2,857 research outputs found
ARPA Whitepaper
We propose a secure computation solution for blockchain networks. The
correctness of computation is verifiable even under malicious majority
condition using information-theoretic Message Authentication Code (MAC), and
the privacy is preserved using Secret-Sharing. With state-of-the-art multiparty
computation protocol and a layer2 solution, our privacy-preserving computation
guarantees data security on blockchain, cryptographically, while reducing the
heavy-lifting computation job to a few nodes. This breakthrough has several
implications on the future of decentralized networks. First, secure computation
can be used to support Private Smart Contracts, where consensus is reached
without exposing the information in the public contract. Second, it enables
data to be shared and used in trustless network, without disclosing the raw
data during data-at-use, where data ownership and data usage is safely
separated. Last but not least, computation and verification processes are
separated, which can be perceived as computational sharding, this effectively
makes the transaction processing speed linear to the number of participating
nodes. Our objective is to deploy our secure computation network as an layer2
solution to any blockchain system. Smart Contracts\cite{smartcontract} will be
used as bridge to link the blockchain and computation networks. Additionally,
they will be used as verifier to ensure that outsourced computation is
completed correctly. In order to achieve this, we first develop a general MPC
network with advanced features, such as: 1) Secure Computation, 2) Off-chain
Computation, 3) Verifiable Computation, and 4)Support dApps' needs like
privacy-preserving data exchange
FastPay: High-Performance Byzantine Fault Tolerant Settlement
FastPay allows a set of distributed authorities, some of which are Byzantine,
to maintain a high-integrity and availability settlement system for pre-funded
payments. It can be used to settle payments in a native unit of value
(crypto-currency), or as a financial side-infrastructure to support retail
payments in fiat currencies. FastPay is based on Byzantine Consistent Broadcast
as its core primitive, foregoing the expenses of full atomic commit channels
(consensus). The resulting system has low-latency for both confirmation and
payment finality. Remarkably, each authority can be sharded across many
machines to allow unbounded horizontal scalability. Our experiments demonstrate
intra-continental confirmation latency of less than 100ms, making FastPay
applicable to point of sale payments. In laboratory environments, we achieve
over 80,000 transactions per second with 20 authorities---surpassing the
requirements of current retail card payment networks, while significantly
increasing their robustness
Execution Models for Choreographies and Cryptoprotocols
A choreography describes a transaction in which several principals interact.
Since choreographies frequently describe business processes affecting
substantial assets, we need a security infrastructure in order to implement
them safely. As part of a line of work devoted to generating cryptoprotocols
from choreographies, we focus here on the execution models suited to the two
levels.
We give a strand-style semantics for choreographies, and propose a special
execution model in which choreography-level messages are faithfully delivered
exactly once. We adapt this model to handle multiparty protocols in which some
participants may be compromised.
At level of cryptoprotocols, we use the standard Dolev-Yao execution model,
with one alteration. Since many implementations use a "nonce cache" to discard
multiply delivered messages, we provide a semantics for at-most-once delivery
Chainspace: A Sharded Smart Contracts Platform
Chainspace is a decentralized infrastructure, known as a distributed ledger,
that supports user defined smart contracts and executes user-supplied
transactions on their objects. The correct execution of smart contract
transactions is verifiable by all. The system is scalable, by sharding state
and the execution of transactions, and using S-BAC, a distributed commit
protocol, to guarantee consistency. Chainspace is secure against subsets of
nodes trying to compromise its integrity or availability properties through
Byzantine Fault Tolerance (BFT), and extremely high-auditability,
non-repudiation and `blockchain' techniques. Even when BFT fails, auditing
mechanisms are in place to trace malicious participants. We present the design,
rationale, and details of Chainspace; we argue through evaluating an
implementation of the system about its scaling and other features; we
illustrate a number of privacy-friendly smart contracts for smart metering,
polling and banking and measure their performance
PrivateEx: Privacy Preserving Exchange of Crypto-assets on Blockchain
Bitcoin introduces a new type of cryptocurrency that does not rely on a central system to maintain transactions. Inspired by the success of Bitcoin, all types of alt cryptocurrencies were invented in recent years. Some of the new cryptocurrencies focus on privacy enhancement, where transaction information such as value and sender/receiver identity can be hidden, such as Zcash and Monero. However, there are few schemes to support multiple types of cryptocurrencies/assets and offer privacy enhancement at the same time. The major challenge for a multiple asset system is that it needs to support two-way assets exchange between participants besides one-way asset transfer. Thus, we propose a privacy-preserving exchange scheme, PrivateEx, which preserves the privacy of the exchange of different assets. PrivateEx utilizes zero-knowledge proof and a novel way to “lock” assets involved in the exchange to guarantee the correctness, fairness, and privacy of exchange of assets in the system. We also implement a prototype of PrivateEx and evaluate its performance to show that it is practical with modern computers
Keeping Authorities "Honest or Bust" with Decentralized Witness Cosigning
The secret keys of critical network authorities - such as time, name,
certificate, and software update services - represent high-value targets for
hackers, criminals, and spy agencies wishing to use these keys secretly to
compromise other hosts. To protect authorities and their clients proactively
from undetected exploits and misuse, we introduce CoSi, a scalable witness
cosigning protocol ensuring that every authoritative statement is validated and
publicly logged by a diverse group of witnesses before any client will accept
it. A statement S collectively signed by W witnesses assures clients that S has
been seen, and not immediately found erroneous, by those W observers. Even if S
is compromised in a fashion not readily detectable by the witnesses, CoSi still
guarantees S's exposure to public scrutiny, forcing secrecy-minded attackers to
risk that the compromise will soon be detected by one of the W witnesses.
Because clients can verify collective signatures efficiently without
communication, CoSi protects clients' privacy, and offers the first
transparency mechanism effective against persistent man-in-the-middle attackers
who control a victim's Internet access, the authority's secret key, and several
witnesses' secret keys. CoSi builds on existing cryptographic multisignature
methods, scaling them to support thousands of witnesses via signature
aggregation over efficient communication trees. A working prototype
demonstrates CoSi in the context of timestamping and logging authorities,
enabling groups of over 8,000 distributed witnesses to cosign authoritative
statements in under two seconds.Comment: 20 pages, 7 figure
Modeling Bitcoin Contracts by Timed Automata
Bitcoin is a peer-to-peer cryptographic currency system. Since its
introduction in 2008, Bitcoin has gained noticeable popularity, mostly due to
its following properties: (1) the transaction fees are very low, and (2) it is
not controlled by any central authority, which in particular means that nobody
can "print" the money to generate inflation. Moreover, the transaction syntax
allows to create the so-called contracts, where a number of
mutually-distrusting parties engage in a protocol to jointly perform some
financial task, and the fairness of this process is guaranteed by the
properties of Bitcoin. Although the Bitcoin contracts have several potential
applications in the digital economy, so far they have not been widely used in
real life. This is partly due to the fact that they are cumbersome to create
and analyze, and hence risky to use.
In this paper we propose to remedy this problem by using the methods
originally developed for the computer-aided analysis for hardware and software
systems, in particular those based on the timed automata. More concretely, we
propose a framework for modeling the Bitcoin contracts using the timed automata
in the UPPAAL model checker. Our method is general and can be used to model
several contracts. As a proof-of-concept we use this framework to model some of
the Bitcoin contracts from our recent previous work. We then automatically
verify their security in UPPAAL, finding (and correcting) some subtle errors
that were difficult to spot by the manual analysis. We hope that our work can
draw the attention of the researchers working on formal modeling to the problem
of the Bitcoin contract verification, and spark off more research on this
topic
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