Joseph Bonneau, Andrew Miller, Jeremy Clark, Arvind Narayanan · 6 authors
Bit coin has emerged as the most successful cryptographic currency in history. Within two years of its quiet launch in 2009, Bit coin grew to comprise billions of dollars of economic value despite only cursory analysis of the system's design. Since then a growing literature has identified hidden-but-important properties of the system, discovered attacks, proposed promising alternatives, and singled out difficult future challenges. Meanwhile a large and vibrant open-source community has proposed and deployed numerous modifications and extensions. We provide the first systematic exposition Bit coin and the many related crypto currencies or 'altcoins.' Drawing from a scattered body of knowledge, we identify three key components of Bit coin's design that can be decoupled. This enables a more insightful analysis of Bit coin's properties and future stability. We map the design space for numerous proposed modifications, providing comparative analyses for alternative consensus mechanisms, currency allocation mechanisms, computational puzzles, and key management tools. We survey anonymity issues in Bit coin and provide an evaluation framework for analyzing a variety of privacy-enhancing proposals. Finally we provide new insights on what we term disinter mediation protocols, which absolve the need for trusted intermediaries in an interesting set of applications. We identify three general disinter mediation strategies and provide a detailed comparison.
The recent increase in reported incidents of surveillance and security breaches compromising users' privacy call into question the current model, in which third-parties collect and control massive amounts of personal data. Bit coin has demonstrated in the financial space that trusted, auditable computing is possible using a decentralized network of peers accompanied by a public ledger. In this paper, we describe a decentralized personal data management system that ensures users own and control their data. We implement a protocol that turns a block chain into an automated access-control manager that does not require trust in a third party. Unlike Bit coin, transactions in our system are not strictly financial -- they are used to carry instructions, such as storing, querying and sharing data. Finally, we discuss possible future extensions to block chains that could harness them into a well-rounded solution for trusted computing problems in society.
Purpose – This paper aims to explore the challenge posed by Bitcoin to regulators, particularly anti-money laundering regulators. Bitcoin is a crypto-currency based on open-source software and protocols that operates in peer-to-peer networks as a private irreversible payment mechanism. The protocol allows cross-border payments, for large and small items, with little or no transactional costs. Design/methodology/approach – Case studies and case law are examined as are relevant reports by regulators. Findings – Bitcoin is based on complex computer code supported by a robust community in a peer-to-peer network. Unlike other virtual currencies, Bitcoin appears to have obtained purchase and as such poses unique challenges to regulators. Research limitations/implications – Bitcoin is at a nascent stage and the evolution of the virtual currency is difficult to predict. Practical implications – Those who study financial systems, anti-money laundering regimes and asset forfeiture laws will have an interest in this topic. Originality/value – This is a new and emerging currency; there is limited literature on the implications of this currency to anti-money laundering systems.
Structure-preserving signature, as a special kind of digital signature, provides a way to construct modular cryptographic protocols with reasonable efficiency while retaining conceptual simplicity. This feature makes it suitable to be applied in the construction of non-interactive anonymous credential systems, which allows the user to convince a verifier of the possession of a certificate issued by the trusted authority anonymously and efficiently without interaction. In this paper, we design a secure and efficient structure-preserving signature scheme (SPSIG), and combine the scheme with Groth–Sahai non-interactive zero-knowledge (GSNIZK) proof system to construct a non-interactive anonymous credential scheme. The SPSIG is based on q-ADH-SDH assumption and can resist existential forgery in the chosen message attack. The message, signature, and verification keys are group elements, which are fully compatible with the GSNIZK system. The SXDH assumption is employed to instantiate the certificate-proving process, which is considered to be the most efficient instantiation at the moment. We analyze the efficiency and formally prove the security in the standard model. The result shows that our scheme satisfies correctness, zero knowledge, and unforgeability, and achieves identity authentication in the way of anonymity. Besides, our scheme has stronger anonymity, traceability, and non-interaction, and has lower communication cost compared with the conventional schemes.
A secure web browser login system has been implemented with the help of any cryptography techniques for authentication purpose. The Zero-Knowledge Proof and RSA algorithm is a concept which has been used here for providing the more authentication cryptographic systems. The Zero knowledge protocol with RSA cryptography algorithm can applied on the client side and it is working between client and server. In this built an algorithm in authentication system as like firewall or with firewall. It allows a party to prove that he/she knows something (i.e. Credential), without having to send over the value of the credential. In this implementation, it will be used to prove the password of the user without sending over the actual password. The system also allows for no password hashes to be stored on the server. The purpose of the implementation is to make confidential and authentication user login password.
Notice of Violation of IEEE Publication Principles"Bitcoin for Smart Trading in Smart Grid"by M.T. Alam, H. Li, and A. Patidarin the Proceedings of the 21st IEEE International Workshop on Local and Metropolitan Area Networks, April 2015After careful and considered review of the content and authorship of this paper by a duly constituted expert committee, this paper has been found to be in violation of IEEE's Publication Principles.This paper duplicates original text from the papers cited below. The original text was copied with insufficient attribution (including appropriate references to the original author(s) and/or paper title) and without permission."Privacy-friendly Tasking and Trading of Energy in Smart Grids"by Tassos Dimitriou and Ghassan Karamein the Proceedings of the 28th Annual ACM Symposium on Applied Computing, March 2013"NRGcoin: Virtual Currency for Trading of Renewable Energy in Smart Grids,"by M. Mihaylov, S. Jurado, N. Avellana, K. Van Moffaert, I. M. de Abril and A. Nowein the Proceedings of the 11th International Conference on the European Energy Market, May 2014Privacy aware anonymous trading for smart grid using digital currency has received very low attention so far. In this paper, we analyze the possibility of Bitcoin serving as the user friendly and effective privacy aware trading currency to facilitate energy exchange for smart grid.
The use of security certificates under the Cloud environment is the foundation to establish mutual trust between the Cloud and the user. In this paper, we propose an authentication method based on zero-knowledge proof and the mind of key escrow. With the method, authentication will not only satisfy the requirement anonymity and security but also can recover the real identity information in special circumstances with the cooperation of multiple parties. We will show that this proposed method is more suitable for promotion through analysis and comparison with an existing scheme.
Zero-knowledge proof protocol is a basic cryptographic technique. And zero-knowledge proof of double discrete logarithm has some particular properties, so it has been widely applied in many security systems. But the efficient problem of zero-knowledge proof of double discrete logarithm has not been solved to this day, since there are some special difficulties in computing this kind of knowledge proof. Hence, the time complexity and the space complexity of existing schemes are all O(k), where k is a security parameter. After redesigning the basic construction of knowledge proof, we provide a new zero-knowledge proof of double discrete logarithm, which is the first scheme with O(1) time complexity and O(1) space complexity. If introducing an off-line TTP (trusted third party), we can provide two additional zeroknowledge proof schemes of double discrete logarithm, one is even more efficient than the first one, the other one solves another open problem, which is how to efficiently prove the equality of double discrete logarithms in zero-knowledge way, and the existing techniques cannot solve this problem. We also provide the detailed security proofs of our designs and efficiency analysis, comparing with the existing schemes. The significant improvement in efficiency of this basic cryptographic technique is also helpful for many security systems.
For any pair $(X,Z)$ of correlated random variables we can think of $Z$ as a randomized function of $X$. Provided that $Z$ is short, one can make this function computationally efficient by allowing it to be only approximately correct. In folklore this problem is known as \emph{simulating auxiliary inputs}. This idea of simulating auxiliary information turns out to be a powerful tool in computer science, finding applications in complexity theory, cryptography, pseudorandomness and zero-knowledge. In this paper we revisit this problem, achieving the following results: \begin{enumerate}[(a)] We discuss and compare efficiency of known results, finding the flaw in the best known bound claimed in the TCC'14 paper "How to Fake Auxiliary Inputs". We present a novel boosting algorithm for constructing the simulator. Our technique essentially fixes the flaw. This boosting proof is of independent interest, as it shows how to handle "negative mass" issues when constructing probability measures in descent algorithms. Our bounds are much better than bounds known so far. To make the simulator $(s,ε)$-indistinguishable we need the complexity $O\left(s\cdot 2^{5\ell}ε^{-2}\right)$ in time/circuit size, which is better by a factor $ε^{-2}$ compared to previous bounds. In particular, with our technique we (finally) get meaningful provable security for the EUROCRYPT'09 leakage-resilient stream cipher instantiated with a standard 256-bit block cipher, like $\mathsf{AES256}$.
Jan Henrik Ziegeldorf, Fred Grossmann, Martin Henze, Nicolas Inden · 5 authors
Bitcoin is a digital currency that uses anonymous cryptographic identities to achieve financial privacy. However, Bitcoin's promise of anonymity is broken as recent work shows how Bitcoin's blockchain exposes users to reidentification and linking attacks. In consequence, different mixing services have emerged which promise to randomly mix a user's Bitcoins with other users' coins to provide anonymity based on the unlinkability of the mixing. However, proposed approaches suffer either from weak security guarantees and single points of failure, or small anonymity sets and missing deniability. In this paper, we propose CoinParty a novel, decentralized mixing service for Bitcoin based on a combination of decryption mixnets with threshold signatures. CoinParty is secure against malicious adversaries and the evaluation of our prototype shows that it scales easily to a large number of participants in real-world network settings. By the application of threshold signatures to Bitcoin mixing, CoinParty achieves anonymity by orders of magnitude higher than related work as we quantify by analyzing transactions in the actual Bitcoin blockchain and is first among related approaches to provide plausible deniability.
Trusted timestamping is a process for proving that certain information existed at a given point in time. This paper presents a trusted timestamping concept and its implementation in form of a web-based service that uses the decentralized Bitcoin block chain to store anonymous, tamper-proof timestamps for digital content. The service allows users to hash files, such as text, photos or videos, and store the created hashes in the Bitcoin block chain. Users can then retrieve and verify the timestamps that have been committed to the block chain. The non-commercial service enables anyone, e.g., researchers, authors, journalists, students, or artists, to prove that they were in possession of certain information at a given point in time. Common use cases include proving that a contract has been signed, a photo taken, a video recorded, or a task completed prior to a certain date. All procedures maintain complete privacy of the user's data.
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Advanced Steganography and Watermarking Techniques
The ability to assess the reputation of a member in a web community is a need addressed in many different ways according to the many different stages in which the nature of communities has evolved over time. In the case of reputation of goods/services suppliers, the solutions available to prevent the feedback abuse are generally reliable but centralized under the control of few big Internet companies. In this paper we show how a decentralized and distributed feedback management system can be built on top of the Bitcoin blockchain
Paul Lajoie-Mazenc, Emmanuelle Anceaume, Gilles Guette, Thomas Sirvent · 5 authors
—Open and large-scale systems do not encourage their users to behave trustworthily, which may entail non-negligible risks when interacting with unknown users, for instance when buying an item on an e-commerce platform. Reputation mech-anisms reduce these risks by associating a reputation score to each user, summarizing their past behavior. To be useful to users, reputation mechanisms need to guarantee two main properties: the non-monotonicity of reputation scores, in order to exactly reflect the users' behavior, and the privacy of their users, so that the history of their transactions is not publicly available. We propose a distributed privacy-preserving reputation mechanism handling non-monotonic ratings. Our proposition relies on two distinct distributed third parties and on cryptographic tools, including zero-knowledge proofs of knowledge, anonymous proxy signatures, and verifiable secret sharing. We show that this proposal is computationally efficient, and thus practical. To the best of our knowledge, this solution is the first one that preserves users' privacy and handles both positive and negative ratings without relying on a central authority.
The protocols for member expansion in secret sharing schemes are very useful for key management in dynamic topology networks. In order to reduce the computation complexity of the existed protocols for member expansion in secret sharing schemes, a new protocol is proposed based on the problem of elliptic curve discrete logarithm. This paper examines fifteen most recent patens that were awarded in the area of secret sharing. Unlike traditional detailed patent reviews that are focused on applying the simple secret sharing method, the proposed protocol has the following merits: 1) there is no trust center ; 2) only requesting broadcast 2 1 t + times to generate the sub-secret for the new participant and the new participant can verify the truth of the sub-secret; 3) the old participants can verify the new sub-secret by the noninteractive zero-knowledge proof protocol; 4) In the sub-secret generation stage, not only sub-secrets of old participants but also the sub-secret of new participant is secure. Compared to the existed protocols, the proposed protocol has lower computational complexity and less communications. Therefore, the proposed protocol has higher performance and is suitable for resource-constrained terminals of dynamic networks.
In this paper, we propose a novel zero knowledge grouping proof protocol for RFID Systems. Over the years, several protocols have been proposed in this area but they are either found to be vulnerable to certain attacks or do not comply with the EPC Class 1 Gen 2 (C1G2) standard because they use hash functions or other complex encryption schemes. Also, the unique design requirements of grouping proofs have not been fully addressed by many. Our protocol addresses these important security and design gaps in grouping proofs. We present a novel approach based on pseudo random squares and quadratic residuosity to realize a zero knowledge system. Tag operations are limited to functions such as modulo (MOD), exclusive-or (XOR) and 128 bit Pseudo Random Number Generators (PRNG). These can be easily implemented on passive tags and hence achieves compliance with the EPC Global standard while meeting the security requirements.
ECDSA has become a popular choice as lightweight alternative to RSA and classic DL based signature algorithms in recent years. As standardized, the signature produced by ECDSA for a pair of a message and a key is not deterministic. This work shows how this non-deterministic choice can be exploited by an attacker to leak private information through the signature without any side channels, an attack first discovered by Young and Yung for classic DL-based cryptosystems in 1997, and how this attack affects the application of ECDSA in the Bitcoin protocol.
Today's Internet is full of applications by which users share potentially private information with each other. Recently, the privacy concerns of users are rising and users gradually become more suspicious with respect to the use of their (personal) information. In this thesis, we aim at bringing secure multi-party computation closer to common Internet users. The main goal is to design and implement privacy-preserving reconciliation-based applications for multiple users which are secure against passive and active attackers. Additionally, our solutions should be efficient enough to be practical and usable enough even for non-technical users.As a main contribution in theory, we present different privacy-preserving multi-party reconciliation protocols based on an additively homomorphic cryptosystem that are secure against passive attackers (semi-honest model). We also propose reconciliation protocols that are secure against active attackers (malicious model) by applying zero-knowledge proof techniques. The stronger security model comes at the price of efficiency. As a prerequisite, we develop several novel cryptographic tools in the areas of privacy-preserving set operations and zero-knowledge proofs of knowledge. We also analyze to what extent fully homomorphic cryptosystems can be used for multi-party privacy-preserving reconciliation protocols. As a main contribution in practice, we introduce SMC-MuSe, a framework for Secure Multi-Party Computation on MultiSets. SMC-MuSe is a carefully designed framework for secure multi-party computation including an implementation of different cryptographic components, a support infrastructure, multi-party privacy-preserving reconciliation protocols, and two user-friendly applications for the desktop and mobile environment. We also evaluate the efficiency of the SMC-MuSe framework. In particular, we measure the computation and communication overhead of all implemented components within the SMC-MuSe framework. As a third line of work, we propose different application scenarios in the areas of event scheduling, e-voting, and electronic auctions for reconciliation protocols. We examine the practicability of one particular user-friendly application of SMC-MuSe by conducting a user study on our Android application Prefer. The user study shows that Prefer is a useful and very interesting application for today's smartphone users. Finally, we show the potential of reconciliation protocols for common Internet users by conducting a user study on privacy-preserving reconciliation in the Internet. The user study shows that our reconciliation protocols are useful in different application scenarios for common Internet users.
For the cheating problem in group signature,With the discrete logarithm problem and zero-knowledge proof protocol,and combined with the participants'identity,agroup signature scheme without trusted center is presented.In the scheme,there is no trusted key distribution center,and the dealer is also a participant,each participant's secret shadow is composed of participants through the shadow of their own secret calculation to get,the group public key recovery is invisible recovery.The analysis shows that the scheme is safe and efficient.
Cryptography relies on Mathematics in all its aspects, beginning from the constructions relying on various mathematical theories, continuing with security evaluation of cryptographic systems, and proving their security, and finally ending in implementation.Recently, new security threats are posed by the emerging quantum computing technology.Specifically, quantum algorithms can break some public-key encryption schemes such as RSA and Elgamal, which are widely used for protection of computer systems and networks.This issue demands us to develop a new generation of cryptographic systems, which will serve as secure alternatives to the currently used ones.Such the new systems are referred to as the post-quantum cryptography.One promising direction in post-quantum cryptography is the systems whose security is based on hardness of mathematical problems arising in the context of coding theory.In particular, the problem of decoding random linear codes has been studied for over 30 years, and still no polynomial-time solution has been proposed, even when using quantum algorithms.In this thesis, we focus on this area, which is called the code-based cryptography.The first code-based public-key encryption (PKE) scheme was introduced by R.J. McEliece in 1978.Since then, various code-based public-key encryption, digital signature and identification schemes were introduced, but currently, one of the main challenges is to introduce more advanced cryptographic functionalities based on coding.In this thesis, first, we give a brief introduction about post-quantum cryptography and codebased cryptography, and then we provide the background information about the cryptographic primitives, which we will study, as well as the relevant notions and results from coding theory and cryptography.Next, we introduce our contributions as follows.Firstly, we study zero-knowledge (ZK) identification schemes based q-ary linear codes.We show that when q < 5, a straightforward generalization of Stern's ZK identification scheme (1993) is more efficient in terms of both communication and computation, as compared to the ZK identification scheme by Cayrel, Vron and El Yousfi Alaoui (2010), which is specifically designed for q-ary codes.Secondly, we introduce the first proof of plaintext knowledge (PPK) for the McEliece PKE and the Niederreiter PKE.These protocols allow the encryptor to prove the knowledge of the plaintext contained in a given ciphertext to any party, who does not hold the secret key for decryption.We also provide a performance evaluation for the proposed schemes.