initial commit

pkg/server/xsrf.go

@@ -0,0 +1,49 @@
+// Copyright (C) 2019 Marius Schellenberger
+
+package server
+
+import (
+	"crypto/rand"
+	"crypto/subtle"
+	"encoding/base64"
+	"git.giftfish.de/ston1th/docstore/pkg/log"
+	"git.giftfish.de/ston1th/jwt/v3"
+)
+
+const keySize = jwt.KeySize / 2
+
+func genKey(length int) (bytes []byte) {
+	bytes = make([]byte, length)
+	if _, err := rand.Reader.Read(bytes); err != nil {
+		log.Println("genKey:", err)
+	}
+	return
+}
+
+func newXsrf(secret []byte) string {
+	rnd := genKey(keySize)
+	return base64.RawURLEncoding.EncodeToString(append(rnd, xor(rnd, secret)...))
+}
+
+func checkXsrf(xsrf string, secret []byte) bool {
+	t, err := base64.RawURLEncoding.DecodeString(xsrf)
+	if err != nil {
+		return false
+	}
+	if len(t) != jwt.KeySize {
+		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
+}