The Transport Layer Security (TLS) protocol is a de facto standard of secure client-server communication on the Internet. Its security can be diminished by a variety of attacks that leverage on weaknesses in its design and implementations. An example of a major weakness is the public-key infrastructure (PKI) that TLS deploys, which is a weakest-link system and introduces hundreds of links (i.e., trusted entities). Consequently, an adversary compromising a single trusted entity can impersonate any website. Notary systems, based on multi-path probing, were early and promising proposals to detect and prevent such attacks. Unfortunately, despite their benefits, they are not widely deployed, mainly due to their long-standing unresolved problems. In this paper, we present Persistent and Accountable Domain Validation (PADVA), which is a next-generation TLS notary service. PADVA combines the advantages of previous proposals, enhancing them, introducing novel mechanisms, and leveraging a blockchain platform which provides new features. PADVA keeps notaries auditable and accountable, introduces service-level agreements and mechanisms to enforce them, relaxes availability requirements for notaries, and works with the legacy TLS ecosystem. We implemented and evaluated PADVA, and our experiments indicate its efficiency and deployability.
Alexander Yakubov, Wazen M. Shbair, Anders Wallbom, David Sanda · 5 authors
Public-Key Infrastructure (PKI) is the cornerstone technology that facilitates secure information exchange over the Internet. However, PKI is exposed to risks due to potential failures of Certificate Authorities (CAs) that may be used to issue unauthorized certificates for end-users. Many recent breaches show that if a CA is compromised, the security of the corresponding end-users will be in risk. As an emerging solution, Blockchain technology potentially resolves the problems of traditional PKI systems - in particular, elimination of single point-of-failure and rapid reaction to CAs shortcomings. Blockchain has the ability to store and manage digital certificates within a public and immutable ledger, resulting in a fully traceable history log. In this paper we designed and developed a blockchain-based PKI management framework for issuing, validating and revoking X.509 certificates. Evaluation and experimental results confirm that the proposed framework provides more reliable and robust PKI systems with modest maintenance costs.
In the second decade of the 21st century, blockchain definitely became one of the most trending computational technologies. This research aims to question the feasibility and suitability of using blockchain technology within e-voting systems, regarding both technical and non-technical aspects. In today's world, although the course of this spreading is considerably slow, several countries already use means of e-voting due to many social and economic reasons, which we further investigated. Nevertheless, the number of countries offering various e-government solutions, apart from e-voting, is significantly high. E-voting systems, naturally, require much more attention and assurance regarding potential security and anonymity issues, since voting is one of the few extremely critical governmental processes. Nevertheless, e-voting is not purely a governmental service, but many companies and nonprofit organizations would benefit the cost-efficiency, scalability, remote accessibility, and ease of use that it provides. Blockchain technology is claimed to be able to address some, obviously not all, important security concerns, including anonymity, confidentiality, integrity, and non-repudiation. The analysis results presented in this article mostly confirm these claims.
Bitcoin provides freshness properties by forming a blockchain where each block is associated with its timestamp and the previous block. Due to these properties, the Bitcoin protocol is being used as a decentralized, trusted, and secure timestamping service. Although Bitcoin participants which create new blocks cannot modify their order, they can manipulate timestamps almost undetected. This undermines the Bitcoin protocol as a reliable timestamping service. In particular, a newcomer that synchronizes the entire blockchain has a little guarantee about timestamps of all blocks. In this paper, we present a simple yet powerful mechanism that increases the reliability of Bitcoin timestamps. Our protocol can provide evidence that a block was created within a certain time range. The protocol is efficient, backward compatible, and surprisingly, currently deployed SSL/TLS servers can act as reference time sources. The protocol has many applications and can be used for detecting various attacks against the Bitcoin protocol.
Bitcoin provides freshness properties by forming a blockchain where each block is associated with its timestamp and the previous block. Due to these properties, the Bitcoin protocol is being used as a decentralized, trusted, and secure timestamping service. Although Bitcoin participants which create new blocks cannot modify their order, they can manipulate timestamps almost undetected. This undermines the Bitcoin protocol as a reliable timestamping service. In particular, a newcomer that synchronizes the entire blockchain has a little guarantee about timestamps of all blocks.
In this paper, we present a simple yet powerful mechanism that increases the reliability of Bitcoin timestamps. Our protocol can provide evidence that a block was created within a certain time range. The protocol is efficient, backward compatible, and surprisingly, currently deployed SSL/TLS servers can act as reference time sources. The protocol has many applications and can be used for detecting various attacks against the Bitcoin protocol.
Recently, there has been a growing interest in using online technologies to design protocols for secure electronic voting. The main challenges include vote privacy and anonymity, ballot irrevocability and transparency throughout the vote counting process. The introduction of the blockchain as a basis for cryptocurrency protocols, provides for the exploitation of the immutability and transparency properties of these distributed ledgers. In this paper, we discuss possible uses of the blockchain technology to implement a secure and fair voting system. In particular, we introduce a secret share-based voting system on the blockchain, the so-called SHARVOT protocol. Our solution uses Shamir's Secret Sharing to enable on-chain, i.e. within the transactions script, votes submission and winning candidate determination. The protocol is also using a shuffling technique, Circle Shuffle, to de-link voters from their submissions.
We design and implement the first private and anonymous decentralized crowdsourcing system ZebraLancer, and overcome two fundamental challenges of decentralizing crowdsourcing, i.e., data leakage and identity breach. First, our outsource-then-prove methodology resolves the tension between the blockchain transparency and the data confidentiality to guarantee the basic utilities/fairness requirements of data crowdsourcing, thus ensuring: (i) a requester will not pay more than what data deserve, according to a policy announced when her task is published via the blockchain; (ii) each worker indeed gets a payment based on the policy, if he submits data to the blockchain; (iii) the above properties are realized not only without a central arbiter, but also without leaking the data to the open blockchain. Second, the transparency of blockchain allows one to infer private information about workers and requesters through their participation history. Simply enabling anonymity is seemingly attempting but will allow malicious workers to submit multiple times to reap rewards. ZebraLancer also overcomes this problem by allowing anonymous requests/submissions without sacrificing accountability. The idea behind is a subtle linkability: if a worker submits twice to a task, anyone can link the submissions, or else he stays anonymous and unlinkable across tasks. To realize this delicate linkability, we put forward a novel cryptographic concept, i.e., the common-prefix-linkable anonymous authentication. We remark the new anonymous authentication scheme might be of independent interest. Finally, we implement our protocol for a common image annotation task and deploy it in a test net of Ethereum. The experiment results show the applicability of our protocol atop the existing real-world blockchain.
In this work, we propose a novel approach, called Conflicts Check Protocol (CCP), which enables preventing potential attacks on bitcoin system. Based on the observation and discovery of a common symptom that many attacks may generate, an arbitration mechanism is proposed to determine the approval or abandon of certain transactions involved in confliction. Experimental results verified our statistical assumption and proved that the CCP is robust in handling many transactions in confliction scenarios and can significantly enhance the security of the current bitcoin systems. Unlike many of the existing efforts, this work examines the security issue of bitcoin from a new perspective, which can be extended further to a much larger scope of attack analysis and prevention.
Since 2004, different research was handling the challenges in the centralized voting systems, e-voting protocols and recently the decentralized voting. So electronic voting puts forward some difficulties regarding the voter anonymity, the secure casting of the votes and to prevent the voting process from frauding. The Decentralized property of the technology called "blockchain" could have the solution for many of the challenges in voting research area and brings a new secure mechanism of safe and transparent voting. In this paper, a broad comparison between ongoing voting systems has studied by analyzing their structure and the drawbacks that should consider in future to improve the whole election process from keeping the privacy of the voter, casting a vote with the possibility to check if it was counted correctly to publishing the results. The result of the paper will give a new approach to extend the target of the election from small scale to large scale despite the fact of Ethereum limitation which can cast on the blockchain just five votes per minute. The primary challenge is to find an answer for this question: "How to balance between voter privacy and transparency without breaking the important rule where the voter can proof for a specific candidate that he voted for him in a bribe situation?".
Alberto Sonnino, Mustafa Al-Bassam, Shehar Bano, Sarah Meiklejohn · 5 authors
Coconut is a novel selective disclosure credential scheme supporting distributed threshold issuance, public and private attributes, re-randomization, and multiple unlinkable selective attribute revelations. Coconut integrates with blockchains to ensure confidentiality, authenticity and availability even when a subset of credential issuing authorities are malicious or offline. We implement and evaluate a generic Coconut smart contract library for Chainspace and Ethereum; and present three applications related to anonymous payments, electronic petitions, and distribution of proxies for censorship resistance. Coconut uses short and computationally efficient credentials, and our evaluation shows that most Coconut cryptographic primitives take just a few milliseconds on average, with verification taking the longest time (10 milliseconds).
This paper investigates a critical access control issue in the Internet of Things (IoT). In particular, we propose a smart contract-based framework, which consists of multiple access control contracts (ACCs), one judge contract (JC), and one register contract (RC), to achieve distributed and trustworthy access control for IoT systems. Each ACC provides one access control method for a subject-object pair, and implements both static access right validation based on predefined policies and dynamic access right validation by checking the behavior of the subject. The JC implements a misbehavior-judging method to facilitate the dynamic validation of the ACCs by receiving misbehavior reports from the ACCs, judging the misbehavior and returning the corresponding penalty. The RC registers the information of the access control and misbehavior-judging methods as well as their smart contracts, and also provides functions (e.g., register, update, and delete) to manage these methods. To demonstrate the application of the framework, we provide a case study in an IoT system with one desktop computer, one laptop and two Raspberry Pi single-board computers, where the ACCs, JC, and RC are implemented based on the Ethereum smart contract platform to achieve the access control.
As we observe a trend towards the recentralisation of the Internet, this paper raises the question of guaranteeing an everlasting decentralisation. We introduce the properties of strong and soft uncentralisability in order to describe systems in which all authorities can be untrusted at any time without affecting the system. We link the soft uncentralisability to another property called perfect forkability. Using that knowledge, we introduce a new cryptographic primitive called uncentralisable ledger and study its properties. We use those properties to analyse what an uncentralisable ledger may offer to classic electronic voting systems and how it opens up the realm of possibilities for completely new voting mechanisms. We review a list of selected projects that implement voting systems using blockchain technol- ogy. We then conclude that the true revolutionary feature enabled by uncentralisable ledgers is a self-sovereign and distributed identity provider.
Husam Al Jawaheri, Mashael Al Sabah, Yazan Boshmaf, Aiman Erbad
With the rapid increase of threats on the Internet, people are continuously seeking privacy and anonymity. Services such as Bitcoin and Tor were introduced to provide anonymity for online transactions and Web browsing. Due to its pseudonymity model, Bitcoin lacks retroactive operational security, which means historical pieces of information could be used to identify a certain user. We investigate the feasibility of deanonymizing users of Tor hidden services who rely on Bitcoin as a payment method by exploiting public information leaked from online social networks, the Blockchain, and onion websites. This, for example, allows an adversary to link a user with @alice Twitter address to a Tor hidden service with private.onion address by finding at least one past transaction in the Blockchain that involves their publicly declared Bitcoin addresses.
To demonstrate the feasibility of this deanonymization attack, we carried out a real-world experiment simulating a passive, limited adversary. We crawled 1.5K hidden services and collected 88 unique Bitcoin addresses. We then crawled 5B tweets and 1M BitcoinTalk forum pages and collected 4.2K and 41K unique Bitcoin addresses, respectively. Each user address was associated with an online identity along with its public profile information. By analyzing the transactions in the Blockchain, we were able to link 125 unique users to 20 Tor hidden services, including sensitive ones, such as The Pirate Bay and Silk Road. We also analyzed two case studies in detail to demonstrate the implications of the resulting information leakage on user anonymity. In particular, we confirm that Bitcoin addresses should always be considered exploitable, as they can be used to deanonymize users retroactively. This is especially important for Tor hidden service users who actively seek and expect privacy and anonymity.
Husam Al Jawaheri, Mashael Al Sabah, Yazan Boshmaf, Aiman Erbad
With the rapid increase of threats on the Internet, people are continuously seeking privacy and anonymity. Services such as Bitcoin and Tor were introduced to provide anonymity for online transactions and Web browsing. Due to its pseudonymity model, Bitcoin lacks retroactive operational security, which means historical pieces of information could be used to identify a certain user. We investigate the feasibility of deanonymizing users of Tor hidden services who rely on Bitcoin as a payment method by exploiting public information leaked from online social networks, the Blockchain, and onion websites. This, for example, allows an adversary to link a user with @alice Twitter address to a Tor hidden service with private.onion address by finding at least one past transaction in the Blockchain that involves their publicly declared Bitcoin addresses. To demonstrate the feasibility of this deanonymization attack, we carried out a real-world experiment simulating a passive, limited adversary. We crawled 1.5K hidden services and collected 88 unique Bitcoin addresses. We then crawled 5B tweets and 1M BitcoinTalk forum pages and collected 4.2K and 41K unique Bitcoin addresses, respectively. Each user address was associated with an online identity along with its public profile information. By analyzing the transactions in the Blockchain, we were able to link 125 unique users to 20 Tor hidden services, including sensitive ones, such as The Pirate Bay and Silk Road. We also analyzed two case studies in detail to demonstrate the implications of the resulting information leakage on user anonymity. In particular, we confirm that Bitcoin addresses should always be considered exploitable, as they can be used to deanonymize users retroactively. This is especially important for Tor hidden service users who actively seek and expect privacy and anonymity.
Homomorphic Cryptography raised as a new solution used in electronic voting systems. In this research, Fully Homomorphic encryption used to design and implement an e-voting system. The purpose of the study is to examine the applicability of Fully Homomorphic encryption in real systems and to evaluate the performance of fully homomorphic encryption in evoting systems. Most of homomorphic cryptography evoting systems based on additive or multiplicative homomorphic encryption. In this research, fully homomorphic encryption used to provide both operations additive and multiplication, which ease the demonstration of none interactive zero-knowledge proof NIZKP. The proposed e-voting system achieved most of the important security issues of the internet-voting systems such as eligibility, privacy, accuracy, verifiability, fairness, and others. One of the most important properties of the implemented internet voting system its applicability to work on cloud infrastructure, while preserving its security characteristics. The implementation is done using homomorphic encryption library HELib. Addition and multiplication properties of fully homomorphic encryption were used to verify the correctness of vote structure as a NIZKP, and for calculating the results of the voting process in an encrypted way. The results show that the implemented internet voting system is secure and applicable for a large number of voters up to 10 million voters.
Open access
Internet Traffic Analysis and Secure E-voting
Advanced Steganography and Watermarking Techniques
Defending against distributed denial of service (DDoS) attacks in the Internet is a fundamental problem. One practical approach to addressing DDoS attacks is to redirect all destination (e.g., via DNS or BGP) to a third-party, DDoS protection-as-a-service provider (e.g., Cloudflare and Akamai), which is well provisioned and equipped with proprietary filtering mechanisms to remove attack traffic before passing the remaining traffic to the destination. Although such an approach is appealing, as it requires no modification to the existing Internet infrastructure and can scale to handle very large attacks, recent industrial interviews with more than 100 interviewees from over 10 industry segments reveal that this approach alone is not sufficient, especially for large organizations (e.g., Web hosting companies and government) that cannot afford to allow third-parity security-service providers to terminate their network connections. Instead, these organizations have to rely on their ISPs to filter attack traffic. In this paper, we discuss the challenges faced by the ISPs in order to disrupt the Internet security-service market and sketch our solutions, powered by smart contracts.
Digital identities and credentials are gradually replacing physical documents, as they can be verified with more accuracy and efficiency. Since online privacy is becoming more crucial than ever, it is essential to preserve the privacy of individuals whenever possible. Therefore, anonymous attestation of digital credentials should be feasible, where provers can selectively disclose attributes and create abstractions over attributes in their credential, in order to solely disclose the minimum amount of information required to complete the goal of verification.<br/><br/>Many schemes in the field of attribute-based credentials consider a single root authority issuing credentials to provers. This is coherent to the traditional way of the issuance of credentials since the process of producing physical documents is costly to distribute to multiple issuers. Digital identities provide the opportunity for authorities to distribute credential issuance rights (consecutively) to smaller entrusted entities.<br/><br/>To the best of our knowledge, we propose the first protocol which combines both anonymous attestation with attribute-based credentials and the delegation of selective signing rights for the issuance of these credentials. Root authorities could delegate signing rights for selective attributes consecutively to trustees, which are able to create anonymous attribute-based credentials with the acquired attributes for provers. Verifiers are able to verify presentation tokens with solely the public key of the root authority, without gaining knowledge about the identities of the prover and intermediate delegators. We introduce three adapted signature schemes based on existing work in order to realize a concrete instantiation of the protocol. Anonymity is achieved by incorporating Schnorr's zero-knowledge proof of knowledge with bilinear pairings to efficiently prove the correctness of presentation tokens.<br/><br/>We realized a prototype of our concrete instantiation and optimized the verification algorithm in order to achieve optimal pairing performance. Complexity analysis of the protocol shows improvement in efficiency by aggregating attribute signatures throughout signing right delegation. Experimental results demonstrate a degree of practical feasibility for the verification of presentation tokens on commodity hardware within the challenging public transportation access control time bound of 300 ms.<br/>
A fraudulent election is one of the biggest problems of the contemporaneity in most countries. Even the world’s largest democracies like India, United States, and Japan still suffer from a flawed electoral system. Vote rigging, hacking of the EVM (Electronic voting machine), election manipulation, and polling booth capturing are the major issues in the current voting system. This fallacious election process calls voting systems into question. With the current Cambridge Analytica scandal a hot topic around the world, it brings the validity of current voting systems into question. In this paper, we investigate the problems in the election voting systems and propose a novel voting model which can resolve these issues. We use a recently introduced blockchain based protocol called PHANTOM, which uses a directed acyclic graph of blocks, also known as blockDAG, to generalize the initial blockchain technology.
This report describes two projects created by the author which are based on ideas which originate from the Bitcoin community. The first, bmd, is a re-implementation of the Bitmessage protocol in go. Bitmessage is an anonymous and secure messaging system invented by Jonathan Warren, who was inspired by the design of Bitcoin's p2p network. [WARR1] The second is Shufflepuff, an implementation of a protocol called CoinShuffle[RUFF1] which allows several people to construct a Bitcoin transaction with an input and an output for each participant without any participant knowing who owns which output. CoinShuffle was invented by Tim Ruffing et al, and it is an upgrade of a protocol called CoinJoin, invented by Gregory Maxwell. This paper discusses the background, properties, applications, and design of bmd and Shufflepuff. There is also a report of a performance analysis on bmd.
The smart terminal and grid protection devices play a very important role in the safe operation of the smart grid. Traditional maintenance and renewal of the center node wastes a lot of manpower and material resources and have huge safety implications. This paper proposes a safety equipment diagnosis mechanism based on consortium blockchain technology to realize more efficient, convenient, and secure device maintenance. When a device has problems or notices improper operation, it can make a device diagnosis request in the consortium blockchain network, and receive a diagnosis response from a vendor or non-original supplier nodes. This scheme designs a decentralized safety equipment diagnosis smart contract, combining response node bid price and credit, and applies a multi-dimensional reverse auction mechanism to determine bid node and transaction price. After a smart device diagnosed, the relevant message will be packaged and sent to a smartphone, which can use the client to set up the smart contract of equipment operation policy. Paillier encryption arithmetic can be used to ensure device diagnosis mechanism safety. The proposed scheme is guaranteed not to reveal sensitive information in the process of device interaction.