diff --git a/src/Mailgun/Mailgun.php b/src/Mailgun/Mailgun.php
index d761f49..fc9224b 100644
--- a/src/Mailgun/Mailgun.php
+++ b/src/Mailgun/Mailgun.php
@@ -17,66 +17,90 @@ use Mailgun\Messages\MessageBuilder;
 */
 
 class Mailgun{
-
     protected $workingDomain;
     protected $restClient;
-
+    protected $apiKey;
+    
     public function __construct($apiKey = null, $apiEndpoint = "api.mailgun.net", $apiVersion = "v2", $ssl = true){
-	    $this->restClient = new RestClient($apiKey, $apiEndpoint, $apiVersion, $ssl);
+        $this->apiKey = $apiKey;
+        $this->restClient = new RestClient($apiKey, $apiEndpoint, $apiVersion, $ssl);
     }
 
-	public function sendMessage($workingDomain, $postData, $postFiles = array()){
+    public function sendMessage($workingDomain, $postData, $postFiles = array()){
+        /*
+         *  This function allows the sending of a fully formed message OR a custom
+         *  MIME string. If sending MIME, the string must be passed in to the 3rd
+         *  position of the function call.
+        */
+        if(is_array($postFiles)){
+            return $this->post("$workingDomain/messages", $postData, $postFiles);
+        }
+        else if(is_string($postFiles)){
 
-	/*
-       This function allows the sending of a fully formed message OR a custom
-	   MIME string. If sending MIME, the string must be passed in to the 3rd
-	   position of the function call.
-	*/
+            $tempFile = tempnam(sys_get_temp_dir(), "MG_TMP_MIME");
+            $fileHandle = fopen($tempFile, "w");
+            fwrite($fileHandle, $postFiles);
 
-	    if(is_array($postFiles)){
-			return $this->post("$workingDomain/messages", $postData, $postFiles);
-	    }
-	    else if(is_string($postFiles)){
-
-	    	$tempFile = tempnam(sys_get_temp_dir(), "MG_TMP_MIME");
-	   		$fileHandle = fopen($tempFile, "w");
-	   		fwrite($fileHandle, $postFiles);
-
-			$result = $this->post("$workingDomain/messages.mime", $postData, array("message" => $tempFile));
+            $result = $this->post("$workingDomain/messages.mime", $postData, array("message" => $tempFile));
             fclose($fileHandle);
             unlink($tempFile);
-			return $result;
-	    }
-	    else{
-			throw new Exceptions\MissingRequiredMIMEParameters(EXCEPTION_MISSING_REQUIRED_MIME_PARAMETERS);
-	    }
-	}
+            return $result;
+        }
+        else{
+            throw new Exceptions\MissingRequiredMIMEParameters(EXCEPTION_MISSING_REQUIRED_MIME_PARAMETERS);
+        }
+    }
+    
+    public function verifyWebhookSignature($postData = NULL) {
+        /*
+         * This function checks the signature in a POST request to see if it is
+         * authentic.
+         *
+         * Pass an array of parameters.  If you pass nothing, $_POST will be
+         * used instead.
+         *
+         * If this function returns FALSE, you must not process the request.
+         * You should reject the request with status code 403 Forbidden.
+        */
+        if(is_null($postData)) {
+            $postData = $_POST;
+        }
+        $hmac = hash_hmac('sha256', "{$postData["timestamp"]}{$postData["token"]}", $this->apiKey);
+        $sig = $postData['signature'];
+        if(function_exists('hash_equals')) {
+            // hash_equals is constant time, but will not be introduced until PHP 5.6
+            return hash_equals($hmac, $sig);
+        }
+        else {
+            return ($hmac == $sig);
+        }
+    }
 
-	public function post($endpointUrl, $postData = array(), $files = array()){
-		return $this->restClient->post($endpointUrl, $postData, $files);
-	}
+    public function post($endpointUrl, $postData = array(), $files = array()){
+        return $this->restClient->post($endpointUrl, $postData, $files);
+    }
 
-	public function get($endpointUrl, $queryString = array()){
-		return $this->restClient->get($endpointUrl, $queryString);
-	}
+    public function get($endpointUrl, $queryString = array()){
+        return $this->restClient->get($endpointUrl, $queryString);
+    }
 
-	public function delete($endpointUrl){
-		return $this->restClient->delete($endpointUrl);
-	}
+    public function delete($endpointUrl){
+        return $this->restClient->delete($endpointUrl);
+    }
 
-	public function put($endpointUrl, $putData){
-		return $this->restClient->put($endpointUrl, $putData);
-	}
+    public function put($endpointUrl, $putData){
+        return $this->restClient->put($endpointUrl, $putData);
+    }
 
-	public function MessageBuilder(){
-		return new MessageBuilder();
-	}
+    public function MessageBuilder(){
+        return new MessageBuilder();
+    }
 
-	public function OptInHandler(){
-		return new OptInHandler();
-	}
+    public function OptInHandler(){
+        return new OptInHandler();
+    }
 
-	public function BatchMessage($workingDomain, $autoSend = true){
-		return new BatchMessage($this->restClient, $workingDomain, $autoSend);
-	}
+    public function BatchMessage($workingDomain, $autoSend = true){
+        return new BatchMessage($this->restClient, $workingDomain, $autoSend);
+    }
 }
diff --git a/tests/Mailgun/Tests/MailgunTest.php b/tests/Mailgun/Tests/MailgunTest.php
index 05e10cd..2fbbc24 100644
--- a/tests/Mailgun/Tests/MailgunTest.php
+++ b/tests/Mailgun/Tests/MailgunTest.php
@@ -13,4 +13,24 @@ class MailgunTest extends \Mailgun\Tests\MailgunTestCase
         $client = new Mailgun();
         $client->sendMessage("test.mailgun.com", "etss", 1);
     }
+
+    public function testVerifyWebhookGood() {
+        $client = new Mailgun('key-3ax6xnjp29jd6fds4gc373sgvjxteol0');
+        $postData = [
+            'timestamp' => '1403645220',
+            'token' => '5egbgr1vjgqxtrnp65xfznchgdccwh5d6i09vijqi3whgowmn6',
+            'signature' => '9cfc5c41582e51246e73c88d34db3af0a3a2692a76fbab81492842f000256d33',
+        ];
+        assert($client->verifyWebhookSignature($postData));
+    }
+
+    public function testVerifyWebhookBad() {
+        $client = new Mailgun('key-3ax6xnjp29jd6fds4gc373sgvjxteol0');
+        $postData = [
+            'timestamp' => '1403645220',
+            'token' => 'owyldpe6nxhmrn78epljl6bj0orrki1u3d2v5e6cnlmmuox8jr',
+            'signature' => '9cfc5c41582e51246e73c88d34db3af0a3a2692a76fbab81492842f000256d33',
+        ];
+        assert(!$client->verifyWebhookSignature($postData));
+    }
 }