diff --git a/vendor/gopkg.in/jcmturner/gokrb5.v7/crypto/rfc4757/keyDerivation.go b/vendor/gopkg.in/jcmturner/gokrb5.v7/crypto/rfc4757/keyDerivation.go
new file mode 100644
index 0000000..5e7ec48
--- /dev/null
+++ b/vendor/gopkg.in/jcmturner/gokrb5.v7/crypto/rfc4757/keyDerivation.go
@@ -0,0 +1,55 @@
+package rfc4757
+
+import (
+	"bytes"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"io"
+
+	"golang.org/x/crypto/md4"
+)
+
+// StringToKey returns a key derived from the string provided according to the definition in RFC 4757.
+func StringToKey(secret string) ([]byte, error) {
+	b := make([]byte, len(secret)*2, len(secret)*2)
+	for i, r := range secret {
+		u := fmt.Sprintf("%04x", r)
+		c, err := hex.DecodeString(u)
+		if err != nil {
+			return []byte{}, errors.New("character could not be encoded")
+		}
+		// Swap round the two bytes to make little endian as we put into byte slice
+		b[2*i] = c[1]
+		b[2*i+1] = c[0]
+	}
+	r := bytes.NewReader(b)
+	h := md4.New()
+	_, err := io.Copy(h, r)
+	if err != nil {
+		return []byte{}, err
+	}
+	return h.Sum(nil), nil
+}
+
+func deriveKeys(key, checksum []byte, usage uint32, export bool) (k1, k2, k3 []byte) {
+	//if export {
+	//	L40 := make([]byte, 14, 14)
+	//	copy(L40, []byte(`fortybits`))
+	//	k1 = HMAC(key, L40)
+	//} else {
+	//	tb := MessageTypeBytes(usage)
+	//	k1 = HMAC(key, tb)
+	//}
+	//k2 = k1[:16]
+	//if export {
+	//	mask := []byte{0xAB,0xAB,0xAB,0xAB,0xAB,0xAB,0xAB,0xAB,0xAB}
+	//	copy(k1[7:16], mask)
+	//}
+	//k3 = HMAC(k1, checksum)
+	//return
+	k1 = key
+	k2 = HMAC(k1, UsageToMSMsgType(usage))
+	k3 = HMAC(k2, checksum)
+	return
+}