Update github.com/Rhymen/go-whatsapp vendor. Fixes #843

vendor/github.com/Rhymen/go-whatsapp/crypto/hkdf/hkdf.go

@@ -9,7 +9,6 @@ second stage "expands" this key into several additional pseudorandom keys (the o
 package hkdf
 
 import (
-	"crypto/hmac"
 	"crypto/sha256"
 	"fmt"
 	"golang.org/x/crypto/hkdf"
@@ -20,33 +19,29 @@ import (
 Expand expands a given key with the HKDF algorithm.
 */
 func Expand(key []byte, length int, info string) ([]byte, error) {
+	var h io.Reader
 	if info == "" {
-		keyBlock := hmac.New(sha256.New, key)
-		var out, last []byte
-
-		var blockIndex byte = 1
-		for i := 0; len(out) < length; i++ {
-			keyBlock.Reset()
-			//keyBlock.Write(append(append(last, []byte(info)...), blockIndex))
-			keyBlock.Write(last)
-			keyBlock.Write([]byte(info))
-			keyBlock.Write([]byte{blockIndex})
-			last = keyBlock.Sum(nil)
-			blockIndex += 1
-			out = append(out, last...)
-		}
-		return out[:length], nil
+		/*
+			Only used during initial login
+			Pseudorandom Key is provided by server and has not to be created
+		*/
+		h = hkdf.Expand(sha256.New, key, []byte(info))
 	} else {
-		h := hkdf.New(sha256.New, key, nil, []byte(info))
-		out := make([]byte, length)
-		n, err := io.ReadAtLeast(h, out, length)
-		if err != nil {
-			return nil, err
-		}
-		if n != length {
-			return nil, fmt.Errorf("new key to short")
-		}
-
-		return out[:length], nil
+		/*
+			Used every other time
+			Pseudorandom Key is created during kdf.New
+			This is the normal that crypto/hkdf is used
+		*/
+		h = hkdf.New(sha256.New, key, nil, []byte(info))
 	}
+	out := make([]byte, length)
+	n, err := io.ReadAtLeast(h, out, length)
+	if err != nil {
+		return nil, err
+	}
+	if n != length {
+		return nil, fmt.Errorf("new key to short")
+	}
+
+	return out, nil
 }