1 files changed, 44 insertions, 0 deletions
diff --git a/internal/cryptocore/nonce.go b/internal/cryptocore/nonce.go
new file mode 100644
index 0000000..72d8588
--- /dev/null
+++ b/internal/cryptocore/nonce.go
@@ -0,0 +1,44 @@
+package cryptocore
+
+import (
+	"bytes"
+	"crypto/rand"
+	"encoding/binary"
+	"encoding/hex"
+	"fmt"
+
+	"github.com/rfjakob/gocryptfs/internal/toggledlog"
+)
+
+// Get "n" random bytes from /dev/urandom or panic
+func RandBytes(n int) []byte {
+	b := make([]byte, n)
+	_, err := rand.Read(b)
+	if err != nil {
+		panic("Failed to read random bytes: " + err.Error())
+	}
+	return b
+}
+
+// Return a secure random uint64
+func RandUint64() uint64 {
+	b := RandBytes(8)
+	return binary.BigEndian.Uint64(b)
+}
+
+type nonceGenerator struct {
+	lastNonce []byte
+	nonceLen  int // bytes
+}
+
+// Get a random "nonceLen"-byte nonce
+func (n *nonceGenerator) Get() []byte {
+	nonce := RandBytes(n.nonceLen)
+	toggledlog.Debug.Printf("nonceGenerator.Get(): %s\n", hex.EncodeToString(nonce))
+	if bytes.Equal(nonce, n.lastNonce) {
+		m := fmt.Sprintf("Got the same nonce twice: %s. This should never happen!", hex.EncodeToString(nonce))
+		panic(m)
+	}
+	n.lastNonce = nonce
+	return nonce
+}