Sidechain technology has been envisioned as a promising solution to accelerate today's public blockchains in terms of scalability and interoperability. By relying on the mainchain for security, different sidechains can formulate their own rules to reach consensus. Although the literature has considered the possibility of using consensus protocols in the sidechain, so far a tailor-made consensus protocol for sidechains with high performance and formal security proof has not been attempted. To fill this gap, we introduce Vulcan, a low overhead, highly efficient, security provable sidechain protocol. Vulcan makes use of smart contracts to ensure that only one block proposed in the sidechain will be enforced on the mainchain in each round, achieving consensus in an efficient manner. We give formal specifications of Vulcan which ensures safety and liveness with @math validators (total number of @math ) without online requirement of clients. For security analysis, we give formal security definitions and proofs under Universally Composable Security (UCS) model. As a proof of concept, we implement Vulcan and evaluate it in Ethereum testnet.
@cite_6: Offchain networks emerge as a promising solution to address the scalability challenge of blockchain. Participants directly make payments through a network of payment channels without the overhead of committing onchain transactions. Routing is critical to the performance of offchain networks. Existing solutions use either static routing with poor performance or dynamic routing with high overhead to obtain the dynamic channel balance information. In this paper, we propose Flash, a new dynamic routing solution that leverages the unique characteristics of transactions in offchain networks to strike a better tradeoff between path optimality and probing overhead. By studying the traces of real offchain networks, we find that the payment sizes are heavy-tailed, and most payments are highly recurrent. Flash thus differentiates the treatment of elephant payments from mice payments. It uses a modified max-flow algorithm for elephant payments to find paths with sufficient capacity, and strategically routes the payment across paths to minimize the transaction fees. Mice payments are directly sent by looking up a routing table with a few precomputed paths to reduce probing overhead. Testbed experiments and data-driven simulations show that Flash improves the success volume of payments by up to 2.3x compared to the state-of-the-art routing algorithm.
@cite_5: Payment channels emerged recently as an efficient method for performing cheap micropayments in cryptocurrencies. In contrast to traditional on-chain transactions, payment channels have the advantage that they allow for nearly unlimited number of transactions between parties without involving the blockchain. In this work, we introduce Perun, an off-chain channel system that offers a new method for connecting channels that is more efficient than the existing technique of routing transactions'' over multiple channels. To this end, Perun introduces a technique called virtual paymentchannels'' that avoids involvement of the intermediary for each individual payment.In this paper we formally model and prove security of this technique in the case of one intermediary, who can be viewed as a payment hub'' that has direct channels with several parties. Our scheme works over any cryptocurrency that provides Turing-complete smart contracts. As a proof of concept, we implemented Perun's smart contracts in Ethereum.
@cite_10: Scaling the transaction throughput of decentralized blockchain ledgers such as Bitcoin and Ethereum has been an ongoing challenge. Two-party duplex payment channels have been designed and used as building blocks to construct linked payment networks, which allow atomic and trust-free payments between parties without exhausting the resources of the blockchain. Once a payment channel, however, is depleted (e.g., because transactions were mostly unidirectional) the channel would need to be closed and re-funded to allow for new transactions. Users are envisioned to entertain multiple payment channels with different entities, and as such, instead of refunding a channel (which incurs costly on-chain transactions), a user should be able to leverage his existing channels to rebalance a poorly funded channel. To the best of our knowledge, we present the first solution that allows an arbitrary set of users in a payment channel network to securely rebalance their channels, according to the preferences of the channel owners. Except in the case of disputes (similar to conventional payment channels), our solution does not require on-chain transactions and therefore increases the scalability of existing blockchains. In our security analysis, we show that an honest participant cannot lose any of its funds while rebalancing. We finally provide a proof of concept implementation and evaluation for the Ethereum network.
@cite_25: With the growing usage of Bitcoin and other cryptocurrencies, many scalability challenges have emerged. A promising scaling solution, exemplified by the Lightning Network, uses a network of bidirectional payment channels that allows fast transactions between two parties. However, routing payments on these networks efficiently is non-trivial, since payments require finding paths with sufficient funds, and channels can become unidirectional over time blocking further transactions through them. Today's payment channel networks exacerbate these problems by attempting to deliver all payments atomically. We present the Spider network, a new packet-switched architecture for payment channel networks that addresses these challenges. Spider splits payments into transaction units and transmits them over a period of time across different paths. Spider uses congestion control, in-network scheduling, and imbalance-aware routing to optimize delivery of payments. Our results show that Spider improves the number and volume of successful payments on the network by 10-75 and 10-35 respectively compared to practical state-of-the-art approaches.
@cite_17: SBFT is a state of the art Byzantine fault tolerant state machine replication system that addresses the challenges of scalability, decentralization and global geo-replication. SBFT is optimized for decentralization and is experimentally evaluated on a deployment of more than 200 active replicas withstanding a malicious adversary controlling f=64 replicas. Our experiments show how the different algorithmic ingredients of SBFT contribute to its performance and scalability. The results show that SBFT simultaneously provides almost 2x better throughput and about 1.5x better latency relative to a highly optimized system that implements the PBFT protocol. To achieve this performance improvement, SBFT uses a combination of four ingredients: using collectors and threshold signatures to reduce communication to linear, using an optimistic fast path, reducing client communication and utilizing redundant servers for the fast path. SBFT is the first system to implement a correct dual-mode view change protocol that allows to efficiently run either an optimistic fast path or a fallback slow path without incurring a view change to switch between modes.
The idea of off-chain scaling originated from @cite_17 , which has emerged as the most promising PCN practice for Bitcoin, followed by and for Ethereum. There exist extensive literature proposing constructions to improve PCN. Revive @cite_10 , Spider @cite_25 , and Flash @cite_6 propose dynamic routing algorithms to maximize the throughput and success volume of PCN, while Perun @cite_5 introduces to avoid the involvement of the intermediary for each individual payment, thereby, significantly reducing communication complexity.