1,834 research outputs found
Atomic commitment in transactional DHTs
We investigate the problem of atomic commit in transactional database systems
built on top of Distributed Hash Tables. DHTs provide a decentralized way to
store and look up data. To solve the atomic commit problem we propose to
use an adaption of Paxos commit as a non-blocking algorithm. We exploit the
symmetric replication technique existing in the DKS DHT to determine which
nodes are necessary to execute the commit algorithm. By doing so we achieve a
lower number of communication rounds and a reduction of meta-data in contrast
to traditional Three-Phase-Commit protocols. We also show how the proposed
solution can cope with dynamism due to churn in DHTs. Our solution works
correctly relying only on an inaccurate failure detection of node failure which is
necessary for systems running over the Internet
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
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A Non-blocking Commitment Protocol
A "non-blocking" commitment protocol is one that ensures that at least some sites of a multi-site transaction do not block in spite of any single failure. This paper describes a quorum-based non-blocking commitment protocol that also subsumes the functions of termination and recovery protocols. The protocol survives any single site crash or network partition provided that the failure is not falsely detected. The protocol is correct despite the occurrence of any number of failures, and whether or not failures are falsely detected. When there is no failure, the protocol requires three phases of message exchange between the coordinator and the subordinates and requires each site to force two log records. Read-only transactions are optimized so that a read-only subordinate typically writes no log records and exchanges only one round of messages with the coordinator. Sites can forget the transaction after it terminates everywhere. Finally, a fundamental result about quorum-based commit protocols is uncovered: they are effective only for transactions involving more than three sites
Partial replication in the database state machine
This paper investigates the use of partial replication in the Database State Machine approach introduced ear- lier for fully replicated databases. It builds on the or- der and atomicity properties of group communication primitives to achieve strong consistency and proposes two new abstractions: Resilient Atomic Commit and Fast Atomic Broadcast. Even with atomic broadcast, partial replication re- quires a termination protocol such as atomic commit to ensure transaction atomicity. With Resilient Atomic Commit our termination protocol allows the commit of a transaction despite the failure of some of the par- ticipants. Preliminary performance studies suggest that the additional cost of supporting partial replica- tion can be mitigated through the use of Fast Atomic Broadcast
Front-running Attack in Sharded Blockchains and Fair Cross-shard Consensus
Sharding is a prominent technique for scaling blockchains. By dividing the
network into smaller components known as shards, a sharded blockchain can
process transactions in parallel without introducing inconsistencies through
the coordination of intra-shard and cross-shard consensus protocols. However,
we observe a critical security issue with sharded systems: transaction ordering
manipulations can occur when coordinating intra-shard and cross-shard consensus
protocols, leaving the system vulnerable to attack. Specifically, we identify a
novel security issue known as finalization fairness, which can be exploited
through a front-running attack. This attack allows an attacker to manipulate
the execution order of transactions, even if the victim's transaction has
already been processed and added to the blockchain by a fair intra-shard
consensus.
To address the issue, we offer Haechi, a novel cross-shard protocol that is
immune to front-running attacks. Haechi introduces an ordering phase between
transaction processing and execution, ensuring that the execution order of
transactions is the same as the processing order and achieving finalization
fairness. To accommodate different consensus speeds among shards, Haechi
incorporates a finalization fairness algorithm to achieve a globally fair order
with minimal performance loss. By providing a global order, Haechi ensures
strong consistency among shards, enabling better parallelism in handling
conflicting transactions across shards. These features make Haechi a promising
solution for supporting popular smart contracts in the real world. To evaluate
Haechi's performance, we implemented the protocol using Tendermint and
conducted extensive experiments on a geo-distributed AWS environment. Our
results demonstrate that Haechi achieves finalization fairness with little
performance sacrifice compared to existing cross-shard consensus protocols
A high-performance communication topology for decentralized protocols
Preserving transaction atomicity and ensuring its commitment is key to the maintenance of data integrity in a distributed database. The distributed consensus protocol is a prominent example of a mechanism used to accomplish safe commitment of a distributed transaction. These protocols are based primarily on repeated message exchange among all sites/nodes and their performance is characterized not only by the number of these messages but also by the underlying communication topology. This thesis proposes a measure of performance known as average message complexity and proposes a communication structure based on folded even graphs called the Folded Even Network (FEN). Performance of FEN is compared to other known structures and is shown to outperform them for various values of the number of nodes in the network. It is also shown that large topologies can be generated by connecting multiple FENs together. The expanded structure is also shown to have the same complexity as a single FEN
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