As an indispensable part of the Internet of Things (IoT), wireless sensor networks (WSNs) need to be completely integrated into the Internet. When an Internet user communicates with multiple sensor nodes in WSNs, secure group key management becomes necessary. However, most current group key management schemes developed for WSNs do not consider the Internet scenario while traditional group key management in the Internet is deemed to be not suitable for WSNs due to the resource constraint characteristics of WSNs. In this paper, we propose a group key distribution scheme for WSNs in the IoT scenario in which we organize sensor nodes into groups in a hierarchical structure. In the upper wired layer, an end-to-end secure communication protocol is used to distribute group keys for subgroups to the trusted head nodes and the head nodes then distribute the group keys through underlying tree-based topology and wireless multicast to minimize energy consumption. We also perform some quantitative analyses as well as experiments to show that our proposed scheme is secure and has
As an indispensable part of the Internet of Things (IoT), wireless sensor networks (WSNs) need to adopt IP technologies to create a seamless, global network infrastructure together with the Internet. To achieve the above goal, many standardization organizations are actively pursuing standardization work for creating a global sensor network infrastructure. IPv6 over low power wireless personal area network (6LoWPAN) is one such technology that can enable complete integration of WSNs into the Internet. 6LoWPAN is aimed by the Internet Engineering Task Force (IETF) 6LoWPAN Working Group at enabling most capabilities of IPv6 on constrained nodes [
In the IoT scenario, any IP-enabled node in the Internet can communicate with any sensor node in a WSN remotely. It has thus become imperative that secure communication be supported between the remote entities. Recently, some secure communication schemes for creating an end-to-end secure channel between an Internet node and a sensor node have been researched in different layers of the Open System Interconnection (OSI) reference model. The research work by Granjal et al. [
With the secure communication protocols mentioned above, a variety of applications for WSNs in the IoT scenario can be developed ranging from defense systems to health care, industrial monitoring, disaster management, home automation, and so forth [
Secure group communication requires secure and robust distribution or negotiation of group keys. A single symmetric key known only to the group in which the authorized user in the Internet and the multiple targeted sensor nodes in WSNs are the members can effectively protect communication for multicast group. Current group key management schemes in WSNs that belong primarily to the broadcast fashion by making use of wireless channels and transmission ranges cannot be directly applied to the IoT context since the user is usually located in different physical locations, even in different networks. Meanwhile, traditional group key management protocols developed for the Internet, such as IP multicast [
In this paper, we propose a group key distribution scheme for WSNs in the IoT scenario. In our proposed scheme, the sensor nodes in WSNs are organized into groups in a hierarchical structure. In the upper wired layer, an end-to-end secure communication protocol is used to distribute group keys for the subgroups to trusted head nodes. In the lower wireless layer, the head nodes distribute the group keys through underlying tree-based topology and wireless multicast to minimize energy consumption of the sensor nodes. The main contributions of this paper can be summarized as follows. We analyze the need for group key management for WSNs in the IoT scenario and propose a secure and efficient solution to overcome the limitations of existing mechanisms in the IoT scenario. We design a hierarchical group key distribution scheme without requiring any preshared keys between the user and the sensor nodes. The scheme has the We demonstrate how our scheme can perform as a secure and efficient countermeasure against some attacks towards WSNs among which the cooperative compromised attack is analyzed emphatically, which is a capability that is absent in most existing mechanisms. We conduct mathematical analysis on our scheme as well as performance comparison between our scheme and the Topological Key Hierarchy (TKH) scheme which is considered to be the most efficient mechanism for group key management in traditional WSNs. The comparison results show that our scheme outperforms the TKH scheme for group key distribution and group key rekeying when a small number of nodes are deleted.
The remainder of this paper is organized as follows. Section
In both the Internet and the WSNs, group key management can be classified into group key distribution (centralized model) and group key negotiation (distributed model).
Group key distribution schemes (e.g., Group Key Management Protocol (GKMP) [
For group communication for WSNs in the IoT scenario, the authorized user in the Internet can act as the group controller, but all of the schemes mentioned above cannot be directly applied due to the following reasons. Firstly, the rekeying messages generated from the user must be transmitted over both the wired and wireless links, which may incur noticeable delay. Secondly, all of the centralized schemes rely on pairwise keys between the user and each sensor node, thus the user must authenticate and negotiate a shared secret key with each sensor node. Any group key distribution scheme should support end-to-end security communication that will make the cost of communication and computation grow linearly with the number of group members.
In distributed group key negotiation, all group members are treated equally. Hence, group keys should be negotiated among all group members through Diffie-Hellman (DH) key exchange or based on secret sharing theory to ensure fairness. In the CLIQUE scheme [
In the IoT scenario, the above group key negotiation schemes are not suitable for WSNs since the cost of communication and computation is more than that of group key distribution schemes. Moreover, the reasons for the infeasibility of group key distribution schemes are also exist.
Hierarchical group key management, for example, the Iolus scheme [
To be self-healing with the
In the TKH scheme that is applied to WSNs, the nodes in the same subtree (ST) share the same tree key (TK). ST is a tree with nodes below each subroot node, and the subroot nodes are direct neighbors of a sink. The nodes sharing the same parent node in a tree, that is, the sibling nodes, share the same sibling key (SK). Every node shares its own individual key (IK) with the sink. The group key (GK) is used to encrypt all data traffic within a group. TKH offers an advantage that the depth of the key tree is bounded to “4” regardless of the size of the network. Therefore, each node is only required to save a maximum of four keys, which is highly suitable for storage-limited sensor nodes.
TKH takes the advantage of the wireless multicast. Since a message transmission can be heard by multiple neighbors, sibling nodes can efficiently receive a message by a single transmission from their parent. An example is shown in Figure
After node 3 is deleted, (a) shows the repaired tree topology while (b) shows the corresponding TKH structure. The keys that need to be updated when node 3 is deleted are shaded.
When node 3 in ST1 is revoked, the rekeying messages for ST2 and ST3 are
A new node should select a parent node to join the network and the existing nodes can change the corresponding GK, TK, and SK by using the preshared one-way function (Formula (
The TKH scheme does not mention the distribution of GK, TK, SK, and IK. Meanwhile, it is assumed that IK is preloaded into every sensor, which is feasible when the head node is a stationary sink node. However, for WSNs in IoT scenario, the head node may be an ordinary node directly or indirectly dynamically chosen by the Internet user. Therefore, it is impossible for every sensor node which may be the potential head node to store all shared IKs with each other.
Our method is motivated by the above analysis that the TKH scheme is suitable for WSNs due to taking use of the underlying sensor network topology to decrease the forwarding through intermediate nodes and the one-hop wireless multicast to save energy. However, in our proposed scheme, we further reduce the forwarding from intermediate nodes through the only once hop-by-hop wireless multicast along with the underlying topology. The legitimate sensor node in the group can recover the GK from the received information without the shared IK with the head node. Moreover, the adversary has to compromise at least
Our proposed scheme organizes sensor nodes in a WSN into groups in a hierarchical structure as shown in Figure
The hierarchical structure of our proposed scheme.
We assume that the edge router is deployed for a WSN by the service provider (SP) and the edge router is credible andhas unlimited resources intermsofenergy, computation,andstorage.
An SP should deploy and manage the WSN to provide services to the Internet users. The SP randomly picks a
After deployment, the secure bootstrapping process in the WSN could be used (referring to [
An authorized Internet user
User
Suppose that the number of STs in the WSN is
The head node
After receiving
The authorized Internet user
In the former case, taking
An example of node addition in our proposed scheme.
In the latter case, assuming that
The authorized Internet user
In the former case, assuming that
An example of node deletion in our proposed scheme. The repaired tree topology (a) after node 4 and 5 are deleted and (b) after node 1 is deleted, respectively. The deleted nodes are shaded in blue.
In the latter case, assuming that
The procedure of node addition and node deletion is illustrated in Figure
The procedure of (a) node addition and (b) node deletion in our proposed scheme.
We can see that the multicast information
Bloom filter is a well-known data structure that can be used for efficient membership checking. Using the method, we can find whether an element belongs to a predefined set. A bloom filter consists of a set
Each hash function
Bloom filter may yield false positives, that is, although an element is not in
A bloom filter of
We analyze and show that our proposed scheme can provide confidentiality, forward secrecy, backward secrecy, and
In our scheme, GK and TK are generated by the authorized user. In the wired link layer, GK and TK are protected by the end-to-end secure channel and transmitted to the authenticated head nodes. In the wireless link layer, firstly, the head node is responsible for distributing GK and TK to other nodes in its ST. Every node must compute TK from
In our scheme, all the deleted nodes are added to the revocation set
In our scheme, the newly added node gets the
In our scheme, in order to know
For any group key management schemes for WSNs, even in the IoT scenario, storage, computation, and communication overhead as well as energy consumption of the sensor node are among the issues mostly concerned about. We therefore conduct performance analysis by comparing our proposed scheme with TKH in the following three aspects: storage, computation, communication. In the wireless link layer,
According to our scheme and TKH scheme, we do not consider the node addition event since the topology change and the corresponding rekeying cost is negligible.
In our analysis, we use the
In our scheme, every node in WSN is preloaded with a personal key
In our scheme, for group key distribution, the head node must compute a point
We define communication overhead as the total cost which reflects both the number of messages and the cost of message transmission.
In the TKH scheme, the head node takes the responsibility of unicasting GK, TK and SK to every ordinary node encrypted using the pairwise key between the head node and an ordinary node. So the total cost of distributing group key is:
In the TKH scheme, the total cost of rekeying key is
Figure
Total cost of group key distribution.
Figure
Total cost of rekeying group key in our scheme.
The total cost of rekeying group key in both schemes is shown in Figure
Total cost of rekeying group key when (a) one node is deleted and (b) (
In conclusion, our scheme outperforms the TKH scheme for group key distribution and group key rekeying when fewer numbers of nodes are deleted but it may become less advantageous in group key rekeying as the size of the network increases and when a large number of nodes are deleted.
We set up a real experimental environment in which the 34 Crossbow’s MICAZ motes that are used as the sensor nodes each has 8-bit ATmegal 128L clocked at about 7.37-MHz microcontroller and complies with the IEEE 802.15.4 standards with data transmission rate of 250 kbps. As depicted in Figure
The real experimental environment with
Experimental results for
We can see from Figure
In this paper, we proposed a group key distribution scheme for WSNs in IoT scenario in which the sensor nodes are organized in two logic layers in a hierarchical structure. In the upper wired link layer, an end-to-end secure communication protocol is used to distribute group key to the head nodes in the subgroups. In the lower wireless link layer, each head node distributes the group key by using the underlying tree-based topology and wireless multicast advantage to minimize energy consumption. An analysis on the proposed scheme showed that our proposed scheme can achieve
The work in this paper has been supported in part by National Natural Science Foundation of China (Grant no. 61272500) and in part by Beijing Education Commission Science and Technology Fund (Grant no. KM201010005027).