diff --git a/lib/PayPal/Auth/OAuthTokenCredential.php b/lib/PayPal/Auth/OAuthTokenCredential.php
index f38cd6f..d84dfe0 100644
--- a/lib/PayPal/Auth/OAuthTokenCredential.php
+++ b/lib/PayPal/Auth/OAuthTokenCredential.php
@@ -11,6 +11,7 @@ use PayPal\Exception\PayPalConfigurationException;
 use PayPal\Exception\PayPalConnectionException;
 use PayPal\Handler\IPayPalHandler;
 use PayPal\Rest\ApiContext;
+use PayPal\Security\Cipher;
 
 /**
  * Class OAuthTokenCredential
@@ -74,6 +75,13 @@ class OAuthTokenCredential extends PayPalResourceModel
      */
     private $tokenCreateTime;
 
+    /**
+     * Instance of cipher used to encrypt/decrypt data while storing in cache.
+     *
+     * @var Cipher
+     */
+    private $cipher;
+
     /**
      * Construct
      *
@@ -84,6 +92,7 @@ class OAuthTokenCredential extends PayPalResourceModel
     {
         $this->clientId = $clientId;
         $this->clientSecret = $clientSecret;
+        $this->cipher = new Cipher($this->clientSecret);
         $this->logger = PayPalLoggingManager::getInstance(__CLASS__);
     }
 
@@ -120,9 +129,20 @@ class OAuthTokenCredential extends PayPalResourceModel
         $token = AuthorizationCache::pull($config, $this->clientId);
         if ($token) {
             // We found it
-            $this->accessToken = $token['accessToken'];
+            // This code block is for backward compatibility only.
+            if (array_key_exists('accessToken', $token)) {
+                $this->accessToken = $token['accessToken'];
+            }
+
             $this->tokenCreateTime = $token['tokenCreateTime'];
             $this->tokenExpiresIn = $token['tokenExpiresIn'];
+
+            // Case where we have an old unencrypted cache file
+            if (!array_key_exists('accessTokenEncrypted', $token)) {
+                AuthorizationCache::push($config, $this->clientId, $this->encrypt($this->accessToken), $this->tokenCreateTime, $this->tokenExpiresIn);
+            } else {
+                $this->accessToken = $this->decrypt($token['accessTokenEncrypted']);
+            }
         }
 
         // Check if Access Token is not null and has not expired.
@@ -137,11 +157,12 @@ class OAuthTokenCredential extends PayPalResourceModel
             $this->accessToken = null;
         }
 
+
         // If accessToken is Null, obtain a new token
         if ($this->accessToken == null) {
             // Get a new one by making calls to API
             $this->updateAccessToken($config);
-            AuthorizationCache::push($config, $this->clientId, $this->accessToken, $this->tokenCreateTime, $this->tokenExpiresIn);
+            AuthorizationCache::push($config, $this->clientId, $this->encrypt($this->accessToken), $this->tokenCreateTime, $this->tokenExpiresIn);
         }
 
         return $this->accessToken;
@@ -231,6 +252,7 @@ class OAuthTokenCredential extends PayPalResourceModel
      *
      * @param array $config
      * @return null
+     * @throws PayPalConnectionException
      */
     private function generateAccessToken($config, $refreshToken = null)
     {
@@ -259,4 +281,26 @@ class OAuthTokenCredential extends PayPalResourceModel
 
         return $this->accessToken;
     }
+
+    /**
+     * Helper method to encrypt data using clientSecret as key
+     *
+     * @param $data
+     * @return string
+     */
+    public function encrypt($data)
+    {
+        return $this->cipher->encrypt($data);
+    }
+
+    /**
+     * Helper method to decrypt data using clientSecret as key
+     *
+     * @param $data
+     * @return string
+     */
+    public function decrypt($data)
+    {
+        return $this->cipher->decrypt($data);
+    }
 }
diff --git a/lib/PayPal/Cache/AuthorizationCache.php b/lib/PayPal/Cache/AuthorizationCache.php
index 32649a2..b37b4eb 100644
--- a/lib/PayPal/Cache/AuthorizationCache.php
+++ b/lib/PayPal/Cache/AuthorizationCache.php
@@ -49,6 +49,7 @@ abstract class AuthorizationCache
      * @param      $accessToken
      * @param      $tokenCreateTime
      * @param      $tokenExpiresIn
+     * @throws \Exception
      */
     public static function push($config = null, $clientId, $accessToken, $tokenCreateTime, $tokenExpiresIn)
     {
@@ -58,7 +59,7 @@ abstract class AuthorizationCache
         $cachePath = self::cachePath($config);
         if (!is_dir(dirname($cachePath))) {
             if (mkdir(dirname($cachePath), 0755, true) == false) {
-                return;
+                throw new \Exception("Failed to create directory at $cachePath");
             }
         }
 
@@ -68,12 +69,14 @@ abstract class AuthorizationCache
         if (is_array($tokens)) {
             $tokens[$clientId] = array(
                 'clientId' => $clientId,
-                'accessToken' => $accessToken,
+                'accessTokenEncrypted' => $accessToken,
                 'tokenCreateTime' => $tokenCreateTime,
                 'tokenExpiresIn' => $tokenExpiresIn
             );
         }
-        file_put_contents($cachePath, json_encode($tokens));
+        if(!file_put_contents($cachePath, json_encode($tokens))) {
+            throw new \Exception("Failed to write cache");
+        };
     }
 
     /**
diff --git a/lib/PayPal/Security/Cipher.php b/lib/PayPal/Security/Cipher.php
new file mode 100644
index 0000000..3168ff0
--- /dev/null
+++ b/lib/PayPal/Security/Cipher.php
@@ -0,0 +1,57 @@
+<?php
+
+namespace PayPal\Security;
+
+/**
+ * Class Cipher
+ *
+ * Helper class to encrypt/decrypt data with secret key
+ *
+ * @package PayPal\Security
+ */
+class Cipher
+{
+    private $secretKey;
+
+    /**
+     * Fixed IV Size
+     */
+    const IV_SIZE = 16;
+
+    function __construct($secretKey)
+    {
+        $this->$secretKey = $secretKey;
+    }
+
+    /**
+     * Encrypts the input text using the cipher key
+     *
+     * @param $input
+     * @return string
+     */
+    function encrypt($input)
+    {
+        // Create a random IV. Not using mcrypt to generate one, as to not have a dependency on it.
+        $iv = substr(uniqid("", true), 0, Cipher::IV_SIZE);
+        // Encrypt the data
+        $encrypted = openssl_encrypt($input, "AES-256-CBC", $this->secretKey, 0, $iv);
+        // Encode the data with IV as prefix
+        return base64_encode($iv . $encrypted);
+    }
+
+    /**
+     * Decrypts the input text from the cipher key
+     *
+     * @param $input
+     * @return string
+     */
+    function decrypt($input)
+    {
+        // Decode the IV + data
+        $input = base64_decode($input);
+        // Remove the IV
+        $iv = substr($input, 0, Cipher::IV_SIZE);
+        // Return Decrypted Data
+        return openssl_decrypt(substr($input, Cipher::IV_SIZE), "AES-256-CBC", $this->secretKey, 0, $iv);
+    }
+}
diff --git a/sample/invoice/CreateInvoice.php b/sample/invoice/CreateInvoice.php
index 8b50721..1f38547 100644
--- a/sample/invoice/CreateInvoice.php
+++ b/sample/invoice/CreateInvoice.php
@@ -23,7 +23,6 @@ $invoice = new Invoice();
 $invoice
     ->setMerchantInfo(new MerchantInfo())
     ->setBillingInfo(array(new BillingInfo()))
-    ->setItems(array(new InvoiceItem()))
     ->setNote("Medical Invoice 16 Jul, 2013 PST")
     ->setPaymentTerm(new PaymentTerm())
     ->setShippingInfo(new ShippingInfo());
@@ -61,7 +60,8 @@ $billing[0]
 // ### Items List
 // You could provide the list of all items for
 // detailed breakdown of invoice
-$items = $invoice->getItems();
+$items = array();
+$items[0] = new InvoiceItem();
 $items[0]
     ->setName("Sutures")
     ->setQuantity(100)
@@ -70,6 +70,17 @@ $items[0]
 $items[0]->getUnitPrice()
     ->setCurrency("USD")
     ->setValue(5);
+// Second Item
+$items[1] = new InvoiceItem();
+$items[1]
+    ->setName("Injection")
+    ->setQuantity(5)
+    ->setUnitPrice(new Currency());
+
+$items[1]->getUnitPrice()
+    ->setCurrency("USD")
+    ->setValue(5);
+$invoice->setItems($items);
 
 $invoice->getPaymentTerm()
     ->setTermType("NET_45");
diff --git a/tests/PayPal/Test/Auth/OAuthTokenCredentialTest.php b/tests/PayPal/Test/Auth/OAuthTokenCredentialTest.php
index 8a6ea68..7874711 100644
--- a/tests/PayPal/Test/Auth/OAuthTokenCredentialTest.php
+++ b/tests/PayPal/Test/Auth/OAuthTokenCredentialTest.php
@@ -48,9 +48,11 @@ class OAuthTokenCredentialTest extends \PHPUnit_Framework_TestCase
             'cache.enabled' => true,
             'cache.FileName' => AuthorizationCacheTest::CACHE_FILE
         );
+         $cred = new OAuthTokenCredential('clientId', 'clientSecret');
+
         //{"clientId":{"clientId":"clientId","accessToken":"accessToken","tokenCreateTime":1421204091,"tokenExpiresIn":288000000}}
-        AuthorizationCache::push($config, 'clientId', 'accessToken', 1421204091, 288000000);
-        $cred = new OAuthTokenCredential('clientId', 'clientSecret');
+        AuthorizationCache::push($config, 'clientId', $cred->encrypt('accessToken'), 1421204091, 288000000);
+
         $apiContext = new ApiContext($cred);
         $apiContext->setConfig($config);
         $this->assertEquals('clientId', $cred->getClientId());
diff --git a/tests/PayPal/Test/Cache/AuthorizationCacheTest.php b/tests/PayPal/Test/Cache/AuthorizationCacheTest.php
index 8df913b..82a5e14 100644
--- a/tests/PayPal/Test/Cache/AuthorizationCacheTest.php
+++ b/tests/PayPal/Test/Cache/AuthorizationCacheTest.php
@@ -76,7 +76,7 @@ class AuthorizationCacheTest extends \PHPUnit_Framework_TestCase
         $tokens = json_decode($contents, true);
         $this->assertNotNull($contents);
         $this->assertEquals('clientId', $tokens['clientId']['clientId']);
-        $this->assertEquals('accessToken', $tokens['clientId']['accessToken']);
+        $this->assertEquals('accessToken', $tokens['clientId']['accessTokenEncrypted']);
         $this->assertEquals('tokenCreateTime', $tokens['clientId']['tokenCreateTime']);
         $this->assertEquals('tokenExpiresIn', $tokens['clientId']['tokenExpiresIn']);
 
@@ -97,7 +97,7 @@ class AuthorizationCacheTest extends \PHPUnit_Framework_TestCase
         $this->assertNotNull($result);
         $this->assertTrue(is_array($result));
         $this->assertEquals('clientId', $result['clientId']);
-        $this->assertEquals('accessToken', $result['accessToken']);
+        $this->assertEquals('accessToken', $result['accessTokenEncrypted']);
         $this->assertEquals('tokenCreateTime', $result['tokenCreateTime']);
         $this->assertEquals('tokenExpiresIn', $result['tokenExpiresIn']);