Data security plays a central role in the design of Internet of Things (IoT). Since most of the "things" in IoT are embedded computing devices it is appropriate to talk about cryptography in embedded of systems. This kind of devices is based on microcontrollers, which have limited resources (processing power, memory, storage, and energy). Therefore, we can apply only lightweight cryptography. The goal of this work is to find the optimal cryptographic solution for IoT devices. It is expected that perception of this solution would be useful for implementation on “limited” devices. In this study, we investigate which lightweight algorithm is better to implement. Also, how we can combine two different algorithms in a hybrid scheme and modify this scheme due to data sending scenario. Compendex, Inspec, IEEE Xplore, ACM Digital Library, and Springer Link databases are used to conduct a comprehensive literature review. Experimental work adopted in this study involves implementations, measurements, and observations from the results. The experimental research covers implementations of different algorithms and experimental hybrid scheme, which includes additional function. Results show the performance of the considered algorithms and proposed hybrid scheme. According to our results, security solutions for IoT have to utilize algorithms, which have good performance. The combination of symmetric and asymmetric algorithms in the hybrid scheme can be a solution, which provides the main security requirements: confidentiality, integrity, and authenticity. Adaptation of this scheme to the possible IoT scenarios shows the results acceptable for implementation due to limited resources of hardware.

Voting is a fundamental decision making instrument in any consensus-based society. It is employed in various applications from student body elections, reality television shows, shareholder meetings, to national elections. With the motivation of better eciency, scalability, speed, and lower cost, voting is currently shifting from paper-based to the use of electronic medium. This is while aiming to achieve better security, such that voting result reflects true opinions of the voters. Our research focuses on the study of cryptographic voting protocols accommodating a flexible ballot structure as a foundation for building a secure electronic voting system with acceptable voting results. In particular, we search for a solution suitable for the preferential voting system employed in the Australian Federal Election. The outcomes of the research include: improvements and applications of batch proof and verication theorems and techniques, a proposed alternative homomorphic encryption based voting scheme, a proposed Extended Binary Mixing Gate (EBMG) mix-network scheme, a new threshold randomisation technique to achieve receipt-freeness property in voting, and the application of cryptographic voting protocol for preferential voting. The threats and corresponding requirements for a secure secret-ballot voting scheme are rst discussed. There are significant security concerns about the conduct of electronic voting, and it is essential that the voting results re ect the true opinions of the voters - especially in political elections. We examine and extend batch processing proofs and verifications theorems and proposed applications of the theorems useful for voting. Many instances of similar operations can be processed in a single instance using a batch technique based on one of the batch theorems. As the proofs and verications provide formal assurances that the voting process is secure, batch processing offers great efficiency improvements while retaining the security required in a real-world implementation of the protocol. The two main approaches in cryptographic voting protocols, homomorphic encryption based voting and mix-network based voting, are both studied in this research. An alternative homomorphic voting scheme using multiplicative homomorphism property, and a number of novel mix-network schemes are proposed. It is shown that compared to the mix-network approach, homomorphic encryption schemes are not scalable for straight-forward adaptation of preferential systems. One important requirement of secret-ballot voting is receipt-freeness. A randomisation technique to achieve receipt-freeness in voting is examined and applied in an ecient and practical voting scheme employing an optimistic mix-network. A more general technique using threshold randomisation is also proposed. Combination of the primitives, both the homomorphic encryption and mixnetwork approach, yields a hybrid approach producing a secure and ecient secret-ballot voting scheme accommodating a exible ballot structure. The resulting solution oers a promising foundation for secure and practical secret-ballot electronic voting accommodating any type of counting system.