Periodic shadowing and Ω\Omega-stability

We show that the following three properties of a diffeomorphism $f$ of a smooth closed manifold are equivalent: (i) $f$ belongs to the $C^1$-interior of the set of diffeomorphisms having periodic shadowing property; (ii) $f$ has Lipschitz periodic shadowing property; (iii) $f$ is $\Omega$-stable.Comment: 21 page

Ethereum: state of knowledge and research perspectives

Ethereum is a decentralized application platform that allows users to write, deploy, and interact with smart contracts -- programs that encode financial agreements. A peer-to-peer network of mutually distrusting nodes maintains a common view of the state of all accounts and executes smart contracts' code upon request. The global state is stored in a blockchain secured by a proof-of-work consensus mechanism similar to that in Bitcoin. The core value proposition of Ethereum is a Turing-complete programming language that enables implementing complex logic in smart contracts. Decentralized applications without a trusted third party are appealing in many areas, such as financial services, crowdfunding, and gambling. Smart contracts as a research topic contains many unsolved challenges and spans over areas ranging from cryptography, consensus algorithms, and programming languages to governance, ethical, and legal issues. This paper is the first to summarize the state of knowledge in this field. We provide a technical overview of Ethereum and outline open challenges along with proposed solutions. We also mention alternative blockchains with Turing complete programming capabilities

Vector Fields with the Oriented Shadowing Property

We give a description of the \Cone-interior (\Int^1(\OrientSh)) of the set of smooth vector fields on a smooth closed manifold that have the oriented shadowing property. A special class \Bb of vector fields that are not structurally stable is introduced. It is shown that the set \Int^1(\OrientSh\setminus\Bb) coincides with the set of structurally stable vector fields. An example of a field of the class \Bb belonging to \Int^1(\OrientSh) is given. Bibliography: 18 titles.Comment: 42 page

Unjamming Lightning: A Systematic Approach

Users of decentralized financial networks suffer from inventive security exploits. Identity-based fraud prevention methods are inapplicable in these networks, as they contradict their privacy-minded design philosophy. Novel mitigation strategies are therefore needed. Their rollout, however, may damage other desirable network properties. In this work, we introduce an evaluation framework for mitigation strategies in decentralized financial networks. This framework allows researchers and developers to examine and compare proposed protocol modifications along multiple axes, such as privacy, security, and user experience. As an example, we focus on the jamming attack in the Lightning Network. Lightning is a peer-to-peer payment channel network on top of Bitcoin. Jamming is a cheap denial-of-service attack that allows an adversary to temporarily disable Lightning channels by flooding them with failing payments. We propose a practical solution to jamming that combines unconditional fees and peer reputation. Guided by the framework, we show that, while discouraging jamming, our solution keeps the protocol incentive compatible. It also preserves security, privacy, and user experience, and is straightforward to implement. We support our claims analytically and with simulations. Moreover, our anti-jamming solution may help alleviate other Lightning issues, such as malicious channel balance probing

Lipschitz shadowing implies structural stability

We show that the Lipschitz shadowing property of a diffeomorphism is equivalent to structural stability. As a corollary, we show that an expansive diffeomorphism having the Lipschitz shadowing property is Anosov.Comment: 11 page

Message Latency in Waku Relay with Rate Limiting Nullifiers

Waku is a privacy-preserving, generalized, and decentralized messaging protocol suite. Waku uses GossipSub for message routing and Rate Limiting Nullifiers (RLN) for spam protection. GossipSub ensures fast and reliable peer-to-peer message delivery in a permissionless environment, while RLN enforces a common publishing rate limit using zero-knowledge proofs. This paper presents a practical evaluation of message propagation latency in Waku. First, we estimate latencies analytically, building a simple mathematical model for latency under varying conditions. Second, we run a large-scale single-host simulation with 1000 nodes. Third, we set up a multi-host Waku deployment using five nodes in different locations across the world. Finally, we compare our analytical estimations to the results of the simulation and the real-world measurement. The experimental results are in line with our theoretical model. Under realistic assumptions, medium-sized messages (25 KB) are delivered within 1 second. We conclude that Waku can achieve satisfactory latency for typical use cases, such as decentralized messengers, while providing scalability and anonymity

SmartCheck: Static Analysis of Ethereum Smart Contracts

Ethereum is a major blockchain-based platform for smart contracts – Turing complete programs that are executed in a decentralized network and usually manipulate digital units of value. Solidity is the most mature high-level smart contract language. Ethereum is a hostile execution environment, where anonymous attackers exploit bugs for immediate financial gain. Developers have a very limited ability to patch deployed contracts. Hackers steal up to tens of millions of dollars from flawed contracts, a well-known example being “The DAO“, broken in June 2016. Advice on secure Ethereum programming practices is spread out across blogs, papers, and tutorials. Many sources are outdated due to a rapid pace of development in this field. Automated vulnerability detection tools, which help detect potentially problematic language constructs, are still underdeveloped in this area. We provide a comprehensive classification of code issues in Solidity and implement SmartCheck – an extensible static analysis tool that detects them. SmartCheck translates Solidity source code into an XML-based intermediate representation and checks it against XPath patterns. We evaluated our tool on a big dataset of real-world contracts and compared the results with manual audit on three contracts. Our tool reflects the current state of knowledge on Solidity vulnerabilities and shows significant improvements over alternatives. SmartCheck has its limitations, as detection of some bugs requires more sophisticated techniques such as taint analysis or even manual audit. We believe though that a static analyzer should be an essential part of contract developers’ toolbox, letting them fix simple bugs fast and allocate more effort to complex issues