Table of Contents
Overview-Background
The Sensor node is the basic building block of the a WSN. The components of a sensor node very based on the context and situation. The units of a sensor node generally include memory, processor, power, sensor, transceiver, position finding system, and a mobilizer. The role transceiver unit is critical to the sensor node as it is responsible for sending and receiving data and/or signals.
The transceiver also accounts for more power consumption than the other units. When designing sensor nodes, the transceiver should be designed to reduce energy consumption when sending and receiving data. While the market offers different sensor nodes, the nodes tend to have a small memory space, limited processing power and a small flash ROM to compile processing data. A general references architecture defines the core functionalities, standards and APIs.
The WSN reference architecture include Physical hardware/Sensor nodes, Operating System/Firmware, System and Storage Services, Programing Abstractions and APIs, and Applications. A WSN is made up of different nodes. The Sensor node sense the events which are collected by the aggregator-nodes. The aggregator-nodes then forward all events to the Base Station.
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The Base Station further forwards all event to a remote server directly or via the Internet. The role of the Base Station node is vital in WSN. The Base Station node a highly equip system in both software and hardware is responsible for collection of critical data, topology generation and malfunctions in the network. The Aggregator node is responsible for hiding the base station node from inside and outside attackers, along with reducing delays and increasing network life.
WSN Applications
Today WSNs are used in Industry, Society, Agriculture and Wild Life, and Environmental Protection just to name a few areas. WSN are interconnected sensor devices that produce a huge amount of data, however they are also resource constraints devices. Sensor devices can be found in college campuses buildings, road traffic monitoring vehicle tracking atomic reactors and other mission critical systems.
Wireless Sensor Networks in Industry include such categories as Gas Sector, Physical and Environmental where sensors monitor temperature, humidity, soil moisture, wind, and pressure to facilitates precision agriculture. WSN facilitate Society in traffic monitoring and health care. With the help of WSN doctors can diagnose a disease on a scientific approach using a body area network to monitor body temperatures, blood pressure, sugar and stress levels.
The WSN could lead to smart cities were everything is interconnected. Smart homes, building, bridges can use WSN to reduce energy wastage and monitor reliability of material used in building and bridges. In Wild Life WSNs are used to monitor information is collected about animal behavior, their interaction, and their different habits.
In Agriculture WSNs provide a scientific approach to collect data and analyze it. Sensors can monitor different soil types, temperature and wind level, water quality, and humidity and sunlight intensity can affect the smart agriculture systems. This data will lead to smart irrigation system reduces wastage of water. In a disaster quick relief emergency situation, sensor nodes are dropped from a helicopter to the affected area, e.g., fire, to monitor the temperature and send back the data to the server. A pre-installed sensor network in wild life timely inform control room about any fire case. WSNs are used for Environment Protection in areas involving atomic reactors, volcano and pollution monitoring
Security Requirements
The basic security requirements of WSNs surrounds Confidentiality, Integrity and Authentication this will ensure network stability and operations. While cryptography can help to protect the system, a secure network should consider authorization and authentication. The researchers grouped WSN security requirements in four levels. data level security, node level security, code/program level security, network level security.
Data Level Security
In WSN date in transit can be capture by adversaries who then alter the captured data and attempt to resend it. Data level security defends against corruption and modification and also guarantees protection from unauthorized access. Data level in WSN relies on authentication, confidentiality, integrity and freshness. Authentication ensures that the data is from the right source. This can be accomplished by user name and password, tokens, digital certificate and smart cards etc.
Confidentiality refers to assuring that only authorized nodes can access data and unauthorized nodes cannot, it protects the content from bad guy while assuring the privacy of the data. Integrity deals with the authenticity of the information. Is the information accurate, compete, and trustworthy? Freshness address the fact that old messages should not be replayed, and the information is the most recent. At the data level we want to strive for strong freshness of data were all packet received are in order.
Node level security
Some situation in WSN like hostile environment require more security such as military operations, fire in wild-fire and atomic reactors for example. Proper node level security protocol will avert adversaries access to a sensor node and to obtaining the cryptographic keys and the underlined designed secure protocol. To ensure appropriate node level security consideration must be given to availability, authorization, non-repudiation and secure localization. At node level security availability refers to the information being accessible to parties who need the information and are authorized to receive it. Availability also ensures the network role to receive, store, process, transmit, and maintain information.
Critical and logical phenomenon such as high temperature communication and node failures floods and storms will affect availability but WSNs should ensure nodes are available at any given time. If a Network is not available, it is useless regardless of how strong I may be. Authorization or a right to access is controlled by a network administrator. In WSN the network admin assigns different rules and polices for user based on the users need. Some users require modification access while other only need read access. Some nodes can read data some can send to the base station while some cannot.
Authorization is critical and is controlled by the network administrator. Non-repudiation in WSN prevents the denial of a node involved in communication not sending data. Non-repudiation provides the digital evidence need to prove the origin and integrity of the data. In WSN secure localization refer to being able to locate a sensor node in the network. The ability to do so automatically and accurately is crucial when designing a sensor to locate fault and errors in a network.
Network level security
Unauthorized data or system access is controlled by a network administrator who manages the overall network level security. The network security is comprised of policies and rules covering activities such safety of the network hardware and data, scalability, reliability and integrity for the network. To be effective, network level security in a WSN must consider self-organizing, time synchronization, scalability surrounding security and less energy consumption and maximum performance. In WSN, eavesdropping, man in the middle and denial of service attacks are relatively easy due to the open media vulnerable nature of the sensor network.
Self-organizing will solve that problem. Time synchronization is a way of synchronizing sensor nodes with the centralized sensor node. Coordination of time between sensor nodes is vital in sensing events such as temperatures, humidity, and movement. Time synchronization will lead to avoiding a replay packets and ensure that sensor nodes guarantee real time data and data freshness. Scalability is important in WSN because the large amounts on nodes in a network. Scalability simply means can the system continue to do it job if the size or input to the system increases. WSN must be built with the capabilities to seamless incorporate new nodes when and if needed without any adverse affects on the network.
Another important aspect of network level security is surrounding security for the WSN environment. Security such as surveillance cameras must be in place to monitor hostile activities. Surrounding security may be more practical in some fields that other. For example, it could be extremely beneficial in wild life monitoring and industrial application, but not so much in military operation involving monitoring the enemy. Energy or power consumption is a major limitation in WSN.
Insufficient or lack of power can result in unavailable or even drop messages. Sensor nodes in the network must be designed to conserve energy when possible. Often time a tough choice must be made between performance and energy consumption in the network. For example, multifaceted cryptography application involving high level security will be a detriment to the senor battery life, while low processing operation like measuring temperature and humidity will conserve more energy.
Operating System and Tools for WSNs
In any computing system all operations are governed by the operating system (OS). A robust OS is necessary in WSN to deal with standard routines such issues to address security holes. Some key points where the OS may provide system level security include but not limited to access permission, memory protection and privilege mode. Due to the limited resource constraints on WSN the design on the OS will be faced with challenges.
Re-programing may be used to overcome some of these challenges and also provide more flexibility. By Implementing reprograming we can see how adaptable and flexible the system is to changes that occur in the network. A system that have static behavior can be changed to dynamic behavior through reprograming. The roles of wireless network tools are crucial to the operating system. Tools manage, configure and update the sensor nodes. Tools also pay a vital role in programing, examining, analyzing media and troubleshooting the entire network.
Attacks
As discussed earlier WSN have numerous application, as such WSN have a long list of possible attacks. Some of the categories of attacks include data alteration, node stealing and tampering, traffic tracing and tampering. Communication between nodes can be monitored by adversaries who attempt to steal data. The attacks on WSN are broken down into groups; physical attacks, communication attacks, code attacks, base station attacks, and routing protocol attacks.
The primary objective of physical attacks in WSN is to remove or physically damage the sensor. Once the sensor is removed and in the possession of the attacker, he can analyze the internal code and extract the cryptographic keys, the later implant the modified node back into the network which will lead to future attacks where the attacker identity is concealed. Some examples of physical attacks in WSN are New Node Injection Attack, Sybil Attack, Reverse
Engineering Attack. With the Sybil Attack the attacker make the node have various identities which make it difficult to tell the difference between a legitimate node and a phony node.
Communication attacks in WSN are logical attacks where the can corrupt or alter the sensor node remotely. Some instances of communication attacks in WSN are Jamming, DoS and Collision Attack. Jamming attack is when the attacker attempts to impeded or jam the communication signal. This attack is usually against the physical layer in the WSN architecture.
Code attacks in WSN refers to vulnerabilities at the application level in weak software programing and coding. Some cases of code attacks in WSN are Overflow Attack, Changing the Existing Node Remotely by Re-Programming. In the overflow attack the attacker over flows the buffer which makes the node unable to make new communication, the will ultimately make the node unavailable.
Base station attacks in WSN attempt to gather data sent to the base station from all the surrounding nodes. Some common of base station attacks in WSN are Source Location Attack, Destination Location Attack Traffic Analysis Attack, Traffic Tracing Attack, Content Analysis Attack. If the base station is compromised all the sensor nodes and associated deployment cost will also be compromised.
Routing protocol attacks in WSN are caused by weak protocols which may give privileged mode to an adversary. Some examples of routing protocol attacks in WSN are Black Hole Attack, Hello Flood Attack.
Defenses/Countermeasures
To prevent the attack discussed in the previous section, multiple approaches are used to protect WSN from attackers. Theses approaches provide data and destination privacy while preventing physical attacks, communication attacks, code attacks, base station attacks, and routing protocol attacks. It is recommended that while implement a cryptographic approach in defense for cryptography triangle use light weight protocol. Sensor nodes are surrounded by wireless signals, this creates a huge impediment to implement an adequate security system.
In defense for wireless link it is almost inconceivable to avoid signal propagation. Availability is one of the key pillars of WSN and data should be available when needed. Some approaches in defense for availability are implementing redundancy for substitute and failure, adequate power routing protocols, crisis energy backup, and guarding against detrimental actions such as DOSatt acks. Application Level defense in WSN requires compact code for resource constraints devices like sensor node.
Challenges
There are several challenges when it comes to. WSN need address performance, cloud computing, reliability, SDN integration, scalability, and virtualization. In addressing these challenges focus on having strong routing protocols that handle mobility nodes and consider base station privacy. Key management and distribution and important challenge for WSN and it continues to be area of research.
