## 3 Background and Related Works
### Authentication Goals in IoT
#### 3.1.1 HIP-Based Solutions  
In this section, we detail the principle techniques provided with authentication solution based on HIP protocol. We also provide an overview and a comparison between studied previous HIP-based authentication solutions discussed in this section (see Table 1). HIP [14] protocol is an alternative solution to IKE/IPsec. HIP BEX is based on the cryptographic host identities for mutual authentication, and it establishes dynamic security associations between HIP peers on the Internet. HIP BEX uses the Diffie-Helman key exchange. The handshake is composed of four messages. The public key is serving as a host identifier that each HIP peer should have, and its counterpart private key is known and used only by its legitimate owner. This pair of keys is useful for identification and authentication aims. Once HIP security SA is established, the end-parties can start communicating data, securely, using ESP [15]. HIP BEX handshake involves heavy asymmetric cryptographic operations using certificates and for this reason, it cannot be supported as it is by constrained small devices. In [5], the authors propose to use HIP DEX as an alternative variant of HIP BEX by reducing its computational cost and introducing elliptic curve cryptography in Diffie-Hellman policy ECDH (Elliptic Curve Diffie-Hellman). Only one public key is used to compute the session key and to identify the communicating HIP peer. Some researchers are focused on improving the efficiency of HIP DEX to be compatible with the most constrained sensor nodes. In [16], the authors propose **LHIP (Lightweight HIP)** solution that keeps the same structure of HIP BEX messages and provides a security mechanism based only on hash functions to provide the integrity of the exchanged messages. Security features are maintained and communicated over the exchanged messages but ignored by the pairs. LHIP is weak because it omits primordial security mechanisms as mutual authentication and key exchange. Even if HIP (both HIP BEX and Diet-HIP) is based on a few signaling messages to establish a secure association between two peers on the Internet, these messages are very long and the expensive cost in terms of energy consumption cannot be ignored and also the fragmentation/reassembly rate resulting from the communication of similar messages within a 6 LoWPAN network. To resolve this problem, the authors in [17] propose a compressed layer for HIP DEX named **Slimfit**. The compression concerns some fields in the HIP header and signaling parameters for the reduction of the communication cost. The evaluation of the proposed compression demonstrates a lower packet fragmentation rate and less energy consumption. Nevertheless, the solution has compatibility problems with the standard HIP in addition to the heavy computational cost that is relatively important, when it is executed by constrained sensornodes. Besides, the given compression is not standardized according to the 6 LoWPAN compression rules. Relating to compression based solutions, **CD-HIP**[18] combines both Compression (**C**-HIP) and Distribution (**D**-HIP**[19]) techniques. This solution shows its performance on the handshake and the delegation of the heavy cryptographic computation to the third party (a collaborator). **[PERSON] and [PERSON]'s solution (CD-HIP) shows its performance against the previous works. Nevertheless, their solution is based on HIP BEX that is not designed for constrained devices and even with the use of the third party because it has an energetic cost (communication and computation) that is significantly high. In [20], [PERSON] et al. focused their work on a collaborative key establishment solution for IoT devices. Consistently, a constrained sensor node delegates its heavy cryptographic operation to a neighborhood that is less constrained. In the same work, the authors show the possibility of integrating the collaborative proposition with TLS handshake and IKE key generation protocols.