diff --git a/vendor/gopkg.in/jcmturner/gokrb5.v7/crypto/rfc4757/checksum.go b/vendor/gopkg.in/jcmturner/gokrb5.v7/crypto/rfc4757/checksum.go
new file mode 100644
index 0000000..45276e9
--- /dev/null
+++ b/vendor/gopkg.in/jcmturner/gokrb5.v7/crypto/rfc4757/checksum.go
@@ -0,0 +1,40 @@
+package rfc4757
+
+import (
+	"bytes"
+	"crypto/hmac"
+	"crypto/md5"
+	"io"
+)
+
+// Checksum returns a hash of the data in accordance with RFC 4757
+func Checksum(key []byte, usage uint32, data []byte) ([]byte, error) {
+	// Create hashing key
+	s := append([]byte(`signaturekey`), byte(0x00)) //includes zero octet at end
+	mac := hmac.New(md5.New, key)
+	mac.Write(s)
+	Ksign := mac.Sum(nil)
+
+	// Format data
+	tb := UsageToMSMsgType(usage)
+	p := append(tb, data...)
+	h := md5.New()
+	rb := bytes.NewReader(p)
+	_, err := io.Copy(h, rb)
+	if err != nil {
+		return []byte{}, err
+	}
+	tmp := h.Sum(nil)
+
+	// Generate HMAC
+	mac = hmac.New(md5.New, Ksign)
+	mac.Write(tmp)
+	return mac.Sum(nil), nil
+}
+
+// HMAC returns a keyed MD5 checksum of the data
+func HMAC(key []byte, data []byte) []byte {
+	mac := hmac.New(md5.New, key)
+	mac.Write(data)
+	return mac.Sum(nil)
+}