Ken Naganuma, Masayuki Yoshino, Hisayoshi SATO, Takayuki Suzuki
Bitcoin is the first widely adopted decentralized digitale-cash system. All Bitcoin transactions that include addresses of senders and receivers are stored in the public blockchain which could cause privacy problems. The Zerocoin protocol hides the link between individual Bitcoin transactions without adding trusted third parties. However such an untraceable remittance system could cause illegal transfers such as money laundering. In this paper we address this problem and propose an auditable decentralized e-cash scheme based on the Zerocoin protocol. Our scheme allows designated auditors to extract link information from Zerocoin transactions while preventing other users including miners from obtaining it. Respecting the mind of the decentralized system, the auditor doesn't have other authorities such as stopping transfers, confiscating funds, and deactivating accounts. A technical contribution of our scheme is that a coin sender embeds audit information with a non-interactive zeroknowledge proof of knowledge (NIZKP). This zero-knowledge prevents malicious senders from embedding indiscriminate audit information, and we construct it simply using only the standard Schnorr protocol for discrete logarithm without zk-SNARKs or other recent techniques for zero-knowledge proof.
Bitcoin is the most famous cryptocurrency currently operating with a total marketcap of almost 7 billion USD. This innovation stands strong on the feature of pseudo anonymity and strives on its innovative de-centralized architecture based on the Blockchain. The Blockchain is a distributed ledger that keeps a public record of all the transactions processed on the bitcoin protocol network in full transparency without revealing the identity of the sender and the receiver. Over the course of 2016, cryptocurrencies have shown some instances of abuse by criminals in their activities due to its interesting nature. Darknet marketplaces are increasing the volume of their businesses in illicit and illegal trades but also cryptocurrencies have been used in cases of extortion, ransom and as part of sophisticated malware modus operandi. We tackle these challenges by developing an analytical capability that allows us to map relationships on the blockchain and filter crime instances in order to investigate the abuse in law enforcement local environment. We propose a practical bitcoin analytical process and an analyzing system that stands alone and manages all data on the blockchain in real-time with tracing and visualizing techniques rendering transactions decipherable and useful for law enforcement investigation and training. Our system adopts combination of analyzing methods that provides statistics of address, graphical transaction relation, discovery of paths and clustering of already known addresses. We evaluated our system in the three criminal cases includes marketplace, ransomware and DDoS extortion. These are practical training in law enforcement, then we determined whether our system could help investigation process and training.
M. J. G. Borge, Eleftherios Kokoris-Kogias, Philipp Jovanovic, Linus Gasser · 6 authors
Permissionless blockchain-based cryptocurrencies commonly use proof-of-work (PoW) or proof-of-stake (PoS) to ensure their security, e.g. to prevent double spending attacks. However, both approaches have disadvantages: PoW leads to massive amounts of wasted electricity and re-centralization, whereas major stakeholders in PoS might be able to create a monopoly. In this work, we propose proof-of-personhood (PoP), a mechanism that binds physical entities to virtual identities in a way that enables accountability while preserving anonymity. Afterwards we introduce PoPCoin, a new cryptocurrency, whose consensus mechanism leverages PoP to eliminate the dis-advantages of PoW and PoS while ensuring security. PoPCoin leads to a continuously fair and democratic wealth creation process which paves the way for an experimental basic income infrastructure.
Bitcoin is a popular alternative to fiat money, widely used for its perceived anonymity properties. However, recent attacks on Bitcoin's peer-to-peer (P2P) network demonstrated that its gossip-based flooding protocols, which are used to ensure global network consistency, may enable user deanonymization---the linkage of a user's IP address with her pseudonym in the Bitcoin network. In 2015, the Bitcoin community responded to these attacks by changing the network's flooding mechanism to a different protocol, known as diffusion. However, no systematic justification was provided for the change, and it is unclear if diffusion actually improves the system's anonymity. In this paper, we model the Bitcoin networking stack and analyze its anonymity properties, both pre- and post-2015. In doing so, we consider new adversarial models and spreading mechanisms that have not been previously studied in the source-finding literature. We theoretically prove that Bitcoin's networking protocols (both pre- and post-2015) offer poor anonymity properties on networks with a regular-tree topology. We validate this claim in simulation on a 2015 snapshot of the real Bitcoin P2P network topology.
This paper presents Prio, a privacy-preserving system for the collection of aggregate statistics. Each Prio client holds a private data value (e.g., its current location), and a small set of servers compute statistical functions over the values of all clients (e.g., the most popular location). As long as at least one server is honest, the Prio servers learn nearly nothing about the clients' private data, except what they can infer from the aggregate statistics that the system computes. To protect functionality in the face of faulty or malicious clients, Prio uses secret-shared non-interactive proofs (SNIPs), a new cryptographic technique that yields a hundred-fold performance improvement over conventional zero-knowledge approaches. Prio extends classic private aggregation techniques to enable the collection of a large class of useful statistics. For example, Prio can perform a least-squares regression on high-dimensional client-provided data without ever seeing the data in the clear.
One of the fundamental applications for a practically useful system of money is remuneration. Information pertaining to the amount of compensation awarded to different individuals is often considered sensitive, commanding a certain degree of privacy. As Bitcoin and similarly designed cryptocurrencies evolve into a recognized medium of exchange for larger swaths of the world economy, an increasing number of people will earn income in the form of blockchain-based payments. The nature of these transactions is such that the minute details of an affected individuals compensation package and spending habits will be exposed to public scrutiny. In some cases this violates cultural norms which respect the confidentiality of salaries, yet in other cases it could be regarded as providing the benefits associated with greater transparency. In this work we analyse the Bitcoin blockchain record of periodic payments accruing to an individual address in exchange for goods or services rendered. For differing levels of available information we seek to determine the extent of insights that can be gleaned about the transacting counter-parties and the privacy implications this entails.
Sistem pemungutan suara di Indonesia yang lebih dikenal dengan nama pemilihan umum (pemilu) sampai saat ini masih dilaksanakan secara manual. Dalam sistem tersebut, dibutuhkan waktu yang lama serta tenaga yang besar untuk menghitung hasil dari pemlihan umum tersebut. Sistem manual juga memiliki banyak kelemahan yang bisa dimanfaatkan oleh pihak tertentu untuk memanipulasi hasil pemilihan umum . Untuk mengatasi masalah ini, salah satu solusinya adalah dengan menerapkan sistem pemilihan umum dengan sistem berbasis perangkat elektronik yang lebih dikenal dengan istilah E-Vote . Berbagai macam metode telah diterapkan dalam sistem E-Vote untuk mengatasi kecurangan, salah satunya dengan menggunakan sistem enkripsi-dekripsi data dari pemilih ke sistem. Namun hal ini kurang efektif apabila kecurangan terjadi ketika data sudah dirubah sebelum masuk ke sistem. Dengan menerapkan mekanisme rantai kepercayaan (chain of trust) untuk mendeteksi adanya perubahan surat suara serta sistem autentikasi digital, mekanisme keamanan bagi peserta pemungutan suara bisa diwujudkan. Proses autentikasi digital menggunakan ponsel pintar dengan teknologi NFC dipadukan dengan sistem enkripsi asimetris dan digital signature . Pemilih bisa mendeteksi adanya perubahan surat suara melalui digital signature yang ada dan sistem E-Vote bisa mengenali peserta dari kunci publik yang ditawarkan oleh autentikator. Kemudian sistem E-Vote bisa memverifikasi keaslian kunci publik peserta melalui autentikasi berbasis zero-knowledge proof challenge . Hasil pilihan peserta kemudian dikirimkan ke autentikator untuk ditandatangani dan tandatangan tersebut digunakan sebagai bukti peserta telah melakukan pemilihan. Dari hasil uji coba yang dilakukan, terbukti bahwa autentikator bisa mendeteksi ketidaksamaan antara data dengan signature, dan autentikator bisa melakukan autentikasi dengan sistem E-Vote dengan tepat. Data hasil pilihan peserta bisa diverifikasi dengan signature yang ada untuk memeriksa integritas data.
Smart grid enables two-way communications between operation centers and smart meters to collect power consumption and achieve demand response to improve flexibility, reliability, and efficiency of electricity system. However, power consumption data may contain users' privacy, e.g., activities, references, and habits. Many smart metering schemes have been proposed utilizing homomorphic encryption for users' privacy preservation. Unfortunately, some abnormality of smart meter reading, e.g., caused by electricity theft, cannot be discovered since data is encrypted. Meanwhile, operation centers could become curious in reality. To address the above issues, we propose a new privacy-preserving smart metering scheme for smart grid, which supports data aggregation, differential privacy, fault tolerance, and range-based filtering simultaneously. Specifically, we extend lifted ElGamal encryption to aggregate users' consumption reports at the gateway to reduce communication overhead, while supporting fault tolerance of malfunctioning smart meters effectively. We also leverage zero-knowledge range proof to filter abnormal measurements caused by electricity theft or false data injection attacks without exposing individual measurements. In addition, our scheme can resist differential attacks, by which the curious operation center can violate users' privacy through comparing two aggregations of the similar data set. Finally, we discuss the properties of the proposed scheme and evaluate its performance in terms of security and efficiency.
Countries like Estonia, Norway or Australia developed electronic voting systems, which could be used to realize parliamentary elections with the help of personal computers and the Internet. These systems are completely different in their design and their way to solve the same problem. In this thesis, we analyze some of the largest real-world systems, describe their building blocks and their general design to focus on possible problems in these electronic voting systems. Furthermore, we present a template for an e-voting system, which we designed to try to fulfill the preliminaries and requirements of a secure electronic voting system. We use the experiences and the building blocks of existing systems to combine them to another more secure system. Afterwards, we compare our concept with real-world systems to evaluate the fulfillments of the requirements. Conclusively, we discuss the occurring problems when designing a secure system. Peer-to-peer networks provide many advantages, like decentralization, which might be applicable to electronic voting systems. Therefore, we take a look on the distributed database called blockchain and the usage in a peer-to-peer voting system. Our contribution to this topic is a modification of the proof-of-stake, which enables the usage of common devices, like smartphones or tablets, for the blockchain verification and inclusion of new ballots to the chain. This proof does not need much computing power and has a lower carbon footprint than the proof-of-work in the Bitcoin protocol.
Bitcoin and other cryptocurrencies have surged in popularity over the last decade. Although Bitcoin does not claim to provide anonymity for its users, it enjoys a public perception of being a `privacy-preserving' financial system. In reality, cryptocurrencies publish users' entire transaction histories in plaintext, albeit under a pseudonym; this is required for transaction validation. Therefore, if a user's pseudonym can be linked to their human identity, the privacy fallout can be significant. Recently, researchers have demonstrated deanonymization attacks that exploit weaknesses in the Bitcoin network's peer-to-peer (P2P) networking protocols. In particular, the P2P network currently forwards content in a structured way that allows observers to deanonymize users. In this work, we redesign the P2P network from first principles with the goal of providing strong, provable anonymity guarantees. We propose a simple networking policy called Dandelion, which achieves nearly-optimal anonymity guarantees at minimal cost to the network's utility. We also provide a practical implementation of Dandelion.
[B]lockchain technology provides a cryptographically secure and transparent method for transferring “digital assets.” Although blockchain technology is most commonly recognized as the technology that underpins virtual currencies, such as Bitcoin, it may also hold the key to facilitating secure online elections in America. To preface the need for blockchain voting, Part II addresses the current problems with voting in the United States. Part III provides an elementary explanation of blockchain. Parts IV and V outline current election laws and explain how implementing blockchain voting would very likely comply with these laws. Transitioning to a new voting system, however, does not come without challenges. Thus, the remainder of Part V outlines valid concerns with and counterarguments against blockchain voting. Part VI advocates for congressional action, tracing the failed regulation of Bitcoin back to the lack of uniform guidance. The time is ripe for modernization, yet current proposals for online voting lack the sophistication necessary to implement a secure and trusted system. Thus, Part VII of this Comment proposes that Congress pass a bill authorizing the use of blockchain voting and incentivizing states to modernize voting systems using this innovative technology.
Internet voting has long been a topic both of public discussion and also of scientific research. While the introduction of Internet voting may bring many advantages, it is further important to ensure an adequate level of security of the systems and underlying schemes that are used for casting and tallying the votes in order to encourage faith and acceptance for this relatively new way of voting.
A number of cryptographic schemes have been proposed, that enable secure Internet voting. One of the most established and well-researched solutions is the Helios scheme, which is also implemented as an open-source system. Both its implementation and the scheme behind it has been extensively studied in the literature, and the Helios system has been used for numerous elections in practice, such as the IACR elections.
However, there are election settings for which Helios is currently not appropriate, either due to infrastructure demands, required functionality for the voters or assurance of the security requirements. These kinds of election settings could benefit from the advantages that secure Internet voting provides.
In this thesis we identify the election settings not currently supported by Helios, propose our extensions for each one of these settings and evaluate their security. Hence, this work describes four Internet voting schemes that are build upon Helios, with each scheme developed towards a specific setting.
The first scheme presented here enables elections within the so-called boardroom voting setting. This setting is characterized by its decentralization, whereby all the tasks within the election are distributively performed by the voters themselves, without the support of a centralized infrastructure. The election in the boardroom voting setting are further conducted in an ad-hoc manner, so that limited time is available for preparation beforehand. We propose an extension of Helios that distributes the tasks of the voting system components in Helios among the voters. For this, we use cryptographic primitives such as decentralized key exchange with short authentication strings, distributed secret sharing and distributed decryption and Byzantine agreement.
The second scheme extends Helios with proxy voting functionality. Proxy voting, as a newly emerged form of voting, enables the voter to delegate her voting right in the election to a trusted third-party, the so-called proxy, who is authorized to vote on the voter's behalf. This extension facilitates such delegation while assuring the security for delegating voters and for the proxies and preserves the security guarantees provided by Helios for the voters who vote directly (instead of delegating). For ensuring the security of our extension, we introduce the so-called delegation credentials that are assigned to the voters and are used to compute anonymized delegation tokens sent to the proxies to enable delegation. We further use cryptographic primitives such as proofs of knowledge and signatures of knowledge.
The third scheme combines the first two settings to extend Helios towards the proxy boardroom voting setting, namely, a setting in which the elections are performed in a decentralized way as in boardroom voting, yet the voters who cannot participate in the election themselves are allowed to delegate their voting right to a trusted proxy before the election. The security of our extension is assured with threshold secret sharing and Pedersen commitments.
The fourth scheme extends Helios by improving its security.
As such, it introduces participation privacy, meaning that the voting system does not reveal which voters have participated in the election, while supporting verification that only the eligible voters have cast their ballots in the election. The extension furthermore introduces receipt-freeness, ensuring that the voter cannot create a receipt that proves to a third party how she voted, thus preventing vote selling. To ensure the security of the extension, a new kind of entity is introduced, the posting trustee, and a new kind of ballot, the so-called dummy ballot that is indistinguishable from a normal ballot cast by the voter, but does not modify the election result. We furthermore use disjunctive zero-knowledge proofs and proofs of signature knowledge to prove, that a sender of a particular ballot knows the private signature key of an eligible voter, or that the ballot is a dummy ballot.
For each one of the extensions, the security model is provided, which describes the security requirements and the assumptions that are necessary for ensuring the security requirements (i.e. vote privacy or vote integrity), is provided. For the first three extensions, the security model is used as a base for the informal security evaluation, in which an informal argument is used to show, that the security requirements hold under the described assumptions. Conducting a formal security evaluation for these extensions is considered an important part of the future work, in which new formal definitions have to be developed.
For the fourth extension, we provide a formal security analysis that relies on the formal definitions for the security requirements of vote privacy, vote integrity and eligibility, available in the literature. We furthermore introduce new formal definitions for participation privacy, receipt-freeness and fairness, which we also use for the formal proofs of our extension.
Marco Baldi, Franco Chiaraluce, Emanuele Frontoni, Giuseppe Gottardi · 6 authors
Public key infrastructures (PKIs) are of crucial importance for the life of online services relying on certificate-based authentication, like e-commerce, e-government, online banking, as well as e-mail, social networking, cloud services and many others. One of the main points of failure (POFs) of modern PKIs concerns reliability and security of certificate revocation lists (CRLs), that must be available and authentic any time a certificate is used. Classically, the CRL for a set of certificates is maintained by the same (and sole) certification authority (CA) that issued the certificates, and this introduces a single POF in the system. We address this issue by proposing a solution in which multiple CAs share a public, decentralized and robust ledger where CRLs are collected. For this purpose, we consider the model of public ledgers based on blockchains, introduced for the use in cryptocurrencies, that is becoming a widespread solution for many online applications with stringent security and reliability requirements.
Nazmul Islam, Kazi Md. Rokibul Alam, Shinsuke Tamura, Yasuhiko Morimoto
This paper proposes a new electronic voting (e-voting) scheme that exploits confirmation numbers (CNs) and revised simplified verifiable re-encryption mixnet (R-SVRM). R-SVRM is a recently introduced mechanism of mixnet also used to develop an e-voting scheme where a vote is decomposed to protect its voter from being coerced to cast a particular vote. Though the scheme avoids complicated zero knowledge proof (ZKP), the verification procedures of its cryptographic operations are still cumbersome. Again, another e-voting scheme based on CNs comes with benefits of vote verifiability and unlinkability between the vote and its voter, lags behind in adopting public keys for encryption and signature verification. Also its exploited mixnet is not verifiable; therefore requires a pair of signatures on each encrypted vote to ensure the verifiability of mixnet. Hence, the computation and communication overhead of the scheme becomes weighty, though ZKP is avoided. In contrast, the proposed scheme deploys both CNs and R-SVRM to eliminate these limitations. Hence, any coercer cannot force the voter to cast a specific vote as well as cryptographic operations and their verifications become simpler. Also the computation and communication overheads for involved entities get decreased. Finally, the security requirements of e-voting are achieved more elegantly.
Internet Traffic Analysis and Secure E-voting
Advanced Steganography and Watermarking Techniques
Bitcoin has emerged as the leading cryptographic currency since its inception in 2009 and at the time of writing holds a market capitalization of $28.4 billion. This ever-increasing figure has attracted adopters seeking to advance their investments, often leaving purely technical aspects on the sidelines. As is the case with any innovative technology, misconceptions are plentiful and information is not always conclusive. The research effort presented in this paper consists of a quantitative study seeking to address the subject of user anonymity in the Bitcoin network by employing an online survey on one of the most prominent Bitcoin forums. This includes 50 eligible participants, whose motivation is derived through the application of temporal motivation theory. The survey seeks to form an understanding of user attitudes towards the aspect of anonymity by following a methodological approach for exploring common tendencies among the representatives and will serve as the underlying data set from which conclusions can be drawn. Furthermore, this paper will present a literary study of the actual state of anonymity in this peer-to-peer technology by reviewing current findings highlighted in the area, thus presenting a comprehensive view of anonymity in the Bitcoin network, which will contrast the user study.
Bitcoin has not only attracted many users but also been considered as a technical breakthrough by academia. However, the expanding potential of Bitcoin is largely untapped due to its limited throughput. The Bitcoin community is now facing its biggest crisis in history as the community splits on how to increase the throughput. Among various proposals, Bitcoin Unlimited recently became the most popular candidate, as it allows miners to collectively decide the block size limit according to the real network capacity. However, the security of BU is heatedly debated and no consensus has been reached as the issue is discussed in different miner incentive models. In this paper, we systematically evaluate BU's security with three incentive models via testing the two major arguments of BU supporters: the block validity consensus is not necessary for BU's security; such consensus would emerge in BU out of economic incentives. Our results invalidate both arguments and therefore disprove BU's security claims. Our paper further contributes to the field by addressing the necessity of a prescribed block validity consensus for cryptocurrencies.