Panait, Andreea-Elena, Ruxandra F. Olimid, Alin Ştefănescu
In the last years, identity management solutions on blockchain were proposed as a possible solution to the digital identity management problem. However, they are still at an early stage and further research needs to be done to conclude whether identity systems could benefit from the use of blockchain or not. Motivated by this, we investigate identity management solutions on blockchain intending to give the reader an overview of the current status and provide a better understanding of the pros and cons of using such solutions. We conduct an analysis on ten of the most known implementations, with a focus on privacy and security aspects. Finally, we identify existing challenges and give new directions for research.
Transactions represent a fundamental component in blockchains as they are the primary means for users to change the blockchain state. Current blockchain systems such as Bitcoin and Ethereum require users to constantly observe the state changes of interest or the events taking place in a blockchain and requires the user to explicitly release the required transactions to respond to the observed events in the blockchain. This paper proposes EventWarden, a decentralized event-driven proxy service for users to outsource transactions in Ethereum-like blockchains. EventWarden employs a novel combination of smart contracts and blockchain logs. EventWarden allows a user to create a proxy smart contract that specifies an interested event and also reserves an arbitrary transaction to release. Upon observing the occurrence of the prescribed event, anyone in the Blockchain network can call the proxy contract to earn the service fee reserved in the contract by proving to the contract that the event has been recorded into blockchain logs, which then automatically triggers the proxy contract to release the reserved transaction. We show that the reserved transaction can only get released from the proxy contract when the prescribed event has taken place. We also demonstrate that as long as a single member in the Blockchain network is incentivized by the service fee to call the proxy contract after the prescribed event has taken place, the reserved transaction is guaranteed to get released. We implement EventWarden over the Ethereum official test network. The results demonstrate that EventWarden is effective and is ready-to-use in practice.
Polkadot is a decentralized blockchain platform to be launched in 2020. It will implement nominated proof-of-stake (NPoS), a proof-of-stake based mechanism where k nodes are selected by the network as validators to participate in the consensus protocol, according to the preferences expressed by token holders who take the role of nominators. This setup leads to an approval-based multi-winner election problem, where each nominator submits a list of trusted candidates, and has a vote strength proportional to their stake. A solution consists of a committee of k validators, together with a fractional distribution of each nominator's vote among them. We consider two objectives, both recently studied in the literature of social choice. The first one is ensuring the property of proportional justified representation (PJR). The second objective, called maximin support, is to maximize the minimum amount of vote support assigned to any elected validator. We argue that the former objective aligns with the notion of decentralization, while the latter aligns with the security level of the consensus protocol.
We prove that the maximin support problem is constant-factor approximable, as we present several approximation algorithms for it, and prove a matching hardness result. Furthermore, we present an efficient post-computation which, when paired with an approximation algorithm for maximin support, returns a new solution that a) preserves the approximation guarantee, b) satisfies the PJR property, and c) can be efficiently verified to satisfy PJR by an untrusting third party. Besides being of independent theoretical interest, our results enable the network to run an efficient validator election protocol that simultaneously achieves the PJR property and a constant-factor approximation for maximin support, thus offering strong theoretical guarantees on decentralization and security.
Time-release cryptography is a special encryption technique that allows a message to be hidden for some time. The previous schemes have shortcomings in that the encryptor should predict the decryptor’s computing power precisely or the trusted agent should be always available. In this paper, we propose a new, practical time-release blockchain, and find the key to decrypt the content after a certain time. In order to verify the effectiveness of the blockchain system automatically, which uses the proof-of-work (PoW) and the consensus algorithm in the the proposed technique, we have implemented a prototype version of our blockchain system using Python. The proposed method has the following advantages. First, the decryption time is automatically adjusted, even if the miner’s computing power changes over time. Second, unlike previous time-lock puzzle schemes, our algorithm does not require additional computation work for solving the puzzle. Third, our scheme does not need any trusted agents (third parties). Fourth, the proposed method uses standard cryptographic algorithms.
Open access
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
The performance of existing permissionless smart contract platforms such as Ethereum is limited by the consensus layer. Prism is a new proof-of-work consensus protocol that provably achieves throughput and latency up to physical limits while retaining the strong guarantees of the longest chain protocol. This paper reports experimental results from implementations of two smart contract virtual machines, EVM and MoveVM, on top of Prism and demonstrates that the consensus bottleneck has been removed. Code can be found at https://github.com/wgr523/prism-smart-contracts.
Monero provides a high level of anonymity for both users and their transactions. However, many criminal activities might be committed with the protection of anonymity in cryptocurrency transactions. Thus, user accountability (or traceability) is also important in Monero transactions, which is unfortunately lacking in the current literature. In this paper, we fill this gap by introducing a new cryptocurrency named Traceable Monero to balance the user anonymity and accountability. Our framework relies on a tracing authority, but is optimistic, in that it is only involved when investigations in certain transactions are required. We formalize the system model and security model of Traceable Monero. We present a detailed construction of Traceable Monero by overlaying Monero with two types of tracing mechanisms, tracing the one-time addresses with money flows and tracing the long-term addresses. We prove the security of Traceable Monero and implement a prototype of the system, which demonstrates that Traceable Monero incurs merely a very small overhead in generating and verifying a transaction compared to Monero transactions.
Resource constraints have prevented comprehensive cryptography and multifactor authentication in numerous Internet of Things (IoT) connectivity scenarios. Existing IoT systems generally adopt lightweight security protocols that lead to compromise and privacy leakage. Edge computing enables better access control and privacy protection, furthermore, blockchain architecture has achieved a trusted store of value by open-source and distributed consensus mechanisms. To embrace these new paradigms, we propose a scheme that employs one-time association multitasking proofs for peer to local authentication (OTMP-P2L). The scheme chooses relevant nondeterministic polynomial (NP) problem tasks, and manages localized trust and anonymity by using smart devices such as phones and pads, thereby enabling IoT devices to autonomously perform consensus validation with an enhanced message authentication code. This nested code is a one-time zero-knowledge proof that comprises multiple logic verification arguments. To increase diversity and reduce the workload of each one, these arguments are chained by a method that establishes some of the inputs of the following task from the output of previous tasks. We implemented a smart lock system and confirmed that the scheme outperforms IoT authentication methods. The result demonstrates superior flexibility through dynamic difficulty strategies and succinct non-interactive peer-to-peer (P2P) verification.
Michał Król, Alberto Sonnino, Argyrios G. Tasiopoulos, Ioannis Psaras · 5 authors
Decentralised cloud computing platforms enable individuals to offer and rent resources in a peer-to-peer fashion. They must assign resources from multiple sellers to multiple buyers and derive prices that match the interests and capacities of both parties. The assignment process must be decentralised, fair and transparent, but also protect the privacy of buyers. We present PASTRAMI, a decentralised platform enabling trustworthy assignments of items and prices between a large number of sellers and bidders, through the support of multi-item auctions. PASTRAMI uses threshold blind signatures and commitment schemes to provide strong privacy guarantees while making bidders accountable. It leverages the Ethereum blockchain for auditability, combining efficient off-chain computations with novel, on-chain proofs of misbehaviour. Our evaluation of PASTRAMI using Filecoin workloads show its ability to efficiently produce trustworthy assignments between thousands of buyers and sellers.
In recent years blockchain technology has become mainstream research topic because of its decentralized, peer to peer transaction and anonymity properties. There are several applications of blockchain which are secure and easy as compare to the current techniques. One of the applications is a smart contract. Smart contracts are lines of code which are stored on a blockchain and automatically executed when the conditions defined by the it (developer) are met. This smart contract with the addition of blockchain technology can do task fast and with high security. In this paper we have developed a smart contract for a generalized notary application on solidity, Ethereum and the application is tested using the truffle suite. Furthermore, applications and their methodology for notary applications are also mentioned.
Muhammed Siraj, Mohd Izuan Hafez Ninggal, Nur Izura Udzir, Muhammad Daniel Hafiz Abdullah · 5 authors
Sensitive records stored in the cloud such as healthcare records, private conversation and credit card information are targets of hackers and privacy abuse. Current information and record management systems have difficulties achieving privacy protection of such sensitive records in a secure, transparent, decentralized and trustless environment. The Blockchain technology is a nascent and a promising technology that facilitates data sharing and access in a secure, decentralized and trustless environment. The technology enables the use of smart contracts that can be leveraged to complement existing traditional systems to achieve security objectives that were never possible before. In this paper, we propose a framework based on Blockchain technology to enable privacy-preservation in a secured, decentralized, transparent and trustless environment. We name our framework SmartCoAuth. It is based on Ethereum Smart Contract functions as the secure, decentralized, transparent authentication and authorization mechanism in the framework. It also enables tamper-proof auditing of access to the protected records. We analysed how SmartCoAuth could be integrated into a cloud application to provide reliable privacy-preservation among stakeholders of healthcare records stored in the cloud. The proposed framework provides a satisfactory level of data utility and privacy preservation.
Federated learning has been widely studied and applied to various scenarios, such as financial credit, medical identification, and so on. Under these settings, federated learning protects users from exposing their private data, while cooperatively training a shared machine learning algorithm model (i.e., the global model) for a variety of realworld applications. The only data exchanged is the gradient of the model or the updated model (i.e., the local model update). However, the security of federated learning is increasingly being questioned, due to the malicious clients or central servers' constant attack on the global model or user privacy data. To address these security issues, we propose a decentralized federated learning framework based on blockchain, that is, a Block-chain-based Federated Learning framework with Committee consensus (BFLC). Without a centralized server, the framework uses blockchain for the global model storage and the local model update exchange. To enable the proposed BFLC, we also devise an innovative committee consensus mechanism, which can effectively reduce the amount of consensus computing and reduce malicious attacks. We then discuss the scalability of BFLC, including theoretical security, storage optimization, and incentives. Finally, based on a FISCO blockchain system, we perform experiments using an AlexNet model on several frameworks with a real-world dataset FEMNIST. The experimental results demonstrate the effectiveness and security of the BFLC framework.
Xun Yi, Russell Paulet, Elisa Bertino, Fang-Yu Rao
In this paper we consider the problem where a client wishes to subscribe to some product or service provided by a server, but maintain their anonymity. At the same time, the server must be able to authenticate the client as a genuine user and be able to discontinue (or revoke) the client's access if the subscription fees are not paid. Current solutions for this problem are typically constructed using some combination of blind signature or zero-knowledge proof techniques, which do not directly support client revocation (that is, revoking a user before expiry of their secret value). In this paper, we present a solution for this problem on the basis of the broadcast encryption scheme, suggested by Boneh et al., by which the server can broadcast a secret to a group of legitimate clients. Our solution allows the registered client to log into the server anonymously and also supports client revocation by the server. Our solution can be used in many applications, such as location-based queries. We formally define a model for our anonymous subscription protocol and prove the security of our solution under this model. In addition, we present experimental results from an implementation of our protocol. These experimental results demonstrate that our protocol is practical.
Duc V. Le, Lizzy Tengana Hurtado, Adil M. Ahmad, Mohsen Minaei · 6 authors
Abstract The Bitcoin network has offered a new way of securely performing financial transactions over the insecure network. Nevertheless, this ability comes with the cost of storing a large (distributed) ledger, which has become unsuitable for personal devices of any kind. Although the simplified payment verification (SPV) clients can address this storage issue, a Bitcoin SPV client has to rely on other Bitcoin nodes to obtain its transaction history and the current approaches offer no privacy guarantees to the SPV clients. This work presents T 3 , a trusted hardware-secured Bitcoin full client that supports efficient oblivious search/update for Bitcoin SPV clients without sacrificing the privacy of the clients. In this design, we leverage the trusted execution and attestation capabilities of a trusted execution environment (TEE) and the ability to hide access patterns of oblivious random access machine (ORAM) to protect SPV clients’ requests from potentially malicious nodes. The key novelty of T 3 lies in the optimizations introduced to conventional ORAM, tailored for expected SPV client usages. In particular, by making a natural assumption about the access patterns of SPV clients, we are able to propose a two-tree ORAM construction that overcomes the concurrency limitation associated with traditional ORAMs. We have implemented and tested our system using the current Bitcoin Unspent Transaction Output (UTXO) Set. Our experiment shows that T 3 is feasible to be deployed in practice while providing strong privacy and security guarantees to Bitcoin SPV clients.
A key communication technology in smart cities and smart buildings for automation is RFID. Proving the simultaneous presence of a group of RFID-tagged objects is a practical need in many application areas within this domain. Some examples of this include vehicle fleets, smart parking, safety in public places (smart cities), security and access control (smart buildings), and asset location (supply chain system, health care industry). Security, privacy, and efficiency are central issues when designing such a grouping-proof protocol. This work is motivated by Sundaresan et al.'s grouping-proof protocol, which applies zero-knowledge techniques. In this paper, we propose a lightweight, offline, serial-dependency grouping-proof protocol. Compared to existing grouping-proof protocols, our scheme improves on efficiency, scalability, security, and communication cost. It resists well-known attacks on grouping-proofs including tag/reader impersonation, tracking, replay, desynchronization, and message integrity.
Holger Kinkelin, Richard von Seck, Christoph Rudolf, Georg Carle
The security of cryptographic communication protocols that use X.509 certificates depends on the correctness of those certificates. This paper proposes a system that helps to ensure the correct operation of an X.509 certification authority and its registration authorities. We achieve this goal by enforcing a policy-defined, multi-party validation and authorization workflow of certificate signing requests. Besides, our system offers full accountability for this workflow for forensic purposes. As a foundation for our implementation, we leverage the distributed ledger and smart contract framework Hyperledger Fabric. Our implementation inherits the strong tamper-resistance of Fabric which strengthens the integrity of the computer processes that enforce the validation and authorization of the certificate signing request, and of the metadata collected during certificate issuance.
In the modern financial sector, interest in providing financial services that employ blockchain technology has increased. Blockchain technology is efficient and can operate without a trusted party to store all transaction information; additionally, it provides transparency and prevents the tampering of transaction information. However, new security threats can occur because blockchain technology shares all the transaction information. Furthermore, studies have reported that the private keys of users who use the same signature value two or more times can be recovered. Because private keys of blockchain identify users, private key leaks can result in attackers stealing the ownership rights to users' property. Therefore, as more financial services use blockchain technology, actions to counteract the threat of private key recovery must be continually investigated. Private key recovery studies are presented here. Based on these studies, duplicated signatures generated by blockchain users are defined. Additionally, scenarios that generate and use duplicated signatures are applied in an actual bitcoin environment to demonstrate that actual bitcoin users' private keys can be recovered.
Institut Teknologi Bandung Bandung, Indonesia, Intan Muchtadi-Alamsyah, Muhammad Thufaili Imdad, Institut Teknologi Bandung Bandung, Indonesia · 6 authors
The Transport Layer Security (TLS) protocol and its public-key infrastructure (PKI) are widely used in the Internet to achieve secure communication. Validating domain ownership by trusted certification authorities (CAs) is a critical step in issuing digital certificates, but unfortunately, this process provides a poor security level. In this work, we present SmartCert, a novel approach based on smart contracts to improve digital certificates. A certificate in SmartCert conveys detailed information about its validation state which is constantly changing but only with respect to the specified smart contract code and individual domain policies. CAs issuing and updating certificates are kept accountable and their actions are transparent and monitored by the code. We present the implementation and evaluation of SmartCert, and discuss its deployability.
Lei Xu, Lin Chen, Zhimin Gao, Keshav Kasichainula · 7 authors
Bitcoin introduces a new type of cryptocurrency that does not rely on a central system to maintain transactions. Inspired by the success of Bitcoin, all types of alt cryptocurrencies were invented in recent years. Some of the new cryptocurrencies focus on privacy enhancement, where transaction information such as value and sender/receiver identity can be hidden, such as Zcash and Monero. However, there are few schemes to support multiple types of cryptocurrencies/assets and offer privacy enhancement at the same time. The major challenge for a multiple asset system is that it needs to support two-way assets exchange between participants besides one-way asset transfer. Thus, we propose a privacy-preserving exchange scheme, PrivateEx, which preserves the privacy of the exchange of different assets. PrivateEx utilizes zero-knowledge proof and a novel way to "lock" assets involved in the exchange to guarantee the correctness, fairness, and privacy of exchange of assets in the system. We also implement a prototype of PrivateEx and evaluate its performance to show that it is practical with modern computers.
Vincent Reniers, Yuan Gao, Ren Zhang, Paolo Viviani · 11 authors
Our main use case features multiple companies that iteratively optimize on the architectural properties of aircraft components in a decentralized manner. In each optimization step of the so-called multi-disciplinary optimization (MDO) process, sensitive data is exchanged between organizations, and we require auditability and traceability of actions taken to assure compliance with signed legal agreements.
Payment channel networks, and the Lightning Network in particular, seem to offer a solution to the lack of scalability and privacy offered by Bitcoin and other blockchain-based cryptocurrencies. Previous research has focused on the scalability, availability, and crypto-economics of the Lightning Network, but relatively little attention has been paid to exploring the level of privacy it achieves in practice. This paper presents a thorough analysis of the privacy offered by the Lightning Network, by presenting several attacks that exploit publicly available information about the network in order to learn information that is designed to be kept secret, such as how many coins a node has available or who the sender and recipient are in a payment routed through the network.
Yuta Nakamura, Yuanyu Zhang, Masahiro Sasabe, Shoji Kasahara
Due to the rapid penetration of the Internet of Things (IoT) into human life, illegal access to IoT resources (e.g., data and actuators) has greatly threatened our safety. Access control, which specifies who (i.e., subjects) can access what resources (i.e., objects) under what conditions, has been recognized as an effective solution to address this issue. To cope with the distributed and trust-less nature of IoT systems, we propose a decentralized and trustworthy Capability-Based Access Control (CapBAC) scheme by using the Ethereum smart contract technology. In this scheme, a smart contract is created for each object to store and manage the capability tokens (i.e., data structures recording granted access rights) assigned to the related subjects, and also to verify the ownership and validity of the tokens for access control. Different from previous schemes which manage the tokens in units of subjects, i.e., one token per subject, our scheme manages the tokens in units of access rights or actions, i.e., one token per action. Such novel management achieves more fine-grained and flexible capability delegation and also ensures the consistency between the delegation information and the information stored in the tokens. We implemented the proposed CapBAC scheme in a locally constructed Ethereum blockchain network to demonstrate its feasibility. In addition, we measured the monetary cost of our scheme in terms of gas consumption to compare our scheme with the existing Blockchain-Enabled Decentralized Capability-Based Access Control (BlendCAC) scheme proposed by other researchers. The experimental results show that the proposed scheme outperforms the BlendCAC scheme in terms of the flexibility, granularity, and consistency of capability delegation at almost the same monetary cost.
With the rapid popularity of blockchain, decentralized human intelligence tasks (HITs) are proposed to crowdsource human knowledge without relying on vulnerable third-party platforms. However, the inherent limits of blockchain cause decentralized HITs to face a few "new" challenges. For example, the confidentiality of solicited data turns out to be the sine qua non, though it was an arguably dispensable property in the centralized setting. To ensure the "new" requirement of data privacy, existing decentralized HITs use generic zero-knowledge proof frameworks (e.g. SNARK), but scarcely perform well in practice, due to the inherently expensive cost of generality. We present a practical decentralized protocol for HITs, which also achieves the fairness between requesters and workers. At the core of our contributions, we avoid the powerful yet highly-costly generic zk-proof tools and propose a special-purpose scheme to prove the quality of encrypted data. By various non-trivial statement reformations, proving the quality of encrypted data is reduced to efficient verifiable decryption, thus making decentralized HITs practical. Along the way, we rigorously define the ideal functionality of decentralized HITs and then prove the security due to the ideal-real paradigm. We further instantiate our protocol to implement a system called Dragoon, an instance of which is deployed atop Ethereum to facilitate an image annotation task used by ImageNet. Our evaluations demonstrate its practicality: the on-chain handling cost of Dragoon is even less than the handling fee of Amazon's Mechanical Turk for the same ImageNet HIT.
Soteria is a user right management system designed to safeguard user-data privacy in a transparent and provable manner in compliance to regulations such as GDPR and CCPA. Soteria represents user data rights as formal executable sharing agreements, which can automatically be translated into a human readable form and enforced as data are queried. To support revocation and to prove compliance, an indelible, audited trail of the hash of data access and sharing agreements are stored on a two-layer distributed ledger. The main chain ensures partition tolerance and availability (PA) properties while side chains ensure consistency and availability (CA), thus providing the three properties of the CAP (consistency, availability, and partition tolerance) theorem. Besides depicting the two-layer architecture of Soteria, this paper evaluates representative consensus protocols and recommends side-chain and inter-chain management strategies for improving latency and throughput.