Bitcoin was introduced in a self-published paper by Satoshi Nakamoto in October, 2008[1, 2]. Bitcoin is a decentralized system which requires no central authority. In recent years, bitcoin has become increasingly accepted and used in many fields in place of physical cash. Bitcoin is a peer-to-peer network of nodes that distribute and record transactions [3]. Bitcoin transaction is a statement that Player 1 (address 1) would like to transfer some bitcoin values to Player 2 (address 2), signed by Player 1 by his private key. Transactions are verified by network nodes and confirmed in a public distributed ledger called the block chain. The block chain consists of a series of blocks in which each block contains the hashed value of subsequent block. Every bitcoin block contains a set of verified transactions that are collected from the bitcoin broadcast network. It is assumed that the majority of nodes in the bitcoin network are honest. This makes the verification done by the nodes is correct with high probability. More technically, bitcoin is an electronic-cash system based on cryptographic algorithms.
Open access
Advanced Steganography and Watermarking Techniques
In this paper, we identify a new form of attack, called the Balance attack, against proof-of-work blockchain systems. The novelty of this attack consists of delaying network communications between multiple subgroups of nodes with balanced mining power. Our theoretical analysis captures the precise tradeoff between the network delay and the mining power of the attacker needed to double spend in Ethereum with high probability. We quantify our probabilistic analysis with statistics taken from the R3 consortium, and show that a single machine needs 20 minutes to attack the consortium. Finally, we run an Ethereum private chain in a distributed system with similar settings as R3 to demonstrate the feasibility of the approach, and discuss the application of the Balance attack to Bitcoin. Our results clearly confirm that main proof-of-work blockchain protocols can be badly suited for consortium blockchains.
This article introduces a method of hiding transaction amounts in the strongly decentralized anonymous cryptocurrency Monero. Similar to Bitcoin, Monero is a cryptocurrency which is distributed through a proof-of-work “mining” process having no central party or trusted setup. The original Monero protocol was based on CryptoNote, which uses ring signatures and one-time keys to hide the destination and origin of transactions. Recently the technique of using a commitment scheme to hide the amount of a transaction has been discussed and implemented by Bitcoin Core developer Gregory Maxwell. In this article, a new type of ring signature, A Multilayered Linkable Spontaneous Anonymous Group signature is described which allows one to include a Pedersen Commitment in a ring signature. This construction results in a digital currency with hidden amounts, origins and destinations of transactions with reasonable efficiency and verifiable, trustless coin generation. The author would like to note that early drafts of this were publicized in the Monero Community and on the #bitcoin-wizards IRC channel. Blockchain hashed drafts are available showing that this work was started in Summer 2015, and completed in early October 2015. An eprint is also available at http://eprint.iacr.org/2015/1098.
With the widespread use of Internet, Web, and mobile technologies, a new category of applications and transactions that requires anonymity is gaining increased interest and importance. Examples of such new applications are innovative payment systems, digital notaries, electronic voting, documents sharing, electronic auctions, medical applications, and many others. In addition to anonymity, these applications and transactions also require standard security services: identification, authentication, and authorization of users and protection of their transactions. Providing those services in combination with anonymity is an especially challenging issue, because all security services require explicit user identification and authentication. To solve this issue and enable applications with security and also anonymity we introduce a new type of cryptographically encapsulated objects called BIX certificates. “BIX” is an abbreviation for “Blockchain Information Exchange.” Their purpose is equivalent to X.509 certificates: to support security services for users and transactions, but also enhanced with anonymity. This paper describes the structure and attributes of BIX certificate objects and all related protocols for their creation, distribution, and use. The BIX Certification Infrastructure (BCI) as a distributed public ledger is also briefly described.
We present cryptocurrency-based lottery protocols that do not require any collateral from the players. Previous protocols for this task required a security deposit that is $O(N^2)$ times larger than the bet amount, where $N$ is the number of players. Our protocols are based on a tournament bracket construction, and require only $O(\log N)$ rounds. Our lottery protocols thus represent a significant improvement, both because they allow players with little money to participate, and because of the time value of money. The Ethereum-based implementation of our lottery is highly efficient. The Bitcoin implementation requires an $O(2^N)$ off-chain setup phase, which demonstrates that the expressive power of the scripting language can have important implications. We also describe a minimal modification to the Bitcoin protocol that would eliminate the exponential blowup.
Open access
3 source records
Blockchain Technology Applications and Security
Cryptography and Data Security
Advanced Steganography and Watermarking Techniques
Pablo Lamela Seijas, Simon Thompson, Darryl McAdams
We give an overview of the scripting languages used in existing cryptocurrencies, and in particular we review in some detail the scripting languages of Bitcoin, Nxt and Ethereum, in the context of a high-level overview of Distributed Ledger Technology and cryptocurrencies. We survey different approaches, and give an overview of critiques of existing languages. We also cover technologies that might be used to underpin extensions and innovations in scripting and contracts, including technologies for verification, such as zero knowledge proofs, proof-carrying code and static analysis, as well as approaches to making systems more efficient, e.g. Merkelized Abstract Syntax Trees.
Ethereum represents new innovation in the fields of cryptocurrency which has become relatively stagnate, promising many things, including an entire programming language and development enviroment built into the network. However the current trend is to write implementations and proof of concepts before doing the rigor involved with proving security. Miller's recent thesis is an attempt to remedy this, and we apply his provable security techniques to the algorithm description of CASPER, the new "proof-of-stake" consensus protocol scheme to be implemented in ethereum. We conclude by stating it satisfies almost all the definitions, except one, leaving room for improvement.
The decentralized cryptocurrency Bitcoin has experienced great success but also encountered many challenges. One of the challenges has been the long confirmation time. Another challenge is the lack of incentives at certain steps of the protocol, raising concerns for transaction withholding, selfish mining, etc. To address these challenges, we propose Solida, a decentralized blockchain protocol based on reconfigurable Byzantine consensus augmented by proof-of-work. Solida improves on Bitcoin in confirmation time, and provides safety and liveness assuming the adversary control less than (roughly) one-third of the total mining power.
Ring signatures are cryptographic protocols designed to allow any member of a group to produce a signature on behalf of the group, without revealing the individual signer's identity. This offers group members a level of anonymity not attainable through generic digital signature schemes. We call this property 'plausible deniability', or anonymity with respect to an anonymity set. We concentrate in particular on implementing privacy on the blockchain, introducing a unique ring signature scheme that works with existing blockchain systems. We implement a unique ring signature (URS) scheme using secp256k1, creating the first implementation compatible with blockchain libraries in this way, so as for easy implementation as an Ethereum smart contract. We review the privacy and security properties offered by the scheme we have constructed, and compare its efficiency with other commonly suggested approaches to privacy on the blockchain.
Cloud was visualized as the authentic elucidation for rising storage space and service expenditure for Information Technology Applications. Outsourcing the data to cloud storage servers ease the client accountability by facilitating stumpy cost, secure, locality independent platforms and scalable resources. With the proliferation of cloud technologies, outsourced data is scrolling among the nodes, client unaware of storage location and no longer have possession of data. Data privacy and integrity are formidable concerns for data owners. So, verification of data integrity is vital. Thus, an efficient auditing scheme is required to guarantee data possessor so as to assure them data safety and accuracy. In this paper, we propose zero knowledge proof interactive system for data integrity verification on cloud. Our method strengthened by using Homomorphic encryption tags, generated on encrypted data with zero knowledge to the interactive members. We consider TPA (Third Party Auditor) as audit agent inside the cloud on behalf of client to reduce the communication cost. The scheme drastically reduces input and output costs by generating the probabilistic proof of possession using sampling sets of data blocks from the server. Client maintains meta data of file for verification, which reduces huge communication cost on network. Our theoretical analysis and experimental results show the efficiency of the scheme for integrity proofs.
Yasser Shoukry, Konstantinos Gatsis, Amr Alanwar, George J. Pappas · 7 authors
We consider a problem where multiple agents participate in solving a quadratic optimization problem subject to linear inequality constraints in a privacy-preserving manner. Several variables of the objective function as well as the constraints are privacy-sensitive and are known to different agents. We propose a privacy-preserving protocol based on partially homomorphic encryption where each agent encrypts its own information before sending it to an untrusted cloud computing infrastructure. To find the optimal solution the cloud applies a gradient descent algorithm on the encrypted data without the ability to decrypt it. The privacy of the proposed protocol against coalitions of colluding agents is analyzed using the cryptography notion of zero knowledge proofs.
Recent interest about the blockchain technology brought questions about its application to other systems than the cryptocurrency one. In this paper we present blockchain and discuss key applications to network systems in the literature.
Joshua Lind, Ittay Eyal, Peter Pietzuch, Emin Gün Sirer
Blockchain protocols are inherently limited in transaction throughput and latency. Recent efforts to address performance and scale blockchains have focused on off-chain payment channels. While such channels can achieve low latency and high throughput, deploying them securely on top of the Bitcoin blockchain has been difficult, partly because building a secure implementation requires changes to the underlying protocol and the ecosystem. We present Teechan, a full-duplex payment channel framework that exploits trusted execution environments. Teechan can be deployed securely on the existing Bitcoin blockchain without having to modify the protocol. It: (i) achieves a higher transaction throughput and lower transaction latency than prior solutions; (ii) enables unlimited full-duplex payments as long as the balance does not exceed the channel's credit; (iii) requires only a single message to be sent per payment in any direction; and (iv) places at most two transactions on the blockchain under any execution scenario. We have built and deployed the Teechan framework using Intel SGX on the Bitcoin network. Our experiments show that, not counting network latencies, Teechan can achieve 2,480 transactions per second on a single channel, with sub-millisecond latencies.
Provable data possession (PDP) is a technique for ensuring the integrity of data in storage outsourcing. In this paper, we address the construction of an efficient PDP scheme for distributed cloud storage to support the scalability of service and data migration, in which we consider the existence of multiple cloud service providers to cooperatively store and maintain the clients' data. We present a cooperative PDP (CPDP) scheme based on homomorphic verifiable response and hash index hierarchy. We prove the security of our scheme based on multi-prover zero-knowledge proof system, which can satisfy completeness, knowledge soundness, and zero-knowledge properties. In addition, we also propose a fuzzy clustering system for analyzing the high dimensional Data bases in cloud Environments. This paper proposes novel effective fuzzy soft clustering systems with the combination of possibilistic c-means.
The blockchain is a distributed network that records digital transactions on a publicly-accessible ledger. This paper explores whether blockchain technology is a suitable platform for the preservation of digital signatures and key pairs (public and private keys). Conventional infrastructures use digital certificates, issued by certification authorities, to declare the authentication of key pairs and digital signatures. However, this paper suggests that the blockchain’s hash functions can replace those certificates on the grounds of better privacy, that the nature of the network removes the problem of a single point of failure and that hashing is a form of authentication that does not require trust in a third-party authority. This article was an appendix to the research paper, Blockchain Technology for Recordkeeping which is available in the Reports section at http://www.blockchainubc.ca/main/dissemination.
Unlinkability and accountability are conflicting yet critical requirements that need to be addressed in order to preserve users' privacy as well as to protect service providers in today identity ecosystems. In this paper we present a pseudonymous identity management system in which users can carry out unlinkable on-line transactions without having to disclose their actual identity information in plain text to the service providers. At the same time, the service providers have strong assurance about the authenticity of the transactions. In our approach, users' identity is cryptographically encoded in pseudonymous identity tokens. % issued by trusted identity providers. Our system includes a lightweight policy language which enables users and service providers to express their requirements pertaining to pseudonymous identity verification and a suite of protocols based on zero-knowledge-proofs which enables the fulfillment of these requirements. We have implemented a prototype of the proposed system and carried out a security and performance analysis.
Space Information Network (SIN) plays an important role in civil and national defense field, and it is highly emphasized by governments. Data transmitted and processed in SIN is massive and dynamic, which is collected by entities in the space. However, with the widely development of SIN, data security in storage and communication is facing a great challenge, and network-based attacks would leak top-secret information, which may lead to social unrest or even threatening national security. Members in SIN like the satellites, spacecrafts and aircrafts normally transmit data in clusters divided according to their function, mission and position, and each member has a superior in the upper layer. Thus we propose a secure and anonymous data transmission system for cluster organised Space Information Network in this paper to improve the security in SIN. Members in this system transmit data in clusters, and there is a cluster head managing all its cluster members. The public key is a meaningful string like the receiver's identity, which is convenient for senders to check the correctness. To reduce the burden of a single public key generator (PKG), private key can be generated from the superior in the upper layer. In addition, messages transmitted in this system are anonymous, while in consideration of non-repudiation, a cluster head can trace the message sender if there are disputes occurring, thus the malicious cluster member will be eliminated by the cluster head. Finally, zero-knowledge proof systems are used to ensure that the ciphertext is generated legally. This system is proved in a full version paper, which is semantic secure, anonymous and traceable, with a perfectly zero-knowledge proof, and its efficient performance shows that it can be applied in SIN.
Digital traces play an increasingly important role in our society. Whether in the context of regulatory compliance, contractual exchanges or simply for general interactions, people need to be able to document trustworthy facts. Most approaches today rely either on Trusted Third Parties, at best, or more generally on collecting such traces after problems occur in ways where their authenticity may be arguable (fabricated, doctored). Blockchain technology offers an interesting alternative to the problem by allowing documenting transactions in a distributed consensus ledger with transparency and immutability properties. This paper proposes a new approach to the problem leveraging blockchain technology towards providing a framework for distributed trustworthy logging of digital facts and traces on the blockchain as they happen or are needed before problems arise. Disintermediation of such processes is likely to significantly help raise trust and accountability in many aspects of our interactions, whether online or offline.
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 μR-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.
In this paper, we initiate a formal study of transparency, which in recent years has become an increasingly critical requirement for the systems in which people place trust. We present the abstract concept of a transparency overlay, which can be used in conjunction with any system to give it provable transparency guarantees, and then apply the overlay to two settings: Certificate Transparency and Bitcoin. In the latter setting, we show that the usage of our transparency overlay eliminates the need to engage in mining and allows users to store a single small value rather than the entire blockchain. Our transparency overlay is generically constructed from a signature scheme and a new primitive we call a dynamic list commitment, which in practice can be instantiated using a collision-resistant hash function.