TEE-based distributed watchtowers for fraud protection in the Lightning Network

The Lightning Network is a payment channel network built on top of the cryptocurrency Bitcoin. It allows Bitcoin to scale by performing transactions off-chain to reduce load on the blockchain. Malicious payment channel participants can try to commit fraud by closing channels with outdated balances. The Lightning Network allows resolving this dispute on the blockchain. However, this mechanism forces the channels\u27 participants to watch the blockchain in regular intervals. It has been proposed to offload this monitoring duty to a third party, called a watchtower. However, existing approaches for watchtowers do not scale as they have storage requirements linear in the number of updates in a channel. In this work, we propose TEE Guard, a new architecture for watchtowers that leverages the features of Trusted Execution Environments to build watchtowers that require only constant memory and are thus able to scale. We show that TEE Guard is deployable because it can run with the existing Bitcoin and Lightning Network protocols. We also show that it is economically viable for a third party to provide watchtower services. As a watchtower needs to be trusted to be watching the blockchain, we also introduce a mechanism that allows customers to verify that a watchtower has been running continuously

TEE-based distributed watchtowers for fraud protection in the Lightning Network

The Lightning Network is a payment channel network built on top of the cryptocurrency Bitcoin. It allows Bitcoin to scale by performing transactions off-chain to reduce load on the blockchain. Malicious payment channel participants can try to commit fraud by closing channels with outdated balances. The Lightning Network allows resolving this dispute on the blockchain. However, this mechanism forces the channels\u27 participants to watch the blockchain in regular intervals. It has been proposed to offload this monitoring duty to a third party, called a watchtower. However, existing approaches for watchtowers do not scale as they have storage requirements linear in the number of updates in a channel. In this work, we propose TEE Guard, a new architecture for watchtowers that leverages the features of Trusted Execution Environments to build watchtowers that require only constant memory and are thus able to scale. We show that TEE Guard is deployable because it can run with the existing Bitcoin and Lightning Network protocols. We also show that it is economically viable for a third party to provide watchtower services. As a watchtower needs to be trusted to be watching the blockchain, we also introduce a mechanism that allows customers to verify that a watchtower has been running continuously

Decentralizing Watchtowers for Payment Channels using IPFS

Payment channels have been proposed as a way to improve the scalability of blockchains such as Bitcoin. However, payment channel protocols require that participating parties watch the blockchain regularly for new transactions. If a party observes, in a given period of time, a fraudulent transaction that closes the payment channel in an outdated state, the fraudulent transaction can be revoked. Previous work has proposed to outsource this task to a third party, a so called watchtower. A user of a payment channel employs a dedicated watchtower and sends the data to the watchtower that the watchtower requires to revoke fraudulent transactions. In this paper, we replace the strict binding of a user to a watchtower by a decentralized approach for watchtowers that requires no direct interaction between a party of a payment channel and the watchtower. This decentralized approach uses IPFS to publicly store the information required by a watchtower. With this approach, anyone can detect and revoke a fraud by watching the blockchain and reading a file from IPFS that contains information for each outdated commitment transaction. A reward for successful revocations can be used as incentive

A Survey of Layer-Two Blockchain Protocols

After the success of the Bitcoin blockchain, came several cryptocurrencies and blockchain solutions in the last decade. Nonetheless, Blockchain-based systems still suffer from low transaction rates and high transaction processing latencies, which hinder blockchains' scalability. An entire class of solutions, called Layer-1 scalability solutions, have attempted to incrementally improve such limitations by adding/modifying fundamental blockchain attributes. Recently, a completely different class of works, called Layer-2 protocols, have emerged to tackle the blockchain scalability issues using unconventional approaches. Layer-2 protocols improve transaction processing rates, periods, and fees by minimizing the use of underlying slow and costly blockchains. In fact, the main chain acts just as an instrument for trust establishment and dispute resolution among Layer-2 participants, where only a few transactions are dispatched to the main chain. Thus, Layer-2 blockchain protocols have the potential to transform the domain. However, rapid and discrete developments have resulted in diverse branches of Layer-2 protocols. In this work, we systematically create a broad taxonomy of such protocols and implementations. We discuss each Layer-2 protocol class in detail and also elucidate their respective approaches, salient features, requirements, etc. Moreover, we outline the issues related to these protocols along with a comparative discussion. Our thorough study will help further systematize the knowledge dispersed in the domain and help the readers to better understand the field of Layer-2 protocols.Comment: 21 pages, 15 figures, 2 table

On the Applicability of Payment Channel Networks for Allocation of Transport Ticket Revenues

In many public transport networks, multiple providers cooperate to offer integrated services and, consequently, provide integrated fare collection. Thus, ticket revenues need to be redistributed so that each provider receives its respective share. Typically, the customers’ travel behavior is surveyed and the fares paid are aggregated over certain periods of time, and the revenue is periodically allocated based on this information. To avoid a centralized trusted third party or the exchange of sensitive information between providers, we present an approach that integrates revenue allocation directly into the payment process: The proposed approach is based on payment channel networks and utilizes multi-hop payments to perform revenue allocation. We thereby show how to make use of payment channel networks in this setting as well as the corresponding benefits

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

Fortress of the Soul

French Huguenots made enormous contributions to the life and culture of colonial New York during the seventeenth and eighteenth centuries. Huguenot craftsmen were the city's most successful artisans, turning out unrivaled works of furniture which were distinguished by unique designs and arcane details. More than just decorative flourishes, however, the visual language employed by Huguenot artisans reflected a distinct belief system shaped during the religious wars of sixteenth-century France.In Fortress of the Soul, historian Neil Kamil traces the Huguenots' journey to New York from the Aunis-Saintonge region of southwestern France. There, in the sixteenth century, artisans had created a subterranean culture of clandestine workshops and meeting places inspired by the teachings of Bernard Palissy, a potter, alchemist, and philosopher who rejected the communal, militaristic ideology of the Huguenot majority which was centered in the walled city of La Rochelle. Palissy and his followers instead embraced a more fluid, portable, and discrete religious identity that encouraged members to practice their beliefs in secret while living safely—even prospering—as artisans in hostile communities. And when these artisans first fled France for England and Holland, then left Europe for America, they carried with them both their skills and their doctrine of artisanal security.Drawing on significant archival research and fresh interpretations of Huguenot material culture, Kamil offers an exhaustive and sophisticated study of the complex worldview of the Huguenot community. From the function of sacred violence and alchemy in the visual language of Huguenot artisans, to the impact among Protestants everywhere of the destruction of La Rochelle in 1628, to the ways in which New York's Huguenots interacted with each other and with other communities of religious dissenters and refugees, Fortress of the Soul brilliantly places American colonial history and material life firmly within the larger context of the early modern Atlantic world

Weimar – a Personal Tribute

Weimar is a relatively small town in the centre of Germany. Around 1552 it became the capital of the small Herzogtum Sachsen-Weimar (Principality Saxony-Weimar), from 1741 until 1918 the capital of the (still relatively small) Principality – since 1815 Grand Principality – (Groß-) Herzogtum Sachsen-Weimar-Eisenach (Saxony-Weimar-Eisenach). After World War I all monarchic structures in Germany were abandoned, the democratic Free State of Thuringia was founded in 1920, and Weimar became its capital until 1950. Despite its moderate size, Weimar managed to gain a cultural profile that extended and still extends far beyond the borders of the (Grand-) Principality, even beyond Germany. The foundations were laid in the 18th and early 19th century, connected to writers and pilosophers like Christoph Martin Wieland, Johann Wolfgang von Goethe, Johann Gottfried von Herder, and Friedrich von Schiller who all lived and worked in Weimar. In the late 19th and early 20th century more writers, musicians and artists contributed to Weimar’s reputation, e.g. Franz Liszt, Richard Strauss, Hugo von Hofmannsthal, Harry Graf Kessler, Henry van de Velde, Edvard Munch, Walter Gropius, Paul Klee, Oskar Schlemmer, Wassily Kandinsky, Lyonel Feininger. In politics, Weimar played ambiguous roles between a comparatively liberal (Grand) Principality, the birth place of the first democratic state in Germany (Weimar Republic), turning “brown” (National-Socialist) from the late 1920s, Communist after World War II, democratic again after the German re-unification in 1990. Weimar is a very special, even intriguing place. This book tries to convey its aura by telling its story from the early beginnings in the 16th century until today, with a main focus on the last three centuries – embedded into pan-German, even pan-European developments

The Revolutions of 1989

Only a few people foresaw the sudden and momentous events of 1989: within weeks the seemingly unshakable communist regimes of Eastern Europe were washed away and with them the postwar international order. This book gives an overview over the national revolutions and external reactions. It contains chapters on the revolutions in all major countries of the former communist bloc as well as on the responses of all major international players. The first part examines the revolutionary events – from above and from below – in Eastern Europe as well as China and their backgrounds. The second part deals with Soviet and Western perceptions and responses. The third part focuses on the aftermath of the revolutions, on societal transformations, the acceptance of the new Central European democracies to NATO and the EU, and on the memory of 1989. “By far the best collective work on this topic … This book will be unique, and is much needed – at a time when social scientists continue to strive to understand the ‘Arab revolutions’.” Pierre Grosser “We get in-depth analysis and diversity of the assessments.” Pierre Grosse

The Revolutions of 1989

Only a few people foresaw the sudden and momentous events of 1989: within weeks the seemingly unshakable communist regimes of Eastern Europe were washed away and with them the postwar international order. This book gives an overview over the national revolutions and external reactions. It contains chapters on the revolutions in all major countries of the former communist bloc as well as on the responses of all major international players. The first part examines the revolutionary events – from above and from below – in Eastern Europe as well as China and their backgrounds. The second part deals with Soviet and Western perceptions and responses. The third part focuses on the aftermath of the revolutions, on societal transformations, the acceptance of the new Central European democracies to NATO and the EU, and on the memory of 1989. “By far the best collective work on this topic … This book will be unique, and is much needed – at a time when social scientists continue to strive to understand the ‘Arab revolutions’.” Pierre Grosser “We get in-depth analysis and diversity of the assessments.” Pierre Grosse