We propose N-choice game (NCG), a decentralized method for generating pseudo-random numbers for smart contracts. NCG involves multiple participants, each of whom chooses a value between 0 and \(N-1\) and whose collective choices determine the generation of a pseudo-random number. The design of NCG has three key objectives: incentivizing participants to make random choices, assessing randomness in a decentralized environment, and achieving high operational performance. Implemented in Solidity and rigorously tested, NCG has shown remarkable effectiveness. Our results show that the randomness of the numbers generated by NCG is high and consistent, even under a strict NIST randomness test, provided that there is no collusion between the majority of participants. Not only is it impossible to customize the outputs generated by NCG, but it is also impractical to make them non-random. Therefore, it is rational to engage NCG for the purpose of rewards rather than the output values it produces. Selecting values in a way that is not predicted by other nodes yields the highest expected value, and NCG incentivizes random selection. Furthermore, NCG demonstrates a significant performance advantage, being up to 158 times faster at generating random numbers than the existing Random Bit Generator framework [ 3 ]. This efficiency underscores NCG’s potential to enhance blockchain applications.

The primary strengths of blockchain systems come from strong guarantees of immutability and reliability, and these systems can be extended with programmatic logic through Smart Contracts. Many such programmatic use cases would benefit from the use of external data. However, the method of bringing that data onto the blockchain needs to be trustworthy and secure. Otherwise, the benefits of blockchain, namely distributed trust, no single points of failure, and immutability, would be at risk. Blockchain oracles are proposed as a conceptual solution to this problem. A blockchain oracle acts as a trusted intermediary to external data. In this work we analyze existing proposals for Discernible event oracle mechanisms, which seek to address oracle queries with a broad knowledgeable answering population, to characterize problems related to the incentives imposed by external value that depends on oracle outcomes. In doing so, we focus on continued challenges to voting based oracles, including trust limitations and the need to match questions to knowledgeable answering parties. To address these difficulties, we propose an extension to existing oracle protocols to utilize reputation as a tool to measure value and as a tool to associate questions with context. By providing a method to track contextual knowledge, our proposal allows for context-based query matching and enables higher probability of correctness for a given population size as well as stronger participation incentives.

Blockchain is an integrated technology to ensure keeping record and process transactions with decentralized manner. It is thought as the foundation of future decentralized ecosystem, and collects much attention. However, the maturity of this technology including security of the fundamental protocol and its applications is not enough, thus we need more research on the security evaluation and verification of Blockchain technology This tutorial explains the current status of the security of this technology, its security layers and possibility of application of formal analysis and verification.

Blockchain technology realizes unforgeable and decentralized ledger by applying P2P network, cryptography and consensus mechanism over distributed network. Its security relies on all of these technologies. One of fundamental problem of the security of blockchain technology is compromise of underlying cryptographic algorithms. This paper shows the impact of compromise of underlying cryptography and the way to extend the validity of blockchain applying the long-term signature scheme which was standardized in ETSI. The long-term signature scheme assume the existence of centralized PKI and secure time-stamp service. In this paper, we propose a method to apply similar concept and data structure with de-centralized manner. Our scheme avoids hard-fork of original blockchain, in the case of compromise of hash function and provides smooth-fork in the case of compromise of digital signature scheme.

Users want to enjoy online services without sacrificing their security. Although there is a trade-off between the security of a service and its usability, the level of security required will differ depending on the user and the situation. To optimize the balance between security and usability, it can be customized for each user and each online transaction. Yet in order to do that, both users and service providers need to stipulate their security requirements. We have been working on a framework that provides security requirement classifications in multiple dimensions to help users identify and select their security requirements, and then apply these requirements to different dimensions. This paper shows how we implemented this framework and then evaluated it by conducting a user study along with our implementation. The study verifies that ordinary users without any particular technical knowledge prefer to clarify their security requirements using a taxonomy-based selection scheme (our scheme) as opposed to a free-form input scheme. It also discusses the coverage of pre-defined taxonomies and users' requirements. Through this study, we clarify the future direction of our research.

This paper proposes a mechanism that realizes accountable security using a security service level agreement (SSLA), which defines the security level of a service agreed to between a user and service provider. The mechanism consists of three major components: security expression, translation, and negotiation techniques. The security expression technique provides a means to describe security requirements and capabilities of a user and service provider, as well as the SSLA between them, in different levels of detail. The translation technique provides a means to translate such information among different levels of detail, and the negotiation technique provides a means to negotiate and agree upon the SSLA between the user and service provider. Both the user and service provider need to be accountable and non-repudiable against the agreed to SSLA in order to empower it. The mechanism uses cryptographic identities and digital signatures for this purpose. This paper demonstrates the feasibility and usability of the mechanism by describing its usage scenario and implementing its prototype, and analyzes this mechanism.

The first contribution of our paper is that we propose a platform, a design strategy, and evaluation criteria for a fair and consistent hardware evaluation of the second-round SHA-3 candidates. Using a SASEBO-GII field-programmable gate array (FPGA) board as a common platform, combined with well defined hardware and software interfaces, we compare all 256-bit version candidates with respect to area, throughput, latency, power, and energy consumption. Our approach defines a standard testing harness for SHA-3 candidates, including the interface specification for the SHA-3 module on our testing platform. The second contribution is that we provide both FPGA and 90-nm CMOS application-specific integrated circuit (ASIC) synthesis results and thereby are able to compare the results. Our third contribution is that we release the source code of all the candidates and by using a common, fixed, publicly available platform, our claimed results become reproducible and open for a public verification.

No abstract available.