diff --git a/vendor/github.com/aead/cmac/xor.go b/vendor/github.com/aead/cmac/xor.go
new file mode 100644
index 0000000..ecc3862
--- /dev/null
+++ b/vendor/github.com/aead/cmac/xor.go
@@ -0,0 +1,15 @@
+// Copyright (c) 2016 Andreas Auernhammer. All rights reserved.
+// Use of this source code is governed by a license that can be
+// found in the LICENSE file.
+
+// +build !amd64
+
+package cmac
+
+// xor xors the bytes in dst with src and writes the result to dst.
+// The destination is assumed to have enough space.
+func xor(dst, src []byte) {
+	for i, v := range src {
+		dst[i] ^= v
+	}
+}