  Software-defined networking (SDN) has become a fundamental technology for
data centers and 5G networks. In an SDN network, routing and traffic management
decisions are made by a centralized controller and communicated to switches via
a control channel. Transport Layer Security (TLS) has been proposed as its
single security layer; however, use of TLS is optional and connections are
still vulnerable to downgrade attacks. In this paper, we propose the
strengthening of security assurance using a protocol dialecting approach to
provide additional and customizable security. We consider and evaluate two
dialecting approaches for OpenFlow protocol operation, adding per-message
authentication to the SDN control channel that is independent of TLS and
provides robustness against downgrade attacks in the optional case of TLS
implementation. Furthermore, we measure the performance impact of using these
dialecting primitives in a Mininet experiment. The results show a modest
increase of communication latency of less than 22%.
