9,402 research outputs found
Group-Oriented Fair Exchange of Signatures
In an Optimistic Fair Exchange (OFE) for digital signatures, two parties exchange their signatures fairly without requiring any online trusted third party. The third party is only involved when a dispute occurs. In all the previous work, OFE has been considered only in a setting where both of the communicating parties are individuals. There is little work discussing about the fair exchange between two \emph{groups} of users, though we can see that this is actually a common scenario in actual OFE applications. In this paper, we introduce a new variant of OFE, called
\emph{Group-Oriented Optimistic Fair Exchange} (GOFE). A GOFE allows two users from two different groups to exchange signatures on behalf of their groups in a fair and anonymous manner. Although GOFE may be considered as a fair exchange for group signatures, it might be inefficient if it is
constructed generically from a group signature scheme. Instead, we show that GOFE is \emph{backward compatible} to the Ambiguous OFE (AOFE). Also, we propose an efficient and concrete construction of GOFE, and prove its security under the security models we propose in this model. The security of the scheme relies on the decision linear assumption and strong Diffie-Hellman assumption under the random oracle model
Preserving transparency and accountability in optimistic fair exchange of digital signatures
Optimistic fair exchange (OFE) protocols are useful tools for two participants to fairly exchange items with the aid of a third party who is only involved if needed. A widely accepted requirement is that the third party\u27s involvement in the exchange must be transparent, to protect privacy and avoid bad publicity. At the same time, a dishonest third party would compromise the fairness of the exchange and the third party thus must be responsible for its behaviors. This is achieved in OFE protocols with another property called accountability. It is unfortunate that the accountability has never been formally studied in OFE since its introduction ten years ago. In this paper, we fill these gaps by giving the first complete definition of accountability in OFE where one of the exchanged items is a digital signature and a generic (also the first) design of OFE where transparency and accountability coexist
An optimistic fair e-commerce protocol for large e-goods
Suppose two entities that do not trust each other want to exchange some arbitrary data over a public channel. A fair exchange protocol ensures that both parties get what they want or neither gets anything. In this paper, a fair e-commerce protocol for large e-goods is proposed and implemented. The proposed protocol provides a method for the fair exchange of e-money for e-products, and a method for verifying the contents of the exchanged items. The protocol is optimistic and efficient such that when none of the parties tries to cheat, only three messages are sufficient. In case of disputes, three more messages are needed. Furthermore, the customer remains anonymous after the transaction; thus, no information about the customers' shopping habits can be gathered through the protocol. The implementation results show that the protocol is efficient and secure and that only a small number of cryptographic operations is sufficient
Fair Exchange in Strand Spaces
Many cryptographic protocols are intended to coordinate state changes among
principals. Exchange protocols coordinate delivery of new values to the
participants, e.g. additions to the set of values they possess. An exchange
protocol is fair if it ensures that delivery of new values is balanced: If one
participant obtains a new possession via the protocol, then all other
participants will, too. Fair exchange requires progress assumptions, unlike
some other protocol properties. The strand space model is a framework for
design and verification of cryptographic protocols. A strand is a local
behavior of a single principal in a single session of a protocol. A bundle is a
partially ordered global execution built from protocol strands and adversary
activities. The strand space model needs two additions for fair exchange
protocols. First, we regard the state as a multiset of facts, and we allow
strands to cause changes in this state via multiset rewriting. Second, progress
assumptions stipulate that some channels are resilient-and guaranteed to
deliver messages-and some principals are assumed not to stop at certain
critical steps. This method leads to proofs of correctness that cleanly
separate protocol properties, such as authentication and confidentiality, from
invariants governing state evolution. G. Wang's recent fair exchange protocol
illustrates the approach
Fair and optimistic quantum contract signing
We present a fair and optimistic quantum contract signing protocol between
two clients that requires no communication with the third trusted party during
the exchange phase. We discuss its fairness and show that it is possible to
design such a protocol for which the probability of a dishonest client to cheat
becomes negligible, and scales as N^{-1/2}, where N is the number of messages
exchanged between the clients. Our protocol is not based on the exchange of
signed messages: its fairness is based on the laws of quantum mechanics. Thus,
it is abuse-free, and the clients do not have to generate new keys for each
message during the Exchange phase. We discuss a real-life scenario when the
measurement errors and qubit state corruption due to noisy channels occur and
argue that for real, good enough measurement apparatus and transmission
channels, our protocol would still be fair. Our protocol could be implemented
by today's technology, as it requires in essence the same type of apparatus as
the one needed for BB84 cryptographic protocol. Finally, we briefly discuss two
alternative versions of the protocol, one that uses only two states (based on
B92 protocol) and the other that uses entangled pairs, and show that it is
possible to generalize our protocol to an arbitrary number of clients.Comment: 11 pages, 2 figure
Instantaneous Decentralized Poker
We present efficient protocols for amortized secure multiparty computation
with penalties and secure cash distribution, of which poker is a prime example.
Our protocols have an initial phase where the parties interact with a
cryptocurrency network, that then enables them to interact only among
themselves over the course of playing many poker games in which money changes
hands.
The high efficiency of our protocols is achieved by harnessing the power of
stateful contracts. Compared to the limited expressive power of Bitcoin
scripts, stateful contracts enable richer forms of interaction between standard
secure computation and a cryptocurrency.
We formalize the stateful contract model and the security notions that our
protocols accomplish, and provide proofs using the simulation paradigm.
Moreover, we provide a reference implementation in Ethereum/Solidity for the
stateful contracts that our protocols are based on.
We also adopt our off-chain cash distribution protocols to the special case
of stateful duplex micropayment channels, which are of independent interest. In
comparison to Bitcoin based payment channels, our duplex channel implementation
is more efficient and has additional features
Centrally Banked Cryptocurrencies
Current cryptocurrencies, starting with Bitcoin, build a decentralized
blockchain-based transaction ledger, maintained through proofs-of-work that
also generate a monetary supply. Such decentralization has benefits, such as
independence from national political control, but also significant limitations
in terms of scalability and computational cost. We introduce RSCoin, a
cryptocurrency framework in which central banks maintain complete control over
the monetary supply, but rely on a distributed set of authorities, or
mintettes, to prevent double-spending. While monetary policy is centralized,
RSCoin still provides strong transparency and auditability guarantees. We
demonstrate, both theoretically and experimentally, the benefits of a modest
degree of centralization, such as the elimination of wasteful hashing and a
scalable system for avoiding double-spending attacks.Comment: 15 pages, 4 figures, 2 tables in Proceedings of NDSS 201
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