1 files changed, 55 insertions, 0 deletions
diff --git a/backend_nonce.go b/backend_nonce.go
new file mode 100644
index 0000000..835a80f
--- /dev/null
+++ b/backend_nonce.go
@@ -0,0 +1,55 @@
+package gocryptfs
+
+import (
+	"encoding/binary"
+	"encoding/hex"
+	"sync"
+	"crypto/rand"
+)
+
+type nonce96 struct {
+	lock sync.Mutex
+	high32 uint32
+	low64 uint64
+	ready int
+}
+
+var gcmNonce nonce96
+
+func (n *nonce96) randBytes(len int) []byte {
+	b := make([]byte, len)
+	_, err := rand.Read(b)
+	if err != nil {
+		panic("Could not get random bytes for nonce")
+	}
+	return b
+}
+
+func (n *nonce96) init() {
+	b := n.randBytes(8)
+	n.low64 = binary.BigEndian.Uint64(b)
+	b = n.randBytes(4)
+	n.high32 = binary.BigEndian.Uint32(b)
+	n.ready = 1
+	return
+}
+
+func (n *nonce96) Get() []byte {
+	n.lock.Lock()
+	if n.ready == 0 {
+		n.init()
+	}
+	n.low64++
+	if n.low64 == 0 {
+		// Counter has wrapped
+		n.high32++
+	}
+	r := make([]byte, 12)
+	binary.BigEndian.PutUint32(r[0:4], n.high32)
+	binary.BigEndian.PutUint64(r[4:12], n.low64)
+	n.lock.Unlock()
+
+	debug.Printf("nonce96.Get(): %s\n", hex.EncodeToString(r))
+
+	return r
+}