With the emergence of the Internet of Things (IoT), many devices organized into network, communicate by themselves on the Internet, and send data or private information on the web. It is essential to secure the transmitted data and the identities that may be disclosed to make these new technologies accepted by the largest number of citizens. However, the security mech-anisms that are widely used on the Internet are too heavy to be integrated on small constrained objects. This paper describes the current protocols and security solutions that can be deployed in constrained resources. It shows the benefits and the limitations of each scheme—the security extension of IEEE 802.15.4e in time-slotted channel hopping (TSCH) mode, compressed IPsec, datagram transport layer security (DTLS)—embedded at differ-ent levels of the OSI model into the 6LoWPAN stack. It opens with the challenge that one must tackle in the coming years. Several use cases are studied to envisage the security integration in cyber physical systems (CPSs) for host-to-host and host-to-network communications. The privacy issue is also addressed and different ways to hide the device identity are discussed.