## 2 Problem Exposure and Motivations  
The authentication process is more critical in a constrained network environment than in a traditional network, since there are many types of IoT applications that can damage the life of a human if the authentication phase fails. In this field, we can give an example of a health sensor that is implanted on the heart of a patient and that must send sensitive information to the medical server. We must not forget that IoT also connects the astronomic application to the appropriate working group. Any error in the authentication may cause hard spoilage in monitoring applications and/or satellites. Hence, for an efficient E2E security establishment association on IoT, it is crucial to propose a solution that can secure communication in (M2T) and in Thing-to-Thing (T2T) architectures. HIP DEX is the most promising protocol designed especially for the constrained environment. HIP DEX is characterized by the following encouraging features:  
* The separation of the identity and the physical location of the communicating peers is the strength of the HIP-based solution that facilitates end-users mobility and ensures a good level of location privacy. HIP separates the end-point identifier and locator roles of IP addresses. These qualities are highly recommended in many IoT deployments, as in health care and military applications;
* The number of exchanged messages to establish a key agreement mechanism is only four messages, which is not the case for the other security protocols;
* HIP is adopted as a lightweight solution for the WSN [8; 9; 11; 12; 13];
* The use of HIP as a Keying material and IPsec for the tunneling for securing the communication between the two parts. This guarantees the security of communication in the network layer (coupling IPsec with HIP) and, as a consequence, securing all types of transport traffic layer (UDP or TCP);
* The protocol is designed to be resistant to Denial of Service (DoS) and man-in-the-middle attacks [5].  
The above-cited features are generic for both types of HIP protocol: HIP BEX (HIP Base EXchange) and HIP DEX. HIP BEX has too-heavy cryptographic operations that could not be supported by resource constraint devices such as mobile devices and base stations. To address constrained devices better, the use of ECC has been proposed to be used with HIP [11]. HIP introduces a cryptographic namespace of stable host identities (HIs) between both network and transport layer. Besides enabling multihoming and mobility, the cryptographic HIs ensure a mutual authentication Diffie-Hellman key exchange, in which the generated symmetric-key usually protects an IPsec association. Consequently, ECC is the best computational technique for generating key material with few operations in comparison with asymmetric cryptographic algorithms such as RSA (Rivest-Shamir-Adleman) without losing security level. The relevant differences that exist between HIP BEX and HIP DEX are the total cancellations of the signature scheme in HIP BEX and the combination of the DH key generation with an ECC variant (ECDH). Indeed, the HIP DEX protocol [5] is primarily designed for resolving computation or memory-constrained sensor/actuator devices. The constrained IP-enabled networks, such as 6 LoWPAN networks, constitute the backbone of research targeting the Internet of Things. In this context, we are studying, by way of real experiments, the efficiency of HIP DEX in the handshake process in terms of packets' transmission delays in a 6 LoWPAN-WSN IoT.