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.
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.
Currently, SLAs assurance forms one of the major challenges for Cloud Computing (CC) in order to guarantee Quality of Service (QoS) in real-time and control SLA violations. Autonomous and flexible agents and Multi-agent systems (MASs) are suitable tools for self-detection of failures and self-monitoring of cloud operations and services, QoS negotiation and SLA management. They're designed to operate in a dynamically changing environment. MASs offer new features such as autonomy, pro-activity, communication, cooperation, and negotiation, which can help cloud computing platforms to offer solutions that aren't available in current cloud infrastructures. Our main motivation to integrating MASs is their ability to make clouds smarter in their interactions. This paper introduces a Trusted third party (TTP) based on Multi-agent systems in order to control the quality of service contract and guarantee transparency and symmetry with respect to the SLA contract between prospective signatories. This TTP will use MASs to apply an advanced penalty model that guarantees the performance and the reliability of the Cloud.
The English version of this paper can be found at: http://ssrn.com/abstract=2709713 Italian Abstract: La tecnologia fondamentale del protocollo Bitcoin, conosciuta come blockchain, è emersa recentemente in tutta la sua straordinaria portata innovativa, teoricamente in grado di riconfigurare le nostre attuali interazioni economiche, politiche e sociali. Sebbene l'interesse accademico per questa tecnologia sia ormai crescente, finora non è stata ancora divulgata un'analisi esaustiva delle sue applicazioni dal punto di vista politologico. Questa ricerca si propone di discutere i punti essenziali di una governance decentralizzata fondata sulla blockchain, che sfida in varia misura i meccanismi tradizionali della autorità statale, della cittadinanza e della democrazia. In particolare, la ricerca si pone l'obiettivo di verificare la performance della blockchain e delle piattaforme decentralizzate come strumenti iperpolitici, in grado cioè di gestire interazioni sociali su ampia scala e di destituire eventualmente le autorità centrali tradizionali. L'analisi evidenzia i rischi relativi a posizioni dominanti di natura privatistica negli ecosistemi distribuiti, che potrebbero spogliare i cittadini dei loro diritti e permettere l'insorgere di una società globale senza stato. Se gli utopisti tecnologici sollecitano la destituzione di qualsiasi autorità centrale, questa ricerca difende invece il ruolo dello Stato come necessario punto di coordinazione nella società civile e dimostra come la decentralizzazione attuata attraverso algoritmi e sistemi di consenso distribuito costituisca una teoria organizzativa, non una teoria politica autonoma. English Abstract: The core technology of Bitcoin, the blockchain, has recently emerged as a disruptive innovation with a wide range of applications, potentially able to redesign our interactions in business, politics and society at large. Although scholarly interest in this subject is growing, a comprehensive analysis of blockchain applications from a political perspective is severely lacking to date. This paper aims to fill this gap and it discusses the key points of blockchain-based decentralized governance, which challenges to varying degrees the traditional mechanisms of State authority, citizenship and democracy. In particular, the paper verifies to which extent blockchain and decentralized platforms can be considered as hyper-political tools, capable to manage social interactions on large scale and dismiss traditional central authorities. The analysis highlights risks related to a dominant position of private powers in distributed ecosystems, which may lead to a general disempowerment of citizens and to the emergence of a stateless global society. While technological utopians urge the demise of any centralized institution, this paper advocates the role of the State as a necessary central point of coordination in society, showing that decentralization through algorithm-based consensus is an organizational theory, not a stand-alone political theory.
Project development in a power enterprise always needs to authorize external devices access to the enterprise intranet for testing. In order to avoid an external device with a virus and pose a security risk to the power information system, external devices should have strict security assessment before access the enterprise intranet. But after the security assessment, the device user still be possible to change the platform configuration. Remote attestation is one of important measures when two sides need to communicate. It is concernful to attest the remote platform is trusty but not revealing the any private information of the platform. For this reason, we designed a novel remote anonymous attestation protocol based on TCM. The proposed protocol does not need extra zero knowledge proof and the involvement of the third trusted party and the composite signature scheme is proved secure against existential forgery on adaptively chosen message. So this protocol has better security and execution property.
As for the security of digital signature,this paper takes advantage of the discrete logarithm problem and zeroknowledge proof protocol,combines with( t,n) threshold signature scheme and the identity of the participants,and presents a digital signature scheme based on secret sharing. In the scheme,there is no trusted key distribution center,and the secret share of the participants is generated by the participants themselves and can be used repeatedly,furthermore,the identity of the participants is generated by their own secret share. Only the public information can be updated,which will not affect the participants' secret share. Anyone can detect whether the dealer is cheating the participants or whether there is cheating between participants. Only the authorized subset client can represent group to sign; the generation and verification of the partial signature and group signature are effective. The discrete logarithm problem and zero-knowledge proof protocol guarantees the security of information transmission,which further improves the security of the scheme. The analysis indicates that the scheme is safe and efficient.
Can an exchange be “dark,” so that orders are not displayed, while simultaneously trustworthy, so that the execution of trades and flow of information occur as promised? SEC actions against dark pools suggest cause for concern, and regulators seem to be moving towards requiring more disclosure. Yet there is a clear tension: trading order information is widely exploited. Therefore, institutional investors have a strong interest in keeping pre-trade information about large trades hidden. Secrecy-preserving proofs of correctness can be used to build trust without revealing unnecessary information. By performing operations on obfuscated representations of orders (perhaps encrypted or otherwise hidden), a zero knowledge proof can be provided, allowing anyone to verify correctness of trades. Crucially, this can be done without revealing any information beyond this correctness. This technology can be usefully applied to construct provably trustworthy dark pools. Additional practical protocols relax the definition of “zero knowledge" to reveal limited information, providing necessary transparency for efficient market operation while limiting information that can be exploited by observers. Coupled with Trusted Computing hardware, these protocols can provide an excellent balance of practicality with secrecy
David Derler, Henrich C. Pöhls, Kai Samelin, Daniel Slamanig
Abstract. A redactable signature scheme (RSS) allows removing parts of a signed message by any party without invalidating the respective signa-ture. State-of-the-art constructions thereby focus on messages represented by one specific data-structure, e.g., lists, sets or trees, and adjust the secu-rity model accordingly. To overcome the necessity for this myriad of models, we present a general framework covering arbitrary data-structures and even more sophisticated possibilities. For example, we cover fixed elements which must not be redactable and dependencies between elements. Moreover, we introduce the notion of designated redactors, i.e., the signer can give some extra information to selected entities which become redactors. In practice, this often allows to obtain more efficient schemes. We then present two RSSs; one for sets and one for lists, both constructed from any EUF-CMA secure signature scheme and indistinguishable cryptographic accumulators in a black-box way and show how the concept of designated redactors can be used to increase the efficiency of these schemes. Finally, we present a black-box construction of a designated redactor RSS by combining an RSS for sets with non-interactive zero-knowledge proof systems. All the three constructions presented in this paper provide transparency, which is an im-portant property, but quite hard to achieve, as we also conceal the length of the original message and the positions of the redactions. 1
Matteo Maffei, Giulio Malavolta, Manuel Reinert, Dominique Schröder
Cloud storage has rapidly become a cornerstone of many IT infrastructures, constituting a seamless solution for the backup, synchronization, and sharing of large amounts of data. Putting user data in the direct control of cloud service providers, however, raises security and privacy concerns related to the integrity of outsourced data, the accidental or intentional leakage of sensitive information, the profiling of user activities and so on. Furthermore, even if the cloud provider is trusted, users having access to outsourced files might be malicious and misbehave. These concerns are particularly serious in sensitive applications like personal health records and credit score systems. To tackle this problem, we present GORAM, a cryptographic system that protects the secrecy and integrity of outsourced data with respect to both an untrusted server and malicious clients, guarantees the anonymity and unlink ability of accesses to such data, and allows the data owner to share outsourced data with other clients, selectively granting them read and write permissions. GORAM is the first system to achieve such a wide range of security and privacy properties for outsourced storage. In the process of designing an efficient construction, we developed two new, generally applicable cryptographic schemes, namely, batched zero-knowledge proofs of shuffle and an accountability technique based on chameleon signatures, which we consider of independent interest. We implemented GORAM in Amazon Elastic Compute Cloud (EC2) and ran a performance evaluation demonstrating the scalability and efficiency of our construction.
Memory-hard functions are becoming an important tool in the design of password hashing schemes, cryptocur-rencies, and more generic proof-of-work primitives that are x86-oriented and can not be computed on dedicated hardware more efficiently. We develop a simple and cryptographically secure approach to the design of such functions and show how to exploit the architecture of modern CPUs and memory chips to make faster and more secure schemes compared to existing alternatives such as scrypt. We also propose cryptographic criteria for the components, that prevent cost reductions using time-memory tradeoffs and side-channel leaks. The concrete proof-of-work instantiation, which we call Argon2, can fill GBytes of RAM within a second, is resilient to various tradeoffs, and is suitable for a wide range of applications, which aim to bind a computation to a certain architecture. Concerning potential DoS attacks, our scheme is lightweight enough to offset the bottleneck from the CPU to the memory bus thus leaving sufficient computing power for other tasks. We also propose parameters for which our scheme is botnet resistant. As an application, we suggest a cryptocurrency design with fast and memory-hard proof-of-work, which allows memoryless verification. 1
Kourosh Davarpanah, Dan Kaufman, Ophelie Pubellier
NeuCoin is a decentralized peer-to-peer cryptocurrency derived from Sunny\nKing's Peercoin, which itself was derived from Satoshi Nakamoto's Bitcoin. As\nwith Peercoin, proof-of-stake replaces proof-of-work as NeuCoin's security\nmodel, effectively replacing the operating costs of Bitcoin miners\n(electricity, computers) with the capital costs of holding the currency.\nProof-of-stake also avoids proof-of-work's inherent tendency towards\ncentralization resulting from competition for coinbase rewards among miners\nbased on lowest cost electricity and hash power.\n NeuCoin increases security relative to Peercoin and other existing\nproof-of-stake currencies in numerous ways, including: (1) incentivizing nodes\nto continuously stake coins over time through substantially higher mining\nrewards and lower minimum stake age; (2) abandoning the use of coin age in the\nmining formula; (3) causing the stake modifier parameter to change over time\nfor each stake; and (4) utilizing a client that punishes nodes that attempt to\nmine on multiple branches with duplicate stakes.\n This paper demonstrates how NeuCoin's proof-of-stake implementation addresses\nall commonly raised "nothing at stake" objections to generic proof-of-stake\nsystems. It also reviews many of the flaws of proof-of-work designs to\nhighlight the potential for an alternate cryptocurrency that solves these\nflaws.\n
We provide a framework for constructing leakage-resilient identification (ID) protocols in the bounded retrieval model (BRM) from proofs of storage (PoS) that hide partial information about the file. More precisely, we describe a generic transformation from any zero-knowledge PoS to a leakage-resilient ID protocol in the BRM. We then describe a ZK-PoS based on RSA which, under our transformation, yields the first ID protocol in the BRM based on RSA (in the ROM). The resulting protocol relies on a different computational assumption and is more efficient than previously-known constructions.
We describe a zero-knowledge proof system in which a prover holds a large dataset M and can repeatedly prove NP relations about that dataset. That is, for any (public) relation R and x, the prover can prove that ∃w: R(M,x,w) = 1. After an initial setup phase (which depends only on M), each proof requires only a constant number of rounds and has communication/computation cost proportional to that of a random-access machine (RAM) implementation of R, up to poly-logarithmic factors. In particular, the cost per proof in many applications is sublinear in |M |. Additionally, the storage requirement between proofs for the verifier is constant. 1
PGP is built upon a Distributed Web of Trust in which the trustworthiness of a user is established by others who can vouch through a digital signature for that particular identity. Preventing its wholesale adoption are a number of inherent weaknesses to include (but not limited to) the following: 1) Trust Relationships are built on a subjective honor system, 2) Only first degree relationships can be fully trusted, 3) Levels of trust are difficult to quantify with actual values, and 4) Issues with the Web of Trust itself (Certification and Endorsement). Although the security that PGP provides is proven to be reliable, it has largely failed to garner large scale adoption. In this paper, we propose several novel contributions to address the aforementioned issues with PGP and associated Web of Trust. To address the subjectivity of the Web of Trust, we provide a new certificate format based on Bitcoin which allows a user to verify a PGP certificate using Bitcoin identity-verification transactions - forming first degree trust relationships that are tied to actual values (i.e., number of Bitcoins transferred during transaction). Secondly, we present the design of a novel Distributed PGP key server that leverages the Bitcoin transaction blockchain to store and retrieve Bitcoin-Based PGP certificates. Lastly, we provide a web prototype application that demonstrates several of these capabilities in an actual environment.
Recent technological advances have given rise to the popularity and success of cloud. This new paradigm is gaining an expanding interest, since it provides cost efficient architectures that support the transmission, storage, and intensive computing of data. However, these promising storage services bring many challenging design issues, considerably due to the loss of data control. These challenges, namely data confidentiality and data integrity, have significant influence on the security and performances of the cloud system. This thesis aims at overcoming this trade-off, while considering two data security concerns. On one hand, we focus on data confidentiality preservation which becomes more complex with flexible data sharing among a dynamic group of users. It requires the secrecy of outsourced data and an efficient sharing of decrypting keys between different authorized users. For this purpose, we, first, proposed a new method relying on the use of ID-Based Cryptography (IBC), where each client acts as a Private Key Generator (PKG). That is, he generates his own public elements and derives his corresponding private key using a secret. Thanks to IBC properties, this contribution is shown to support data privacy and confidentiality, and to be resistant to unauthorized access to data during the sharing process, while considering two realistic threat models, namely an honest but curious server and a malicious user adversary. Second, we define CloudaSec, a public key based solution, which proposes the separation of subscription-based key management and confidentiality-oriented asymmetric encryption policies. That is, CloudaSec enables flexible and scalable deployment of the solution as well as strong security guarantees for outsourced data in cloud servers. Experimental results, under OpenStack Swift, have proven the efficiency of CloudaSec in scalable data sharing, while considering the impact of the cryptographic operations at the client side. On the other hand, we address the Proof of Data Possession (PDP) concern. In fact, the cloud customer should have an efficient way to perform periodical remote integrity verifications, without keeping the data locally, following three substantial aspects : security level, public verifiability, and performance. This concern is magnified by the client’s constrained storage and computation capabilities and the large size of outsourced data. In order to fulfill this security requirement, we first define a new zero-knowledge PDP proto- col that provides deterministic integrity verification guarantees, relying on the uniqueness of the Euclidean Division. These guarantees are considered as interesting, compared to several proposed schemes, presenting probabilistic approaches. Then, we propose SHoPS, a Set-Homomorphic Proof of Data Possession scheme, supporting the 3 levels of data verification. SHoPS enables the cloud client not only to obtain a proof of possession from the remote server, but also to verify that a given data file is distributed across multiple storage devices to achieve a certain desired level of fault tolerance. Indeed, we present the set homomorphism property, which extends malleability to set operations properties, such as union, intersection and inclusion. SHoPS presents high security level and low processing complexity. For instance, SHoPS saves energy within the cloud provider by distributing the computation over multiple nodes. Each node provides proofs of local data block sets. This is to make applicable, a resulting proof over sets of data blocks, satisfying several needs, such as, proofs aggregation
Digital signature schemes are a foundational cryptographic building block in certification and the projection of trust. Based on a signature scheme on committed graphs, we propose a framework of certification and proof methods to sign topology graphs and to prove properties of their certificates in zero-knowledge. This framework allows an issuer, such as an auditing system, to sign the topology representation of an infrastructure. The prover, such as an infrastructure provider, can then convince a verifier of topology properties including connectivity and isolation without disclosing the blueprint of the topology itself. By that, we can certify the structure of critical systems while still maintaining confidentiality. We offer zero-knowledge proofs of knowledge for a general specification language of security goals for virtualized infrastructures such that high-level security goals can be proven over topology certificates. We offer an efficient and practical construction, built upon the Camenisch-Lysyanskaya signature scheme, honest-verifier proofs and the strong RSA assumption.
The increasing demand in promoting cloud computing in either business or other areas requires more security of a cloud storage system. Traditional cloud storage systems fail to protect data integrity information (DII), when the interactive messages between the client and the data storage server are sniffed. To protect DII and support public verifiability, we propose a data integrity verification scheme by deploying a designated confirmer signature DCS as a building block. The DCS scheme strikes the balance between public verifiable signatures and zero-knowledge proofs which can address disputes between the cloud storage server and any user, whoever acting as a malicious player during the two-round verification. In addition, our verification scheme remains blockless and stateless, which is important in conducting a secure and efficient cryptosystem. We perform security analysis and performance evaluation on our scheme, and compared with the existing schemes, the results show that our scheme is more secure and efficient.
Provable data possession (PDP) is one of the techniques to ensure the integrity of data in storage outsourcing. Here in this paper, we speak to the creation of an efficient PDP method for distributed cloud storage to maintain the scalability of service and data migration. On the basis on homomorphic verifiable response and hash index hierarchy we projected a cooperative PDP (CPDP) method. We confirm the security of our method based on multi-prover zeroknowledge proof scheme, which can satisfy knowledge soundness, fullness , and zero-knowledge properties. As well, we expressive performance optimization mechanisms for our method, and in particular present an capable method for selecting finest parameter values to reduce the addition expenses of storage service providers and client. Our experiment shows that our solution introduces lower addition and communication overheads in evaluation with noncooperative approaches.