A resilient key predistribution scheme for multiphase wireless sensor networks

In wireless sensor networks, sensor nodes eventually die due to battery depletion. Wireless sensor networks (WSNs) in which new nodes are periodically redeployed with certain intervals, called generations, to replace the dead nodes are called multi-phase wireless sensor networks. In the literature, there are several key predistribution schemes proposed for secure operation of WSNs. However, these schemes are designed for single phase networks which are not resilient against continuous node capture attacks; even under temporary attacks on the network, the harm caused by the attacker does not heal in time. However, the periodic deployments in multi-phase sensor networks could be utilized to improve the resiliency of the WSNs by deploying nodes with fresh keys. In the literature, there is limited work done in this area. In this paper, we propose a key predistribution scheme for multi-phase wireless sensor networks which is highly resilient under node capture attacks. In our scheme, called RGM (random generation material) key predistribution scheme, each generation of deployment has its own random keying material and pairwise keys are established between node pairs of particular generations. These keys are specific to these generations. Therefore, a captured node cannot be abused to obtain keys of other generations. We compare the performance of our RGM scheme with a well-known multi-phase key predistribution scheme and showed that RGM achieves up to three-fold more resiliency. Even under heavy attacks, our scheme's resiliency performance is 50% better in steady state

HaG: Hash graph based key predistribution scheme for multiphase wireless sensor networks

Wireless Sensor Networks (WSN) consist of small sensor nodes which operate until their energy reserve is depleted. These nodes are generally deployed to the environments where network lifespan is much longer than the lifetime of a node. Therefore, WSN are typically operated in a multiphase fashion, as in [1-3, 9-10], which use different key pools for nodes deployed at different generations. In multiphase WSN, new nodes are periodically deployed to the environment to ensure constant local and global network connectivity. Also, key ring of these newly deployed nodes is selected from their deployment generation key pool to improve the resiliency of WSN. In this paper, we propose a key predistribution scheme for multiphase WSN which is resilient against permanent and temporary node capture attacks. In our Hash Graph based (HaG) scheme, every generation has its own key pool which is generated using the key pool of the previous generation. This allows nodes deployed at different generations to have the ability to establish secure channels. Likewise, a captured node can only be used to obtain keys for a limited amount of successive generations. We compare the connectivity and resiliency performance of our scheme with other multiphase key predistribution schemes and show that our scheme performs better when the attack rate is low. When the attack rate is high, our scheme still has better resiliency performance inasmuch as using less key ring size compared to the existing multiphase schemes

A highly resilient and zone-based key predistribution protocol for multiphase wireless sensor networks

Pairwise key distribution among the sensor nodes is an essential problem for providing security in Wireless Sensor Networks (WSNs). The common approach for this problem is random key predistribution, which suffers from resiliency issues in case of node captures by adversaries. In the literature, the resiliency problem is addressed by zone-based deployment models that use prior deployment knowledge. Another remedy in the literature, which is for multiphase WSNs, aims to provide self-healing property via periodic deployments of sensor nodes with fresh keys over the sensor field. However, to the best of our knowledge, these two approaches have never been combined before in the literature. In this paper, we propose a zone-based key predistribution approach for multiphase WSNs. Our approach combines the best parts of these approaches and provides self-healing property with up to 9-fold more resiliency as compared to an existing scheme. Moreover, our scheme ensures almost 100% secure connectivity, which means a sensor node shares at least one key with almost all of its neighbors

Multiphase deployment models for fast self healing in wireless sensor networks

The majority of studies on security in resource limited wireless sensor networks (WSN) focus on finding an efficient balance among energy consumption, computational speed and memory usage. Besides these resources, time is a relatively immature aspect that can be considered in system design and performance evaluations. In a recent study(Castelluccia and Spognardi, 2007), the time dimension is used to lower the ratio of compromised links, thus, improving resiliency in key distribution in WSNs. This is achieved by making the old and possibly compromised keys useful only for a limited amount of time. In this way, the effect of compromised keys diminish in time, so the WSN selfheals. In this study we further manipulate the time dimension and propose a deployment model that speeds up the resilience improvement process with a tradeoff between connectivity and resiliency. In our method, self healing speeds up by introducing nodes that belong to future generations in the time scale. In this way, the duration that the adversary can make use of compromised keys become smaller

Uneven key pre-distribution scheme for multi-phase wireless sensor networks

In multi-phase Wireless Sensor Networks (WSNs), sensor nodes are redeployed periodically to replace nodes whose batteries are depleted. In order to keep the network resilient against node capture attacks across different deployment epochs, called generations, it is necessary to refresh the key pools from which cryptographic keys are distributed. In this paper, we propose Uneven Key Pre-distribution (UKP) scheme that uses multiple different key pools at each generation. Our UKP scheme provides self healing that improves the resiliency of the network at a higher level as compared to an existing scheme in the literature. Moreover, our scheme provides perfect local and global connectivity. We conduct our simulations in mobile environment to see how our scheme performs under more realistic scenarios

Uneven key predistribution scheme for multiphase wireless sensor networks

In multiphase Wireless Sensor Networks (WSNs), sensor nodes are redeployed periodically to replace nodes with depleted batteries. In order to keep the network resilient against node capture attacks across different deployment epochs, called generations, it is necessary to refresh the key pools from which cryptographic keys are distributed. In this thesis, we propose Uneven Key Predistribution (UKP) scheme that uses multiple different key pools at each generation. Keys are drawn unevenly from these key pools and loaded to sensor nodes prior to deployment. Nodes are loaded with keys not only from their current generation, but also from future generations. We conduct simulation based performance evaluation in mobile environments using three different mobility models. One of them, Circular Move Mobility model, is first proposed in this thesis. Our UKP scheme provides self healing that improves the resiliency of the network up to 50% under heavy attack as compared to an existing scheme in the literature. Moreover, our scheme provides almost perfect local and global connectivity

Hash graph based key predistribution scheme for mobile and multiphase wireless sensor networks

Wireless Sensor Networks (WSN) consist of small sensor nodes which operate until their energy reserve is depleted. These nodes are generally deployed to the environments where network lifespan is much longer than the lifetime of a node. Therefore, WSN are typically operated in a multiphase fashion, where new nodes are periodically deployed to the environment to ensure constant local and global network connectivity. Besides, significant amount of the research in the literature studies only static WSN and there is very limited work considering mobility of the sensor nodes. In this thesis, we present a key predistribution scheme for mobile and multiphase WSN which is resilient against eager and temporary node capture attacks. In our Hash Graph based (HaG) scheme, every generation has its own key pool which is generated using the key pool of the previous generation. This allows nodes deployed at different generations to have the ability to establish secure channels. Likewise, a captured node can only be used to obtain keys for a limited amount of successive generations. We also consider sensor nodes as mobile and use different mobility models to show its effects on the performance. We compare the connectivity and resiliency performance of our scheme with a well-known multiphase key predistribution scheme and show that our scheme performs better when the attack rate is low. When the attack rate increases, our scheme still has better resiliency performance considering that it requires less key ring size compared to a state-of-the-art multiphase scheme

Resilient and highly connected key predistribution schemes for wireless sensor networks

Wireless sensor networks are composed of small, battery-powered devices called sensor nodes with restricted data processing, storage capabilities. Sensor nodes collect environmental data, such as temperature, humidity, light conditions, and transmit them using their integrated radio communication interface. In real life scenarios, the exact position of a node is not determined prior to deployment because their deployment methods are arbitrary. Wireless sensor networks may be used for critical operations such as military tracking, scientific and medical experiments. Sensor nodes may carry sensitive information. In such cases, securing communication between sensor nodes becomes an essential problem. Sensor nodes may easily be impersonated and compromised by malicious parties. In order to prevent this, there is a need for some cryptographic infrastructure. Public key cryptography is infeasible for sensor nodes with limited computation power. Hence symmetric key cryptography mechanisms are applied in order to provide security foundations. Due to resource constraints in sensor nodes, best solution seems to be symmetric key distribution prior to deployment. For each node, a number of keys are drawn uniformly random without replacement from a pool of symmetric keys and loaded in the node’s memory. After deployment, neighboring sensor nodes may share a key with a certain probability since all the keys are drawn from the same key pool. This is the basic idea of key predistribution schemes in wireless sensor networks. Also there are more advanced deployment models that take the change of network in time into consideration. The nodes are powered by batteries and the batteries eventually deplete in time. However the network needs to operate longer than the lifetime of a single node. In order to provide continuity, nodes are deployed and integrated in the network at different times along the operation of the network. These networks are called multiphase wireless sensor networks. The main challenge of these networks is to provide connectivity between node pairs deployed at different times. In this thesis, we proposed three different key predistribution schemes. In the first scheme, we introduce the concept of XORed key, which is the bitwise XOR of two regular (a.k.a single) keys. Sensor nodes are preloaded with a mixture of single and XORed keys. Nodes establish secure links by shared XORed keys if they can. If no shared XORed key exists between two neighboring nodes, they try single keys loaded in their memory. If node pairs do not have any shared XORed or single keys, they transfer keys from their secure neighbors in a couple of ways, and use them to match with their XORed keys. In this scheme, we aim to have a more resilient network to malicious activities by using XORed keys since an attacker has to know either both single key operands or the XORed key itself. We performed several simulations of our scheme and compared it with basic scheme [4]. Our scheme is up to 50% more connected as compared to basic scheme. Also it has better resilience performance at the beginning of a node capture attack and when it starts to deteriorate the difference between the resilience of our proposed scheme and basic scheme is not greater than 5%. The second scheme that we proposed is actually an extension that can be applied to most of the schemes. We propose an additional phase that is performed right after shared keys between neighboring nodes are discovered. As mentioned above, neighboring node pairs share a common key with a certain probability. Obviously some neighboring node pairs fail to find any shared key. In our proposed new phase, keys preloaded in memories of secure neighbors of a node a are transferred to a, if necessary, in order for a to establish new links with its neighboring nodes that they do not share any key. In this way, we achieve the same connectivity with traditional schemes with significantly fewer keys. We compared the performance of our scheme with basic scheme [4] after shared-key discovery phase and our results showed that our scheme achieved the same local connectivity performance with basic scheme, moreover while doing that, nodes in our scheme are loaded with three fourth of keys fewer than the keys loaded in nodes in basic scheme. In addition to that, our scheme is up to 50% more resilient than basic scheme with shared-key discovery phase under node capture attacks. The last scheme that we proposed is designed to be used for multi-phase wireless sensor networks. In our model, nodes are deployed at the beginning of some time epochs, called generations, in order to replace the dead nodes. Each generation has completely different key pool. Nodes are predistributed keys drawn uniformly random from key pools of different generations in order to have secure communication with nodes deployed at those generations. In other words, in our scheme keys are specific to generation pairs. This makes the job of attacker more difficult and improves the resiliency of our scheme. We compared our scheme to another key predistribution scheme designed for multi-phase wireless sensor networks. Our results showed that our scheme is up to 35% resilient in steady state even under heavy attacks

The effect of time dimension and network dynamics on key distribution in wireless sensor networks

The majority of studies on security in resource limited wireless sensor networks (WSN) focus on finding an efficient balance among energy consumption, computational speed and memory usage. Besides these resources, time, network dynamics (e.g. routing), and implementation and integration issues of the security solutions are relatively immature aspects that can be considered in system design and performance evaluations. In the first part of this thesis, we develop and analyze different implementation options of a Random Key Predistribution scheme in a real network simulation environment. Implementation options include Proactive Key Establishment and Reactive Key Establishment. In Proactive Key Establishment, pairwise keys are established at the beginning, prior to start of application. In Reactive Key Establishment, keys are established only whenever needed by the application during its execution. In literature the latter is known to preserve energy since it reduces useless key establishments; however, it also introduces delay in application traffic. We implement the reactive key establishment in such a way that key establishment traffic and energy consumption are reduced. As a result our reactive key establishment implementation has similar throughput performance with proactive scenarios despite the longer lifetime of reactive scenario. We also simulate an attack scenario and measure different metrics including a novel one. This new metric, the packet compromise ratio, reflects the harm caused by the adversary in a more realistic way. In our simulations, we show that packet compromise ratios are very high as compared to link compromise ratios for a long period. However, when the majority of nodes die, link compromise ratios exceed packet compromise ratios. This is an indication to the fact that link compromise ratios seem high even though there is no high amount of traffic in network to be compromised by adversary. Due to the results showing that classical key distribution schemes in WSNs have actually low resiliency, in the second part of this thesis, we propose new deployment models that improve resiliency. In a recent study by Castelluccia and Spognardi, the time dimension is used to lower the ratio of compromised links, thus, improving resiliency in key distribution in WSNs. This is achieved by making the old and possibly compromised keys useful only for a limited amount of time. In this way, the effect of compromised keys diminishes in time, so the WSN selfheals. We further manipulate the time dimension and propose a deployment model that speeds up the resiliency improvement process with a tradeo between connectivity and resiliency. In our method, self healing speeds up by introducing nodes that belong to future generations in the time scale. In this way, the duration that the adversary can make use of compromised keys becomes smaller

Key management for wireless sensor network security

Wireless Sensor Networks (WSNs) have attracted great attention not only in industry but also in academia due to their enormous application potential and unique security challenges. A typical sensor network can be seen as a combination of a number of low-cost sensor nodes which have very limited computation and communication capability, memory space, and energy supply. The nodes are self-organized into a network to sense or monitor surrounding information in an unattended environment, while the self-organization property makes the networks vulnerable to various attacks.Many cryptographic mechanisms that solve network security problems rely directly on secure and efficient key management making key management a fundamental research topic in the field of WSNs security. Although key management for WSNs has been studied over the last years, the majority of the literature has focused on some assumed vulnerabilities along with corresponding countermeasures. Specific application, which is an important factor in determining the feasibility of the scheme, has been overlooked to a large extent in the existing literature.This thesis is an effort to develop a key management framework and specific schemes for WSNs by which different types of keys can be established and also can be distributed in a self-healing manner; explicit/ implicit authentication can be integrated according to the security requirements of expected applications. The proposed solutions would provide reliable and robust security infrastructure for facilitating secure communications in WSNs.There are five main parts in the thesis. In Part I, we begin with an introduction to the research background, problems definition and overview of existing solutions. From Part II to Part IV, we propose specific solutions, including purely Symmetric Key Cryptography based solutions, purely Public Key Cryptography based solutions, and a hybrid solution. While there is always a trade-off between security and performance, analysis and experimental results prove that each proposed solution can achieve the expected security aims with acceptable overheads for some specific applications. Finally, we recapitulate the main contribution of our work and identify future research directions in Part V