diff --git a/phpseclib/Crypt/DES.php b/phpseclib/Crypt/DES.php
index e0b333f2..903fdc5c 100644
--- a/phpseclib/Crypt/DES.php
+++ b/phpseclib/Crypt/DES.php
@@ -362,7 +362,7 @@ class Crypt_DES {
      */
     function setKey($key)
     {
-        $this->keys = ( CRYPT_DES_MODE == CRYPT_DES_MODE_MCRYPT ) ? substr($key, 0, 8) : $this->_prepareKey($key);
+        $this->keys = ( CRYPT_DES_MODE == CRYPT_DES_MODE_MCRYPT ) ? str_pad(substr($key, 0, 8), 8, chr(0)) : $this->_prepareKey($key);
         $this->changed = true;
     }
 
diff --git a/phpseclib/Crypt/Rijndael.php b/phpseclib/Crypt/Rijndael.php
index f2212c69..f6f281f8 100644
--- a/phpseclib/Crypt/Rijndael.php
+++ b/phpseclib/Crypt/Rijndael.php
@@ -532,7 +532,7 @@ class Crypt_Rijndael {
      */
     function setKey($key)
     {
-        $this->key = $key;
+        $this->key = str_pad(substr($key, 0, $this->key_size), $this->key_size, chr(0));
         $this->changed = true;
     }