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1. Cross-chain Transactions

   https://doi.org/10.1109/ICBC48266.2020.9169477  

   Shadab, Narges; Houshmand, Farzin; Lesani, Mohsen (May 2020, 2020 IEEE International Conference on Blockchain and Cryptocurrency (ICBC))

   null (Ed.)

   The value of cryptocurrencies is highly volatile and investors require fast and reliable exchange systems. In cross-chain transactions, multiple parties exchange assets across multiple blockchains which can be represented as a directed graph with vertexes V as parties and edges E as asset transfers. In a simple form, cross-chain transactions are cross-chain swaps where each edge e transfers an asset that the head of e already owns. However, in general, a cross-chain transaction includes a sequence of exchanges at each blockchain. Further, transactions may have off-chain steps and hence may not be strongly connected. Given a transaction, protocols are desired that guarantee the following property called uniformity. If all parties conform to the protocol, all the assets should be transferred. Further, if any party deviates from the protocol, the conforming parties should not experience any loss. Previous work introduced a uniform protocol for strongly connected cross-chain swaps and showed that no uniform protocol exists for transactions that are not strongly connected. We present a uniform protocol for general cross-chain transactions with sequenced and off-chain steps when a few certain parties are conforming. Further, we prove a new property called end-to-end that guarantees that if the source parties pay, the sink parties are paid. We present a synthesis tool called XCHAIN that given a high-level description of a cross-transaction can automatically generate smart contracts in Solidity for all the parties. 

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2. Privacy-Preserving Cross-Chain Atomic Swaps

   https://doi.org/10.1007/978-3-030-54455-3_38  

   Deshpande A., Herlihy M (August 2020, Lecture notes in computer science)

   null (Ed.)

   Recently, there has been a lot of interest in studying the transfer of assets across different blockchains in the form of cross-chain atomic swaps. Unfortunately, the current candidates of atomic swaps (hash-lock time contracts) offer no privacy; the identities as well as the exact trade that happened between any two parties is publicly visible. In this work, we explore the different notions of privacy that we can hope for in an atomic swap protocol. Concretely, we define an atomic swap as a two-party protocol and formalize the different notions of privacy in the form of anonymity, confidentiality and indistinguishability of swap transactions. As a building block, we abstract out the primitive of Atomic Release of Secrets ( ARS ) which captures atomic exchange of a secret for a pre-decided transaction. We then show how ARS can be used to build privacy-preserving cross-chain swaps. We also show that the recently introduced notion of adapter signatures [Poe18, War17] is a concrete instantiation of ARS under the framework of Schnorr signatures [Sch91] and thus, construct a private cross-chain swap using Schnorr signatures. 

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3. Quantum routing with fast reversals

   https://doi.org/10.22331/q-2021-08-31-533  

   Bapat, Aniruddha; Childs, Andrew M.; Gorshkov, Alexey V.; King, Samuel; Schoute, Eddie; Shastri, Hrishee (August 2021, Quantum)

   null (Ed.)

   We present methods for implementing arbitrary permutations of qubits under interaction constraints. Our protocols make use of previous methods for rapidly reversing the order of qubits along a path. Given nearest-neighbor interactions on a path of length n , we show that there exists a constant ϵ ≈ 0.034 such that the quantum routing time is at most ( 1 − ϵ ) n , whereas any swap-based protocol needs at least time n − 1 . This represents the first known quantum advantage over swap-based routing methods and also gives improved quantum routing times for realistic architectures such as grids. Furthermore, we show that our algorithm approaches a quantum routing time of 2 n / 3 in expectation for uniformly random permutations, whereas swap-based protocols require time n asymptotically. Additionally, we consider sparse permutations that route k ≤ n qubits and give algorithms with quantum routing time at most n / 3 + O ( k 2 ) on paths and at most 2 r / 3 + O ( k 2 ) on general graphs with radius r . 

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4. Blockchains for Transactive Energy Systems: Opportunities, Challenges, and Approaches

   https://doi.org/10.1109/MC.2020.3002997  

   Eisele, Scott; Barreto, Carlos Dubey; Mavridou, Anastasia (January 2020, Computer)

   The emergence of blockchains and smart contracts have renewed interest in electrical cyber-physical systems, especially in the area of transactive energy systems. However, despite recent advances, there remain significant challenges that impede the practical adoption of blockchains in transactive energy systems, which include implementing complex market mechanisms in smart contracts, ensuring safety of the power system, and protecting residential consumers’ privacy. To address these challenges, we present TRANSAX, a blockchain-based transactive energy system that provides an efficient, safe, and privacy-preserving market built on smart contracts. Implementation and deployment of TRANSAX in a verifiably correct and efficient way is based on VeriSolid, a framework for the correct-by-construction development of smart contracts, and RIAPS, a middleware for resilient distributed power systems 

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5. Riggs: Decentralized Sealed-Bid Auctions

   Tyagi, Nirvan; Arun, Arasu; Freitag, Cody; Wahby, Riad; Bonneau, Joseph; Mazières, David (November 2023, ACM Conference on Computer and Communications Security (CCS))

   Cremers, Cas; Kirda, Engin (Ed.)

   We introduce the first practical protocols for fully decentralized sealed-bid auctions using timed commitments. Timed commitments ensure that the auction is finalized fairly even if all participants drop out after posting bids or if bidders collude to try to learn the bidder’s bid value. Our protocols rely on a novel non-malleable timed commitment scheme which efficiently supports range proofs to establish that bidders have sufficient funds to cover a hidden bid value. This allows us to penalize users who abandon bids for exactly the bid value, while supporting simultaneous bidding in multiple auctions with a shared collateral pool. Our protocols are concretely efficient and we have implemented them in an Ethereum- compatible smart contract which automatically enforces payment and delivery of an auctioned digital asset. 

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