Encryption is the most important method to enhance security of network transmitting. SDN (Software Defined Networking) Security Transmission Service can provide multi-connection transmitting service, which scatters data to multiple network connections for transmission so that data on different connections is isolated from each other. Based on the service, encrypting the isolated data prevents overall data from intercepted and deciphered. In the above scenario, we propose an encryption algorithm that uses the data themselves as encryption keys, and use the data isolation effect of multi-connection transmission to distribute the encrypted ciphertext to different network transmission paths, which is equivalent to using a rather random sequence as an encryption key for each data fragment without sharp increase in transmitting data, so that data transmitted on every connection are ensured to be safe. After compared with other encryption algorithms such as DES, AES and RSA, it is proved that in the multi-connection transmitting scenario this algorithm has better encryption effect and operating efficiency, which provides an effective guarantee for network security.

Abstract. We present an improved incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) system based on iterative retrieval algorithm for simultaneous detection of atmospheric nitrous acid (HONO) and nitrogen dioxide (NO2). The conventional IBBCEAS retrieval algorithm depends on the absolute change of light intensity, which requires high stability of light source and stable transmission of light intensity of all optical components. The new algorithm has an iterative module to obtain the effective absorption optical path length, and then the concentrations of HONO and NO2 are determined by differential optical absorption spectroscopy (DOAS) retrieval, so it is insensitive to the fluctuation of absolute light intensity. The robustness of the system is verified by simulating the influence of the relative change of light intensity on the spectral retrieval results. The effect of nitrogen purging in front of the cavity mirrors on shortening the actual cavity length was measured and corrected by using NO2 gas samples. Allan deviation analysis was conducted to determine the system stability, indicating the detection limits (2δ) of HONO and NO2 are 0.08 ppbv and 0.14 ppbv at an integration time of 60 s, respectively. Furthermore, Kalman filtering was used to improve the detection precision of the system. The detection sensitivity of the system at an integration time of 3 s can be improved by 4.5-fold with applying Kalman filtering, which is equivalent to the detection sensitivity at an integration time of 60 s without applying Kalman filtering. The atmospheric HONO and NO2 were observed by the IBBCEAS system based on iterative algorithm, and compared with those measured by conventional IBBCEAS.