  The first OpenFlow Software-Defined Network (SDN) Controller, NOX, was
developed by Nicira Networks and donated to the research community in 2008.
Almost 10 years later, there are at least 29 open-source SDN Controllers and
many more proprietary solutions. Two of the open-source SDN controllers stand
out in terms of broad deployment and strong contributor base; Open Network
Operating System (ONOS) and OpenDaylight (ODL). Both have been deployed in live
networks. However, despite increasing adoption of SDN, the security of the SDN
control plane has developed at a snail's pace. In this paper, the evolution of
ONOS and ODL security is discussed. The reflection of this on secure SDN
Controller design is analyzed.
