[Resource Topic] 2005/370: Resource Fairness and Composability of Cryptographic Protocols

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Resource Fairness and Composability of Cryptographic Protocols

Authors: Juan A. Garay, Philip MacKenzie, Manoj Prabhakaran, Ke Yang


We introduce the notion of {\em resource-fair} protocols.
Informally, this property states that if one party learns the
output of the protocol, then so can all other parties, as long as
they expend roughly the same amount of resources. As opposed to
similar previously proposed definitions, our definition follows
the standard simulation paradigm and enjoys strong composability
properties. In particular, our definition is similar to the
security definition in the universal composability (UC) framework,
but works in a model that allows any party to request additional
resources from the environment to deal with dishonest parties that
may prematurely abort.

In this model we specify the ideally fair functionality as
allowing parties to invest resources'' in return for outputs, but in such an event offering all other parties a fair deal. (The formulation of fair dealings is kept independent of any particular functionality, by defining it using a wrapper.‘’) Thus, by
relaxing the notion of fairness, we avoid a well-known
impossibility result for fair multi-party computation with
corrupted majority; in particular, our definition admits
constructions that tolerate arbitrary number of corruptions. We
also show that, as in the UC framework, protocols in our framework
may be arbitrarily and concurrently composed.

Turning to constructions, we define a commit-prove-fair-open'' functionality and design an efficient resource-fair protocol that securely realizes it, using a new variant of a cryptographic primitive known as time-lines.‘’ With (the fairly wrapped
version of) this functionality we show that some of the existing
secure multi-party computation protocols can be easily transformed
into resource-fair protocols while preserving their security.

ePrint: https://eprint.iacr.org/2005/370

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