Shannon's source entropy formula is not appropriate to measure the uncertainty of non-stationary processes. In this paper, we propose a new entropy measure for non-stationary processes, which is greater than or equal to Shannon's source entropy. The maximum entropy of the non-stationary process has been considered, and it can be used as a design guideline in cryptography.

Underwater Sensor Network (UWSN) is a powerful technique for aquatic applications. Although the international researches on this topic are quite prosperous, it is still in its early stage of development. UWSN is vulnerable to various kinds of attacks because it is usually deployed in hostile environments. This paper systematically summarizes and analyzes the existing security attacks and defensive mechanisms of the UWSN. We expect it can offer a theoretical reference for the establishment of the UWSN security system.

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In this paper, we propose a kind of pseudorandom bit generator based on varying time delayed logistic map. The variation of delay time is chaotic. The experiments show that the generated binary sequences have good cryptographic properties, and can pass all the well known statistical tests.