Secure wireless communication requires the establishment of a secure channel, which is challenging and costly in a lot of scenarios. To provide secret keys for symmetric cryptosystems in wireless networks, previous research has studied the pairwise secret key generation based on the shared information between legitimate entities by exploiting the characteristics of the wireless channel. However, most of the variables they use are measured in the time domain, and heavily depend on the dynamic environments to get enough entropy. Fast key generation is impossible with stationary entities when the environment is relatively stable. To release this constraint, we choose the pairwise radio power spectrum as an alternative, i.e., the radio signal strength (RSS) measurements in the frequency domain, collected at two ends of a link to extract the keys. To our best knowledge, this variable is for the first time utilized in the secret key generation to get two highly correlated bit streams as ``fuzzy'' secret keys and advances the RSS measurements in the time domain in prior research. Instead of carrying out information reconciliation on the fuzzy keys, a traditional method to handle the inevitable mismatching between keys due to non-ideal working environments before using them, the design developed in this thesis uses the fuzzy keys directly in the proposed symmetric cryptosystem by borrowing the error correcting ability of Forward Error Correction code. The design can not only be used as a light-weight cryptosystem, but also distribute keys to support other cryptosystems. It's resistive to both passive and active attacks. In fact, the design is motivated by the spatial irregularity of the radio power spectrum, a critical observation that paves the function of the proposed mechanism and is carefully verified with both empirical experiments and theoretical analysis. Advisor: Ziguo Zhong
Secure wireless communication requires the establishment of a secure channel, which is challenging and costly in a lot of scenarios. To provide secret keys for symmetric cryptosystems in wireless networks, previous research has studied the pairwise secret key generation based on the shared information between legitimate entities by exploiting the characteristics of the wireless channel. However, most of the variables they use are measured in the time domain, and heavily depend on the dynamic environments to get enough entropy. Fast key generation is impossible with stationary entities when the environment is relatively stable. To release this constraint, we choose the pairwise radio power spectrum as an alternative, i.e., the radio signal strength (RSS) measurements in the frequency domain, collected at two ends of a link to extract the keys. To our best knowledge, this variable is for the first time utilized in the secret key generation to get two highly correlated bit streams as ``fuzzy'' secret keys and advances the RSS measurements in the time domain in prior research. Instead of carrying out information reconciliation on the fuzzy keys, a traditional method to handle the inevitable mismatching between keys due to non-ideal working environments before using them, the design developed in this thesis uses the fuzzy keys directly in the proposed symmetric cryptosystem by borrowing the error correcting ability of Forward Error Correction code. The design can not only be used as a light-weight cryptosystem, but also distribute keys to support other cryptosystems. It's resistive to both passive and active attacks. In fact, the design is motivated by the spatial irregularity of the radio power spectrum, a critical observation that paves the function of the proposed mechanism and is carefully verified with both empirical experiments and theoretical analysis. Advisor: Ziguo Zhong
We evaluate the effectiveness of secret key extraction, for private communication between two wireless devices, from the received signal strength (RSS) variations on the wireless channel between the two devices. We use real world measurements of RSS in a variety of environments and settings. Our experimental results show that (i) in certain environments, due to lack of variations in the wireless channel, the extracted bits have very low entropy making these bits unsuitable for a secret key, (ii) an adversary can cause predictable key generation in these static environments, and (iii) in dynamic scenarios where the two devices are mobile, and/or where there is a significant movement in the environment, high entropy bits are obtained fairly quickly. Building on the strengths of existing secret key extraction approaches, we develop an environment adaptive secret key generation scheme that uses an adaptive lossy quantizer in conjunction with Cascade-based information reconciliation [7] and privacy amplification [14]. Our measurements show that our scheme, in comparison to the existing ones that we evaluate, performs the best in terms of generating high entropy bits at a high bit rate. The secret key bit streams generated by our scheme also pass the randomness tests of the NIST test suite [21] that we conduct.
We evaluate the effectiveness of secret key extraction, for private communication between two wireless devices, from the received signal strength (RSS) variations on the wireless channel between the two devices. We use real world measurements of RSS in a variety of environments and settings. The results from our experiments with 802.11-based laptops show that in certain environments, due to lack of variations in the wireless channel, the extracted bits have very low entropy making these bits unsuitable for a secret key, an adversary can cause predictable key generation in these static environments, and in dynamic scenarios where the two devices are mobile, and/or where there is a significant movement in the environment, high entropy bits are obtained fairly quickly. Building on the strengths of existing secret key extraction approaches, we develop an environment adaptive secret key generation scheme that uses an adaptive lossy quantizer in conjunction with Cascade-based information reconciliation and privacy amplification. Our measurements show that our scheme, in comparison to the existing ones that we evaluate, performs the best in terms of generating high entropy bits at a high bit rate. The secret key bit streams generated by our scheme also pass the randomness tests of the NIST test suite that we conduct. We also build and evaluate the performance of secret key extraction using small, low-power, hand-held devices-Google Nexus One phones-that are equipped 802.11 wireless network cards. Last, we evaluate secret key extraction in a multiple input multiple output (MIMO)-like sensor network testbed that we create using multiple TelosB sensor nodes. We find that our MIMO-like sensor environment produces prohibitively high bit mismatch, which we address using an iterative distillation stage that we add to the key extraction process. Ultimately, we show that the secret key generation rate is increased when multiple sensors are involved in the key extraction process.
In this paper, we evaluate the effectiveness of secret key extraction from the Received signal strength (RSS) variations on the wireless channel between the two devices for private communication between them. We use real world measurements of RSS in a variety of environments and settings. The results from our experiments with 802.11-based laptops show that 1)An adversary can cause predictable key generation in these static environments, and 2)In dynamic scenarios where the two devices are mobile, high entropy bits are obtained . Building on the strengths of existing secret key extraction approaches, we develop an environment adaptive secret key generation scheme that uses an adaptive Cascade-based information reconciliation and privacy amplification. In our scheme, to provide good scalability in terms of the number of nodes, we utilize a combinatorial design of public-private key pairs, which means nodes combine more than one key pair to encrypt and decrypt messages. We also show that it provides controllable resilience when malicious nodes compromise a limited number of nodes before key revocation and renewal.
Due to the unavoidable shared nature of the wireless radio spectrum, providing security for wireless communications presents unique challenges. Cryptographic keys have been used as a primary technique for securing wireless networks but are not completely secure. The symmetric keys used for cryptographic purposes are vulnerable to man-in-the-middle and brute force attacks. More recently, PHY-layer based techniques have gained significant attention, where the principle of channel reciprocity and the natural randomness of the measured wireless channel to generate secret keys is leveraged. Although, PHY-layer secret key generation has been investigated and presented in the literature before, there has been a lack of discussion in terms of obtaining symmetric keys on both ends of the link. In this work, we present a novel PHY-layer secret key generation technique that aims for symmetric encryption keys while limiting the information leaked to an eavesdropper to ensure complete secrecy and to prevent potential intelligent attacks. Our algorithm utilizes forward and backward channel state information in a given wireless link and combats the minute differences observed in these pairs by generating channel trend information. We demonstrate our technique using experimental results from a realtime SDR testbed connected to a wireless channel emulator. Our results indicate that the algorithm is successful in generating symmetric keys under various wireless environments without revealing any information pertaining to the key via the open wireless channel. Our secret key extraction rate can reach values in excess of 17.3 Kbps.
Wireless networks are vulnerable to various attacks due to their open nature, making them susceptible to eavesdropping and other security threats. Eavesdropping attack takes place at the physical layer. Traditional wireless network security relies on cryptographic techniques to secure data transmissions. However, these techniques may not be suitable for all scenarios, especially in resource-constrained environments such as wireless sensor networks and adhoc networks. In these networks having limited power resources, generating cryptographic keys between mobile entities can be challenging. Also, the cryptographic keys are computationally complex and require key management infrastructure. Physical Layer Key Generation (PLKG) is an emerging solution to address these challenges. It establishes secure communication between two users by taking advantage of the wireless channel's inherent features. PLKG process involves channel probing, quantization, information reconciliation (IR) and privacy amplification to generate symmetric secret key. The researchers have used various PLKG techniques to get the secret key, sTop of Form till they face problems in the IR scheme to obtain symmetric keys between the users who share the same channel for communication. Both the code based and protocol based methods proposed in the literature have advantages and limitations related to their performance parameters such as information leakage, interaction delay and computation complexity. This research work proposes a novel IR mechanism that combines the protocol and code-based error correction methods to obtain reduced Bit Mismatch Rate (BMR), reduced information leakage, reduced interaction delay, and reduced computational time to enhance physical layer secret key's quality. In the proposed research work, the channel samples are generated using the Received Signal Strength (RSS) and Channel Impulse Response (CIR) parameters. These samples are quantized using Vector Quantization with Affinity Propagation Clustering (VQAPC) method to generate the preliminary key. The samples collected by the two users who wish to communicate, (for example Alice and Bob) will be different due to noise in the channel and hardware limitations. Hence their preliminary keys will be different. Removing this discrepancy between Bob's and Alice's initial keys, using novel Hybrid Protocol and Code related Information Reconciliation (HPC-IR) scheme to generate error corrected key, is the most important contribution of this research work. This key is further encoded by the MD5 hash function to generate a final secret key for exchanging information between two users over the wireless channel. It is observed that the proposed HPC-IR scheme achieves BMR of 19.4%, information leakage is 0.002, interaction delay is 0.001 seconds and computation time is 0.02 seconds.
The broadcast nature of wireless communication imposes the risk of information leakage to adversarial or unauthorized receivers. Therefore, information security between intended users remains a challenging issue. Currently, wireless security relies on cryptographic techniques and protocols that lie at the upper layers of the wireless network. One main drawback of these existing techniques is the necessity of a complex key management scheme in the case of symmetric ciphers and high computational complexity in the case of asymmetric ciphers. On the other hand, physical layer security has attracted significant interest from the research community due to its potential to generate information-theoretic secure keys. In addition, since the vast majority of physical layer security techniques exploit the inherent randomness of the communication channel, key exchange is no longer mandatory. However, additive white Gaussian noise, interference, channel estimation errors and the fact that communicating transceivers employ different radio frequency (RF) chains are among the reasons that limit utilization of secret key generation (SKG) algorithms to high signal to noise ratio levels. The scope of this dissertation is to design novel secret key generation algorithms to overcome this main drawback. In particular, we design a channel based SKG algorithm that increases the dynamic range of the key generation system. In addition, we design an algorithm that exploits angle of arrival (AoA) as a common source of randomness to generate the secret key. Existing AoA estimation systems either have high hardware and computation complexities or low performance, which hinder their incorporation within the context of SKG. To overcome this challenge, we design a novel high performance yet simple and efficient AoA estimation system that fits the objective of collecting sequences of AoAs for SKG. Cognitive radio networks (CRNs) are designed to increase spectrum usage efficiency by allowing secondary users (SUs) to exploit spectrum slots that are unused by the spectrum owners, i.e., primary users (PUs). Hence, spectrum sensing (SS) is essential in any CRN. CRNs can work both in opportunistic (interweaved) as well as overlay and/or underlay (limited interference) fashions. CRNs typically operate at low SNR levels, particularly, to support overlay/underlay operations. Similar to other wireless networks, CRNs are susceptible to various physical layer security attacks including spectrum sensing data falsification and eavesdropping. In addition to the generalized SKG methods provided in this thesis and due to the peculiarity of CRNs, we further provide a specific method of SKG for CRNs. After studying, developing and implementing several SS techniques, we design an SKG algorithm that exploits SS data. Our algorithm does not interrupt the SS operation and does not require additional time to generate the secret key. Therefore, it is suitable for CRNs.