iOS 6中引入的UIDevice identifierForVendor可以满足你的需求。

identifierForVendor是一个字母数字字符串，用于唯一标识应用程序供应商的设备。(只读)

@property(nonatomic, readonly, retain) NSUUID *identifierForVendor

对于运行在同一设备上的来自同一供应商的应用程序，此属性的值是相同的。对于同一设备上来自不同供应商的应用程序返回不同的值，对于不同设备上的应用程序返回不同的值，与供应商无关。

在iOS 6.0及更高版本中可用，在UIDevice.h中声明

对于iOS 5，请参考此链接UIDevice-with-UniqueIdentifier-for-iOS-5

您已经可以使用Apple UDID的替代方案了。gekitz在UIDevice上写了category，它会根据设备mac地址和包标识符生成某种UDID。

你可以在github上找到代码

+ (NSString *) getUniqueUUID {
    NSError * error;
    NSString * uuid = [KeychainUtils getPasswordForUsername:kBuyassUser andServiceName:kIdOgBetilngService error:&error];
    if (error) {
    NSLog(@"Error geting unique UUID for this device! %@", [error localizedDescription]);
    return nil;
    }
    if (!uuid) {
        DLog(@"No UUID found. Creating a new one.");
        uuid = [IDManager GetUUID];
        uuid = [Util md5String:uuid];
        [KeychainUtils storeUsername:USER_NAME andPassword:uuid forServiceName:SERVICE_NAME updateExisting:YES error:&error];
        if (error) {
            NSLog(@"Error getting unique UUID for this device! %@", [error localizedDescription]);
            return nil;
        }
    }
    return uuid;
}

下面的代码有助于获得UDID:

        udid = [[[UIDevice currentDevice] identifierForVendor] UUIDString];
        NSLog(@"UDID : %@", udid);

获得UDID的有效方法:

Launch a web server inside the app with two pages: one should return specially crafted MobileConfiguration profile and another should collect UDID. More info here, here and here. You open the first page in Mobile Safari from inside the app and it redirects you to Settings.app asking to install configuration profile. After you install the profile, UDID is sent to the second web page and you can access it from inside the app. (Settings.app has all necessary entitlements and different sandbox rules).

一个使用RoutingHTTPServer的例子:

import UIKit
import RoutingHTTPServer

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var bgTask = UIBackgroundTaskInvalid
    let server = HTTPServer()

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        application.openURL(NSURL(string: "http://localhost:55555")!)
        return true
    }

    func applicationDidEnterBackground(application: UIApplication) {
        bgTask = application.beginBackgroundTaskWithExpirationHandler() {
            dispatch_async(dispatch_get_main_queue()) {[unowned self] in
                application.endBackgroundTask(self.bgTask)
                self.bgTask = UIBackgroundTaskInvalid
            }
        }
    }
}

class HTTPServer: RoutingHTTPServer {
    override init() {
        super.init()
        setPort(55555)
        handleMethod("GET", withPath: "/") {
            $1.setHeader("Content-Type", value: "application/x-apple-aspen-config")
            $1.respondWithData(NSData(contentsOfFile: NSBundle.mainBundle().pathForResource("udid", ofType: "mobileconfig")!)!)
        }
        handleMethod("POST", withPath: "/") {
            let raw = NSString(data:$0.body(), encoding:NSISOLatin1StringEncoding) as! String
            let plistString = raw.substringWithRange(Range(start: raw.rangeOfString("<?xml")!.startIndex,end: raw.rangeOfString("</plist>")!.endIndex))
            let plist = NSPropertyListSerialization.propertyListWithData(plistString.dataUsingEncoding(NSISOLatin1StringEncoding)!, options: .allZeros, format: nil, error: nil) as! [String:String]

            let udid = plist["UDID"]! 
            println(udid) // Here is your UDID!

            $1.statusCode = 200
            $1.respondWithString("see https://developer.apple.com/library/ios/documentation/NetworkingInternet/Conceptual/iPhoneOTAConfiguration/ConfigurationProfileExamples/ConfigurationProfileExamples.html")
        }
        start(nil)
    }
}

下面是udid.mobileconfig的内容:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>PayloadContent</key>
        <dict>
            <key>URL</key>
            <string>http://localhost:55555</string>
            <key>DeviceAttributes</key>
            <array>
                <string>IMEI</string>
                <string>UDID</string>
                <string>PRODUCT</string>
                <string>VERSION</string>
                <string>SERIAL</string>
            </array>
        </dict>
        <key>PayloadOrganization</key>
        <string>udid</string>
        <key>PayloadDisplayName</key>
        <string>Get Your UDID</string>
        <key>PayloadVersion</key>
        <integer>1</integer>
        <key>PayloadUUID</key>
        <string>9CF421B3-9853-9999-BC8A-982CBD3C907C</string>
        <key>PayloadIdentifier</key>
        <string>udid</string>
        <key>PayloadDescription</key>
        <string>Install this temporary profile to find and display your current device's UDID. It is automatically removed from device right after you get your UDID.</string>
        <key>PayloadType</key>
        <string>Profile Service</string>
    </dict>
</plist>

配置文件安装将失败(我没有费心实现预期的响应，请参阅文档)，但应用程序将获得正确的UDID。你还应该在mobileconfig上签名。

iOS 11引入了DeviceCheck框架。它有一个完整的解决方案，唯一地识别设备。