We address two problems: first, we study a variant of block withholding (BWH) attack in Bitcoins and second, we propose solutions to prevent all existing types of BWH attacks in Bitcoins. We analyze the strategies of a selfish Bitcoin miner who in connivance with one pool attacks another pool and receives reward from the former mining pool for attacking the latter. We name this attack as âsponsored block withholding attack.â We present detailed quantitative analysis of the monetary incentive that a selfish miner can earn by adopting this strategy under different scenarios. We prove that under certain conditions, the attacker can maximize her revenue by adopting some strategies and by utilizing her computing power wisely. We also show that an attacker may use this strategy for attacking both the pools for earning higher amount of incentives. More importantly, we present a strategy that can effectively counter block withholding attack in any mining pool. First, we propose a generic scheme that uses cryptographic commitment schemes to counter BWH attack. Then, we suggest an alternative implementation of the same scheme using hash function. Our scheme protects a pool from rogue miners as well as rogue pool administrators. The scheme and its variant defend against BWH attack by making it impossible for the miners to distinguish between a partial proof of work and a complete proof of work. The scheme is so designed that the administrator cannot cheat on the entire pool. The scheme can be implemented by making minor changes to existing Bitcoin protocol. We also analyze the security of the scheme.
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
Tao Jiang, Xiaofeng Chen, Qianhong Wu, Jianfeng Ma · 6 authors
Cross-client data deduplication has been widely used to eliminate redundant storage overhead in cloud storage system. Recently, Abadi et al. introduced the primitive of MLE2 with nice security properties for secure and efficient data deduplication. However, besides the computationally expensive noninteractive zero-knowledge proofs, their fully randomized scheme (R-MLE2) requires the inefficient equality-testing algorithm to identify all duplicate ciphertexts. Thus, an interesting challenging problem is how to reduce the overhead of R-MLE2 and propose an efficient construction for R-MLE2. In this paper, we introduce a new primitive called ÎŒR-MLE2, which gives a partial positive answer for this challenging problem. We propose two schemes: static scheme and dynamic scheme, where the latter one allows tree adjustment by increasing some computation cost. Our main trick is to use the interactive protocol based on static or dynamic decision trees. The advantage gained from it is, by interacting with clients, the server will reduce the time complexity of deduplication equality test from linear time to efficient logarithmic time over the whole data items in the database. The security analysis and the performance evaluation show that our schemes are Path-PRV-CDA2 secure and achieve several orders of magnitude higher performance for data equality test than R-MLE2 scheme when the number of data items is relatively large.
Fan Zhang, Ethan Cecchetti, Kyle Croman, Ari Juels · 5 authors
Smart contracts are programs that execute autonomously on blockchains. Their key envisioned uses (e.g. financial instruments) require them to consume data from outside the blockchain (e.g. stock quotes). Trustworthy data feeds that support a broad range of data requests will thus be critical to smart contract ecosystems.
Blockchain is an information technology solution for distributed digital record. Its main properties are secure, traceable, and transparent. Blockchain was first proposed for bitcoin, a decentralized virtual digital currency. Recently, blockchain draws attentions of researchers, entrepreneurs, and investors, because people found that blockchain technology can revolutionize many business practices. This paper describes the fundamentals of blockchain technology, including data structure, data distribution, and transaction execution and validation. This paper also discusses the representative blockchain protocols and development platforms. In addition, this paper outlines the potential applications of blockchain technology and the broader impact it might bring to industry, business, and beyond.
Cloud storage services allow users to outsource their data to cloud servers to save on local data storage costs. However, unlike using local storage devices, users don't physically own the data stored on cloud servers and can't be certain about the integrity of the cloud-stored data. Many public verification schemes have been proposed to allow a third-party auditor to verify the integrity of outsourced data. However, most of these schemes assume that the auditors are honest and reliable, so are vulnerable to malicious auditors. Moreover, in most of these schemes, an external adversary could modify the outsourced data and tamper with the interaction messages between the cloud server and the auditor, thus invalidating the outsourced data integrity verification. This article proposes an efficient and secure public verification of data integrity scheme that protects against external adversaries and malicious auditors. The proposed scheme adopts a random masking technique to protect against external adversaries, and requires users to audit auditors' behaviors to prevent malicious auditors from fabricating verification results. It uses Bitcoin to construct unbiased challenge messages to thwart collusion between malicious auditors and cloud servers. A performance analysis demonstrates that the proposed scheme is efficient in terms of the user's auditing overhead.
Blockchain is a radical innovation that has a significant impact on payments, stock exchanges, cybersecurity, and computational law. However, it has significant limitations regarding uncertainty for a transaction to be confirmed. This paper proposes a new system for exact confirmation of transactions in a block. Replacing original signature, a new Interactive Incontestable Signature (IIS) scheme is used between dealer and owner to confirm a transaction. By this signature, the dealer can assure the owner that a transaction will be included into blockchain in a non-repudiation way. The scheme is proved to be secure for owner's unforgeability and dealer's incontestability.
BenoĂźt Libert, Fabrice Mouhartem, Thomas Peters, Moti Yung
Digital signatures are perhaps the most important base for authentication and trust relationships in large scale systems. More specifically, various applications of signatures provide privacy and anonymity preserving mechanisms and protocols, and these, in turn, are becoming critical (due to the recently recognized need to protect individuals according to national rules and regulations). A specific type of signatures called "signatures with efficient protocols", as introduced by Camenisch and Lysyanskaya (CL), efficiently accommodates various basic protocols and extensions like zero-knowledge proofs, signing committed messages, or re-randomizability. These are, in fact, typical operations associated with signatures used in typical anonymity and privacy-preserving scenarios.
Jeril Kuriakose, Pushpendra Singh Sisodia, V. Amruth, Dhvani Shah · 5 authors
Cryptography and complexity theory have gained a lot of importance because of zero-knowledge proofs. The motive behind zero-knowledge proofs are to provide an obfuscation to the verifier, so that the verifier will not understand the information sent by the prover. Zero-knowledge proofs are normally used to verify a prover's theorem to a verifier, in such a way that the verifier will not be able to discover any supplementary evidence other than the proof given to him. An enigmatic conception was formalized, that lead to the formation zero-knowledge proof systems. In this paper, we have reviewed different zero-knowledge argument / proof techniques. We have also reviewed the proof system implications in the presence of malicious prover and malicious verifier. Examples related to zero-knowledge argument systems are also given.
Bitcoin [24] is a fully decentralized electronic cash system. The generation of the proof-of-work in Bitcoin requires large amount of computing resources. However, this huge amount of energy is wasted as one cannot make something useful out of it. In this paper, we propose a scheme called Retricoin which replaces the heavy computational proof-of-work of Bitcoin by proofs of retrievability that have practical benefits. To guarantee the availability of an important but large file, we distribute the segments of the file among the users in the Bitcoin network. Every user who wants to mine Bitcoins must store a considerable portion of this file and prove her storage to other peers in the network using proofs of retrievability. The file can be constructed at any point of time from the users storing their respective segments untampered. Retricoin is more efficient than the existing Permacoin scheme [23] in terms of storage overhead and network bandwidth required to broadcast the proof to the Bitcoin network. The verification time in our scheme is comparable to that of Permacoin and reasonable for all practical purposes. We also design an algorithm to let the miners in a group (or pool) mine collectively.
Cryptographic accumulators allow to succinctly represent a set by an accumulation value with respect to which short non-membership proofs about the set can be efficiently constructed and verified. Traditionally, their security captures soundness but offers no privacy: Convincing proofs reliably encode set membership, but they may well leak information about the accumulated set.
In this paper we put forward a strong privacy-preserving enhancement by introducing and devising zero-knowledge accumulators that additionally provide hiding guarantees: Accumulation values and proofs leak nothing about a dynamic set that evolves via element insertions/deletions. We formalize the new property using the standard real-ideal paradigm, namely demanding that an adaptive adversary with access to query/update oracles, cannot tell whether he interacts with honest protocol executions or a simulator fully ignorant of the set even of the type of updates on it. We rigorously compare the new primitive to existing ones for privacy-preserving verification of set membership or other relations and derive interesting implications among related security definitions, showing that zero-knowledge accumulators offer stronger privacy than recent related works by Naor et al. [TCCiŸ?2015] and Derler et al. [CT-RSAiŸ?2015]. We construct the first dynamic universal zero-knowledge accumulator that we show to be perfect zero-knowledge and secure under the q-Strong Bilinear Diffie-Hellman assumption.
Finally, we extend our new privacy notion and our new construction to provide privacy-preserving proofs also for an authenticated dynamic set collection--a primitive for efficiently verifying more elaborate set operations, beyond set-membership. We introduce a primitive that supports a zero-knowledge verifiable set algebra: Succinct proofs for union, intersection and set difference queries over a dynamically evolving collection of sets can be efficiently constructed and optimally verified, while--for the first time--they leak nothing about the collection beyond the query result.
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.
Internet of Things (IoT) are being adopted for industrial and manufacturing applications such as manufacturing automation, remote machine diagnostics, prognostic health management of industrial machines and supply chain management. Cloud-Based Manufacturing is a recent on-demand model of manufacturing that is leveraging IoT technologies. While Cloud-Based Manufacturing enables on-demand access to manufacturing resources, a trusted intermediary is required for transactions between the users who wish to avail manufacturing services. We present a decentralized, peer-to-peer platform called BPIIoT for Industrial Internet of Things based on the Block chain technology. With the use of Blockchain technology, the BPIIoT platform enables peers in a decentralized, trustless, peer-to-peer network to interact with each other without the need for a trusted intermediary.
Liang-Ao Zhang, Xingming Sun, Zhihua Xia, Qiuju Ji
Attribute-Based Encryption (ABE) is a promising cryptographic primitive to implement access control for secure data storage in the cloud. Since the data owner may frequently change the access policies defined in the ciphertext, it is significant to provide the capacity for dynamic policy updating. However the cloud should also authenticate the owner because the adversary may modify the access policies of the files in the cloud to prevent the legal users from accessing them. In this paper, we focus on the owner's authentication in the ABE systems and propose a novel scheme which enables access control with authenticated dynamic policy updating in the cloud. We adapt the Pedersen commitment and Zero Knowledge Proof of Knowledge (ZKPK) to realize the anonymous authentication of the owner's policy updating key without increasing any secret information to the owner side. The analysis shows that our scheme is authentic and efficient as well as adaptive to different types of access policies.
Eli BenâSasson, Alessandro Chiesa, Matthew Green, Eran Tromer · 5 authors
Non-interactive zero-knowledge proofs (NIZKs) are a powerful cryptographic tool, with numerous potential applications. However, succinct NIZKs (e.g., zk-SNARK schemes) necessitate a trusted party to generate and publish some public parameters, to be used by all provers and verifiers. This party is trusted to correctly run a probabilistic algorithm (specified by the the proof system) that outputs the public parameters, and publish them, without leaking any other information (such as the internal randomness used by the algorithm), violating either requirement may allow malicious parties to produce convincing "proofs" of false statements. This trust requirement poses a serious impediment to deploying NIZKs in many applications, because a party that is trusted by all users of the envisioned system may simply not exist. In this work, we show how public parameters for a class of NIZKs can be generated by a multi-party protocol, such that if at least one of the parties is honest, then the result is secure (in both aforementioned senses) and can be subsequently used for generating and verifying numerous proofs without any further trust. We design and implement such a protocol, tailored to efficiently support the state-of-the-art NIZK constructions with short and easy-to-verify proofs (Parno et al. IEEE S&P '13, Ben-Sasson et al. USENIX Sec '14, Danezis et al., ASIACRYPT '14). Applications of our system include generating public parameters for systems such as Zero cash (Ben-Sasson et al. IEEE S&P '13) and the scalable zero-knowledge proof system of (Ben-Sasson et al. CRYPTO '14).