diff --git a/nova/tests/unit/virt/libvirt/storage/test_dmcrypt.py b/nova/tests/unit/virt/libvirt/storage/test_dmcrypt.py
index df16f53bfd24..a09ee3931953 100644
--- a/nova/tests/unit/virt/libvirt/storage/test_dmcrypt.py
+++ b/nova/tests/unit/virt/libvirt/storage/test_dmcrypt.py
@@ -13,6 +13,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import binascii
 import mock
 from oslo_concurrency import processutils
 
@@ -29,8 +30,8 @@ class LibvirtDmcryptTestCase(test.NoDBTestCase):
         self.NAME = 'disk'
         self.TARGET = dmcrypt.volume_name(self.NAME)
         self.PATH = '/dev/nova-lvm/instance_disk'
-        self.KEY = range(0, self.KEY_SIZE)
-        self.KEY_STR = ''.join(["%02x" % x for x in range(0, self.KEY_SIZE)])
+        self.KEY = bytes(bytearray(x for x in range(0, self.KEY_SIZE)))
+        self.KEY_STR = binascii.hexlify(self.KEY).decode('utf-8')
 
     @mock.patch('nova.utils.execute')
     def test_create_volume(self, mock_execute):
diff --git a/nova/virt/libvirt/storage/dmcrypt.py b/nova/virt/libvirt/storage/dmcrypt.py
index cb82a06a0720..7b21de7ab3eb 100644
--- a/nova/virt/libvirt/storage/dmcrypt.py
+++ b/nova/virt/libvirt/storage/dmcrypt.py
@@ -13,6 +13,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import binascii
 import os
 
 from oslo_concurrency import processutils
@@ -52,7 +53,7 @@ def create_volume(target, device, cipher, key_size, key):
     :param device: underlying block device
     :param cipher: encryption cipher string digestible by cryptsetup
     :param key_size: encryption key size
-    :param key: encryption key as an array of unsigned bytes
+    :param key: encoded encryption key bytestring
     """
     cmd = ('cryptsetup',
            'create',
@@ -61,7 +62,7 @@ def create_volume(target, device, cipher, key_size, key):
            '--cipher=' + cipher,
            '--key-size=' + str(key_size),
            '--key-file=-')
-    key = ''.join(map(lambda byte: "%02x" % byte, key))
+    key = binascii.hexlify(key).decode('utf-8')
     try:
         utils.execute(*cmd, process_input=key, run_as_root=True)
     except processutils.ProcessExecutionError as e: