Jul 1, 2018·2018 IEEE International Conference on Internet of Things (iThings) and IEEE Green Computing and Communications (GreenCom) and IEEE Cyber, Physical and Social Computing (CPSCom) and IEEE Smart Data (SmartData)
Damiano Di Francesco Maesa, Paolo Mori, Laura Ricci
This paper presents a new design approach for Access Control services leveraging smart contracts provided by blockchain technology. The key idea of our proposal is to codify Access Control policies as executable smart contracts on a blockchain. This transforms the policy evaluation process into completely distributed smart contract executions. In our fully blockchain based approach also the Attribute Managers required for the evaluation of the Access Control policies are managed by the blockchain, i.e., they are implemented as smart contracts as well. To study the feasibility of our proposal we present a working reference implementation using XACML policies and Solidity written smart contracts deployed on Ethereum. Finally we evaluate the advantages and drawbacks of the proposal, making also use of experimental results of our reference implementation.
As blockchain technologies mature and ecosystems over blockchain evolve, peers on blockchain networks often face situations in which they need to conduct voting for decision-making; as happened in the case of the DAO hard fork event on Ethereum. However, a natively built-in voting mechanism is not available on any of the existing blockchain platforms. Thus, the decision making either is delegated to a few network members who make such decisions offline or is dependent on third party online voting services. In both cases, peers directly or indirectly rely on trusted parties or centralized systems. This is against the basic decentralization principle of blockchain and exposes the election to frauds. To facilitate decision-making in a decentralized and secure manner, we propose a native blockchain voting protocol for peers to vote over their existing blockchain network without the need of any trusted or third party. Our protocol preserves end-to-end privacy and possesses desirable properties such as detectability and correctability against cheating. A reference implementation of our protocol on Hyperledger Fabric that demonstrates the validity and practical applicability of our protocol is also provided.
Blockchain is one of the technology innovations for sharing data across organizations through a peer to peer overlay network. Many blockchain- based data sharing applications, such as sharing Electronic Health Records (EHRs) among different Care Delivery Organizations (CDOs), require privacy preserving verification services with dual capabilities. On one hand, the users want to verify the authenticity of EHR data as well as the identity of the signer. On the other hand, the signer wants to keep his real identity private such that others cannot trace and infer his identity information. However, typical blockchain systems that use pseudonyms as public keys, such as Bitcoin's blockchain, cannot support such privacy-preserving verification. In such systems, it is hard to verify the authenticity of signer's identity, and adversaries or curious parties can guess the real identity from the series of statements and actions taken with a specific pseudonym through inference attacks, such as by transaction graph analysis. In this paper, we propose a decentralized attribute- based signature scheme for healthcare blockchain, which provides efficient privacy-preserving verification of authenticity of EHR data and signer's identity. We also describe a holistic on-chain and off- chain collaborative storage system for efficient storage and verification EHR data. The analysis and experiments show that our scheme is effective and deployable.
The blockchain emerged as a novel distributed consensus scheme that allows transactions, and any other data, to be securely stored and verified without the need of any centralized authority. Distributed trust and therefore security and privacy are at the core of the blockchain technologies, and have the potential to either make them a success or cause them to fail. This special issue of IEEE Security & Privacy is an attempt to collect the most interesting ideas from the community of researchers and professionals working on blockchain security and privacy.
Jul 1, 2018·2018 IEEE International Conference on Internet of Things (iThings) and IEEE Green Computing and Communications (GreenCom) and IEEE Cyber, Physical and Social Computing (CPSCom) and IEEE Smart Data (SmartData)
A review system is a valuable component in E-commerce applications. Existing centralized review systems are prone to review frauds and manipulations. A decentralized, immutable and auditable blockchain system is a natural fit to prevent fraudulent and manipulated reviews. We develop and implement ReviewChain, a decentralized review system using Ethereum smart contract. ReviewChain validates new reviews by querying the identity of purchasers from a supply chain system. We assume that the supply chain system is based on blockchain technology. We develop and implement a mechanism to tie two disparate Ethereum based blockchain networks. Ethereum smart contract code is limited and cannot make external procedure calls. Therefore, we introduce multi-blockchain gateway nodes called notaries. Our proposed smart contracts and notaries allow us to interface two blockchains effectively. We run ReviewChain and discuss how various design parameters impact the system performance.
Digital currencies such as Bitcoin rely on cryptographic primitives to operate. However, past experience shows that cryptographic primitives do not last forever: increased computational power and advanced cryptanalysis cause primitives to break and motivate the development of new ones. It is therefore crucial for maintaining trust in a cryptocurrency to anticipate such breakage. We present the first systematic analysis of the effect of broken primitives on Bitcoin. We analyze the ways in which Bitcoin’s core cryptographic building blocks can break and the subsequent effect on the main Bitcoin security guarantees. Our analysis reveals a wide range of possible effects depending on the primitive and type of breakage, ranging from minor privacy violations to a complete breakdown of the currency. Our results lead to several suggestions for the Bitcoin migration plans and insights for other cryptocurrencies in case of broken or weakened cryptographic primitives.
Jul 1, 2018·2018 IEEE International Conference on Internet of Things (iThings) and IEEE Green Computing and Communications (GreenCom) and IEEE Cyber, Physical and Social Computing (CPSCom) and IEEE Smart Data (SmartData)
Internet of Things (IoT) devices proliferation is on the rise, where the number of connected devices has surpassed 7 billion devices in 2017, whereas insights foresee a number of 20-50 billion connections by year 2020. Most of those devices are deployed in heterogeneous and complex networks which imposes many challenges on the devices management functionality. Among those challenges is the identity management which pertains to how devices' identities are authenticated and verified in addition to how devices establish the means for authorizing and controlling access to data and services. Blockchain as a distributed ledger technology positions itself as a suitable candidate to address this challenge. That is mainly attributed to Blockchain's use of cryptographic identifiers, records immutability, and provenance. These features, together, provide a platform to implement the functions of IoT devices identity management that can ensure a global and unique identity for the devices, and also provide the mechanism to maintain it throughout the device life cycle. This paper presents a semi-decentralized Blockchain-based IoT identity management framework that provides features of identity creation and transfer of ownership, along with the capability of identity portability among networks visited by the devices. For validation, we describe a set of smart contracts that provide the functions of the registrar and management contracts.
Sambit Nayak, Nanjangud C. Narendra, Anshu Shukla, James Kempf
While blockchains and smart contracts are primarily known for their use as the technologies underlying cryptocurrencies like Bitcoin and Ethereum, these technologies also have applicability in other areas. In this paper, we present an application of smart contracts running on a permissioned distributed ledger (essentially a private blockchain where only credentialed participants are allowed to read and write) to managing tenant and service accounts in a cloud computing data center. The system is called Saranyu and it supports four services: identity management, authentication, authorization, and charging. Identity management and authentication are handled using client-generated public/private key pairs in the usual fashion. Authorization is handled as a contract from a grantee of service access rights to a recipient which is a tenant or other service. Charging is supported by Saranyu integration with payment gateways for payments related to service resource usage. We describe an implementation of Saranyu on top of the Quorum blockchain system. We believe the security, non-repudiation, tamper-resistance, and easy transaction history access brought by blockchain technology will increase transparency and trust in cloud tenant and service management and that the fundamentally distributed nature of the blockchain will make Saranyu an excellent match with developing distributed cloud architectures.
Mallikarjun Reddy Dorsala, V. N. Sastry, Chapram Sudhakar
Outsourcing a computation has been a major research area in cryptography. A delegatorDoutsources a computation to a workerW, who expects to get paid in return for delivering correct outputs. The delegator has to verify the output returned, to guard against malicious or malfunctioning worker. The worker may not trust the delegator to pay for computations performed by him. Blockchain systems like Bitcoin and Ethereum offer public verifiability of transactions generated in their networks. These transactions are of the form of a set of opcodes in Bitcoins or initiate execution of a contract in Ethereum, thus offering execution of small programs publicly. A fair protocol for verifiable computation between two parties$D$and$W$must provide the following guarantee: (1) Fast verification: The work performed to verify the correctness of output of a function is less than the work performed to compute function. (2) Pay to learn output: W obtains pay from D iff D received the correct output of the computation from W. In this work, we design two ideal functionalities$\mathcal{F}_{CRR}^{\ast}$for single worker case and$\mathcal{F}_{CCRR}^{\ast}$for multiple workers case. Existing methods do not allow Mutual revocation of deposit transaction which reduces the cost of script execution. Our ideal functionalities offer mutual revocation of the deposit transaction made byD. We show the realization of our ideal functionality$\mathcal{F}_{CRR}^{\ast}$in Bitcoin, and we also discuss fair protocols for verifiable computations of GCD of two large numbers and optimization problems. As our final work, we show a fair protocol for proof-based verifiable computing schemes.
Voice over Long Term Evolution (VoLTE) technology defines standards to deliver real-time services such as voice and video over LTE based on IP Multimedia Subsystem (IMS) networks. The security implementation in VoLTE is End-to-Access (e2a), which means that the sessions are only encrypted between the mobile terminals and the IMS network. In this paper we propose a new approach for securing End-to-End (e2e) VoLTE media based the Ethereum Blockchain. The solution consists of creating public and private keypairs for VoLTE user equipments (UEs) and storing the public keys in the Ethereum Blockchain. The media is encrypted e2e using the Secure Real Time Protocol (SRTP) protocol with a variety of session key distribution mechanisms. Results showed that the solution implementation has minimal impact on the existing IMS network, and the secure call setup time between two terminals is negligible compared to the original VoLTE setup time.
Rachid El Bansarkhani, Matthias Geihs, Johannes Buchmann
Blockchain technology has arisen as a promising protocol to replace centralized and less efficient systems. In fact, for the first time, it is possible to achieve decentralized consensus without the need for trusted authorities, resulting in more efficient processes and saving both money and time.
John R. Adler, Ryan Berryhill, Andreas Veneris, Zissis Poulos · 6 authors
The public blockchain was originally conceived to process monetary transactions in a peer-to-peer network while preventing double-spending. It has since been extended to numerous other applications including execution of programs that exist on the blockchain called "smart contracts." Smart contracts have a major limitation, namely they only operate on data that is on the blockchain. Trusted entities called oracles attest to external data in order to bring it onto the blockchain but they do so without the robust security guarantees that blockchains generally provide. This has the potential to turn oracles into centralized points-of-failure. To address this concern, this paper introduces Astraea, a decentralized oracle based on a voting game that decides the truth or falsity of propositions. Players fall into two roles: voters and certifiers. Voters play a low-risk/low-reward role that is resistant to adversarial manipulation while certifiers play a high-risk/high-reward role so they are required to play with a high degree of accuracy. This paper also presents a formal analysis of the parameters behind the system to measure the probability of an adversary with bounded funds being able to successfully manipulate the oracle's decision, that shows that the same parameters can be set to make manipulation arbitrarily difficult---a desirable feature for the system. Further, this analysis demonstrates that under those conditions a Nash equilibrium exists where all rational players are forced to behave honestly.
Jul 1, 2018·2018 IEEE International Conference on Internet of Things (iThings) and IEEE Green Computing and Communications (GreenCom) and IEEE Cyber, Physical and Social Computing (CPSCom) and IEEE Smart Data (SmartData)
Mathis Steichen, Beltran Fiz, Robert Norvill, Wazen M. Shbair · 5 authors
Large files cannot be efficiently stored on blockchains. On one hand side, the blockchain becomes bloated with data that has to be propagated within the blockchain network. On the other hand, since the blockchain is replicated on many nodes, a lot of storage space is required without serving an immediate purpose, especially if the node operator does not need to view every file that is stored on the blockchain. It furthermore leads to an increase in the price of operating blockchain nodes because more data needs to be processed, transferred and stored. IPFS is a file sharing system that can be leveraged to more efficiently store and share large files. It relies on cryptographic hashes that can easily be stored on a blockchain. Nonetheless, IPFS does not permit users to share files with selected parties. This is necessary, if sensitive or personal data needs to be shared. Therefore, this paper presents a modified version of the InterPlanetary Filesystem (IPFS) that leverages Ethereum smart contracts to provide access controlled file sharing. The smart contract is used to maintain the access control list, while the modified IPFS software enforces it. For this, it interacts with the smart contract whenever a file is uploaded, downloaded or transferred. Using an experimental setup, the impact of the access controlled IPFS is analyzed and discussed.
We consider zero-knowledge proofs, a class of cryptographic protocols by which an agent (a Prover) can prove to another agent (a Verifier) that a statement is true without revealing any additional information. For example, a zero-knowledge proof allows one to prove knowledge of a password to somebody at the other end of the communication without actually revealing the password. \nWe present an introduction to and survey literature on zero-knowledge proofs, covering the history, formal definition, and classical applications of zero-knowledge proofs. In addition, we consider connections to complexity, demonstrating that all problems in the complexity class NP have zero-knowledge proofs, and also discuss more exotic applications of zero-knowledge, namely in electronic voting and nuclear disarmament. \nWe then consider applications of zero-knowledge to financial regulation, specifically in balancing transparency and confidentiality in financial reporting. Namely, we polled professionals in the financial industry to identify three major classes of regulatory problems. We then utilize zero-knowledge proofs to develop and present cryptographic protocols/mechanisms and solutions to these regulatory problems: (1) An employer verifying an employee has no financial holdings on a blacklist without revealing the other (allowed) holdings of the employee, (2) A fund convincing its investors that its holdings subscribe to particular risk constraints, without disclosing the actual holdings, (3) A collection of investors of a fund verifying aggregate information provided by the fund, while preserving pairwise anonymity. Applications (1) and (3) are novel applications developed in this paper, while (2) is drawn from [47].
Thomas Locher, Sebastian Obermeier, Yvonne-Anne Pignolet
The functionality that distributed ledger technology provides, i.e., an immutable and fraud-resistant registry with validation and verification mechanisms, has traditionally been implemented with a trusted third party. Due to the distributed nature of ledger technology, there is a strong recent trend towards using ledgers to implement novel decentralized applications for a wide range of use cases, e.g., in the financial sector and sharing economy. While there can be several arguments for the use of a ledger, the key question is whether it can fully replace any single trusted party in the system as otherwise a (potentially simpler) solution can be built around the trusted party. In this paper, we introduce an abstract view on ledger use cases and present two fundamental criteria that must be met for any use case to be implemented using a ledger-based approach without having to rely on any particular party in the system. Moreover, we evaluate several ledger use cases that have recently received considerable attention according to these criteria, revealing that often participants need to trust each other despite using a distributed ledger. Consequently, the potential of using a ledger as a replacement for a trusted party is limited for these use cases.
The Enterprise Ethereum Client Specification by the Enterprise Ethereum Alliance defines the requirements which Ethereum Clients offering private smart contract capabilities should comply with. This specification though ground breaking, misses some important blockchain requirements and does not fully consider the requirements of Ethereum Clients offering Private Sidechain capabilities. This paper presents the case for Private Sidechains and defines requirements to be complied with to deliver this technology. The capabilities of three blockchain clients have been analysed based on the requirements: Quorum, Parity, and Hyperledger Fabric. Quorum and Hyperledger Fabric operate as private consortium blockchains where as Parity delivers private transaction capabilities on top of Ethereum MainNet. These differing approaches has led to different strengths and weaknesses which has resulted in each client not complying with one or more key requirement. In particular, none of the reviewed blockchain clients support the ability to determine bootstrap information to establish on-demand blockchains and none of the clients support secure management and pinning from Ethereum MainNet. This paper presents Ethereum Private Sidechains and a range of technologies which allow it to deliver on complex sidechain requirements. Ethereum Registration Authorities are presented, which allow entities which have not previously interacted to securely obtain information to bootstrap a sidechain, and a Management and Pinning strategy is described which allows the state of a sidechain to be securely pinned to Ethereum MainNet without compromising privacy.
The Bitcoin cryptocurrency records its transactions in a public log called the blockchain. Its security rests critically on the distributed protocol that maintains the blockchain, run by participants called miners. Conventional wisdom asserts that the mining protocol is incentive-compatible and secure against colluding minority groups, that is, it incentivizes miners to follow the protocol as prescribed. We show that the Bitcoin mining protocol is not incentive-compatible. We present an attack with which colluding miners' revenue is larger than their fair share. The attack can have significant consequences for Bitcoin: Rational miners will prefer to join the attackers, and the colluding group will increase in size until it becomes a majority. At this point, the Bitcoin system ceases to be a decentralized currency. Unless certain assumptions are made, selfish mining may be feasible for any coalition size of colluding miners. We propose a practical modification to the Bitcoin protocol that protects Bitcoin in the general case. It prohibits selfish mining by a coalition that command less than 1/4 of the resources. This threshold is lower than the wrongly assumed 1/2 bound, but better than the current reality where a coalition of any size can compromise the system.
Yan Zhu, Yao Qin, Guohua Gan, Yang Shuai · 5 authors
In this paper we focus on a new generation of secure resource sharing platform in a decentralized blockchain environment with flexible and diverse permission management, as well as verifiable and transparent access process. To do it, we present a new Transaction-based Access Control (TBAC) platform which integrates the standard attribute-based access control (ABAC) model and the blockchain system. In this platform, four types of transactions and Bitcoin-type cryptographic scripts are presented to describe the TBAC access control procedure corresponding to subject registration, object escrowing and publication, access request and grant. We also present a cryptosystem associated with TBAC (CryptoTBAC) for ensuring secure attribute-exchanging and decision-making of dynamic policy. We evaluate the security of CryptoTBAC from three aspects: transaction, authorization, and decision-making security.
There are several studies that propose identity management that utilizes blockchain technology. In Ethereum, the main programmable blockchain system, data on a blockchain are saved as encoded binaries for executing automatic verification. To decode a binary, users need to know the application binary interfaces (ABI) that describes the data structure of the registered information. However, the manner by which ABI are shared in the current blockchain protocol is opaque. To resolve this problem, we describe a new protocol for embedding the ABI on a blockchain transaction when a registrant registers information. Our method enables users to read registered data with information on the blockchain alone, and it guarantees transparency without requiring users to trust third parties.
A fundamental problem for electronic commerce is the buying and selling of digital goods between individuals that may not know or trust each other. Traditionally, this problem has been addressed by the use of trusted third-parties such as credit-card companies, mediated escrows, legal adjudication, or reputation systems. Despite the rise of blockchain protocols as a way to send payments without trusted third parties, the important problem of exchanging a digital good for payment without trusted third parties has been paid much less attention. We refer to this problem as the Buyer and Seller's Dilemma and present for it a dual-deposit escrow trade protocol which uses double-sided payment deposits in conjunction with simple cryptographic primitives, and that can be implemented using a blockchain-based smart contract. We analyze our protocol as an extensive-form game and prove that the Sub-game Perfect Nash Equilibrium for this game is for both the buyer and seller to cooperate and behave honestly. We address this problem under the assumption that the digital good being traded is known and verifiable, with a fixed price known to both parties.