Atomic swaps enable the transfer of value between the cryptocurrencies of various blockchains without the need to trust an intermediary. In this paper, we propose the concept of atomic loans, which utilize atomic swap technology to allow market participants to create overcollateralized debt instruments in a trustless and disintermediated manner. The primary use cases for atomic loans include enabling fiat/stablecoin access for cryptocurrency holders to participate within legacy systems, as well as enabling leverage for margin trading. We also introduce a bidding process for liquidating collateral in the case of default which provides the ability for a more fair distribution of collateral.
Dominic Deuber, Bernardo Magri, Sri Aravinda Krishnan Thyagarajan
Bitcoin is an immutable permissionless blockchain system that has been extensively used as a public bulletin board by many different applications that heavily relies on its immutability. However, Bitcoin's immutability is not without its fair share of demerits. Interpol exposed the existence of harmful and potentially illegal documents, images and links in the Bitcoin blockchain, and since then there have been several qualitative and quantitative analysis on the types of data currently residing in the Bitcoin blockchain. Although there is a lot of attention on blockchains, surprisingly the previous solutions proposed for data redaction in the permissionless setting are far from feasible, and require additional trust assumptions. Hence, the problem of harmful data still poses a huge challenge for law enforcement agencies like Interpol (Tziakouris, IEEE S&P'18). We propose the first efficient redactable blockchain for the permissionless setting that is easily integrable into Bitcoin, and that does not rely on heavy cryptographic tools or trust assumptions. Our protocol uses a consensus-based voting and is parameterised by a policy that dictates the requirements and constraints for the redactions; if a redaction gathers enough votes the operation is performed on the chain. As an extra feature, our protocol offers public verifiability and accountability for the redacted chain. Moreover, we provide formal security definitions and proofs showing that our protocol is secure against redactions that were not agreed by consensus. Additionally, we show the viability of our approach with a proof-of-concept implementation that shows only a tiny overhead in the chain validation of our protocol when compared to an immutable one.
Blockchains are distributed secure ledgers to which transactions are issued
continuously and each block is tightly coupled to its predecessors.
Permissioned blockchains place special emphasis on transactions throughput. In
this paper we present TOY, which leverages the iterative nature of blockchains
in order to improve their throughput in optimistic execution scenarios. TOY
trades latency for throughput in the sense that in TOY the last f+1 blocks of
each node's blockchain are considered tentative, i.e., they may be rescinded in
case one of the last f+1 blocks proposers was Byzantine. Yet, when optimistic
assumptions are met, a new block is decided in each communication step, which
consists of a proposer that sends only its proposal and all other participants
are sending a single bit each. Our performance study demonstrates that in a
single Amazon data-center, TOY running on 10 mid-range Amazon nodes obtains a
throughput of up to 160K transactions per second for (typical Bitcoin size) 512
bytes transactions. In a 10 nodes Amazon geo-distributed setting with 512 bytes
transactions, TOY obtains a throughput of 30K transactions per second.
Blockchains are distributed secure ledgers to which transactions are issued continuously and each block of transactions is tightly coupled to its predecessors. Permissioned blockchains place special emphasis on transactions throughput. In this paper we present FireLedger, which leverages the iterative nature of blockchains in order to improve their throughput in optimistic execution scenarios. FireLedger trades latency for throughput in the sense that in FireLedger the last f + 1 blocks of each node's blockchain are considered tentative, i.e., they may be rescinded in case one of the last f + 1 blocks proposers was Byzantine. Yet, when optimistic assumptions are met, a new block is decided in each communication step, which consists of a proposer that sends only its proposal and all other participants are sending a single bit each. Our performance study demonstrates that in a single Amazon data-center, FireLedger running on 10 mid-range Amazon nodes obtains a throughput of up to 160K transactions per second for (typical Bitcoin size) 512 bytes transactions. In a 10 nodes Amazon geo-distributed setting with 512 bytes transactions, FireLedger obtains a throughput of 30K tps. Moreover, on higher end Amazon machines, FireLedger obtains $20%-600%$ better throughput than state of the art protocols like HotStuff and BFT-SMaRt, depending on the exact configuration.
Privacy was one of the key points mentioned in Nakamoto's Bitcoin whitepaper, and one of the selling points of Bitcoin in its early stages. In hindsight, however, de-anonymising Bitcoin users turned out to be more feasible than expected. Since then, privacy focused cryptocurrencies such as Zcash and Monero have surfaced. Both of these examples cannot be described as fully successful in their aims, as recent research has shown. Incentives are integral to the security of cryptocurrencies, so it is interesting to investigate whether they could also be aligned with privacy goals. A lack of privacy often results from low user counts, resulting in low anonymity sets. Could users be incentivised to use the privacy preserving implementations of the systems they use? Not only is Zcash much less used than Bitcoin (which it forked from), but most Zcash transactions are simply transparent transactions, rather than the (at least intended to be) privacy-preserving shielded transactions. This paper and poster briefly discusses how incentives could be incorporated into systems like cryptocurrencies with the aim of achieving privacy goals. We take Zcash as example, but the ideas discussed could apply to other privacy-focused cryptocurrencies. This work was presented as a poster at OPERANDI 2018, the poster can be found within this short document.
Peter B. Rønne, Arash Atashpendar, Kristian Gjøsteen, Peter Y. A. Ryan
We present an approach for performing the tallying work in the coercion-resistant JCJ voting protocol, introduced by Juels, Catalano, and Jakobsson, in linear time using fully homomorphic encryption (FHE). The suggested enhancement also paves the path towards making JCJ quantum-resistant, while leaving the underlying structure of JCJ intact. The exhaustive, comparison-based approach of JCJ using plaintext equivalence tests leads to a quadratic blow-up in the number of votes, which makes the tallying process rather impractical in realistic settings with a large number of voters. We show how the removal of invalid votes can be done in linear time via a solution based on recent advances in various FHE primitives such as hashing, zero-knowledge proofs of correct decryption, verifiable shuffles and threshold FHE. We conclude by touching upon some of the advantages and challenges of such an approach, followed by a discussion of further security and post-quantum considerations.
We propose a framework for threshold cryptosystems under a permissionless-economic model in which the participants are rational profit-maximizing entities. To date, threshold cryptosystems have been considered under permissioned settings with a limited adversary. Our framework relies on an escrow service that slashes and redistributes deposits to incentivize participants to adhere desired behaviors. Today, more than ever, sophisticated escrow services can be implemented over public blockchains like Ethereum, without additional trust assumptions. The key threat to rational threshold cryptosystems is collusion---by cooperating `illegally', a subset of participants can reveal the cryptosystem's secret, which, in turn is translated to unfair profit. Our countermeasure to collusion is framing. If the escrow is notified of collusion, it rewards the framer and slashes the deposits of all other participants. We show that colluding parties find themselves in the prisoner's dilemma, where the dominant strategy is framing.
For many identification systems, including those in government, finance and healthcare, it is critical that at most one identity exists for each human individual within a given system. Many existing approaches identify individuals through an exchange of verifiable documents attesting to basic identification information. However, the same basic information is collected for identification in almost every system, meaning that persons are linkable across different identity systems and are not in control of how their identity is used. We propose Unique Self-Sovereign Identity, (USI), combining Cancelable Biometrics [6] and W3C Verifiable Claims [8] to achieve privacy preserving and non-linkable identification, with guarantees against double enrolment with any system. Because our protocol is based on biometrics, it permits individuals to enrol without official identification documents. Our protocol can be used in a wide range of situations, offering data security for large organisations, access to basic services for over one billion people who lack official identifying documents, and personal identity control for all individuals.
M. Francisca Hinarejos, Josep Lluís Ferrer Gomila, Llorenç Huguet-Rotger
The certified mail is a value-added service that is widely used in the paper world. However, the scientific community has not yet provided a solution for certified e-mail that has achieved widespread acceptance. This lack of a certified e-mail solution is not due to a lack of proposed approaches; because over the past 40 years, more than 100 protocols have been reported in journals and at conferences. The vast majority of these proposed protocols use a trusted third party (TTP) to achieve fairness. The few solutions without a TTP have not been successful due to their high computational and/or communication cost. Blockchain provides a new approach to develop the protocols without a TTP but without the prior drawbacks of the previous solutions without a TTP. Here, we present a new protocol for certified e-mail based on a blockchain without a conventional TTP that is integrated with the conventional e-mail infrastructure. The protocol is secure, efficient, and viable from a practical perspective.
Since Gentry's breakthrough construction of fully homomorphic encryption from lattice-based assumptions (STOC 2009), homomorphic cryptography has attracted a lot of attention. In short, homomorphic cryptography schemes allow performing computation on encrypted data without knowing anything about the underlying plaintext. This branch of cryptography has become increasingly useful in building new protocols and schemes with intriguing security and functionality features. In this thesis, we continue to study the applications of homomorphic cryptography and the lattice-based techniques underlying them in realizing new and enhanced cryptographic primitives. We obtain the following results: -We construct the first noninteractive zero knowledge argument (and proof) system for all of NP from standard lattice assumptions. Noninteractive zero knowledge argument systems have found many applications in enhancing the functionality as well as the security of cryptographic schemes and protocols. Constructing noninteractive zero knowledge arguments from lattice assumption has been a long standing open question. We finally close this problem. -We consider multi-key fully homomorphic encryption (FHE) schemes. Traditional fully homomorphic encryption schemes allow computation on plaintext encrypted under a single key. The notion of multi-key fully homomorphic encryption allows homomorphic computation on data encrypted under different keys. We construct multi-key FHE schemes which are naturally dynamic: ciphertexts under new keys can join even during the homomorphic computation. -Finally, we focus on constrained pseudorandom functions (C-PRFs), which are pseudorandom functions (PRFs) with additional functional capabilities. We propose a new approach for building C-PRFs from lattices, and also significantly enhance the underlying lattice parameters.
Many Internet users employ a multitude of online services. Many services require the same data to be entered and users enter it repeatedly. Instead of entering information for every new service a user wants to use, we propose a system that allows users to simply share a set of information with any service they want to use. The information is entered once and stored in a distributed storage system. Users can easily share the data with any service provider, in order to use a service. Our proposed system makes use of the distributed ledger, provided by blockchains, to manage access rights. By taking the data away from the service providers, the personal data is also protected against unwanted data leaks.
M. Magdalena Payeras–Capellà, Macià Mut–Puigserver, Miquel À. Cabot-Nadal
European Regulation (EU) 910/2014 lays down the rules for electronic identification and trust services for electronic transactions. Qualified Electronic Registered Delivery is one of the trust services included in the regulation, and it requires nonrepudiation of origin and reception together with the integrity of the data. This kind of services usually relies heavily on the use of trusted third parties. These entities are an obstacle to extend the use of protocols. In this paper, we use the blockchain-based technologies to provide, for the first time, two multiparty registered eDelivery schemes that reduce the involvement of trusted third parties compared with traditional approaches while satisfying the requirements of the norms created by the European Union for registered eDeliveries. Since confidentiality is not considered a compulsory property in the directive, we propose two protocols. The first one is well suited for those deliveries that do not require the confidentiality of the message or delivered data or even for those in which it is required that the message can be public and accessible to everybody. The second solution for multiparty registered eDelivery allows the message to be hidden to others than the receiver. We present the smart contracts for both proposals and also a complete analysis of their properties and performance.
With the emergence of large scale data collection from Internet of Things and mobile devices, the notion of trust is now an increasingly important aspect of the next generation of data processing systems. We propose a blockchain enabled relational storage system that supports immutable transactions and temporal snapshots. By embedding blockchains in relational tables, the database stores trust related information in a tamper proof fashion, making the data provenance provably verifiable. To support large query workloads, we further propose an optimization algorithm that determines the best temporal snapshots to materialize in order to minimize the total time cost of answering a given query workload. Experimental evaluation shows that our materialized snapshot approach improves the performance of large analytical query workloads by as much as 50 times.
Luca Brunese, Francesco Mercaldo, Alfonso Reginelli, Antonella Santone
Blockchain technology is one of the most important and disruptive technologies in the world. Multiple industries are adopting the blockchain technology to innovate the way they work. One of the industries that are looking to adopt the blockchain is the healthcare industry. In fact, the protection of the private information stored in hospital database is a critical issue. In this paper we propose a method aimed to protect information exchanged in hospital networks, with particular regard to magnetic resonance images. As required from blockchain technology, each host network must validate the transiting data network: we exploit formal equivalence checking to perform this validation, by modeling magnetic resonance images in terms of automata by exploiting radiomic features.
Open access
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
The architecture of integrating blockchain with Industry 4.0 IoT network has emerged in recent years. Industry 4.0 refers to the new concept of intelligent manufacturing paradigm, including Internet of Things (IoT), Cloud computing and Cyber-Physical System (CPS). Blockchain is a decentralized, distributed ledger system used to record transactions across multiple participants. Blockchain offers a way of recording data that is designed to be secure, reliable and auditable, which makes it a preferred solution for securing IoT network. However, traditional blockchain suffers from storage scalability issue because each blockchain node stores the entire blockchain. The storage scalability problem can be even worse when blockchain is used in IoT network due to the high volume of data generated by massive number of IoT sensors. In this thesis, we propose a distributed storage architecture for blockchain based on erasure coding. The property of erasure coding makes it possible to greatly reduce storage overhead for each node without affecting the overall data integrity. Furthermore, to minimize the latency of rebuilding data in this distributed storage architecture, we formulate a latency-cost trade-off optimization problem and propose an efficient and scalable algorithm. Simulation results show that our architecture can achieve up to 80% latency reduction compared with other widely used distributed storage architectures. In addition, our architecture can save up to 90% storage space for each node, which removes the largest obstacle for integrating blockchain into IoT network.
Nylig lansert åpen kildekode blokkjede mellomvareteknologi kalt Chainlink har gjort det mulig å enkelt kombinere og koble smarte kontrakter sammen med eksterne systemer med varierende grad av sikkerhet og pålitelighet. Måten dette oppnås på er ved å koble de smarte kontraktene sammen med flere tredjeparter eller ”orakler” som tilbyr tjenesten å knytte smart kontrakten til det eksterne\nsystemet.\n\nDenne oppgaven tar for seg om det er etterspørsel for og hvordan kunstig intelligens kan bli solgt til og kombinert i smarte konrakter på en måte som minimerer behovet for tillit. For å gjøre dette blir markedet og økosystemet rundt Chainlink nettverket beskrevet. Ulike orakeltyper i Chainlink nettverket blir identifisert og det blir identifisert at det ikke er et umiddelbar mulighet å selge til kunstig intelligens til smarte kontrakter i dag på grunn av at teknologien fortsatt er umoden og nødvendig infrastruktur fortsatt mangler.\n\nVidere så blir det identifisert flere måter å kombinere smarte kontrakter med kunstig intelligens ved hjelp av orakler og at det finnes måter hvor kravet til tillit er minimalt. For å motivere leseren blir det gitt eksempler på bruksområder for kunstig intelligens og smarte kontrakter i introduksjonskapittelet og disse blir gjenbesøkt senere i oppgaven hvor de relateres opp mot kombinasjonene av kunstig intelligens og smarte kontrakter som er funnet.
The blockchain represented by Bitcoin, the distributed ledger system can prevent double spending effectively and other issues. But it has caused the concentration of bitcoin mining power, which completely contradicts the essential feature of the complete decentralization of the blockchain. In the blockchain system, transaction data information among users is transparently stored on the chain, and each participant can obtain a complete data backup. These transaction data are stored in an open and transparent manner on each node of the entire network, although it can prevent data forgery and tampering, it brings data privacy problems. In this paper, we propose a multi-level reward structure for the problem of centralized power calculation in the mining pool. This structure can make the miners work alone to prove the workload and obtain the reward through their own calculation power, in order to weaken the role of the mining pool. At the same time, for the data privacy security problem in the bitcoin trading system, we have improved the bitcoin puzzle, and proposed a puzzle scheme based on non-interactive zero-knowledge proof to ensure data transaction security.
Group signature schemes enable a set of members to anonymously sign data on behalf of the entire group. In order to prevent misuse, a designated group manager<br>has the ability to trace a given signature back to a member. Other extensions can also be realized in speci ffically designed schemes, such as veri fier local revocation (VLR) wherein only the verifi er needs information about the validity status of signing key pairs. This paper contributes two results towards group signature schemes. First, we present a new design for a group signature scheme that is secure under the standard<br>model, with common relaxations for anonymity. The scheme also enables VLR and allows for fully-dynamic groups; i.e. groups that allow members to both leave and join after creation. Secondly, we implement a preliminary version of the scheme to begin investigating the effi ciencies gained through utilizing one-time signing keys, instead of the traditional non-interactive, zero-knowledge proof systems.