71 research outputs found
Majority is not Enough: Bitcoin Mining is Vulnerable
The Bitcoin cryptocurrency records its transactions in a public log called
the blockchain. Its security rests critically on the distributed protocol that
maintains the blockchain, run by participants called miners. Conventional
wisdom asserts that the protocol is incentive-compatible and secure against
colluding minority groups, i.e., it incentivizes miners to follow the protocol
as prescribed.
We show that the Bitcoin protocol is not incentive-compatible. We present an
attack with which colluding miners obtain a revenue larger than their fair
share. This attack can have significant consequences for Bitcoin: Rational
miners will prefer to join the selfish miners, and the colluding group will
increase in size until it becomes a majority. At this point, the Bitcoin system
ceases to be a decentralized currency.
Selfish mining is feasible for any group size of colluding miners. We propose
a practical modification to the Bitcoin protocol that protects against selfish
mining pools that command less than 1/4 of the resources. This threshold is
lower than the wrongly assumed 1/2 bound, but better than the current reality
where a group of any size can compromise the system
A Game-Theoretic Model Motivated by the DARPA Network Challenge
In this paper we propose a game-theoretic model to analyze events similar to
the 2009 \emph{DARPA Network Challenge}, which was organized by the Defense
Advanced Research Projects Agency (DARPA) for exploring the roles that the
Internet and social networks play in incentivizing wide-area collaborations.
The challenge was to form a group that would be the first to find the locations
of ten moored weather balloons across the United States. We consider a model in
which people (who can form groups) are located in some topology with a
fixed coverage volume around each person's geographical location. We consider
various topologies where the players can be located such as the Euclidean
-dimension space and the vertices of a graph. A balloon is placed in the
space and a group wins if it is the first one to report the location of the
balloon. A larger team has a higher probability of finding the balloon, but we
assume that the prize money is divided equally among the team members. Hence
there is a competing tension to keep teams as small as possible.
\emph{Risk aversion} is the reluctance of a person to accept a bargain with
an uncertain payoff rather than another bargain with a more certain, but
possibly lower, expected payoff. In our model we consider the \emph{isoelastic}
utility function derived from the Arrow-Pratt measure of relative risk
aversion. The main aim is to analyze the structures of the groups in Nash
equilibria for our model. For the -dimensional Euclidean space ()
and the class of bounded degree regular graphs we show that in any Nash
Equilibrium the \emph{richest} group (having maximum expected utility per
person) covers a constant fraction of the total volume
Theoretical Bitcoin Attacks with less than Half of the Computational Power (draft)
A widespread security claim of the Bitcoin system, presented in the original
Bitcoin white-paper, states that the security of the system is guaranteed as
long as there is no attacker in possession of half or more of the total
computational power used to maintain the system. This claim, however, is proved
based on theoretically flawed assumptions.
In the paper we analyze two kinds of attacks based on two theoretical flaws:
the Block Discarding Attack and the Difficulty Raising Attack. We argue that
the current theoretical limit of attacker's fraction of total computational
power essential for the security of the system is in a sense not
but a bit less than , and outline proposals for protocol change
that can raise this limit to be as close to as we want.
The basic idea of the Block Discarding Attack has been noted as early as
2010, and lately was independently though-of and analyzed by both author of
this paper and authors of a most recently pre-print published paper. We thus
focus on the major differences of our analysis, and try to explain the
unfortunate surprising coincidence. To the best of our knowledge, the second
attack is presented here for the first time
A Survey on Block Chain and Bitcoin β Challenges & Applications
Block chain is as of late presented and changing the advanced world conveying another point of view to security, flexibility and productivity of framework. While at first promoted by Bit Coin, Block chain is significantly more than an establishment for digital money. It offers a safe method to trade any sort of good administration or exchange. This paper exhibits an exhaustive review on Block chain Technology and Bit coin. Bitcoin has emerged as the most successful crypto currency since its appearance back in 2009. Besides its security robustness, two main properties have probably been its key to success: anonymity and decentralization. In this paper, we provide a comprehensive description on the details that make such crypto currency an interesting research topic in the privacy community. We perform an exhaustive review of the bitcoin anonymity research papers that have been published so far and we outline some research challenges on that topic
Transaction Propagation on Permissionless Blockchains: Incentive and Routing Mechanisms
Existing permissionless blockchain solutions rely on peer-to-peer propagation
mechanisms, where nodes in a network transfer transaction they received to
their neighbors. Unfortunately, there is no explicit incentive for such
transaction propagation. Therefore, existing propagation mechanisms will not be
sustainable in a fully decentralized blockchain with rational nodes. In this
work, we formally define the problem of incentivizing nodes for transaction
propagation. We propose an incentive mechanism where each node involved in the
propagation of a transaction receives a share of the transaction fee. We also
show that our proposal is Sybil-proof. Furthermore, we combine the incentive
mechanism with smart routing to reduce the communication and storage costs at
the same time. The proposed routing mechanism reduces the redundant transaction
propagation from the size of the network to a factor of average shortest path
length. The routing mechanism is built upon a specific type of consensus
protocol where the round leader who creates the transaction block is known in
advance. Note that our routing mechanism is a generic one and can be adopted
independently from the incentive mechanism.Comment: 2018 Crypto Valley Conference on Blockchain Technolog
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