Atomic Swapping Bitcoins and Ethers

International audienceBlockchains interoperability is one of the hardest problems to be solved in the nowadays blockchain ecosystem that contains thousands of different blockchains. This paper focuses on swapping assets from a blockchain to another without a trusted third party. One recent scheme for atomically swapping assets, Atomic Cross Chain Swap (ACCS), has been formally analyzed in [2]. This paper proposes an implementation of an ACCS between the two most valued crypto-currencies today: Bitcoin and Ether

Universal Atomic Swaps: Secure Exchange of Coins Across All Blockchains

Trading goods lies at the backbone of the modern economy and the recent advent of cryptocurrencies has opened the door for trading decentralized (digital) assets: A large fraction of the value of cryptocurrencies comes from the inter-currency exchange and trading, which has been arguably the most successful application of decentralized money. The security issues observed with centralized, custodial cryptocurrency exchanges have motivated the design of atomic swaps, a protocol for coin exchanges between any two users. Yet, somewhat surprisingly, no atomic swap protocol exists that simultaneously satisfies the following simple but desired properties: (i) non-custodial, departing from a third party trusted holding the coins from users during the exchange; (ii) universal, that is, compatible with all (current and future) cryptocurrencies; (iii) multi-asset, supporting the exchange of multiple coins in a single atomic swap. From a theoretical standpoint, in this work we show a generic protocol to securely swap $n$ coins from any (possible multiple) currencies for $\tilde{n}$ coins of any other currencies, for any $n$ and $\tilde{n}$. We do not require any custom scripting language supported by the corresponding blockchains, besides the bare minimum ability to verify signatures on transactions. For the special case when the blockchains use ECDSA or Schnorr signatures, we design a practically efficient protocol based on adaptor signatures and time-lock puzzles. As a byproduct of our approach, atomic swaps transactions no longer include custom scripts and are identical to standard one-to-one transactions. We also show that our protocol naturally generalizes to any cycle of users, i.e., atomic swaps with more than two participants. To demonstrate the practicality of our approach, we have evaluated a prototypical implementation of our protocol for Schnorr/ECDSA signatures and observed that an atomic swap requires below one second on commodity machines. Even on blockchains with expressive smart contract support (e.g., Ethereum), our approach reduces the on-chain cost both in terms of transaction size and gas cost

Trustless communication across distributed ledgers: impossibility and practical solutions

Since the advent of Bitcoin as the first decentralized digital currency in 2008, a plethora of distributed ledgers has been created, differing in design and purpose. Considering the heterogeneous nature of these systems, it is safe to say there shall not be ``one coin to rule them all". However, despite the growing and thriving ecosystem, blockchains continue to operate almost exclusively in complete isolation from one another: by design, blockchain protocols provide no means by which to communicate or exchange data with external systems. To this date, centralized providers hence remain the preferred route to exchange assets and information across blockchains~-- undermining the very nature of decentralized currencies. The contribution of this thesis is threefold. First, we critically evaluate the (im)possibilty, requirements, and challenges of cross-chain communication by contributing the first systematization of this field. We formalize the problem of Cross-Chain Communication (CCC) and show it is impossible without a trusted third party by relating CCC to the Fair Exchange problem. With this impossibility result in mind, we develop a framework to design new and evaluate existing CCC protocols, focusing on the inherent trust assumptions thereof, and derive a classification covering the field of cross-chain communication to date. We then present XCLAIM, the first generic framework for transferring assets and information across permissionless distributed ledgers without relying on a centralized third party. XCLAIM leverages so-called cryptocurrency-backed assets, blockchain-based assets one-to-one backed by other cryptocurrencies, such as Bitcoin-backed tokens on Ethereum. Through the secure issuance, transfer, and redemption of these assets, users can perform cross-chain exchanges in a financially trustless and non-interactive manner, overcoming the limitations of existing solutions. To ensure the security of user funds, XCLAIM relies on collateralization of intermediaries and a proof-or-punishment approach, enforced via smart contracts equipped with cross-chain light clients, so-called chain relays. XCLAIM has been adopted in practice, among others by the Polkadot blockchain, as a bridge to Bitcoin and other cryptocurrencies. Finally, we contribute to advancing the state of the art in cross-chain light clients. We develop TxChain, a novel mechanism to significantly reduce storage and bandwidth costs of modern blockchain light clients using contingent transaction aggregation, and apply our scheme to Bitcoin and Ethereum individually, as well as in the cross-chain setting.Open Acces

Preparation of CBs immobilized on different types of magnetic nanoparticles for application in selective complexation and catalysis

[eng] Cucurbiturils are known to present potential applications in molecular recognition, self- assembly, and nanotechnology. The discovery of ultra-high affinity CB–guest complexes with binding constant values similar than those found in natural complexes beckoned the attention of many groups, that focused their research in the functionalization of cucurbiturils in order to modify their structure and properties, to enhance their solubility, and to provide different functional groups for further transformations. In fact, cucurbiturils have been supported onto different solid surfaces such as gold surface, polymer beads, or nanoparticles. Iron is a bioactive metal with magnetic properties and low toxicity to mammalian cells. The formation of 10 nm magnetic nanoparticles (MNPs) of iron oxide (Fe3O4) can be achieved in an affordable and easily reproducible manner by thermal decomposition. This small size of nanoparticles provides a double advantage: first, biodegradability, because particles up to 100 nm can be phagocytosed through liver cells; second, superparamagnetic behavior, so that they become magnetized upon exposure to a magnetic field but have no permanent magnetization once the field is turned off. Prompted by the breadth of possible applications provided by cucurbiturils and our previous experience immobilizing organic molecules on MNPs of Fe3O4 and polystyrene resin (PR) (generally, to covalently immobilize catalysts for the preparation of easily recoverable and recyclable catalysts), we speculated that covalently attached cucurbiturils onto MNPs could open up new routes concerning drug delivery and biocatalysis, enable applications in many areas including sensor, transport, separation, and nanomaterials. Hence, the first research project included in this dissertation (chapter II), unveils the development of polystyrene and magnetic nanoparticles coated with a cucurbituril layer. The intrinsic properties of these compounds have been tested on the extraction of selected molecules (guests that bind to cucurbiturils). Also, in this chapter, the preparation and characterization of a library of these novel compounds—that exhibit a potential use in molecular recognition, transport, and separation—is described. The second project, described in chapter III, illustrates the synthesis of catalysts tagged with an adamantyl moiety to enhance their affinity towards cucurbiturils—for their selective extraction from the reaction media. This is achieved by covalent linking of the cucurbituril receptor to the superparamagnetic Fe3O4 nanoparticles to allow magnetic decantation. These compounds were prepared, and their catalytic activity and reusability were tested: first, on the model aldol reaction between ketones and benzaldehydes; secondly, on the enantioselective Robinson annulation with the well-established Wieland-Miescher ketone. Chapter IV showcases the preparation of a quaternary amino derivatizing reagent decorated with an adamantyl moiety. This reagent reacts with ketone-containing steroids such as testosterone. Upon reaction, the resulting derivative can be selectively extracted from the solution mixture and driven away by the magnetically powered nanoparticles. Finally, chapter V provides some computational insights on the nature and the strength of the cucurbit[7]uril interactions with some adamantyl-based guests. The studies are built on novel and unprecedented computational models able to reproduce experimental procedures on the determination of enthalpic and entropic changes. Therefore, the main goal of the present thesis is the development of novel magnetically powered nanodevices for the efficient and selective extraction of chemical cargos. Supramolecular chemistry—especial emphasis on cucurbiturils—will play a central lead in this manuscript due to the endogenous chemical properties of the supramolecules, and the robust and modulable nature of their guests. Moreover, we will cover the entire manufacture of the nanodevices or chemical shuttles, their potential use in asymmetric catalysis, and their applicability in molecular recognition and enrichment.[cat] El primer projecte de recerca, inclòs al capítol II, revela el desenvolupament de poliestirè i nanopartícules magnètiques recobertes amb una capa de cucurbituril. Durant aquesta secció, s’han provat les propietats intrínseques d’aquests compostos per a l’extracció de molècules seleccionades (hostes) que s’uneixen als cucurbiturils. A més, en aquest capítol, s’ha fet un esforç per caracteritzar amb precisió una varietat d’aquests nous compostos que presenten un potencial ús en el reconeixement molecular, el transport i la separació. El segon projecte, descrit al capítol III, il·lustra la síntesi de catalitzadors etiquetats amb un fragment adamantil per millorar la seva afinitat cap als cucurbiturils, i promoure la seva extracció selectiva. Això s’aconsegueix per mitjà de l’enllaç covalent entre el receptor de cucurbituril i les nanopartícules superparamagnètiques (Fe3O4), que permetent la decantació magnètica del sistema format. Una varietat d’aquests compostos s’ha preparat, i la seva activitat catalítica així com la reutilitzabilitat s’han posat també a prova: primer, en la reacció aldòlica entre cetones i benzaldehids; després, en la reacció enantioselectiva de Robinson, amb la ben consolidada cetona de Wieland i Miescher. Al capítol IV es mostra la preparació d’un reactiu derivatitzant que inclou una amina quaternària i un grup adamantil. Aquesta molècula presenta reactivitat amb esteroides que contenen cetones com la testosterona. Després de reaccionar, el derivat resultant es pot extreure selectivament de la barreja de solució i desplaçar-lo a parer, fent ús de les propietats magnètiques de les nanopartícules. Finalment, el capítol V aporta unes idees sobre la naturalesa i força de les interaccions entre els cucurbiturils i uns determinats hostes, basant-nos en uns models computacionals innovadors i sense precedents que són capaços de reproduir resultats experimentals per a la determinació de canvis entàlpics i entròpic

Atomic Swapping Bitcoins and Ethers

International audienceBlockchains interoperability is one of the hardest problems to be solved in the nowadays blockchain ecosystem that contains thousands of different blockchains. This paper focuses on swapping assets from a blockchain to another without a trusted third party. One recent scheme for atomically swapping assets, Atomic Cross Chain Swap (ACCS), has been formally analyzed in [2]. This paper proposes an implementation of an ACCS between the two most valued crypto-currencies today: Bitcoin and Ether