Blockchain Papers

Ahmad‐Reza Sadeghi

No abstract is available for this record.

Murat Kantarcıoğlu, Onur Kardes

Most of the cryptographic work in privacy-preserving distributed data mining deals with semi-honest adversaries, which are assumed to follow the prescribed protocol but try to infer private information using the messages they receive during the protocol. Although the semi-honest model is reasonable in some cases, it is unrealistic to assume that adversaries will always follow the protocols exactly. In particular, malicious adversaries could deviate arbitrarily from their prescribed protocols. Secure protocols that are developed against malicious adversaries require utilisation of complex techniques. Clearly, protocols that can withstand malicious adversaries provide more security. However, there is an obvious trade-off: protocols that are secure against malicious adversaries are generally more expensive than those secure against semi-honest adversaries only. In this paper, our goal is to make an analysis of trade-offs between performance and security in privacy-preserving distributed data mining algorithms in the two models. In order to make a realistic comparison, we enhance commonly used subprotocols that are secure in the semi-honest model with zero knowledge proofs to be secure in the malicious model. We compare the performance of these protocols in both models.

Chunming Tang, Dingyi Pei, Xiao Feng Wang, Zhuojun Liu

A delegateable signature scheme(DSS)which was first introduced by Barak is mainly based on the non-interactive zero-knowledge proof(NIZK)for preventing the signing verifier from telling which witness(i.e.,restricted subset)is being used. However,the scheme is not significantly efficient due to the difficulty of constructing NIZK.We first show that a non-interactive witness indistinguishable(NIWI)proof sys- tem and a non-interactive witness hiding(NIWH)proof system are easier and more efficient proof models than NIZK in some cases.Furthermore,the witnesses em- ployed in these two protocols(NIWI and NIWT)cannot also be distinguished by the verifiers.Combined with theΣ-protocol,we then construct NIWI and NIWH proofs for any NP statement under the existence of one-way functions and show that each proof is different from those under the existence of trapdoor permutations.Finally,based on our NIWI and NIWH proofs,we construct delegateable signature schemes under the existence of one-way functions,which are more efficient than Barak's scheme under the existence of trapdoor permutations.

Sanjay Saini, Joydip Dhar

In this paper we have formulated an online voting framework which ensures that the voter is able to vote in a public environment without his vote being eavesdropped on by a neighbor i.e. his vote becomes known to his neighbor or a third party when he marks his choice on a particular candidate. We also give a model for secure online voting system using zero knowledge proof and other cryptographic schemes encompassing the voting process of the user and the backend process of servers and the tallying and display of results and verification by the user of the vote cast by him at a later stage.

Melissa Chase

Non-interactive zero-knowledge (NIZK) proofs can be an extremely powerful tool, allowing one to prove a statement in a single message without revealing any information besides the truth of the statement. Blum et al. showed that NIZK proof systems exist for all languages in NP. However, in practice, NIZK proofs are rarely used, because existing protocols are extremely inefficient. Here we examine some useful languages for which we can give efficient proof system. We define two useful building blocks: one for proving that a message has been signed, and a second for proving that a value has been chosen according to a pseudorandom function. We give applications of these building blocks to anonymous credential systems, to electronic cash, and to the design of other efficient NIZK proofs systems.

Donald Beaver, Joan Feigenbaum, Victor Shoup

No abstract is available for this record.

Jens Groth, Steve Lu

No abstract is available for this record.

Murat Kantarcıoğlu, Onur Kardes

Although the semi-honest model is reasonable in some cases, it is unrealistic to assume that adversaries will al- ways follow the protocols exactly. In particular, malicious adversaries could deviate arbitrarily from their prescribed protocols. Clearly, protocols that can withstand malicious adversaries provide more security. However, there is an ob- vious trade-off: protocols that are secure against malicious adversaries are generally more expensive than those secure against semi-honest adversaries only. In this paper, our goal is to make an analysis of trade-offs between perfor- mance and security in privacy-preserving distributed data mining algorithms in the two models. In order to make a realistic comparison, we enhance commonly used subpro- tocols that are secure in the semi-honest model with zero knowledge proofs to be secure in the malicious model. We compare the performance of these protocols in both models.

Nishanth Chandran, Vipul Goyal, Rafail Ostrovsky, Amit Sahai

In STOC'05, Aim, Hopper and Longford introduced the notion of covert computation. A covert computation protocol is one in which parties am run a protocol without knowing if other parties ore also participating in the protocol or not. At the end of the protocol, if all parties participated in the protocol and if the function output is favorable to all parties, then the output is revealed. Ahn et al. constructed a protocol for covert two-partv computation in the random oracle model In this paper, we offer a construction for covert multiparty computation. Our construction is in the standard model and does not require random oracles. In order to achieve this goal, we introduce a number of new techniques. Central to our work is the development of "zero-knowledge proofs to garbled circuits," which we believe could be of independent interest. Along the way, we also develop a definition of covert computation as per the Ideal/Real model simulation paradigm.

Yvo Desmedt, Moti Yung

No abstract is available for this record.

Divyesh Shah, Sheng Zhong

No abstract is available for this record.

Akihiro Yamamura, Kurokawa Takashi, Junji Nakazato

No abstract is available for this record.

Kun Peng, Colin Boyd, Ed Dawson

The batch verification technique of Bellare et al. is extended to verification of several frequently employed zero-knowledge proofs. The new techniques are correct, sound, efficient, and can be widely applied. Specific applications are discussed in detail, including batch ZK proof and verification of validity of encryption (or reencryption) and batch ZK proof and verification of validity of decryption. Considerable efficiency improvements are gained in these two applications without compromising security. As a result, efficiency of the practical cryptographic systems (such as mix networks) based on these two applications is dramatically improved.

Wei Han, Dong Zheng, Kefei Chen

Abstract: Cryptography is an important tool in the design and implementation of electronic voting schemes for it provides the property of verifiability, which is not provided in the traditional voting. But in the real life, neither can most voters understand the profound theory of cryptographic e-voting nor can they perform the complicated cryptographic computation. An e-voting system is presented in this paper to leverage the use of cryptography between theory and practice. It combines the advantages of Moran-Naor’s voting scheme and voting schemes based on homomorphic encryption. It makes use of cryptographic techniques, but it hides the details of cryptographic computation from voters. Voters can be convinced that the ballot is cast as intended. The tally can be verified in public. Compared with Moran-Naor’s voting scheme, the new system has three advantages: the ballots can be recovered when the voting machine breaks down, the costly cut-and-choose zero-knowledge proofs for shuffling votes made by the voting machine are avoided and the partial tally result in each voting machine is kept secret. Key words: electronic voting, homomorphic commitment, homomorphic encryption, threshold decryption 1.

Gerald V. Post

The current political climate has almost ruled out the use of Internet voting.Many politicians, led by vocal computer scientists, are pushing for voter verified paper receipts; which is likely to push us even further away from even electronic voting systems.On the other hand, cryptographers have created homomorphic encryption and non-interactive zero-knowledge proofs with features that can support Internet voting.Adding a few more protocols, including an extended voting period and repeat voting can solve the remaining problems need to make Internet voting at least as secure as existing systems.

Huafei Zhu, Ying Qiu, Feng Bao

Ad-hoc networks formed by peers without relying on any preexisting infrastructure, have been a very attractive field of academic and industrial research in recent years due to their potential applications. An ad-hoc network allows a peer node further to form a task-driven sub-network such that each node in the generated sub-network may exchange data with each other but any other non-member node is prohibited to access the subnetwork. As a result, a task-driven subnetwork generated by a peer node definitely requires membership proof mechanism (in the scenario of anonymous communications, anonymous membership proof systems are required). In this paper, we provide a novel mechanism for anonymous access control (anonymous membership proof systems) in ad- hoc networks based on a new notion which we call or-protocols in the common reference string model. An or-protocol in essence is a three move zero-knowledge proof system that allows a peer node to prove its membership of a given set which is publicly verifiable. Our protocol is of constant size, i.e., the length of a proof is independent with number of users in a given set, and thus is suitable for practice. Furthermore we show that our protocol is provably secure assuming that the discrete logarithm problem defined over prime field is hard.

Amitabh Saxena

In this paper, we study the opacity property of verifiably encrypted signatures (VES) of Boneh et al. (proposed in Eurocrypt 2003). Informally, opacity implies that although some given aggregate signatures can verified, no useful information about the individual signatures is leaked. However, the very fact that an aggregate signature can be verified leaks certain information- that the individual signature is indeed well-formed. Apart from this, is there any other information leaked? In this paper, we show that there is absolutely no other information leaked about the individual signatures when the aggregation contains only two signatures. In more formal terms, we show that VES are Zero-Knowledge (ZK). We then extend the ZK property of VES to propose efficient Additive Non-Interactive Witness-Indistinguishable (A-NIWI) proofs. Intuitively an A-NIWI proof can be considered as a Proof of Knowledge (PoK) of another A-NIWI proof. 1

Bo Yang, Lin Piyuan, Zhang Wenzheng

Fingerprinting schemes are technical means to discourage people from illegally redistributing the digital data they have legally purchased. These schemes enable the original merchant to identify the original users of the digital data. Anonymous fingerprinting schemes allow a seller to fingerprint information sold to a user without knowing the identity of the user and without the seller seeing the fingerprinted copy. Finding a (redistributed) fingerprinted copy enables the seller to find out and prove to third party whose copy it was. In this paper, we propose a new scheme of anonymous fingerprinting by using electronic wallet, in which, the user doesn't need making a computationally expensive zero-knowledge proof on finding a fingerprinted copy, the seller can directly determine the redistributor by a simple computation without the help of a registration authority and without making a search for the redistributor's public key in purchase record. In addition, our scheme can prevent the collusion of merchant and registration center to make false-accusation to honest users. By using electronic wallet, our scheme can be integrated with electronic payment system

Mehmet Tahir Sandıkkaya, Bülent Örencik

Many electronic voting systems, classified mainly as homomorphic cryptography based, mix-net based and blind signature based, appear after the eighties when zero knowledge proofs were introduced. The common ground for all these three systems is that none of them works without real time cryptologic calculations that should be held on a server. As far as known, the agent-based approach has not been used in a secure electronic voting system. In this study, an agent-based electronic voting schema, which does not contain real time calculations on the server side, is proposed. Conventional cryptologic methods are used in the proposed schema and some of the requirements of an electronic voting system are constructed within the schema. The schema seems quite secure if the used cryptologic methods and agents are secure. In this paper, proposed schema will be explained and compared with already known electronic voting systems.

Justin Brickell, Vitaly Shmatikov

The output of a data mining algorithm is only as good as its inputs, and individuals are often unwilling to provide accurate data about sensitive topics such as medical history and personal finance. Individuals maybe willing to share their data, but only if they are assured that it will be used in an aggregate study and that it cannot be linked back to them. Protocols for anonymity-preserving data collection provide this assurance, in the absence of trusted parties, by allowing a set of mutually distrustful respondents to anonymously contribute data to an untrusted data miner.To effectively provide anonymity, a data collection protocol must be collusion resistant, which means that even if all dishonest respondents collude with a dishonest data miner in an attempt to learn the associations between honest respondents and their responses, they will be unable to do so. To achieve collusion resistance, previously proposed protocols for anonymity-preserving data collection have quadratically many communication rounds in the number of respondents, and employ (sometimes incorrectly) complicated cryptographic techniques such as zero-knowledge proofs.We describe a new protocol for anonymity-preserving, collusion resistant data collection. Our protocol has linearly many communication rounds, and achieves collusion resistance without relying on zero-knowledge proofs. This makes it especially suitable for data mining scenarios with a large number of respondents.

Bent Kristoffer Rosvold Onshus

This thesis describes an electronic voting system based on Damg\\aa rd, Jurik and Nielsen's generalization of Paillier's probabilistic public key system. A threshold variant of this homomorphic cryptosystem is used to provide universally verifiable elections, where zero-knowledge proofs are used for proving correctness of votes.\n\nUsing this cryptosystem, an electronic voting system that supports voting for 1 out of $L$ candidates is described. Two types of encoding may be used to prove the validity of the votes. The number of proofs needed using normal encoding is linear in $L$, while the number of proofs needed using binary encoding is logarithmic in $L$. It is shown how to extend the system to allow casting a vote for $t$ out of $L$ candidates. This method may easily be used to carry out elections with weighted votes without any added complexity to the system.\n\nThe system is shown to satisfy the requirements for elections at The Norwegian University of Science and Technology (NTNU). A fully functional implementation of the electronic voting system as a distributed system, using Java Remote Method Invocation, is presented. The implementation is used to analyze the feasibility of using this voting system for future elections at NTNU. The implementation is tested using various keylengths and various election parameters. With a keylength of 1024 bits, the simulated time for verification of complex elections is small enough to be considered universally verifiable.

Sungho Maeung

Recent studies argue that traditional voting systems do not encourage increased voter participation due to constraints in time, location, accuracy, and, accessibility. To ensure the rights of a democratic society and to enhance and secure the voting rights of citizens by surpassing all the limitations of the traditional voting system, the development of an electronic voting system is an attractive solution. Research on secure electronic voting systems has been conducted for at least the past two decades. We propose to develop an electronic voting system, called the Rochester Institute of Technology Student Government Election System (SGEES) based on Damgard et al. This voting scheme will use efficient honest-verifier zero-knowledge, which, unlike previous election schemes, are both easy to compute and to verify for both voters and authorities. Our proposed electronic voting system will allow convenient and confident voting while maintaining the accuracy of election results. This project will address the security requirements for electronic voting over the Internet, including privacy, completeness, soundness, receipt-freeness, and universal verifiability. In particular, we will research the feasibility of the voting scheme and protocols by studying three related cryptographical theories: homomorphic encryption, efficient honest-verifier zero-knowledge proofs, and threshold decryption cryptosystem.

Sven Laur, Helger Lipmaa

No abstract is available for this record.

David Wagner

No abstract is available for this record.