fix xsrf and added nonce

pkg/server/xsrf.go

@@ -3,25 +3,28 @@
 package server
 
 import (
+	"crypto/hmac"
 	"crypto/rand"
-	"crypto/subtle"
+	"crypto/sha256"
 	"encoding/base64"
-
-	"git.giftfish.de/ston1th/jwt/v3"
 )
 
-const keySize = jwt.KeySize / 2
+const (
+	keySize  = 16
+	fullSize = keySize * 2
+)
 
-func genKey(size int) (b []byte, err error) {
-	b = make([]byte, size)
-	_, err = rand.Reader.Read(b)
+func genKey(length int) (bytes []byte) {
+	bytes = make([]byte, length)
+	rand.Read(bytes)
 	return
 }
 
-func newXsrf(secret []byte) (s string, err error) {
-	rnd, err := genKey(keySize)
-	s = base64.RawURLEncoding.EncodeToString(append(rnd, xor(rnd, secret)...))
-	return
+func newXsrf(secret []byte) string {
+	mac := hmac.New(sha256.New, secret)
+	rnd := genKey(keySize)
+	mac.Write(rnd)
+	return base64.RawURLEncoding.EncodeToString(append(rnd, mac.Sum(nil)[:keySize]...))
 }
 
 func checkXsrf(xsrf string, secret []byte) bool {
@@ -29,20 +32,10 @@ func checkXsrf(xsrf string, secret []byte) bool {
 	if err != nil {
 		return false
 	}
-	if len(t) != jwt.KeySize {
+	if len(t) != fullSize {
 		return false
 	}
-	return subtle.ConstantTimeCompare(secret, xor(t[keySize:], t[:keySize])) == 1
-}
-
-func xor(a, b []byte) (c []byte) {
-	n := len(a)
-	if len(b) < n {
-		return nil
-	}
-	c = make([]byte, n)
-	for i := 0; i < n; i++ {
-		c[i] = a[i] ^ b[i]
-	}
-	return
+	mac := hmac.New(sha256.New, secret)
+	mac.Write(t[:keySize])
+	return hmac.Equal(t[keySize:], mac.Sum(nil)[:keySize])
 }