CryptoMaze: Atomic Off-Chain Payments in Payment Channel Network

Payment protocols developed to realize off-chain transactions in Payment channel network (PCN) assumes the underlying routing algorithm transfers the payment via a single path. However, a path may not have sufficient capacity to route a transaction. It is inevitable to split the payment across multiple paths. If we run independent instances of the protocol on each path, the execution may fail in some of the paths, leading to partial transfer of funds. A payer has to reattempt the entire process for the residual amount. We propose a secure and privacy-preserving payment protocol, CryptoMaze. Instead of independent paths, the funds are transferred from sender to receiver across several payment channels responsible for routing, in a breadth-first fashion. Payments are resolved faster at reduced setup cost, compared to existing state-of-the-art. Correlation among the partial payments is captured, guaranteeing atomicity. Further, two party ECDSA signature is used for establishing scriptless locks among parties involved in the payment. It reduces space overhead by leveraging on core Bitcoin scripts. We provide a formal model in the Universal Composability framework and state the privacy goals achieved by CryptoMaze. We compare the performance of our protocol with the existing single path based payment protocol, Multi-hop HTLC, applied iteratively on one path at a time on several instances. It is observed that CryptoMaze requires less communication overhead and low execution time, demonstrating efficiency and scalability.Comment: 30 pages, 9 figures, 1 tabl

Chrisimos: A useful Proof-of-Work for finding Minimal Dominating Set of a graph

Hash-based Proof-of-Work (PoW) used in the Bitcoin Blockchain leads to high energy consumption and resource wastage. In this paper, we aim to re-purpose the energy by replacing the hash function with real-life problems having commercial utility. We propose Chrisimos, a useful Proof-of-Work where miners are required to find a minimal dominating set for real-life graph instances. A miner who is able to output the smallest dominating set for the given graph within the block interval time wins the mining game. We also propose a new chain selection rule that ensures the security of the scheme. Thus our protocol also realizes a decentralized minimal dominating set solver for any graph instance. We provide formal proof of correctness and show via experimental results that the block interval time is within feasible bounds of hash-based PoW.Comment: 20 pages, 3 figures. An abridged version of the paper got accepted in The International Symposium on Intelligent and Trustworthy Computing, Communications, and Networking (ITCCN-2023) held in conjunction with the 22nd IEEE International Conference on Trust, Security and Privacy in Computing and Communications (TrustCom-2023

LightSwap: An Atomic Swap Does Not Require Timeouts At Both Blockchains

Security and privacy issues with centralized exchange services have motivated the design of atomic swap protocols for decentralized trading across currencies. These protocols follow a standard blueprint similar to the 2-phase commit in databases: (i) both users first lock their coins under a certain (cryptographic) condition and a timeout; (ii-a) the coins are swapped if the condition is fulfilled; or (ii-b) coins are released after the timeout. The quest for these protocols is to minimize the requirements from the scripting language supported by the swapped coins, thereby supporting a larger range of cryptocurrencies. The recently proposed universal atomic swap protocol [IEEE S&P’22] demonstrates how to swap coins whose scripting language only supports the verification of a digital signature on a transaction. However, the timeout functionality is cryptographically simulated with verifiable timelock puzzles, a computationally expensive primitive that hinders its use in battery-constrained devices such as mobile phones. In this state of affairs, we question whether the 2-phase commit paradigm is necessary for atomic swaps in the first place. In other words, is it possible to design a secure atomic swap protocol where the timeout is not used by (at least one of the two) users? In this work, we present LightSwap, the first secure atomic swap protocol that does not require the timeout functionality (not even in the form of a cryptographic puzzle) by one of the two users. LightSwap is thus better suited for scenarios where a user, running an instance of LightSwap on her mobile phone, wants to exchange coins with an online exchange service running an instance of LightSwap on a computer. We show how LightSwap can be used to swap Bitcoin and Monero, an interesting use case since Monero does not provide any scripting functionality support other than linkable ring signature verification

GPU accelerated novel particle filtering method

In this paper, a graphics processor unit (GPU) accelerated particle filtering algorithm is presented with an introduction to a novel resampling technique. The aim remains in the mitigation of particle impoverishment as well as computational burden, problems which are commonly associated with classical (systematic) resampled particle filtering. The proposed algorithm employs a priori-space dependent distribution in addition to the likelihood, and hence is christened as dual distribution dependent (D3) resampling method. Simulation results exhibit lesser values for root mean square error (RMSE) in comparison to that for systematic resampling. D3 resampling is shown to improve particle diversity after each iteration, thereby affecting the overall quality of estimation. However, computational burden is significantly increased owing to few excessive computations within the newly formulated resampling framework. With a view to obtaining parallel speedup we introduce a CUDA version of the proposed method for necessary acceleration by GPU. The GPU programming model is detailed in the context of this paper. Implementation issues are discussed along with illustration of empirical computational efficiency, as obtained by executing the CUDA code on Quadro 2000 GPU. The GPU enabled code has a speedup of 3 and 4 over the sequential executions of systematic and D3 resampling methods respectively. Performance both in terms of RMSE and running time have been elaborated with respect to different selections for threads per block towards effective implementations. It is in this context that, we further introduce a cost to performance metric (CPM) for assessing the algorithmic efficiency of the estimator, involving both quality of estimation and running time as comparative factors, transformed into a unified parameter for assessment. CPM values for estimators obtained from all such different choices for threads per block have been determined and a final value for the chosen parameter is resolved for generation of a holistic effective estimator