Ethereum | EPFL Graph Search

Ethereum (prononcé ) est un protocole d'échanges décentralisés permettant la création par les utilisateurs de contrats intelligents. Ces contrats intelligents sont basés sur un protocole informatique permettant de vérifier ou de mettre en application un contrat mutuel. Ils sont déployés et consultables publiquement dans une blockchain. Ethereum utilise une unité de compte dénommée Ether comme moyen de paiement de ces contrats. Son sigle correspondant, utilisé par les plateformes d'échanges, est « ETH ». Ethereum est la deuxième plus importante monnaie cryptographique décentralisée avec une capitalisation supérieure à d'euros en octobre 2021. En , l'équipe de développement d'Ethereum a dû procéder à un hard fork après une attaque réussie par un groupe de pirates sur un fonds d'investissement en Ether appelé (organisation autonome décentralisée) dans laquelle près de (soit plus de 5 % du montant total de la crypto-monnaie en circulation) ont été détournés sur une adresse non contrô

Analysis of the BIKE post-quantum cryptographic protocols and the Legendre pseudorandom function

Dusan Kostic

The field of post-quantum cryptography studies cryptographic systems that are secure against an adversary in possession of a quantum computer. In 2017, the National Institute of Standards and Technology (NIST) initiated a process to standardize quantum-resistant public-key cryptographic algorithms (NIST PQC Project). In this thesis we analyze the performance and security of the Bit-Flipping Key Encapsulation Mechanism (BIKE) -- one of the candidates in the NIST PQC project which advanced to the second round of the standardization process. BIKE is a code-based cryptographic system featuring three different variants of the protocol. In the first round of the NIST PQC project BIKE offered security only against chosen-plaintext attacks (CPA). In the second round, BIKE introduced three new variants that are claimed to be secure also against chosen-ciphertext attacks (CCA). Firstly, we build a secure implementation of the CCA protocol and show that its performance characteristics are only negligibly worse than the CPA variant. In the key decapsulation phase of the protocol BIKE uses a decoding algorithm which fails with some probability, called the Decoding Failure Rate (DFR). We analyze the DFR of two decoders used in BIKE, Back-Flip and Black-Gray, and propose a new decoder, called Black-Gray-Flip, that achieves the same DFR as the two previously used decoders while being almost twice as fast. Finally, we propose an algorithm for inversion of binary polynomials in a polynomial ring used in BIKE-2, the second variant of BIKE. Our implementation of the inversion significantly outperforms previously used algorithms. With this and the fact that the bandwidth requirement for BIKE-2 is the smallest among the three variants, BIKE-2 is positioned as the preferable variant of BIKE. The second part of this thesis studies the Legendre pseudorandom function (PRF) which is proposed to be used in the context of blockchains. We present a new algorithm for cryptanalysis of the Legendre PRF. The complexity of our algorithm is lower than the previous best known algorithm. Moreover, we show the results of breaking three Legendre PRF challenges posed by the Ethereum foundation. The most difficult challenge that we solved set the new record which is not broken so far.

EPFL2020

Essays in Financial Economics

Marc André Frattaroli

This thesis consists of three chapters that study separate subjects in the area of corporate governance and financial intermediation. In the first chapter, I study a protectionist anti-takeover law introduced in 2014 in France that covers a subset of all firms in the economy. The law decreased affected firms' likelihood of becoming the target of a merger or acquisition and had a negative impact on shareholder value. There is no evidence that management of those firms subsequently altered firm policies in its interest. Investment, employment, wages, profitability, and capital structure remain unchanged. The share of annual CEO compensation consisting of equity instruments increased by 8.4 percentage points, suggesting that boards reacted to the loss in monitoring by the takeover market by increasing the pay-for-performance sensitivity. In the second chapter, which is co-authored work with Rüdiger Fahlenbrach, we conduct a detailed analysis of investors in successful initial coin offerings (ICOs). The average ICO has 4,700 contributors. The median participant contributes small amounts and many investors sell their tokens before the underlying product is developed. Large presale investors obtain tokens at a discount and flip part of their allocation shortly after the ICO. ICO contributors lack the protections traditionally afforded to investors in early stage financing. Nevertheless, returns nine months after the ICO are positive on average, driven mostly by an increase in the value of the Ethereum cryptocurrency. In the third chapter, which is joint work with Christoph Herpfer, we investigate how bankers use information from lending relationships to help borrowers combine resources in strategic alliances. Firms that have borrowed from the same banker or share an indirect connection through a network of bankers are significantly more likely to enter an alliance. Consistent with bankers overcoming informational frictions, their ability to facilitate alliances decreases with network distance, and is stronger for opaque borrowers. Firms connected to more potential partners via banker networks enter more alliances. These alliances are associated with positive announcement returns and brokering banks are more likely to receive future underwriting mandates.

EPFL2020

Networks of Ethereum Non-Fungible Tokens: A graph-based analysis of the ERC-721 ecosystem

Simone Casale Brunet, Marco Mattavelli

Non-fungible tokens (NFTs) as a decentralized proof of ownership represent one of the main reasons why Ethereum is a disruptive technology. This paper presents the first systematic study of the interactions occurring in a number of NFT ecosystems. We illustrate how to retrieve transaction data available on the blockchain and structure it as a graph-based model. Thanks to this methodology, we are able to study for the first time the topological structure of NFT networks and show that their properties (degree distribution and others) are similar to those of interaction graphs in social networks. Time-dependent analysis metrics, useful to characterize market influencers and interactions between different wallets, are also introduced. Based on those, we identify across a number of NFT networks the widespread presence of both investors accumulating NFTs and individuals who make large profits.

IEEE2021

Analysis of the BIKE post-quantum cryptographic protocols and the Legendre pseudorandom function

Dusan Kostic

EPFL2020

Essays in Financial Economics

Marc André Frattaroli

EPFL2020