46 research outputs found
Elaine Goodale Eastman, Modernist Author? Re-visiting a Border-crossing Woman Writer's Place in Literary History
No full textElaine Goodale Eastman is not a name generally associated with transnational literary modernism. Yet, a review of her extensive oeuvre demonstrates that her writings interacted in diverse complex ways with that cultural movement. She wrote in a range of genres, including lyric poetry, journalism, didactic children's books and what she herself termed "potboilers" aimed primarily at supporting her family's finances. As an editor and co-author with her husband Charles, she contributed to the development of Native American literatures in an intense period of U.S. suppression of indigenous culture--a process in which she played conflicting roles. Through autobiographical texts published late in her life, we see that Eastman continued to have aspirations consistent with a number of modernism's familiar tenets, even as she also struggled to reconcile the intersectional elements in her gendered personal history with both the successes and the limitations of her multi-faceted publishing career. On associe rarement le nom d’Elaine Goodale Eastman au modernisme littéraire transnational. Prise dans son ensemble, toutefois, son oeuvre prolifique peut se lire comme une réponse complexe et variée au mouvement moderniste. Eastman a expérimenté avec divers genres, comme la poésie lyrique, le journalisme ou la littérature enfantine ¿ visée didactique, en sus de produire ce qu’elle considérait comme des « oeuvres alimentaires » destinées ¿ subvenir aux besoins de sa famille. Son travail de rédactrice et sa collaboration avec son époux Charles Eastman ont contribué ¿ l’essor de la littérature amérindienne ¿ une période marquée par la volonté des États-Unis de supprimer la culture indigène, processus auquel l’écrivaine s’est opposée de manière parfois ambivalente. Les écrits autobiographiques publiés tard dans sa carrière montrent que les aspirations d’Eastman ne sont pas sans lien avec celles du modernisme, alors même que l’écrivaine s’efforce de concilier les éléments intersectionnels de son parcours personnel avec les succès et les revers d’une carrière littéraire protéiforme
The Post-Quantum Security of Bitcoin\u27s Taproot as a Commitment Scheme
No full textAs of November 2021, Bitcoin supports “Taproot” spending policies whose on-chain format is a single elliptic curve point. A transaction spending the funds associated with a Taproot policy can be authorized by interpreting the curve point either (a) as a public key of the Schnorr signature scheme and providing a suitable signature, or (b) as a commitment to alternative spending conditions and satisfying those.
Since a sufficiently powerful quantum adversary would be able to forge Schnorr signatures, an upgrade to Bitcoin may, at some point in the future, disable the ability to spend existing funds via Schnorr signatures in order to prevent the havoc created by leaving a large fraction of the currency supply prone to theft. However, to avoid irrevocably losing all funds not migrated in time to (yet to be added) post-quantum signature schemes, it will be desirable for an upgrade disabling Schnorr signatures to retain the ability to spend funds by interpreting the curve point in a Taproot policy as a commitment to alternative spending conditions.
This paper justifies such an upgrade strategy by demonstrating the post-quantum security of Taproot as a commitment scheme. Specifically, it provides concrete upper bounds on the probability that a quantum adversary making some number of queries to a quantum random oracle can break the binding or hiding property. Since the bounds follow from powerful existing results, which enable reasoning as if dealing with a classical adversary, the proofs are accessible without a background in quantum computing
Cryptography for Bitcoin and friends
No full textNumerous cryptographic extensions to Bitcoin have been proposed since Satoshi Nakamoto introduced the revolutionary design in 2008. However, only few proposals have been adopted in Bitcoin and other prevalent cryptocurrencies, whose resistance to fundamental changes has proven to grow with their success. In this dissertation, we introduce four cryptographic techniques that advance the functionality and privacy provided by Bitcoin and similar cryptocurrencies without requiring fundamental changes in their design: First, we realize smart contracts that disincentivize parties in distributed systems from making contradicting statements by penalizing such behavior by the loss of funds in a cryptocurrency. Second, we propose CoinShuffle++, a coin mixing protocol which improves the anonymity of cryptocurrency users by combining their transactions and thereby making it harder for observers to trace those transactions. The core of CoinShuffle++ is DiceMix, a novel and efficient protocol for broadcasting messages anonymously without the help of any trusted third-party anonymity proxies and in the presence of malicious participants. Third, we combine coin mixing with the existing idea to hide payment values in homomorphic commitments to obtain the ValueShuffle protocol, which enables us to overcome major obstacles to the practical deployment of coin mixing protocols. Fourth, we show how to prepare the aforementioned homomorphic commitments for a safe transition to post-quantum cryptography.Seit seiner revolutionären Erfindung durch Satoshi Nakamoto im Jahr 2008 wurden zahlreiche kryptographische Erweiterungen für Bitcoin vorgeschlagen. Gleichwohl wurden nur wenige Vorschläge in Bitcoin und andere weit verbreitete Kryptowährungen integriert, deren Resistenz gegen tiefgreifende Veränderungen augenscheinlich mit ihrer Verbreitung wächst. In dieser Dissertation schlagen wir vier kryptographische Verfahren vor, die die Funktionalität und die Datenschutzeigenschaften von Bitcoin und ähnlichen Kryptowährungen verbessern ohne deren Funktionsweise tiefgreifend verändern zu müssen. Erstens realisieren wir Smart Contracts, die es erlauben widersprüchliche Aussagen einer Vertragspartei mit dem Verlust von Kryptogeld zu bestrafen. Zweitens schlagen wir CoinShuffle++ vor, ein Mix-Protokoll, das die Anonymität von Benutzern verbessert, indem es ihre Transaktionen kombiniert und so deren Rückverfolgung erschwert. Sein Herzstück ist DiceMix, ein neues und effizientes Protokoll zur anonymen Veröffentlichung von Nachrichten ohne vertrauenswürdige Dritte und in der Präsenz von bösartigen Teilnehmern. Drittens kombinieren wir dieses Protokoll mit der existierenden Idee, Geldbeträge in Commitments zu verbergen, und erhalten so das ValueShuffle-Protokoll, das uns ermöglicht, große Hindernisse für den praktischen Einsatz von Mix-Protokollen zu überwinden. Viertens zeigen wir, wie die dabei benutzten Commitments für einen sicheren Übergang zu Post-Quanten-Kryptographie vorbereitet werden können
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Anonymity in Bitcoin and Bitmessage
No full textThis report describes two projects created by the author which are based on ideas which originate from the Bitcoin community. The first, bmd, is a re-implementation of the Bitmessage protocol in go. Bitmessage is an anonymous and secure messaging system invented by Jonathan Warren, who was inspired by the design of Bitcoin's p2p network. [WARR1] The second is Shufflepuff, an implementation of a protocol called CoinShuffle[RUFF1] which allows several people to construct a Bitcoin transaction with an input and an output for each participant without any participant knowing who owns which output. CoinShuffle was invented by Tim Ruffing et al, and it is an upgrade of a protocol called CoinJoin, invented by Gregory Maxwell. This paper discusses the background, properties, applications, and design of bmd and Shufflepuff. There is also a report of a performance analysis on bmd.Electrical and Computer Engineerin
Switch Commitments: A Safety Switch for Confidential Transactions
No full textCryptographic agility is the ability to switch to larger cryptographic parameters or different algorithms in the case of security doubts. This very desirable property of cryptographic systems is inherently difficult to achieve in cryptocurrencies due to their permanent state in the blockchain: for example, if it turns out that the employed signature scheme is insecure, a switch to a different scheme can only protect the outputs of future transactions but cannot fix transaction outputs already recorded in the blockchain, exposing owners of the corresponding money to risk of theft. This situation is even worse with Confidential Transactions, a recent privacy-enhancing proposal to hide transacted monetary amounts in homomorphic commitments. If an attacker manages to break the computational binding property of a commitment, he can create money out of thin air, jeopardizing the security of the entire currency. The obvious solution is to use statistically or perfectly binding commitment schemes but they come with performance drawbacks due to the need for less efficient range proofs.
In this paper, our aim is to overcome this dilemma. We introduce switch commitments, which constitute a cryptographic middle ground between computationally binding and statistically binding commitments. The key property of this novel primitive is the possibility to switch existing commitments, e.g., recorded in the blockchain, from computational bindingness to statistical bindingness if doubts in the underlying hardness assumption arise. This switch trades off efficiency for security. We provide a practical and simple construction of switch commitments
by proving that ElGamal commitments with a restricted message space are secure switch commitments. The combination of switch commitments and statistically sound range proofs yields an instantiation of Confidential Transactions that can be switched to be resilient against post-quantum attackers trying to inflate the currency
Mixing Confidential Transactions: Comprehensive Transaction Privacy for Bitcoin
No full textThe public nature of the blockchain has been shown to be a severe threat for the privacy of Bitcoin users. Even worse, since funds can be tracked and tainted, no two coins are equal, and fungibility, a fundamental property required in every currency, is at risk. With these threats in mind, several privacy-enhancing technologies have been proposed to improve transaction privacy in Bitcoin. However, they either require a deep redesign of the currency, breaking many currently deployed features, or they address only specific privacy issues and consequently provide only very limited guarantees when deployed separately.
The goal of this work is to overcome this trade-off. Building on CoinJoin, we design ValueShuffle, the first coin mixing protocol compatible with Confidential Transactions, a proposed enhancement to the Bitcoin protocol to hide payment values in the blockchain. ValueShuffle ensures the anonymity of mixing participants as well as the confidentiality of their payment values even against other possibly malicious mixing participants. By combining CoinJoin with Confidential Transactions and additionally Stealth Addresses, ValueShuffle provides comprehensive privacy (payer anonymity, payee anonymity, and payment value privacy) without breaking with fundamental design principles or features of the current Bitcoin system. Assuming that Confidential Transactions will be integrated in the Bitcoin protocol, ValueShuffle makes it possible to mix funds of different value as well as to mix and spend funds in the same transaction, which overcomes the two main limitations of previous coin mixing protocols
ValueShuffle: Mixing Confidential Transactions for Comprehensive Transaction Privacy in Bitcoin
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