Add thread local secure random

Author: SalusaSecondus

src/main/java/com/amazonaws/services/dynamodbv2/datamodeling/internal/Utils.java

@@ -0,0 +1,28 @@
+package com.amazonaws.services.dynamodbv2.datamodeling.internal;
+
+import java.security.SecureRandom;
+
+public class Utils {
+    private static final ThreadLocal<SecureRandom> RND = new ThreadLocal<SecureRandom>() {
+        @Override
+        protected SecureRandom initialValue() {
+            final SecureRandom result = new SecureRandom();
+            result.nextBoolean(); // Force seeding
+            return result;
+        }
+    };
+
+    private Utils() {
+        // Prevent instantiation
+    }
+
+    public static SecureRandom getRng() {
+        return RND.get();
+    }
+
+    public static byte[] getRandom(int len) {
+        final byte[] result = new byte[len];
+        getRng().nextBytes(result);
+        return result;
+    }
+}