diff --git a/lib/Payone/Api/Request/Abstract.php b/lib/Payone/Api/Request/Abstract.php
index ace1dbcd..12d07c38 100644
--- a/lib/Payone/Api/Request/Abstract.php
+++ b/lib/Payone/Api/Request/Abstract.php
@@ -258,7 +258,7 @@ public function getEncoding()
      */
     public function setKey($key)
     {
-        $this->key = md5($key);
+        $this->key = hash('sha384', $key);
     }
 
     /**
diff --git a/lib/Payone/Api/Request/Authorization/Abstract.php b/lib/Payone/Api/Request/Authorization/Abstract.php
index ca49fbe9..c1521b3e 100644
--- a/lib/Payone/Api/Request/Authorization/Abstract.php
+++ b/lib/Payone/Api/Request/Authorization/Abstract.php
@@ -409,7 +409,7 @@ protected function _getFrontendHash($aHashParams)
             $sHashString .= $sValue;
         }
 
-        return md5($sHashString);
+        return hash_hmac('sha384', $sHashString, $aHashParams['key']);
     }
     
 }
diff --git a/lib/Payone/ClientApi/Request/Abstract.php b/lib/Payone/ClientApi/Request/Abstract.php
index 78afa27c..4b78e0ce 100644
--- a/lib/Payone/ClientApi/Request/Abstract.php
+++ b/lib/Payone/ClientApi/Request/Abstract.php
@@ -233,7 +233,7 @@ public function getEncoding()
      */
     public function setKey($key)
     {
-        $this->key = md5($key);
+        $this->key = hash('sha384', $key);
     }
 
     /**