Bestmögliche Realisierung meiner Idee - Brauche Rat -

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Random;

import android.content.Context;
import android.content.SharedPreferences;
import android.provider.Settings.Secure;
import android.telephony.TelephonyManager;
import android.util.Log;

public class DeviceID 
{
    private static String ID = null;
    static Context context;
    public static final String PREFS_NAME = "prefs";

    public static String getID(Context c) 
    {
        context = c;
        
        if (ID == null) 
        {
            SharedPreferences shared = context.getSharedPreferences(PREFS_NAME, 0);
            ID = shared.getString("deviceId", "0");
        }
        if (ID.equals("0")) 
        {
            ID = generateID();

            if (ID != null) 
            {
                SharedPreferences shared = context.getSharedPreferences(PREFS_NAME, 0);
                SharedPreferences.Editor editor = shared.edit();
                editor.putString("deviceId", ID);
                editor.commit();
            }
        }
        
        Log.i("OVerti", "DeviceID=" + String.valueOf(ID));

        return ID;
    }

    private static String generateID() 
    {
        String deviceId = Secure.getString(context.getContentResolver(), Secure.ANDROID_ID);

        if (deviceId == null) 
        {
            deviceId = ((TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE)).getDeviceId();

            if (deviceId == null) 
            {
                Random tmpRand = new Random();
                deviceId = String.valueOf(tmpRand.nextLong());
            }
        }
        return getHash(deviceId);
    }

    public static String getHash(String stringToHash) 
    {
        MessageDigest digest = null;
        try 
        {
            digest = MessageDigest.getInstance("SHA-1");
        } 
        catch (NoSuchAlgorithmException e) 
        {
            e.printStackTrace();
        }

        byte[] result = null;
        try 
        {
            result = digest.digest(stringToHash.getBytes("UTF-8"));
        } catch (UnsupportedEncodingException e) 
        {
            e.printStackTrace();
        }

        StringBuilder sb = new StringBuilder();

        for (byte b : result)
        {
            sb.append(String.format("%02X", b));
        }

        String messageDigest = sb.toString();
        return messageDigest;
    }

<uses-permission android:name="android.permission.READ_PHONE_STATE" />