Physical-layer group secret-key (GSK) generation is an effective way of generating secret keys in wireless networks, wherein the nodes exploit inherent randomness in the wireless channels to generate group keys, which are subsequently applied to secure messages while broadcasting, relaying, and other network-level communications. While existing GSK protocols focus on securing the common source of randomness from external eavesdroppers, they assume that the legitimate nodes of the group are trusted. In this paper, we address insider attacks from the legitimate participants of the wireless network during the key generation process. Instead of addressing conspicuous attacks such as switching-off communication, injecting noise, or denying consensus on group keys, we introduce stealth attacks that can go undetected against state-of- the-art GSK schemes. We propose two forms of attacks, namely: (i) different-key attacks, wherein an insider attempts to generate different keys at different nodes, especially across nodes that are out of range so that they fail to recover group messages despite possessing the group key, and (ii) low-rate key attacks, wherein an insider alters the common source of randomness so as to reduce the key-rate. We also discuss various detection techniques, which are based on detecting anomalies and inconsistencies on the channel measurements at the legitimate nodes. Through simulations we show that GSK generation schemes are vulnerable to insider-threats, especially on topologies that cannot support additional secure links between neighbouring nodes to verify the attacks.
Physical-layer group secret-key (GSK) generation is an effective way of generating secret keys in wireless networks, wherein the nodes exploit inherent randomness in the wireless channels to generate group keys, which are subsequently applied to secure messages while broadcasting, relaying, and other network-level communications. While existing GSK protocols focus on securing the common source of randomness from external eavesdroppers, they assume that the legitimate nodes of the group are trusted. In this paper, we address insider attacks from the legitimate participants of the wireless network during the key generation process. Instead of addressing conspicuous attacks such as switching-off communication, injecting noise, or denying consensus on group keys, we introduce stealth attacks that can go undetected against state-of- the-art GSK schemes. We propose two forms of attacks, namely: (i) different-key attacks, wherein an insider attempts to generate different keys at different nodes, especially across nodes that are out of range so that they fail to recover group messages despite possessing the group key, and (ii) low-rate key attacks, wherein an insider alters the common source of randomness so as to reduce the key-rate. We also discuss various detection techniques, which are based on detecting anomalies and inconsistencies on the channel measurements at the legitimate nodes. Through simulations we show that GSK generation schemes are vulnerable to insider-threats, especially on topologies that cannot support additional secure links between neighbouring nodes to verify the attacks.
It is well known that physical-layer Group Secret-Key (GSK) generation techniques allow multiple nodes of a wireless network to synthesize a common secret-key, which can be subsequently used to keep their group messages confidential. As one of its salient features, the wireless nodes involved in physical-layer GSK generation extract randomness from a subset of their wireless channels, referred as the common source of randomness (CSR). Unlike two-user key generation, in GSK generation, some nodes must act as facilitators by broadcasting quantized versions of the linear combinations of the channel realizations, so as to assist all the nodes to observe a CSR. However, we note that broadcasting linear combination of channel realizations incurs non-zero leakage of the CSR to an eavesdropper, and moreover, quantizing the linear combination also reduces the overall key-rate. Identifying these issues, we propose a practical GSK generation protocol, referred to as Algebraic Symmetrically Quantized GSK (A-SQGSK) protocol, in a network of three nodes, wherein due to quantization of symbols at the facilitator, the other two nodes also quantize their channel realizations, and use them appropriately over algebraic rings to generate the keys. First, we prove that the A-SQGSK protocol incurs zero leakage to an eavesdropper. Subsequently, on the CSR provided by the A-SQGSK protocol, we propose a consensus algorithm among the three nodes, called the Entropy-Maximization Error-Minimization (EM-EM) algorithm, which maximizes the entropy of the secret-key subject to an upper-bound on the mismatch-rate. We use extensive analysis and simulation results to lay out guidelines to jointly choose the parameters of the A-SQGSK protocol and the EM-EM algorithm.
It is well known that physical-layer Group Secret-Key (GSK) generation techniques allow multiple nodes of a wireless network to synthesize a common secret-key, which can be subsequently used to keep their group messages confidential. As one of its salient features, the wireless nodes involved in physical-layer GSK generation extract randomness from a subset of their wireless channels, referred as the common source of randomness (CSR). Unlike two-user key generation, in GSK generation, some nodes must act as facilitators by broadcasting quantized versions of the linear combinations of the channel realizations, so as to assist all the nodes to observe a CSR. However, we note that broadcasting linear combination of channel realizations incurs non-zero leakage of the CSR to an eavesdropper, and moreover, quantizing the linear combination also reduces the overall key-rate. Identifying these issues, we propose a practical GSK generation protocol, referred to as Algebraic Symmetrically Quantized GSK (A-SQGSK) protocol, in a network of three nodes, wherein due to quantization of symbols at the facilitator, the other two nodes also quantize their channel realizations, and use them appropriately over algebraic rings to generate the keys. First, we prove that the A-SQGSK protocol incurs zero leakage to an eavesdropper. Subsequently, on the CSR provided by the A-SQGSK protocol, we propose a consensus algorithm among the three nodes, called the Entropy-Maximization Error-Minimization (EM-EM) algorithm, which maximizes the entropy of the secret-key subject to an upper-bound on the mismatch-rate. We use extensive analysis and simulation results to lay out guidelines to jointly choose the parameters of the A-SQGSK protocol and the EM-EM algorithm.
Physical-layer Group Secret-Key (GSK) generation is an effective way of synthesizing symmetric keys across multiple nodes in wireless networks. Unlike the case of two-user key generation, GSK generation necessitates some nodes to act as facilitators, which broadcast linear combinations of the channel realizations thereby assisting all the nodes to witness the intended common source of randomness. However, in practice, radio devices are designed to transmit symbols from finite complex constellations, and as a result, the channel realizations are typically quantized by the facilitator which in turn impacts the overall secret-key rate. Identifying this issue, we propose a class of GSK generation protocols, called Symmetrically Quantized GSK (SQGSK) protocols, in a network of three nodes. In the proposed protocols, due to quantization of symbols at the facilitator, the other two nodes also quantize their channel realizations, and use them appropriately to generate the keys. Under special conditions, we analytically show that the SQGSK protocols provide higher key-rate than the baselines wherein only the facilitator quantizes the channel realizations. We use extensive simulations to demonstrate the benefits of the proposed protocols when the facilitator employs finite constellations such as 4-, 16-, and 64-QAM.
Group secret-key (GSK) generation using temporal variation in wireless channels is an effective way of synthesizing symmetric keys across multiple nodes (more than two) in wireless networks. Unlike the case of two-node key-generation, GSK generation necessitates some nodes to act as facilitators by transmitting linear combinations of the channel realizations. However, in practice, radio devices are designed to transmit baseband signals from finite complex constellations. Due to such constraints, the linear combinations of channel realizations are typically quantized by the facilitator which in turn impacts the overall secret-key rate. Identifying this issue, we propose a practical GSK generation protocol in a network of three nodes. Under special conditions, we analytically show that the proposed method provides higher key-rate than the case when only the facilitator quantizes the channel realizations before transmission. Through simulations, we show that the proposed method yields higher key-rate than the baselines when the facilitator employs finite constellations such as 4-, 16-, and 64-QAM.
The Internet of Things technology is one of the important directions of Smart Grid research, involving many wireless sensors and communication facilities, and has high requirements for security. The physical layer security technology can effectively solve the security problems under wireless communication. As the most common application scenario of wireless communication is multi-node wireless network communication, group secret key (GSK) based on physical layer security and information theory security is gradually attracting investigator’s interest. In this paper, a novel physical layer GSK generation scheme based on code-domain exchange of channel information in mesh network is proposed. Instead of traditional side-information exchange in symbol-domain, error-correcting code is applied to finish information exchange and reconciliation simultaneously in code-domain. Each node processes the known channel bit sequence and then encodes it to generate a check sequence. After broadcasting the check bit sequence to other nodes, each node decodes the received check bit sequences to obtained the unknown channel information. The simulation results show that the scheme can effectively reduce the times of information exchanges while keeping a good performance including low bit error rate and low block error rate.
Secret group key generation based on physical layer in wireless communications has a lot of practical applications. A few studies focused on the theoretical bounds of the secret key rate based on the sets of received signals rather than a particular secret key generation scheme. We propose a secret group key generation scheme for an arbitrary number of legitimate nodes, n, in mesh topology in the presence of a passive eavesdropper. In the scheme, after general pilot signal transmissions at all nodes, each node broadcasts a weighted combination of its received signals with optimized coefficients, so that legitimate nodes can obtain the information of channels used for group key generation while the eavesdropper cannot. We also apply different quantization schemes for quantizing and encoding the estimated channels into keys. To provide detailed transmissions and processing steps of group key generation, we also describe the proposed scheme for 4-node mesh topology case. The simulation results show that the proposed scheme achieves a higher secret group key rate and a lower key disagreement rate than a benchmark scheme.