We propose an improved method of secret key generation using the variations in wireless channel. We construct reciprocal channel profiles at a pair of transceivers and enhance it using the l 1 -norm minimization technique. Thereafter preliminary keys are obtained that are synchronized by a localized information reconciliation technique. The privacy of the synchronized keys is enhanced by generating secure hashes. We implement the proposed method on a testbed and validate its performance to show decreased rates of bit disagreement of preliminary keys, at an increased key generation rate.
We propose an improved method of secret key generation using the variations in wireless channel. We construct reciprocal channel profiles at a pair of transceivers and enhance it using the l 1 -norm minimization technique. Thereafter preliminary keys are obtained that are synchronized by a localized information reconciliation technique. The privacy of the synchronized keys is enhanced by generating secure hashes. We implement the proposed method on a testbed and validate its performance to show decreased rates of bit disagreement of preliminary keys, at an increased key generation rate.
Secret key generation at physical layer has attracted more and more attentions as an emerging cryptography method. Compared to traditional security approaches, secret key generation at physical layer not only avoids the problem of key distribution, but also holds high efficiency and low complexity in application. Based on the principle of channel reciprocity, Alice and Bob both estimate the channel conditions and extract shared keys from this source of common randomness. In this paper, we first analyze the basic steps (channel estimation, sample quantization and key reconciliation) of secret key generation, key match rate with different quantization levels and key reconciliation times are also simulated. While in practical situations, different non-reciprocity factors affect the channel estimation step, key match rate can be greatly decreased and hardly meet real time cryptography requirements. In order to increase the key match rate, the unified framework of physical layer key generation has been extended to utilizing multiple observations of wireless channels to generate secret keys. An improved key generation approach with multiple observations can well deal with discrepancies between transceivers and keep increasing the key match rate. Theoretical analysis and simulation results both validate the significant improvement due to multiple observations. With an increased number of observations on both sides, the desired key match rate can be achieved much greater than with a single observation, and also the probability of key recovery by Eve can be decreased.
Key generation is essential for protecting wireless networks. Based on wireless channel reciprocity, transceivers can generate shared secret keys by measuring their communicating channels. However, due to non-simultaneous measurements, asymmetric noises and other interferences, channel measurements collected by different transceivers are highly correlated but not identical and thus might have some discrepancies. Further, these discrepancies might lead to mismatches of bit sequences after quantization. The referred mismatches significantly affect the efficiency of key generation. In this paper, an efficient key generation scheme leveraging wireless channel reciprocity is proposed. To reduce the bit mismatch rate and enhance the efficiency of key generation, the involved transceivers separately apply discrete cosine transform (DCT) and inverse discrete cosine transform (IDCT) to pre-process their measurements. Then, the outputs of IDCT are quantified and encoded to establish the bit sequence. With the implementations of information reconciliation and privacy amplification, the shared secret key can be generated. Several experiments in real environments are conducted to evaluate the proposed scheme. During each experiment, the shared key is established from the received signal strength (RSS) of heterogeneous devices. The results of experiments demonstrate that the proposed scheme can efficiently generate shared secret keys between transceivers.
Channel reciprocity is a very crucial component in establishing a secret key generation scheme. Non-simultaneous measurement conditions and noise cause low channel reciprocity, which is indicated by measurements of channel parameters that are not perfectly identical in both users. The stages of the secret key generation scheme that directly quantifies the channel parameters will have an impact on the high difference in the bits produced. In this paper, we propose the use of Modified Polynomial Regression methods to enhance channel reciprocity that would lower the rate of key disagreement between two users. We also propose a combination of the Modified Polynomial Regression method with multilevel quantization to overcome the trade-off between performance parameters, i.e. the key disagreement rate and key generation rate. The test results conducted in an indoor wireless environment show that our proposed scheme has better performance compared to the existing scheme in terms of increasing reciprocity, key generation rate and decreasing key disagreement rate. The resulting secret key has also fulfilled the randomness requirements set by the National Institutes of Standards and Technology statistical suite.
The inherent randomness of wireless radio channels can be employed to extract secrets, whenever the channel reciprocity holds. Privacy amplification is an ingredient step for removing the redundancy of key, of which, the mount of information leaked to potential eavesdroppers, is often difficult to determine. In this paper, we propose a secret-key generation scheme without privacy amplification, of which the disagreement of key is coordinated through the reconciliation of sample positions as did in the level-crossing scheme. Compared to the level-crossing scheme, the proposed approach accumulates the reliable samples and further employs multi-bit quantization for improving the rate of secret-key generation. The accumulated samples should be decorrelated for generating random keys. Through extensive simulations, we find that the Karhunen-Loève transform for decorrelation is very sensitive in implementation.
There is a growing interest in physical layer security. Recent work has demonstrated that wireless devices can generate a shared secret key by exploiting variations in their channel. The rate at which the secret bits are generated, however, depends heavily on how fast the channel changes. As a result, existing schemes have a low secrecy rate and are mainly applicable to mobile environments. In contrast, this paper presents a new physical-layer approach to secret key generation that is both fast and independent of channel variations. Our approach makes a receiver jam the signal in a manner that still allows it to decode the data, yet prevents other nodes from decoding. Results from a testbed implementation show that our method is significantly faster and more accurate than state of the art physical-layer secret key generation protocols. Specifically, while past work generates up to 44 secret bits/s with a 4% bit disagreement between the two devices, our design has a secrecy rate of 3-18 Kb/s with 0% bit disagreement.
Due to non-ideal conditions in the measurements of the wireless channel, high initial bit error rate (BER) in the preliminary key is resulted, which reduces the final secret key generation rate and even causes the secret key generation process fail. Aiming to resolve this problem, we first present and verify an optimal information reconciliation protocol; the validation experiment shows that not only the BER comes down more quickly, but also a higher information rate is achieved. Then, to address the problem of very high initial BER and further improve the efficiency of the secret key generation, we introduce the idea of pre-distillation into the secret key generation system, and present a pre-distillation method, which makes the initial BER comes down quickly, and ensures the subsequent information reconciliation be easily performed; hence the total key generation rate is improved. Experimental results demonstrate that the pre-distillation method has excellent ability of reducing the initial BER, especially in the case of very high initial BER. The combination of our proposed pre-distillation and our optimal information reconciliation is the most efficient one when the initial BER is larger than 0.15, and the information rate is improved by more than forty-nine times when the initial BER is 0.3