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One of the challenges in implementing an encryption system for a connected object in the IoT environment is the availability of appropriate software libraries that respect the constraints governing IoT objects in terms of memory, computation ability and energy consumption. In this context, certain research projects have been carried out to address this problem, which still poses a challenge and requires more advanced studies that are better adapted to the needs of the IoT in order to provide optimal security services. An example of an existing library that can be used in an IoT environment is the “AVR-Crypto-Lib” (Cantora 2013), which provides special implementations that respect the limited resources of microcontrollers. This library offers symmetric key encryption such as AES, RC5, RC6 and DES. Another library, “Relic-Toolkit” (2018), offers a large variety of asymmetric encryption algorithms such as RSA and Rabin crypto system. “Relic-Toolkit” is used in the TinyPBC project implemented on the TOSSIM simulator (2018) on the TinyOS operating system. The libraries we have just described provide, among other things, a confidentiality service in an IoT environment, which allows secure communications, so that unauthorized access to the content of the data is prohibited and that content is protected during its transfer between two entities in the IoT environment.

European research projects have also focused on data confidentiality on the IoT. The SMARTIE project (Pokric et al. 2015), for example, uses CP-ABE (Ciphertext Policy Attribute-Based Encryption), a technique that allows the IoT user to decrypt the message from objects with a secret key if the policy attributes match the attributes of the key. CP-ABE makes it possible to encrypt data for a group of users, instead of encrypting it individually, in accordance with access policies. This technique links access control and encryption and is used when data from an object must be received by several users of that IoT service. Data are thus encrypted only once (SMARTIE 2014a; Pokric et al. 2015). The European project BUTLER (CORDIS 2018) is focused on the protection of the communication channel in the IoT. This channel is vulnerable because of its wireless feature and information dissemination. BUTLER proposes improvements to security standards used in IoT communication technologies. For ZigBee, it offers a security system based on the use of symmetric keys to complement and enhance the security features provided by the ZigBee standard, which uses two mandatory keys and one optional key. The Master Key and the Network Key are mandatory, while the Link Key is optional. The Master Key is used in the initialization phase and implemented at the nodes through an out-of-band channel. The Network Key guarantees the security of the network layer and is shared by all nodes. It is derived from the Master Key. The optional Link Key is derived from the Master key and guarantees the security of the link between two peers at the application level. In this context, the BUTLER project put in place mechanisms to manage the deployment, maintenance and revocation of the Master key. It also proposed implementing an additional symmetric key (called the Global Key) at the node, at the time of manufacture. This key is used by the Medium Access Control (MAC) layer and is shared by all nodes. The Global Key guarantees security for the lower layers. The Network Key provided by the ZigBee standard will thus be used as a Group Key, which will be shared between the nodes and managed by the ZigBee Network layer. This makes it possible to securely address a group of nodes sharing a common feature. As a result, objects communicating via ZigBee will be guaranteed greater security as well as additional security when using the optional Link Key (Sottile et al. 2014).