[Guide] Android Secure Random Bytes

Hi,
took me a while to figure out how to use java's SecureRandom in Unity.
I hope this might help someone whos looking for a secure random in Unity Android.

Code (CSharp):

1. using UnityEngine;
2. using System;
3.  
4. public class AndroidSecureRandom
5. {
6.  
7.     private static IntPtr SecureRandomPtr, NextBytes;
8.  
9.     static AndroidSecureRandom ()
10.     {
11.         IntPtr clazz = new AndroidJavaClass ("java.security.SecureRandom").GetRawClass ();
12.         SecureRandomPtr = AndroidJNI.NewObject (clazz, AndroidJNIHelper.GetConstructorID (clazz), new jvalue[]{ });
13.         SecureRandomPtr = AndroidJNI.NewGlobalRef (SecureRandomPtr);
14.         NextBytes = AndroidJNIHelper.GetMethodID (clazz, "nextBytes");
15.     }
16.  
17.     public static byte[] TrueRandom (int count)
18.     {
19.             jvalue[] array = new jvalue[]{ new jvalue{ l = AndroidJNI.NewByteArray (count) } };
20.             AndroidJNI.CallVoidMethod (SecureRandomPtr, NextBytes, array);
21.             byte[] result = AndroidJNI.FromByteArray (array [0].l);
22.             AndroidJNI.DeleteLocalRef (array [0].l);
23.             return result;
24.     }
25. }

Edit:
So somehow my game crashes if the static constructor isnt invoked from the main thread. I just came up with an other solution, which is also working for ios:

Code (CSharp):

1.        
2. using System.IO;
3.  
4. public class SecureRandom {
5.  public static byte[] TrueRandom (int count)
6.         {
7. byte[] result = new byte[count];
8. #if (UNITY_ANDROID || UNITY_IOS) && !UNITY_EDITOR
9.             FileStream s = File.OpenRead ("/dev/urandom");
10.             s.Read (result, 0, count);
11.             s.Close ();
12.             return result;
13. #else
14. //Only pseudo random here
15.             for (int i = 0; i < result.Length; i++) {
16.                 result [i] = (byte)UnityEngine.Random.Range (0, 255);
17.             }
18.             return result;
19. #endif
20. }
21. }
22.