mohammad rohollah yazdani

In this paper, a new non-isolated soft switched DC-DC converter with high step-down conversion ratio is proposed. The proposed converter consists of two switch cells that their inputs and outputs are cascaded. This converter provides ultra-high step-down conversion ratio and due to all semiconductor devices are soft switched, switching losses are reduced, also reverse recovery losses of diodes are reduced because of ZCS turn off condition. The duty cycle of proposed converter is much larger than step-down converter and therefore does not have the problems of the converter with a narrow duty cycle and since no auxiliary switch is used to achieve soft switching, the control circuit remains simple. In this paper, the convertor operating modes are discussed and to verify the performance of the converter a 50W prototype with 100 kHz switching frequency, 100V input and 16V output is built. The converter efficiency is measured and the peak efficiency is 94% also the conducted electromagnetic interference peak in the proposed converter is reduced by 6dBµv.

In recent years, the Internet of Things (IoT) networks have extensively been used in various practical field, one of the most important of which is medical Internet of Things (MIoT). In these networks, radio frequency identification (RFID) is one of the main technologies in creating an authentication system that is able to efficiently identify and identify medical equipment and patients. Therefore, researchers in this field have proposed different authentication protocols for RFID-based MIOT systems and claimed that they are resistant to active and passive attacks. Contrary to their claims, most of these protocols are not resistant to conventional attacks. Fan et al. have recently proposed a lightweight RFID authentication scheme for cloud-based RFID health-care systems and claimed that it is sufficiently efficient and secure. In this paper , we analyzed the Fan et al protocole and demonstrated that their protocol is vulnerable to replay, reader impersonation, tag tracking, and de-synchronization attacks. Moreover, we show how the similarity of some of their protocol messages causes attack. Then, we propose an improved protocol (LRAMP) that is resistant to these and other known attacks in RFID authentication protocol. According to security analysis, we can see that the LRAPM protocol has a high level of security. This high security can only be achieved by adding a new message and changing other messages. A comparison of the performance of the LRAPM protocol shows that this protocol is comparable to similar protocols in terms of computational costs, storage costs and communication costs.

Rapid and ever-increasing Internet of things (IoT) developments have brought about great hopes of improving the quality of human life. Radio-frequency identification (RFID) employed as a backup technology in the IoT is widely used in different aspects of life. Therefore, high priority should be given to security problems and user privacy protection. However, limited computational power and storage resources in passive tags have made the implementation of security measures difficult in RFID. In other words, the design of lightweight authentication protocols for RFID systems is still a major challenge in RFID security. A lightweight authentication protocol has been recently proposed for passive tags by Liu et al. Using specific inverse operations in the IOLAS protocol, they claimed that the lightweight bitwise operations would make this protocol resistant against known and potential attacks in RFID systems. This study aimed to show that the same inverse operations pose the main problem so that this protocol fails to guarantee backward security. It was also indicated that the IOLAS protocol is vulnerable to replay, reader impersonation, tag tracking attacks, and secret disclosure attack. Finally, we improved the IOLAS protocol and proposed the POLAS protocol, which is resistant to the currently known attacks. We analyze the security level of the proposed protocols and prove the security of the proposed design using BAN (Burrows-Abadi-Needham) logic. We also formally confirmed the security of the proposal using the Scyther simulation tool. According to security analysis, we can observe that this protocol have a high level of security. A comparison of the performance of the POLAS protocol shows that this protocol is comparable to similar protocols in terms of computational costs, storage costs, and communication costs.