Blockchain architecture in Smart Pedagogy offers valuable social propositions like trust, identity, transparency, immutability, smart contracts and disintermediation. There are multiple practices how to record learners' achievements and present learning transcripts where the most common practices are university issued diplomas and vendor issued certificates. There are social networks which allow users to publish their learning achievements for possible stakeholders; however, the common problem is to verify if published diplomas and certificates are valid.
Chaoyang Li, Gang Xu, Yuling Chen, Haseeb Ahmad · 5 authors
Blockchain technology has become a research hotspot in recent years with the prominent characteristics as public, distributed and decentration. And blockchain-enabled internet of things (BIoT) has a tendency to make a revolutionary change for the internet of things (IoT) which requires distributed trustless consensus. However, the scalability and security issues become particularly important with the dramatically increasing number of IoT devices. Especially, with the development of quantum computing, many extant cryptographic algorithms applied in blockchain or BIoT systems are vulnerable to the quantum attacks. In this paper, an anti-quantum proxy blind signature scheme based on the lattice cryptography has been proposed, which can provide user anonymity and untraceability in the distributed applications of BIoT. Then, the security proof of the proposed scheme can derive that it is secure in random oracle model, and the efficiency analysis can indicate it is efficient than other similar literatures.
Military science has faced new challenges at the end of the 20th century with the emergence of the Internet. Challenges and threats to traditional security got a new interpretation with a new concept as cybersecurity, which leads to an organic transformation of military engineering and IT. As the Internet has fundamentally changed the way the world works, new technologies have emerged on the network that can revolutionise the multitude of industries. Such innovation is Distributed Ledger Technology (DLT) and Blockchain Technology supplemented with Artificial Intelligence and computer vision. The potential uses of the blockchain represent a multitude of military technical scientific challenges. The technology makes it possible to co-operate freely with cryptographic procedures on distributed networks without state control, but can also serve military and defence management purposes.
Zero-knowledge password policy checks (ZKPPC) were introduced in Kiefer and Manulisâ report from 2014. The protocol aimed to solve the longstanding issue with servers requiring clients to provide their password in plain text to ensure its strength. Their protocol was intended to eliminate the need for users to trust the server to store and handle passwords correctly while simultaneously allowing the server to know that the registered password was strong enough. This thesis has investigated the soundness of the protocol by Kiefer and Manulis and will present three new zero-day vulnerabilities discovered in the process. The vulnerabilities allow a dishonest user to prove adherence to the policy for invalid passwords. Additionally, the thesis presents our new Proof of Inequality which prevents one of these vulnerabilities, as well as an extension for an incomplete part of the protocol. The two remaining zero-day vulnerabilities are weaknesses in the protocol left for future research.
We study the problem of approximating the commuting-operator value of a two-player non-local game. It is well-known that it is $\mathrm{NP}$-complete to decide whether the classical value of a non-local game is 1 or $1- Δ$. Furthermore, as long as $Δ$ is small enough, this result does not depend on the gap $Δ$. In contrast, a recent result of Fitzsimons, Ji, Vidick, and Yuen shows that the complexity of computing the quantum value grows without bound as the gap $Δ$ decreases. In this paper, we show that this also holds for the commuting-operator value of a game. Specifically, in the language of multi-prover interactive proofs, we show that the power of $\mathrm{MIP}^{co}(2,1,1,s)$ (proofs with two provers, one round, completeness probability $1$, soundness probability $s$, and commuting-operator strategies) can increase without bound as the gap $1-s$ gets arbitrarily small. Our results also extend naturally in two ways, to perfect zero-knowledge protocols, and to lower bounds on the complexity of computing the approximately-commuting value of a game. Thus we get lower bounds on the complexity class $\mathrm{PZK}$-$\mathrm{MIP}^{co}_Ύ(2,1,1,s)$ of perfect zero-knowledge multi-prover proofs with approximately-commuting operator strategies, as the gap $1-s$ gets arbitrarily small. While we do not know any computable time upper bound on the class $\mathrm{MIP}^{co}$, a result of the first author and Vidick shows that for $s = 1-1/\text{poly}(f(n))$ and $Ύ= 1/\text{poly}(f(n))$, the class $\mathrm{MIP}^{co}_Ύ(2,1,1,s)$, with constant communication from the provers, is contained in $\mathrm{TIME}(\exp(\text{poly}(f(n))))$. We give a lower bound of $\mathrm{coNTIME}(f(n))$ (ignoring constants inside the function) for this class, which is tight up to polynomial factors assuming the exponential time hypothesis.
We suggest that flexible majority rules for currency issuance decisions foster the stability of a cryptocurrency. With flexible majority rules, the voteshare needed to approve a particular currency issuance growth is increasing with this growth rate. By choosing suitable parameters for these flexible majority rules, we show that optimal growth rates can be achieved in simple settings. Moreover, with flexible majority rules, changes in the composition of growth-friendly and growth-adverse agents only have a comparatively moderate impact on growth rates, and extreme growth rates are avoided. Finally, we show that optimal money growth rates are realized if agents entering financial contracts anticipate ensuing inflation rates determined by these flexible majority rules.
Today more and more enterprises and individuals are outsourcing their data to cloud storage system. Data deduplication is one of the important technologies to reduce the storage cost of cloud storage system. In a cloud storage system with deduplication technology, the client can outsource the data files to the cloud storage server and pay for them. Fair payment is one of key issues in the cloud deduplication storage system. At present, a variety of secure deduplication encryption schemes have been designed to protect the privacy of client data. However, most existing fair payment solutions use traditional electronic cash systems to generate payment tokens, which requires a trusted authority to prevent double-spending. Trusted authorities will become bottlenecks in the payment system. Faced with this problem, in this paper, we propose a new decentralized fair payment protocol for cloud deduplication storage system by utilizing ethereum blockchain technology. The new protocol takes advantage of the decentralization of blockchain technology, allowing direct transactions without the participation of trusted third parties. In the new protocol, if a malicious situation occurs, the system can guarantee fair payment by pre-storing penalty money in the smart contract. Safety analysis and experimental analysis show that our new protocol is feasible.
The focus of this thesis is twofold: on one hand we study the query complexity of equilibrium computation in games, and on the other hand, we use equilibrium concepts from game theory as a tool to understand miner incentives in Bitcoin. In terms of query complexity, we mostly focus on algorithms that have access to utility queries in large games and best response queries in bimatrix games. For the former, we demonstrate query-efficient completely uncoupled dynamics that achieve non-trivial approximate equilibria. For the latter, we reduce the problem of query-efficient approximate equilibrium computation to a natural geometric learning problem: approximately learning partitions of an đ-dimensional simplex into disjoint convex polytopes via membership queries. Given this reduction we show query-efficient algorithms for the geometric problem, and ultimately provide an algorithm for computing e-well-supported Nash equilibria in đĂđ bimatrix games with a query cost that is polynomial in log(1/e)and max(đ,đ) provided that min(đ,đ) is constant.This leads to a polynomial query complexity algorithm for 2-player games,provided that one of the players has a constant number of strategies. As for incentives in Bitcoin, we shed some light into how robust honest mining protocols are to the presence of strategic agents. Our focus is on the strategic aspects of both solo mining and pool mining in Bitcoin. For the former, we take a multiplayer approach and exhibit specific strategy profiles of multiple strategic miners that outperform honest mining, even if said miners would not be incentivised to be dishonest individually. This effectively renders the Bitcoin protocol less secure than previously thought. As for the latter, we propose a new mining pool protocol that is a randomised variant of the already-ubiquitous pay-per-last-N-shares (PPLNS) mining pool scheme in Bitcoin. Our pool protocol, randomised pay-per-last-N-shares (RPPLNS),enjoys the same desirable properties of PPLNS, but with the added benefit of an exponentially reduced state space required to maintain the protocol. More importantly, this reduced state space also allows us to prove robust guarantees against a richer class of strategic pool mining than before.
With the widespread popularity of Internet-enabled devices, mobile users can request and receive messages anytime and anywhere, which facilitates information feedback for smart city management. However, few people are willing to reflect or report some violations of law and discipline around them, and more people choose to ignore. In general, there are two major reasons for this phenomenon. First, reporting with a real name is highly recommended, but it is difficult to send trusted and reliable reporting messages without revealing the reporter's identity. Second, generally no benefit, users usually lack the motivation to report due to worrying about being retaliated. In this paper, we propose an effective anonymous reporting system called ReportCoin, a novel Blockchain-based incentive anonymous reporting system. ReportCoin guarantees user identity privacy and reporting message reliability throughout the reporting process. On the one hand, ReportCoin allows nondeterministic mobile users to vote the reporting by signing and to send anonymous announcements in the non-fully trusted network. On the other hand, ReportCoin motivates users with incentives to report without worrying about the disclosure of identity information to be retaliated. Meanwhile, account information and transaction records in ReportCoin are open, transparent, and tamper-resistant. The theoretical analysis and extensive experimental results show that ReportCoin is efficient and practical.
Open access
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
In today's digital information age, the conflict between the public's growing awareness of their own data protection and the data owners' inability to obtain data ownership has become increasingly prominent. The emergence of blockchain provides a new direction for data protection and data tokenization. Nonetheless, existing cryptocurrencies such as Bitcoin using Proof-of-Work are particularly energy intensive. On the other hand, classical protocols such as Byzantine agreement do not work efficiently in an open environment. Therefore, in this paper, we propose a permission-less blockchain with a novel double-DAG (directed acyclic graph) architecture called DLattice, where each account has its own Account-DAG and all accounts make up a greater Node-DAG structure. DLattice parallelizes the growth of each account's Account-DAG, each of which is not influenced by other accounts' irrelevant transactions. DLattice uses a new DPoS-BA-DAG(PANDA) protocol to reach consensus among users only when the forks are observed. Based on proposed DLattice, we introduce a process of data tokenization, including data assembling, data anchoring, and data authorization. We implement DLattice and evaluate its performance on 25 ECS virtual machines, simulating up to 500 nodes. The experimental results show that DLattice reaches a consensus in 10 seconds, achieves desired throughput, and incurs almost no penalty for scaling to more users.
Among the zero-knowledge succinct non-interactive arguments of knowledge (zk-SNARK), the simulation-extractable zk-SNARK (SE-SNARK) introduces a security notion of non-malleability. The existing pairing-based zk-SNARKs designed from linear encoding are known to be vulnerable to algebraic manipulation of the proof. The latest SE-SNARKs check the proof consistency by increasing the proof size and the verification cost. In particular, the number of pairings increases almost doubles due to further verification. In this article, we propose two novel SE-SNARK constructions with a single verification. The consistency check is subsumed in a single verification through employing a hash function. The proof size and verification time of the proposed SE-SNARK schemes are minimal in that it is the same as the state-of-the-art zk-SNARK without non-malleability. The proof in our SE-SNARK constructions comprises only three group elements (type III) in the QAP-based scheme and two group elements (type I) in the SAP-based scheme. The verification time in both requires only 3 pairings. The soundness of the proposed schemes is proven under the hash-algebraic knowledge (HAK) assumption and the (linear) collision-resistant hash assumption.
In a general secure multi-party computation (MPC) protocol, two or more participants who do not trust each other, use their respective secret inputs to calculate a joint function in a distributed environment without a centralized organization. They can get correct outputs on the premise of ensuring privacy and independence of input. In this paper, to solve the problem of fairness and robustness in MPC, a blockchain-based multi-party computation scheme (BFR-MPC) was proposed. The blockchain maintains an open reputation system for parties as a public ledger where a more reputable party has a greater chance to be selected. The block height is used as a trusted timestamp. In each round, parties must send the correct information before the deadline. In our scheme, all parties are considered to be foresighted, and an incentive mechanism encourages parties to cooperate rather than deviate from the protocol. Because of non-cooperative parties will be immediately expelled from the protocol and will be penalized financially, the proposed scheme is robust. The penalty will be used to reward honest parties. We also proved the fairness of our scheme through Game Theory. The comparison results of the proposed scheme with other schemes show that it is a more practical scheme for MPC with high fairness and robustness.
Compact multisignature is vital for shrinking the signature size of decentralized blockchain. All practical compact multisignature schemes have been constructed from the discrete logarithm problem which is potentially vulnerable to quantum computing attacks. Lattice-based multisignature schemes are potential candidates for resisting quantum attacks. However, the existing lattice-based multisignature schemes suffer either loose signatures or large public key and signature sizes after compressing, which makes them unsuitable for blockchains. In this paper, we first present a practical lattice-based multisignature scheme with much smaller signature sizes than previous lattice-based multisignature schemes. Then, we extend our scheme to support public key aggregation with almost the same performance. Both of our multisignature schemes are provably secure in the random oracle model under the ring version of the short integer solution (Ring-SIS) assumption. They outperform the recent lattice-based multisignature scheme proposed by Bansarkhani and Sturm (BS) in terms of both signature size and communication overhead.
Daniel Kales, Sebastian Ramacher, Christian Rechberger, Roman Walch · 5 authors
Post-quantum cryptography has received increased attention in recent years, in particular, due to the standardization effort by NIST. One of the second-round candidates in the NIST post-quantum standardization project is Picnic, a post-quantum secure signature scheme based on efficient zero-knowledge proofs of knowledge. In this work, we present the first FPGA implementation of Picnic. We show how to efficiently calculate LowMC, the block cipher used as a one-way function in Picnic, in hardware despite the large number of constants needed during computation. We then combine our LowMC implementation and efficient instantiations of Keccak to build the full Picnic algorithm. Additionally, we conform to recently proposed hardware interfaces for post-quantum schemes to enable easier comparisons with other designs. We provide evaluations of our Picnic implementation for both, the standalone design and a version wrapped with a PCIe interface, and compare them to the state-of-the-art software implementations of Picnic and similar hardware designs. Concretely, signing messages on our FPGA takes 0.25 ms for the L1 security level and 1.24 ms for the L5 security level, beating existing optimized software implementations by a factor of 4.