"sharedManager");
        id sharedManager = ((id (*)(id, SEL))[ASIdentifierManagerClass methodForSelector:sharedManagerSelector])(ASIdentifierManagerClass, sharedManagerSelector);
        SEL advertisingIdentifierSelector = NSSelectorFromString(@"advertisingIdentifier");
        NSUUID *advertisingIdentifier = ((NSUUID* (*)(id, SEL))[sharedManager methodForSelector:advertisingIdentifierSelector])(sharedManager, advertisingIdentifierSelector);
        ifa = [advertisingIdentifier UUIDString];
    }
    return ifa;
}

+ (NSString *)appleIFV {
    if(NSClassFromString(@"UIDevice") && [UIDevice instancesRespondToSelector:@selector(identifierForVendor)]) {
        // only available in iOS >= 6.0
        return [[UIDevice currentDevice].identifierForVendor UUIDString];
    }
    return nil;
}

+ (NSString *)randomUUID {
    if(NSClassFromString(@"NSUUID")) {
        return [[NSUUID UUID] UUIDString];
    }
    CFUUIDRef uuidRef = CFUUIDCreate(kCFAllocatorDefault);
    CFStringRef cfuuid = CFUUIDCreateString(kCFAllocatorDefault, uuidRef);
    CFRelease(uuidRef);
    NSString *uuid = [((__bridge NSString *) cfuuid) copy];
    CFRelease(cfuuid);
    return uuid;
}

@end

Source : https://medium.com/@miguelcma/persistent-cross-install-device-identifier-on-ios-using-keychain-ac9e4f84870f

Answer 2

You will have to keep UUID into keychain since keychain data persist after uninstallation of the app

iOS manages keychain information as sensitive information. you can use SwiftKeychainWrapper library to easily access your keychain.

what apple doc says on SIM change: https://developer.apple.com/documentation/coretelephony/cttelephonynetworkinfo

CodingExample:

let uuid = UIDevice.current.identifierForVendor?.uuidString
KeychainWrapper.standard.set(uuid, forKey: "appUUID")

And whenever you want to get appUUID just fetch from keychain:

let uuid = KeychainWrapper.standard.string(forKey: "appUUID")

Note: You can also check if your UUID is changed after reinstallation of the app and update it into a keychain.