use cryptographic random to generate new connection IDs

fixes #348

utils/connection_id.go

@@ -0,0 +1,18 @@
+package utils
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+
+	"github.com/lucas-clemente/quic-go/protocol"
+)
+
+// GenerateConnectionID generates a connection ID using cryptographic random
+func GenerateConnectionID() (protocol.ConnectionID, error) {
+	b := make([]byte, 8, 8)
+	_, err := rand.Read(b)
+	if err != nil {
+		return 0, err
+	}
+	return protocol.ConnectionID(binary.LittleEndian.Uint64(b)), nil
+}