Biblio

Entropy sources are designed to provide unpredictable random numbers for cryptographic systems. As an assessment of the sources, Shannon entropy is usually adopted to quantitatively measure the unpredictability of the outputs. In several related works about the entropy evaluation of ring oscillator-based (RO-based) entropy sources, authors evaluated the unpredictability with the average conditional Shannon entropy (ACE) of the source, moreover provided a lower bound of the ACE (LBoACE). However, in this paper, we have demonstrated that when the adversaries have access to the history outputs of the entropy source, for example, by some intrusive attacks, the LBoACE may overestimate the actual unpredictability of the next output for the adversaries. In this situation, we suggest to adopt the specific conditional Shannon entropy (SCE) which exactly measures the unpredictability of the future output with the knowledge of previous output sequences and so is more consistent with the reality than the ACE. In particular, to be conservative, we propose to take the lower bound of the SCE (LBoSCE) as an estimation of the worst-case entropy of the sources. We put forward a detailed method to estimate this worst-case entropy of RO-based entropy sources, which we have also verified by experiment on an FPGA device. We recommend to adopt this method to provide a conservative assessment of the unpredictability when the entropy source works in a vulnerable environment and the adversaries might obtain the previous outputs.

The target of security protection of the power distribution automation system (the distribution system for short) is to ensure the security of communication between the distribution terminal (terminal for short) and the distribution master station (master system for short). The encryption and authentication gateway (VPN gateway for short) for distribution system enhances the network layer communication security between the terminal and the VPN gateway. The distribution application layer encryption authentication device (master cipher machine for short) ensures the confidentiality and integrity of data transmission in application layer, and realizes the identity authentication between the master station and the terminal. All these measures are used to prevent malicious damage and attack to the master system by forging terminal identity, replay attack and other illegal operations, in order to prevent the resulting distribution network system accidents. Based on the security protection scheme of the power distribution automation system, this paper carries out the development of multi-chip encapsulation, develops IPSec Protocols software within the security chip, and realizes dual encryption and authentication function in IP layer and application layer supporting the national cryptographic algorithm.

Macroscopic hysteresis loops and microscopic magnetic moment distributions have been determined by 3-D model for Co nanowire with various easy axis deviations from applied field. It is found that both the coercivity and the remanence decrease monotonously with the increase of easy axis deviation as well as the maximum magnetic product, indicating the large impact of the easy axis orientation on the magnetic performance. Moreover, the calculated angular distributions and the evolution of magnetic moments have been shown to explain the magnetic reversal process. It is demonstrated that the large demagnetization field in the two ends of the nanowire makes the occurrence of reversal domain nucleation easier, hence the magnetic reversal. In addition, the magnetic reversal was illustrated in terms of the analysis of the energy evolution.