# A Survey of Internet of Things (IoT) Authentication Schemes +
## 3 Security Issues in IoT
### Security Challenges in IoT Layers
#### 3.2.1 Perception Layer Security Issues and Requirements  
The perception layer consists of sensors that are characterized by limited processing power and storage capacity [31]. Several security issues and attack risks rise due to such limitations. Several attacks on the perception layer are noticed:  
1. _Node Capture_: Nodes (base node or gateway) can be easily controlled by the attackers. Catching a node empowers an adversary not only to get tightly of cryptographic keys and protocol states, but also to clone and redistribute malicious nodes in the network, which affects the security of the entire network [32; 33]. 2. _Denial of Service (DoS) Attack_: A type of attacks that shuts down the system or network and prevents authorized users from accessing it. This could be achieved by overwhelming the system or network with large amount of spam requests all at the same time, thus overloading the system and preventing it from delivering the normal service [34]. 3. _Denial of Sleep Attack_: One of the essential objective of an IoT network is the capability of sensing through an extensive number of distributed nodes, each providing small data, such as temperature, humidity, vibration, etc., at a set interval and then going to sleep for another time interval in order to allow the nodes to operate for long service life. The denial of sleep attack works on the power supply of the node with a significant goal to increase the power consumption in order to reduce the service lifetime of the node by preventing the node from going asleep after sending the appropriate sensed data [35; 36]. 4. _Distributed Denial of Service (DDoS) Attack_: A large scale variant of DoS attacks. The most challenging issue is the ability to use the large amount of IoT nodes to pass traffic collected toward the victim server [37; 38]. There are indications that the DDoS attack called \"Mirai\" [5; 6] occuring on October 2016 benefited from a large number of IoT nodes. 5. _Fake Node/Sybil Attack_: A type of attacks where the attacker can deploy fake identities using fake nodes. With the presence of a sybil node, the whole system might generate wrong data or even the neighbor nodes will receive spam data and will mislay their privacy [39; 40]. The fake nodes could be used to transmit data to \"legitimate\" nodes leading them to consume their energy, which could lead the whole service to go down. 6. _Replay Attack_: In this attack, information is stored and re-transmitted later without having the authority to do that. Such attacks are commonly used against authentication protocols [41; 42]. 7. _Routing Threats_: This type of attacks is the most fundamental attack at the network layer but it could occur at the perception layer in data forwarding process. An attacker can create a routing loop causing the shortage or extension of the routing path, increasing the end-to-end delay, and increasing the error messages [43]. Side-Channel AttackThis type of attacks occurs on encryption devices by taking advantage of the hardware information where the crypto-system is applied on (chips), such as the execution time, power consumption, power dissipation, and electromagnetic interference produced by electronic devices throughout the encryption procedure. Such information could be analyzed to discover secret keys used during the encryption process [44; 45; 46; 47]. 9. _Mass Node Authentication:_ The process of authenticating large amount of devices in an IoT system, which requires massive amount of network communication for the authentication phase to finish and this could affect the performance of the whole system. Taking into consideration the above-mentioned risks, there is a need for node authentication to prevent fake node and illegal access, in addition to the need for data encryption to protect the confidentiality of data while being transmitted between nodes (end node, gateway or server).