Francesco Bruschi, Tommaso Paulon, Vincenzo Rana, Donatella Sciuto
If on one hand the possibility of using pseudonymous identities is an important feature of blockchains and smart contracts, on the other hand official identity can be required in some applications to comply with regulations such as Know Your Customer and Anti Money Laundering. These regulatory compliance issues are usually dealt with either through âcusto-dialâ approaches, which however neutralize the decentralization of these systems, or with âwhitelistingâ mechanisms, that present critical issues with regard to privacy. In this paper we propose a protocol that allows only potentially identifiable users to use a given decentralized applications. The system ensures that users are identifiable only by a competent authority, under certain conditions, and that in any other case they remain pseudonyms. To evaluate performance and costs, we present an Ethereum implementation of the protocol.
Abstract The Bitcoin P2P network currently represents a reference benchmark for modern cryptocurrencies. Its underlying protocol defines how transactions and blocks are distributed through all participating nodes. To protect user privacy, the identity of the node originating a message is kept hidden. However, an adversary observing the whole network can analyze the spread pattern of a transaction to trace it back to its source. This is possible thanks to the so-called rumor centrality , which is caused by the symmetry in the spreading of gossip -like protocols. Recent works try to address this issue by breaking the symmetry of the Diffusion protocol, currently used in Bitcoin, and leveraging proxied broadcast. Nonetheless, the complexity of their design can be a barrier to their adoption in real life. In this work, we propose Clover, a novel transaction relay protocol that protects the source of transaction messages with a simple, yet effective, design. Compared to previous solutions, our protocol does not require building propagation graphs, and reduces the ability of the adversary to gain precision by opening multiple connections towards the same node. Experimental results show that the deanonymization accuracy of an eavesdropper adversary against Clover is up to 10 times smaller compared to Diffusion.
Ethereum is the second-largest cryptocurrency, which is an open-source public blockchain platform with smart contract functionality. With the increasing popularity of Ethereum, considerable attention has been paid to its privacy and anonymity. Previous work in Ethereum deanonymization mostly focused on the analysis of its transaction graph and user behaviors. In this paper, for the first time we explored the feasibility of deanonymizing Ethereum users based on P2P network analysis. By measurement and analysis, we observed that the attacker can make connections with approximately 90% mainnet synced full nodes. Based on the well-connected supernode, the deanonymization experiments with basic estimators preliminarily indicate that the anonymity of Ethereum P2P network is pretty limited. To further improve the effect of deanonymization, we implemented and evaluated a machine learning based estimator, which reduces the influence of network delay on deanonymization and thus increases the success rate to 88%. At last, we provide the discussion about the anonymity and efficiency of the propagation mechanisms.
Online voting is a trend that is gaining momentum in modern society. It has great potential to decrease organizational costs and increase voter turnout. It eliminates the need to print ballot papers or open polling stations-voters can vote from wherever there is an Internet connection. Despite these benefits, online voting solutions are viewed with a great deal of caution because they introduce new threats. A single vulnerability can lead to large-scale manipulations of votes. Electronic voting systems must be legitimate, accurate, safe, and convenient when used for elections. Nonetheless, adoption may be limited by potential problems associated with electronic voting systems. Blockchain technology came into the ground to overcome these issues and offers decentralized nodes for electronic voting and is used to produce electronic voting systems mainly because of their end-to-end verification advantages. This technology is a beautiful replacement for traditional electronic voting solutions with distributed, non-repudiation, and security protection characteristics. The following article gives an overview of electronic voting systems based on blockchain technology. The main goal of this analysis was to examine the current status of blockchain-based voting research and online voting systems and any related difficulties to predict future developments. This study provides a conceptual description of the intended blockchain-based electronic voting application and an introduction to the fundamental structure and characteristics of the blockchain in connection to electronic voting. As a consequence of this study, it was discovered that blockchain systems may help solve some of the issues that now plague election systems. On the other hand, the most often mentioned issues in blockchain applications are privacy protection and transaction speed. For a sustainable blockchain-based electronic voting system, the security of remote participation must be viable, and for scalability, transaction speed must be addressed. Due to these concerns, it was determined that the existing frameworks need to be improved to be utilized in voting systems.
Open access
Blockchain Technology Applications and Security
Internet Traffic Analysis and Secure E-voting
Advanced Steganography and Watermarking Techniques
We propose a definition of ballot secrecy as an indistinguishability game in the computational model of cryptography. Our definition improves upon earlier definitions to ensure ballot secrecy is preserved in the presence of an adversary that controls ballot collection. We also propose a definition of ballot independence as an adaptation of an indistinguishability game for asymmetric encryption. We prove relations between our definitions. In particular, we prove ballot independence is sufficient for ballot secrecy in voting systems with zero-knowledge tallying proofs. Moreover, we prove that building systems from non-malleable asymmetric encryption schemes suffices for ballot secrecy, thereby eliminating the expense of ballot-secrecy proofs for a class of encryption-based voting systems. We demonstrate applicability of our results by analysing the Helios voting system and its mixnet variant. Our analysis reveals that Helios does not satisfy ballot secrecy in the presence of an adversary that controls ballot collection. The vulnerability cannot be detected by earlier definitions of ballot secrecy, because they do not consider such adversaries. We adopt non-malleable ballots as a fix and prove that the fixed system satisfies ballot secrecy.
Blockchain system is the novel decentralized trustworthy network and it is widely used for the digital asset management. In the bitcoin-like blockchain systems, the transactions are finished via the cryptography scripts. The user's public key hash code and address information are recorded in a locking script, and posted on the blockchain for verification. By analyzing all transaction records of an address, we can obtain the transaction behaviors of the address, including transaction frequency, number of transactions, and typical address for long-term usage. Sometimes, user privacy will be impacted according to the above analysis. To solve the problem, this paper proposes an anonymous hidden transaction model of the blockchain systems through modifying the original blockchain transaction script. In the proposed multi-layer model, the blockchain transaction system is divided into three layers. For top to bottom, they are shell account (under the public address) layer, hidden account (under the private address) layer and the user layer respectively. The hidden accounts can map to different shell account to complete the transactions. We combine the zero-knowledge proof mechanism so that the finished transaction can be verified by any user. The theoretical analysis shows that our proposed method can effectively protect transaction user information and realize truly anonymous transactions.
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
For a citizen, voting is the fundamental tool to bring change in the country for good governance, through electing suitable candidates or a party to give them the power to govern. There are many forms of elections be it in the democratic or monarch systems. Each way, the vote has the power to elect the next peopleâs representatives. For a long time, paper-based voting was the only system being used globally for years; after the dot-com bubble, many countries emerged with electronic voting. But the problems such as security, transparency, and integrity of elections and the voting process are still under question. The issue with paper-based voting was accessibility, voter turns around and tallies, electronic voting has its own advantages and disadvantages such as a single point of failure, trustful systems, and loopholes to forge the electronic voting systems to alter the outcomes. To solve the problems related to the electronic voting process security, integrity, and transparency, an advanced approach is required to adopt. With the advancement of technologies, 4th industry revolution technologies give us Blockchain, Distributed Ledger and Smart Contract types of technologies which may be beneficial to solve the current problems in electronic voting systems. In this paper, we proposed a research-based case study to implement Decentralized Electronic Voting using Smart Contracts (DEV-SC) to solve security, transparency, and integrity-related problems available in the electronic voting process. This will ensure and enhance the voting process easily, trustable, and verifiable.
Caciano dos Santos Machado, Renan R. S. dos Santos, Carla Merkle Westphall
Community networks are prone to free-riders, i.e., participants who take advantage of cooperation from others' routers but do not contribute reciprocally. In this paper, we present HARPIA, a system for credit-based incentive mechanisms for data forwarding in community networks aimed to prevent selfish behavior. HARPIA does not require a trusted third-party or tamper-resistant security modules as in other incentive mechanisms. Instead, it uses a distributed accounting scheme (DPIFA) to estimate the balance of data forwarding contribution and consumption of each network router and settle correspondent cryptocurrency debts on an Ethereum smart contract. On-chain settlement transactions are performed every HARPIA cycle (e.g., daily, weekly, monthly) and must be validated by at least m-of-n network routers using a multi-signature scheme (MuSig). We also realized a performance evaluation, security threat assessment, and cryptocurrency costs estimation. Results show that our proposal is suitable for community networks with up to 64 infrastructure routers under specific m-of-n MuSig thresholds.
Blockchain technology innovatively removes the need for intermediaries and establishes a trust-less trust system by peer-to-peer networks and distributed ledger technology. It is still difficult to clarify the specific degree of decentralization of blockchain even though the decentralized characteristic of the system is derived from this system structure. Namely, the criteria for determining whether decentralized are not well established and do not reflect the real world well. So we propose two approaches to measure the degree of decentralization of blockchain system that currently exists: Censorship resistance and geographical diversity. This paper outlines the meaning of each decentralization quotient and explains how those indices can be applied in respect of the user protection.
Gongxian Zeng, Meiqi He, Siu Ming Yiu, Zhengan Huang
Abstract Electronic voting (e-voting) has been studied for many years. Recently, researchers find that blockchain can provide an alternative secure platform for e-voting systems, because of its properties of tamper resistance and transparency. However, existing blockchain-based schemes either require central authorities to tally ballots or can only handle a limited number of voters. This paper tries to propose a self-tallying e-voting system, i.e. the public can verify the validity of all ballots and tally the ballots without a centralized authority. To achieve this goal, we solve two challenges, namely how to cancel out all random numbers used for ballots and to prove the validity of ballots using a non-interactive zero knowledge proof. Our scheme is proved to be secure and shown to be practical by experiments.
Even with all the advances we have seen in secure digital technology, the most secure way to currently cast a vote on election day consist of a hand-marked paper ballot. When extenuating circumstances arise, offering a voting environment that is accessible and safe for everyone, but also secure can be a difficult task under the current voting system. This paper discusses one proposed electronic voting system which uses blockchain technology. Based on a review of literature on blockchain technology and specific implementations of voting systems, a summary of relevant background information as well as implementation protocol are provided. Even though experts believe that societies are not currently ready to implement systems like the one described in this paper, the technology to create a secure and efficient system does exist, and could one day become available.
Open access
Blockchain Technology Applications and Security
Internet Traffic Analysis and Secure E-voting
Advanced Steganography and Watermarking Techniques
The Internet of things (IoT) is an active, real-world area in need of more investigation. One of the top weaknesses in security challenges that IoTs face, the centralized access control server, which can be a single point of failure. In this paper, Dynamic-IoTrust, a decentralized access control smart contract based aims to overcome distrusted, dynamic, trust and authentication issues for access control in IoT. It also integrates dynamic trust value to evaluate users based on behavior. In particular, the Dynamic-IoTrust contains multiple Main Smart Contract, one Register Contract, and one Judging Contract to achieve efficient distributed access control management. Dynamic-IoTrust provides both static access rights by allowing predefined access control policies and also provides dynamic access rights by checking the trust value and the behavior of the user. The system also provides to detected user misbehavior and make a decision for user trust value and penalty. There are several levels of trusted users to access the IoTs device. Finally, the case study demonstrates the feasibility of the Dynamic-IoTrust model to offer a dynamic decentralized access control system with trust value attribute to evaluate the internal user used IoTs devices.
E-commerce platforms incorporate reputation systems that allow customers to rate suppliers following financial transactions. Existing reputation systems cannot defend the centralized server against arbitrarily tampering with the supplierâs reputation. Furthermore, they do not offer reputation access across platforms. Rates are faced with privacy leakages because rating activities are correlated with privacy (e.g., identity and rating). Meanwhile, raters could be malicious and initiate multiple rating attacks and abnormal rating attacks. Determining how to address these issues have both research and practical value. In this paper, we propose a blockchain-based privacy-preserving reputation system for e-commerce platforms named RepChain; our system allows cross-platform reputation access and anonymous and private ratings. Using RepChain, all e-commerce platforms collaborate and share usersâ reputations by co-constructing a consortium blockchain and modeling the rating process as a finite state machine. In particular, we facilitate one-show anonymous credentials constructed from two-move blind signatures to protect customersâ identities and resist multiple rating attacks, leverage zero-knowledge range proof to verify the correctness of ratings and defend against abnormal rating attacks, design a secure sum computation protocol among nodes to update reputations, and verify ratings via batch processing and consensus hashes. Finally, we demonstrate the security and privacy of RepChain via a formal analysis and evaluate its performance based on Ethereum test network.
IoT group communication allows users to control multiple IoT devices simultaneously. A convenient method for implementing this communication paradigm is by leveraging software-defined networking (SDN) and allowing IoT endpoints to âadvertiseâ the resources that can be accessed through group communication. In this paper, we propose a solution for securing this process by preventing IoT endpoints from advertising âfakeâ resources. We consider group communication using the constrained application protocol (CoAP), and we leverage Web of Things (WoT) Thing Description (TD) to enable resourcesâ advertisement. In order to achieve our goal, we are using linked-data proofs. Additionally, we evaluate the application of zero-knowledge proofs (ZKPs) for hiding certain properties of a WoT-TD file.
Smart cities use the Internet of Things (IoT) devices such as connected sensors, lights, and meters to collect and analyze data to improve infrastructure, public utilities, and services. However, the true potential of smart cities cannot be leveraged without addressing many security concerns. In particular, there is a significant challenge for provisioning a reliable access control solution to share IoT data among various users across organizations. We present a novel entitlement-based blockchain-enabled access control architecture that can be used for smart cities (and for any ap-plication domains that require large-scale IoT deployments). Our proposed entitlement-based access control model is flexible as it facilitates a resource owner to safely delegate access rights to any entities beyond the trust boundary of an organization. The detailed design and implementation on Ethereum blockchain along with a qualitative evaluation of the security and access control aspects of the proposed scheme are presented in the paper. The experimental results from private Ethereum test networks demonstrate that our proposal can be easily implemented with low latency. This validates that our proposal is applicable to use in the real world IoT environments.
Blockchain is a distributed and secure database that can be applied to all types of transactions. Blockchain technology is growing in popularity because it allows for the development of applications whose information is traceable, immutable, transparent and reliable. Given the advantages that blockchain provides over other traditional systems, in this paper we present a decentralized application, called RectorDApp, for the management of university rector voting in a private, but transparent and immutable way, being able to verify publicly and in real time the election results. RectorDApp, capable of interacting with the Ethereum public blockchain network, was developed using the Truffle framework and the MetaMask software. The results demonstrate that RectorDApp is a highly useful application to address the digital transformation of university rector elections.
Although nearly all information regarding smart contract addresses is shared via websites, emails, or other forms of digital communication, blockchains and distributed ledger technologies are unable to establish secure bindings between web sites and the corresponding smart contracts. A user cannot differentiate between a website link to a legitimate smart contract set up by a reputable business owner and that to an illicit contract aiming to defraud the user. Surprisingly, current attempts to resolve this issue are based mostly on information redundancy, e.g., displaying contract addresses multiple times in varying forms of images and text. These verification processes are burdensome because the user is responsible for verifying the accuracy of an address. More importantly, these measures do not address the core problem because the contract itself does not contain information on its authenticity. To resolve such limitations and to increase security, we propose a solution that leverages publicly issued Transport Layer Security (TLS)/Secure Sockets Layer (SSL) certificates of Fully-Qualified Domain Names (FQDN) to ensure the authenticity of smart contracts and their owners. Our approach combines on-chain endorsement storage that utilizes signatures from the respective certificate and off-chain authentication of the smart contract. The system is open and transparent because the only requirement for usage is ownership of a TLS/SSL certificate. Further, moderate deployment and maintenance costs, a widely accepted public key infrastructure, and a simple interface enable TLS/SSL endorsed smart contracts (TeSC) to bridge the gap between websites and smart contracts.
Blockchain-based voting, including liquid voting, has been extensively studied in recent years. However, it remains challenging to implement liquid voting on blockchain using Ethereum smart contract. The challenge comes from the gas limit, which is that the number of instructions for processing a ballot cannot exceed a certain amount. This restricts the application scenario with respect to algorithms whose time complexity is linear to the number of voters, i.e., O(n). As the blockchain technology can well share and reuse the resources, we study a model of liquid voting on blockchain and propose a fast algorithm, named Flash, to eliminate the restriction. The key idea behind our algorithm is to shift some on-chain process to off-chain. In detail, we first construct a Merkle tree off-chain which contains all voters' properties. Second, we use Merkle proof and interval tree to process each ballot with O(log n) on-chain time complexity. Theoretically, the algorithm can support up to 21000 voters with respect to the current gas limit on Ethereum. Experimentally, the result implies that the consumed gas fee remains at a very low level when the number of voters increases. This means our algorithm makes liquid voting on blockchain practical even for massive voters.