Research On Physical Layer Encryption Of LoRa Internet Of Things Based On Modulation Characteristics

LoRa(Long Range)is an emerging low-power wide area network(LPWAN)technology,which has received wide attention due to its wide coverage and low power consumption.At present,LoRa's information security is mainly based on Public Key Cryptography(PKC),using public key infrastructure(PKI)for key distribution,and AES-128 encryption at the network layer and application layer.The existing information security method of LoRa has the risks of data leakage and data tampering caused by key leakage;meanwhile,the encryption/integrity protection key is derived using AES-128 encryption,and the security level and encryption strength are insufficient.Compared with the PKC-based security technology,the physical layer security technology has the advantages of perfect security,low computational complexity,resource consumption,and good adaptation to changes in the physical layer.Therefore,the physical layer security technology is more suitable for Io T devices than the PKC method.Therefore,based on the generation of keys in the physical layer,this topic has conducted a physical layer security study based on the characteristics of the LoRa physical layer.First,the physical layer of LoRa Internet of Things is analyzed in detail.LoRa modulation is based on Chirp Spread Spectrum(Chirp Spread Spectrum,CSS).The essence of LoRa modulation is to map SF bits to a cyclic shift value.Then within a symbol period,the basic Chirp signal is cyclically shifted according to the magnitude of the cyclic shift value.Therefore,the bit information to be transmitted is converted into the cyclic shift value of the LoRa symbol,and the Chirp signal exists as a carrier signal.When performing LoRa demodulation at the receiving end,the received continuous LoRa modulated signal undergoes de-chirp,sampling and Discrete Fourier Transform(DFT)to obtain the demodulated signal spectrum.The cyclic shift value can be obtained from the spectrogram,and then the bit information is demodulated.Secondly,the physical layer key generation protocol LoRa-Key based on LoRa is proposed.The LoRa-Key protocol includes two stages: signal processing and key generation.In the signal processing process,first use outlier detection and Savitzky Golay filter to reduce the difference caused by environmental noise,and then use linear interpolation technology to construct missing data points based on the filtered RSSI values?In the key generation process,the RSSI value is first converted into a bit string by using a multi-level quantization technique.Then,a negotiation method based on Compressive Sensing(CS)is used to reduce the bit mismatch rate.Finally,the general Hsah function is used to improve the randomness of the key.Then,for the physical layer characteristics of LoRa,we designed a cyclic shift encryption algorithm.The algorithm uses the physical layer key shared by the legal receivers to generate a cyclic shift encryption factor,encrypt the cyclic shift value,so that the encrypted cyclic shift value range becomes a decimal.When the range of the cyclic shift value becomes a decimal,the Chirp signal waveform of the LoRa modulation signal will change,increasing the type of waveform.And after LoRa demodulation at the receiving end,accurate cyclic shift values cannot be obtained from the frequency spectrum.