Wireless Secret Key Agreement
Step 1 (channel survey). Experiments  have shown that in some environments, due to the absence of variations in the wireless channel, the extracted bits have very low entropy, making these bits unsuitable for a secret key, which can lead to predictable key realization by an opponent in these static environments. To avoid this, we use random signals during channel analysis to examine the channel. Suppose Bob is selected to study the channel and quantify the channel`s measurements. Thus, Alice transmits the random probe signal to Bob where , for , and is the number of the sub-carrier of the OFDM system. The random signal is unknown to Bob and Eve. For example, without loss of universality, we only take the () subcarrier. Thus, in Bob, the received signal can be expressed in such a way that it refers to the th subcanal response of the legitimate channel in the frequency band and constitutes the underlying sub-channel sub-channel subchannel response. The sub-channels are distributed independently and identically (i.i.d.) and . is i.i.d.
the complex Gauss noise with zero average and variance. Based on the signal received, Bob obtains the estimate of the response of the subcanalon phases, because the phase estimation error is. Keep in mind that the random probe signal phase is included in the subchannel response estimate, so we process the estimate of the equivalent lower phase response. If Eva is near Bob (here, the closure means that the distance between Eva and Bob is much smaller than what can be heavily correlated and lead, she can easily deduce the temporary key based on her observations. To reduce the risk, Bob adds a stochastic coefficient when the place is evenly distributed and . Bob gets vector data like. These three patterns use the same method of quantification, i.e. the method of quantifying the same interval, where the space of the characteristics is divided into subspaces on average.
The same information is consistent and approaches to extending data protection are used. Note that, in theory, the length of the resulting quantification should be limited by the mutual information between Alice and Bob . In other words, the level of quantification should not exceed the secret key capacity, that is,. However, in order to simplify the analysis, the quantification levels of the three schemes are defined. It is intuitive that, among a jamming opponent, the number of transmissions needed to establish a secret key for the direct method is very high, because nodes 402 and 412 lack an effective channel to protect their communication from jamming.