diff --git a/RobThree/TwoFactorAuth/Providers/Rng/HashRNGProvider.php b/RobThree/TwoFactorAuth/Providers/Rng/HashRNGProvider.php
index 8a7b06d..645c7dc 100644
--- a/RobThree/TwoFactorAuth/Providers/Rng/HashRNGProvider.php
+++ b/RobThree/TwoFactorAuth/Providers/Rng/HashRNGProvider.php
@@ -13,11 +13,16 @@ class HashRNGProvider implements IRNGProvider
     }
     
     public function getRandomBytes($bytecount) {
-        $result = array();
+        $result = '';
+        $hash = mt_rand();
         for ($i = 0; $i < $bytecount; $i++) {
             $hash = hash($this->algorithm, $hash.mt_rand(), true);
-            array_push($result, $hash[mt_rand(0, sizeof($hash))]);
+            $result .= $hash[mt_rand(0, sizeof($hash))];
         }
         return $result;
     }
+    
+    public function isCryptographicallySecure() {
+        return false;
+    }
 }
diff --git a/RobThree/TwoFactorAuth/Providers/Rng/IRNGProvider.php b/RobThree/TwoFactorAuth/Providers/Rng/IRNGProvider.php
index d401827..44bb9d5 100644
--- a/RobThree/TwoFactorAuth/Providers/Rng/IRNGProvider.php
+++ b/RobThree/TwoFactorAuth/Providers/Rng/IRNGProvider.php
@@ -5,4 +5,5 @@ namespace RobThree\TwoFactorAuth\Providers\Rng;
 interface IRNGProvider
 {
     public function getRandomBytes($bytecount);
+    public function isCryptographicallySecure();
 }
\ No newline at end of file
diff --git a/RobThree/TwoFactorAuth/Providers/Rng/MCryptRNGProvider.php b/RobThree/TwoFactorAuth/Providers/Rng/MCryptRNGProvider.php
index 8618ca3..b97be1a 100644
--- a/RobThree/TwoFactorAuth/Providers/Rng/MCryptRNGProvider.php
+++ b/RobThree/TwoFactorAuth/Providers/Rng/MCryptRNGProvider.php
@@ -16,4 +16,8 @@ class MCryptRNGProvider implements IRNGProvider
             throw new RNGException('mcrypt_create_iv returned an invalid value');
         return $result;
     }
+    
+    public function isCryptographicallySecure() {
+        return true;
+    }
 }
\ No newline at end of file
diff --git a/RobThree/TwoFactorAuth/Providers/Rng/OpenSSLRNGProvider.php b/RobThree/TwoFactorAuth/Providers/Rng/OpenSSLRNGProvider.php
index edab2cd..2105136 100644
--- a/RobThree/TwoFactorAuth/Providers/Rng/OpenSSLRNGProvider.php
+++ b/RobThree/TwoFactorAuth/Providers/Rng/OpenSSLRNGProvider.php
@@ -18,4 +18,8 @@ class OpenSSLRNGProvider implements IRNGProvider
             throw new RNGException('openssl_random_pseudo_bytes returned an invalid value');
         return $result;
     }
+    
+    public function isCryptographicallySecure() {
+        return $this->requirestrong;
+    }
 }
\ No newline at end of file
diff --git a/RobThree/TwoFactorAuth/TwoFactorAuth.php b/RobThree/TwoFactorAuth/TwoFactorAuth.php
index 08fa1be..4273bbb 100644
--- a/RobThree/TwoFactorAuth/TwoFactorAuth.php
+++ b/RobThree/TwoFactorAuth/TwoFactorAuth.php
@@ -21,16 +21,16 @@ class TwoFactorAuth
         $this->issuer = $issuer;
 
         if (!is_int($digits) || $digits <= 0)
-            throw new Exception('Digits must be int > 0');
+            throw new TwoFactorAuthException('Digits must be int > 0');
         $this->digits = $digits;
         
         if (!is_int($period) || $period <= 0)
-            throw new Exception('Period must be int > 0');
+            throw new TwoFactorAuthException('Period must be int > 0');
         $this->period = $period;
         
         $algorithm = strtolower(trim($algorithm));
         if (!in_array($algorithm, self::$_supportedalgos))
-            throw new Exception('Unsupported algorithm: ' . $algorithm);
+            throw new TwoFactorAuthException('Unsupported algorithm: ' . $algorithm);
         $this->algorithm = $algorithm;
         
         // Set default QR Code provider if none was specified
@@ -38,7 +38,7 @@ class TwoFactorAuth
             $qrcodeprovider = new Providers\Qr\GoogleQRCodeProvider();
         
         if (!($qrcodeprovider instanceof Providers\Qr\IQRCodeProvider))
-            throw new Exception('QRCodeProvider must implement IQRCodeProvider');
+            throw new TwoFactorAuthException('QRCodeProvider must implement IQRCodeProvider');
         
         $this->qrcodeprovider = $qrcodeprovider;
         
@@ -54,7 +54,7 @@ class TwoFactorAuth
         }
         
         if (!($rngprovider instanceof Providers\Rng\IRNGProvider))
-            throw new Exception('RNGProvider must implement IRNGProvider');
+            throw new TwoFactorAuthException('RNGProvider must implement IRNGProvider');
         
         $this->rngprovider = $rngprovider;
         
@@ -65,10 +65,12 @@ class TwoFactorAuth
     /**
      * Create a new secret
      */
-    public function createSecret($bits = 80) 
+    public function createSecret($bits = 80, $requirecryptosecure = true) 
     {
         $secret = '';
         $bytes = ceil($bits / 5);   //We use 5 bits of each byte (since we have a 32-character 'alphabet' / BASE32)
+        if ($requirecryptosecure && !$this->rngprovider->isCryptographicallySecure())
+            throw new TwoFactorAuthException('RNG provider is not cryptographically secure');
         $rnd = $this->rngprovider->getRandomBytes($bytes);
         for ($i = 0; $i < $bytes; $i++)
             $secret .= self::$_base32[ord($rnd[$i]) & 31];  //Mask out left 3 bits for 0-31 values
@@ -112,7 +114,7 @@ class TwoFactorAuth
     public function getQRCodeImageAsDataUri($label, $secret, $size = 200) 
     {
         if (!is_int($size) || $size < 0)
-            throw new  Exception('Size must be int > 0');
+            throw new TwoFactorAuthException('Size must be int > 0');
         
         return 'data:'
             . $this->qrcodeprovider->getMimeType()
diff --git a/RobThree/TwoFactorAuth/TwoFactorAuthException.php b/RobThree/TwoFactorAuth/TwoFactorAuthException.php
new file mode 100644
index 0000000..9de9d3a
--- /dev/null
+++ b/RobThree/TwoFactorAuth/TwoFactorAuthException.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace RobThree\TwoFactorAuth;
+
+class TwoFactorAuthException extends \Exception
+{
+    function __construct($message = "", $code = 0, $exception = null)
+    {
+    	parent::__construct($message, $code, $exception);
+    }
+}
\ No newline at end of file
diff --git a/TwoFactorAuth.phpproj b/TwoFactorAuth.phpproj
index f9f9b3d..07fb20b 100644
--- a/TwoFactorAuth.phpproj
+++ b/TwoFactorAuth.phpproj
@@ -38,6 +38,7 @@
     <Compile Include="RobThree\TwoFactorAuth\TwoFactorAuth.php" />
     <Compile Include=".gitignore" />
     <Compile Include="README.md" />
+    <Compile Include="RobThree\TwoFactorAuth\TwoFactorAuthException.php" />
   </ItemGroup>
   <ItemGroup>
     <Folder Include="RobThree\" />