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4,146 results · page 157 of 173
Sergi Delgado-Segura, Cristina Pérez‐Solà, Jordi Herrera‐Joancomartí, Guillermo Navarro‐Arribas
No abstract is available for this record.
Yong Yu, Yannan Li, Man Ho Au, Willy Susilo · 6 authors
No abstract is available for this record.
Siddharth Misra, Vishal Kashyap, Poonacha K.B., Arjun Mukund · 5 authors
Tema ovog rada su kriptovalute. Budući da većina ljudi nije pravodobno upoznata s ovom temom, ovaj rad prikazuje i opisuje kriptovalute te način na koji se upotrjebljuju u svakodnevnom životu. Kriptovalute (eng. cryptocurrency) digitalne su valute dizajnirane kao sredstvo razmjene. Poznate su po tome što su državne agencije i banke isključene iz procesa razmjene. Kriptovalute omogućuju jednostavnu, jeftinu i brzu transakciju na području cijeloga svijeta. Trenutno najisplativije kriptovalute su Bitcoin i Ethereum, a u radu je opisana njihova korisnost, prednosti i mane. Budući da se Bitcoinu predviđa uspješna budućnost i sve je prisutniji i prihvatljiviji na tržištu, u radu su navedeni primjeri iz Hrvatske koji to potvrđuju. Sve veći broj poduzetnika odlučuje se za uvođenje kriptovaluta. U primjerima je obuhvaćen širok spektar djelatnosti, od frizerskih usluga, preko raznih tvrtki koji se bave prodajom računalne opreme, ugostiteljskih usluga preko mogućnosti brzog i lakog podizana gotovine na kripto bankomatima pa sve do plaćanja komunalnih usluga, pa čak i humanitarno djelovanje. Mnogi smatraju da su kriptovalute samo sinonim za prijevare i pranje novca, no programeri tvrde da su kriptovalute samo jedna vrsta tehnologije, alat koji sam po sebi ne može biti ni dobar ni loš, ovisno o tome za što se koristi. Autor ovoga rada proveo je istraživanje o tome kako se može besplatno započeti trgovanje kriptovalutama te je anketom ispitao stavove ispitanika o implementaciji kriptovaluta u društvu.
Benoît Libert, San Ling, Fabrice Mouhartem, Khoa Nguyen · 5 authors
Abstract Group encryption ( GE ) is the natural encryption analogue of group signatures in that it allows verifiably encrypting messages for some anonymous member of a group while providing evidence that the receiver is a properly certified group member. Should the need arise, an opening authority is capable of identifying the receiver of any ciphertext. As introduced by Kiayias, Tsiounis and Yung (Asiacrypt'07), GE is motivated by applications in the context of oblivious retriever storage systems, anonymous third parties and hierarchical group signatures. This paper provides the first realization of group encryption under lattice assumptions. Our construction is proved secure in the standard model (assuming interaction in the proving phase) under the Learning-With-Errors ( LWE ) and Short-Integer-Solution ( SIS ) assumptions. As a crucial component of our system, we describe a new zero-knowledge argument system allowing to demonstrate that a given ciphertext is a valid encryption under some hidden but certified public key, which incurs to prove quadratic statements about LWE relations. Specifically, our protocol allows arguing knowledge of witnesses consisting of X ∈ Z q m × n , s ∈ Z q n and a small-norm e ∈ Z m which underlie a public vector b = X ⋅ s + e ∈ Z q m while simultaneously proving that the matrix X ∈ Z q m × n has been correctly certified. We believe our proof system to be useful in other applications involving zero-knowledge proofs in the lattice setting.
Tomaso Aste
No abstract is available for this record.
Benoît Libert, San Ling, Khoa Nguyen, Huaxiong Wang
Abstract An accumulator is a function that hashes a set of inputs into a short, constant-size string while preserving the ability to efficiently prove the inclusion of a specific input element in the hashed set. It has proved useful in the design of numerous privacy-enhancing protocols, in order to handle revocation or simply prove set membership. In the lattice setting, currently known instantiations of the primitive are based on Merkle trees, which do not interact well with zero-knowledge proofs. In order to efficiently prove the membership of some element in a zero-knowledge manner, the prover has to demonstrate knowledge of a hash chain without revealing it, which is not known to be efficiently possible under well-studied hardness assumptions. In this paper, we provide an efficient method of proving such statements using involved extensions of Stern’s protocol. Under the Small Integer Solution assumption, we provide zero-knowledge arguments showing possession of a hash chain. As an application, we describe new lattice-based group and ring signatures in the random oracle model. In particular, we obtain: (i) the first lattice-based ring signatures with logarithmic size in the cardinality of the ring and (ii) the first lattice-based group signature that does not require any GPV trapdoor and thus allows for a much more efficient choice of parameters.
Dimaz Ankaa Wijaya, Joseph K. Liu, Ron Steinfeld, Shi-Feng Sun · 5 authors
No abstract is available for this record.
FC 2017 Sliema, Michael 1974- Brenner, Kurt Rohloff, Joseph Bonneau · 12 authors
No abstract is available for this record.
Broadbent Anne, Zhengfeng Ji, Song Fang, Watrous John
Prior work has established that all problems in NP admit classical zero-knowledge proof systems, and under reasonable hardness assumptions for quantum computations, these proof systems can be made secure against quantum attacks. We prove a result representing a further quantum generalization of this fact, which is that every problem in the complexity class QMA has a quantum zero-knowledge proof system. More specifically, assuming the existence of an unconditionally binding and quantum computationally concealing commitment scheme, we prove that every problem in the complexity class QMA has a quantum interactive proof system that is zero-knowledge with respect to efficient quantum computations. Our QMA proof system is sound against arbitrary quantum provers, but only requires an honest prover to perform polynomial-time quantum computations, provided that it holds a quantum witness for a given instance of the QMA problem under consideration. The proof system relies on a new variant of the QMA-complete local Hamiltonian problem in which the local terms are described by Clifford operations and standard basis measurements. We believe that the QMA-completeness of this problem may have other uses in quantum complexity.
Karl Wüst, Arthur Gervais
No abstract is available for this record.
Alin Tomescu, Srinivas Devadas
© 2017 IEEE. We present Catena, an efficiently-verifiable Bitcoinwitnessing scheme. Catena enables any number of thin clients, such as mobile phones, to efficiently agree on a log of application-specific statements managed by an adversarial server. Catenaimplements a log as an OP-RETURN transaction chain andprevents forks in the log by leveraging Bitcoin's security againstdouble spends. Specifically, if a log server wants to equivocate ithas to double spend a Bitcoin transaction output. Thus, Catenalogs are as hard to fork as the Bitcoin blockchain: an adversarywithout a large fraction of the network's computational powercannot fork Bitcoin and thus cannot fork a Catena log either. However, different from previous Bitcoin-based work, Catenadecreases the bandwidth requirements of log auditors from 90GB to only tens of megabytes. More precisely, our clients onlyneed to download all Bitcoin block headers (currently less than35 MB) and a small, 600-byte proof for each statement in a block. We implement Catena in Java using the bitcoinj library and use itto extend CONIKS, a recent key transparency scheme, to witnessits public-key directory in the Bitcoin blockchain where it can beefficiently verified by auditors. We show that Catena can securemany systems today, such as public-key directories, Tor directoryservers and software transparency schemes.
Rosario Gennaro, Steven Goldfeder, Arvind Narayanan
No abstract is available for this record.
Roman Beck, Jacob Stenum Czepluch, Nikolaj Lollike, Simon Malone
No abstract is available for this record.
Giuseppe Ateniese, Bernardo Magri, Daniele Venturi, Ewerton R. Andrade
We put forward a new framework that makes it possible to re-write or compress the content of any number of blocks in decentralized services exploiting the blockchain technology. As we argue, there are several reasons to prefer an editable blockchain, spanning from the necessity to remove inappropriate content and the possibility to support applications requiring re-writable storage, to "the right to be forgotten." Our approach generically leverages so-called chameleon hash functions (Krawczyk and Rabin, NDSS '00), which allow determining hash collisions efficiently, given a secret trapdoor information. We detail how to integrate a chameleon hash function in virtually any blockchain-based technology, for both cases where the power of redacting the blockchain content is in the hands of a single trusted entity and where such a capability is distributed among several distrustful parties (as is the case with Bitcoin). We also report on a proof-of-concept implementation of a redactable blockchain, building on top of Nakamoto's Bitcoin core. The prototype only requires minimal changes to the way current client software interprets the information stored in the blockchain and to the current blockchain, block, or transaction structures. Moreover, our experiments show that the overhead imposed by a redactable blockchain is small compared to the case of an immutable one.
Mike Sharples, John Domingue
The ‘blockchain’ is the core mechanism for the Bitcoin digital payment system. It embraces a set of inter-related technologies: the blockchain itself as a distributed record of digital events, the distributed consensus method to agree whether a new block is legitimate, automated smart contracts, and the data structure associated with each block. We propose a permanent distributed record of intellectual effort and associated reputational reward, based on the blockchain that instantiates and democratises educational reputation beyond the academic community. We are undertaking initial trials of a private blockchain or storing educational records, drawing also on our previous research into reputation management for educational systems.
Konstantinos Christidis, Michael Devetsikiotis
ABSTRACT: Motivated by the recent explosion of interest around Blockchains, we examine whether they make a good t for the Internet of Things (IoT) sector. Blockchains allow us to have a distributed peer-to-peer network where non-trusting members can interact with each other without a trusted intermediary, in a variable manner. We review how this mechanism works and also look into smart contracts scripts that reside on the Blockchain that allow for the automation of multi-step processes. We then move into the IoT domain, and describe how a Blockchain-IoT combination: 1) facilitates the sharing of services and resources leading to the creation of a marketplace of services between devices and 2) allows us to automate in a cryptographically variable manner several existing, time- consuming work owns. We also point out certain issues that should be considered before the deployment of a Blockchain network in an IoT setting: from transactional privacy to the expected value of the digitized assets traded on the network. Wherever applicable, we identify solutions and workarounds. Our conclusion is that the Blockchain-IoT combination is powerful and can cause sign cant transformations across several industries, paving the way for new business models and novel, distributed applications.
Benny Applebaum, Pavel Raykov
No abstract is available for this record.
M. Albrecht, Pooya Farshim, Shuai Han, Dennis Hofheinz · 6 authors
Abstract We provide constructions of multilinear groups equipped with natural hard problems from indistinguishability obfuscation, homomorphic encryption, and NIZKs. This complements known results on the constructions of indistinguishability obfuscators from multilinear maps in the reverse direction. We provide two distinct, but closely related constructions and show that multilinear analogues of the $${\text {DDH}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>DDH</mml:mtext></mml:math> assumption hold for them. Our first construction is symmetric and comes with a $$\kappa $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>κ</mml:mi></mml:math> -linear map $$\mathbf{e }: {{\mathbb {G}}}^\kappa \longrightarrow {\mathbb {G}}_T$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>e</mml:mi><mml:mo>:</mml:mo><mml:msup><mml:mrow><mml:mi>G</mml:mi></mml:mrow><mml:mi>κ</mml:mi></mml:msup><mml:mo>⟶</mml:mo><mml:msub><mml:mi>G</mml:mi><mml:mi>T</mml:mi></mml:msub></mml:mrow></mml:math> for prime-order groups $${\mathbb {G}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>G</mml:mi></mml:math> and $${\mathbb {G}}_T$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>G</mml:mi><mml:mi>T</mml:mi></mml:msub></mml:math> . To establish the hardness of the $$\kappa $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>κ</mml:mi></mml:math> -linear $${\text {DDH}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>DDH</mml:mtext></mml:math> problem, we rely on the existence of a base group for which the $$\kappa $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>κ</mml:mi></mml:math> -strong $${\text {DDH}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>DDH</mml:mtext></mml:math> assumption holds. Our second construction is for the asymmetric setting, where $$\mathbf{e }: {\mathbb {G}}_1 \times \cdots \times {\mathbb {G}}_{\kappa } \longrightarrow {\mathbb {G}}_T$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>e</mml:mi><mml:mo>:</mml:mo><mml:msub><mml:mi>G</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>×</mml:mo><mml:mo>⋯</mml:mo><mml:mo>×</mml:mo><mml:msub><mml:mi>G</mml:mi><mml:mi>κ</mml:mi></mml:msub><mml:mo>⟶</mml:mo><mml:msub><mml:mi>G</mml:mi><mml:mi>T</mml:mi></mml:msub></mml:mrow></mml:math> for a collection of $$\kappa +1$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>κ</mml:mi><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math> prime-order groups $${\mathbb {G}}_i$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>G</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:math> and $${\mathbb {G}}_T$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>G</mml:mi><mml:mi>T</mml:mi></mml:msub></mml:math> , and relies only on the 1-strong $${\text {DDH}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>DDH</mml:mtext></mml:math> assumption in its base group. In both constructions, the linearity $$\kappa $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>κ</mml:mi></mml:math> can be set to any arbitrary but a priori fixed polynomial value in the security parameter. We rely on a number of powerful tools in our constructions: probabilistic indistinguishability obfuscation, dual-mode NIZK proof systems (with perfect soundness, witness-indistinguishability, and zero knowledge), and additively homomorphic encryption for the group $$\mathbb {Z}_N^{+}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>Z</mml:mi><mml:mi>N</mml:mi><mml:mo>+</mml:mo></mml:msubsup></mml:math> . At a high level, we enable “bootstrapping” multilinear assumptions from their simpler counterparts in standard cryptographic groups and show the equivalence of PIO and multilinear maps under the existence of the aforementioned primitives.
Xun Yi, Xuechao Yang, Andrei Kelarev, Kwok‐Yan Lam · 5 authors
Kriptovalute su digitalni novac utemeljen na kriptografiji i decentraliziranom sustavu. Postoje samo u elektroničkom obliku kao jedinstveni digitalni novčići ("tokeni"). Iza njih ne stoji autoritet države niti ih je moguće svojevoljno proizvesti. Rad se fokusira na značajkama, postavkama, razvoju i svim međuodnosima važnih ekonomskih faktora koji utječu na kriptovalute. U prvom poglavlju navedena su obilježja kriptovaluta. Drugo poglavlje daje primjere i govori o primjeni kriptovaluta u svakodnevnom životu. U trećem poglavlju je raspravljano o trenutnim i budućim regulacijama najmoćnijih zemalja svijeta (G20) , kao i njihovoj zajedničkoj suradnji u želji za jedinstvenim i standardiziranim pravilima, a sve u svrhu što kvalitetnijeg nadzora nad kriptovalutama kako bi se spriječile malverzacije i zaštitili potrošači. Četvrto poglavlje govori o inicijalnoj ponudi kovanica, a peto poglavlje je namijenjeno sigurnosti kriptovaluta. Cilj istraživanja je utvrditi koliko je studentska populacija upoznata i usmjerena prema novim oblicima digitalnog novca, koje značajke kriptovaluta smatraju pozitivnima, a koje negativnima i u kojoj su mjeri investirali ili su spremni investirati dio svojih ulaganja u kriptovalute i sl. Metode istraživanja korištene u radu su kompilacija na temelju proučavanja postojeće literature o temi rada, prikupljanje i analiza podataka vezanih uz kriptovalute, ponajprije podataka vezanih uz cijene i tržišnu kapitalizaciju, anketiranje studenata Ekonomskog fakulteta u Rijeci i metoda dedukcije putem koje su pokazane sve važne karakteristike i obilježja kriptovaluta. Na temelju provedene ankete u kojoj je sudjelovalo 90 studenata Ekonomskog fakulteta u Rijeci zaključak toga dijela istraživanja je da je mlada populacija dobro upoznata s kriptovalutama i njenim glavnim značajkama, ali i određenim nedostatkom informiranosti o tehnologiji (trećina studenata nije čula za pojam "blockchain") i nedovoljnoj odlučnosti oko investiranja i trgovanja u kriptovalute. Povrh toga, dokazan je i negativan utjecaj hakerskih napada i određenih kriminalnih radnji, kao i nestabilnost tržišne cijene na povjerenje studenata, ali i ukupne populacije vezane uz globalni financijski sustav u kriptovalute. Ishod istraživanja omogućio je da zaključimo kako su kriptovalute trenutno u ranoj fazi razvoja i nisu se dovoljno implementirale za široku primjenu u trgovini roba i usluga ili općenito kao sredstvo razmjene. Faktor koji je uključen u istraživanje kako bi opisao veličinu, odnosno obujam neke kriptovalute je tržišna kapitalizacija u dolarima. Temeljna ideja ovog rada je informirati čitatelja o pozitivnim i negativnim značajkama koje se se vežu uz kriptovalute. Na taj način čitatelji će biti bolje informirani i educirani o potencijalnom riziku ulaganja u kriptovalute, kao i većoj razini zaštite prilikom posjedovanja neke digitalne valute.
Richard Dennis, Gareth Owen
This paper presents the first generalized reputation system that can be applied to multiple networks that is based on the blockchain. We first discuss current reputation systems, conducting a critical analysis of their current security vulnerabilities, before looking at how new blockchain based technologies are used. We propose an innovative new reputation system that is based on blockchain technologies which aims to solve many unanswered questions in today's current generation reputation systems. We then consider the limitations of such a system, before using simulations and analyses to demonstrate methods of overcoming these limitations. We conclude by suggesting areas for future studies, and summarizing our findings.
Kaylash Chaudhary, Ansgar Fehnker, Jaco van de Pol, Mariëlle Stoelinga
Bitcoin is a popular digital currency for online payments, realized as a decentralized peer-to-peer electronic cash system. Bitcoin keeps a ledger of all transactions; the majority of the participants decides on the correct ledger. Since there is no trusted third party to guard against double spending, and inspired by its popularity, we would like to investigate the correctness of the Bitcoin protocol. Double spending is an important threat to electronic payment systems. Double spending would happen if one user could force a majority to believe that a ledger without his previous payment is the correct one. We are interested in the probability of success of such a double spending attack, which is linked to the computational power of the attacker. This paper examines the Bitcoin protocol and provides its formalization as an UPPAAL model. The model will be used to show how double spending can be done if the parties in the Bitcoin protocol behave maliciously, and with what probability double spending occurs.
Mohsen Toorani
Abstract This paper considers security analysis of the YAK, a public key‐based authenticated key agreement protocol. The YAK protocol is a variant of the two‐pass HMQV protocol but uses zero‐knowledge proofs for proving knowledge of ephemeral values. In this paper, we show that the YAK protocol lacks joint key control and perfect forward secrecy attributes and is vulnerable to some attacks including unknown key‐share and key‐replication attacks. This invalidates the semantic security of the protocol in several security models. There are also other considerations regarding the impersonation and small subgroup attacks. Copyright © 2015 John Wiley & Sons, Ltd.
Marcos Portnoi, Chien-Chung Shen
We introduce LOCATHE (Location-Enhanced Authenticated Key Exchange), a generic protocol that pools location, user attributes, access policy and desired services into a multi-factor authentication, allowing two peers to establish a secure, encrypted session and perform mutual authentication with pre-shared keys, passwords and other authentication factors. LOCATHE contributes to: (1) forward secrecy through ephemeral session keys; (2) security through zero-knowledge password proofs (ZKPP), such that no passwords can be learned from the exchange; (3) the ability to use not only location, but also multiple authentication factors from a user to a service; (4) providing a two-tiered privacy authentication scheme, in which a user may be authenticated either based on her attributes (hiding her unique identification), or with a full individual authentication; (5) employing the expressiveness and flexibility of Decentralized or Multi-Authority Ciphertext-Policy Attribute-Based Encryption, allowing multiple service providers to control their respective key generation and attributes.
Ittay Eyal, Adem Efe Gencer, Emin Gün Sirer, Robbert van Renesse
Cryptocurrencies, based on and led by Bitcoin, have shown promise as infrastructure for pseudonymous online payments, cheap remittance, trustless digital asset exchange, and smart contracts. However, Bitcoin-derived blockchain protocols have inherent scalability limits that trade-off between throughput and latency and withhold the realization of this potential. This paper presents Bitcoin-NG, a new blockchain protocol designed to scale. Based on Bitcoin's blockchain protocol, Bitcoin-NG is Byzantine fault tolerant, is robust to extreme churn, and shares the same trust model obviating qualitative changes to the ecosystem. In addition to Bitcoin-NG, we introduce several novel metrics of interest in quantifying the security and efficiency of Bitcoin-like blockchain protocols. We implement Bitcoin-NG and perform large-scale experiments at 15% the size of the operational Bitcoin system, using unchanged clients of both protocols. These experiments demonstrate that Bitcoin-NG scales optimally, with bandwidth limited only by the capacity of the individual nodes and latency limited only by the propagation time of the network.