3 research outputs found
Efficient Constructions for Almost-everywhere Secure Computation
The importance of efficient MPC in today\u27s world needs no retelling. An obvious barebones requirement to execute protocols for MPC is the ability of parties to communicate with each other. Traditionally, we solve this problem by assuming that every pair of parties in the network share a dedicated secure link that enables reliable message transmission. This assumption is clearly impractical as the number of nodes in the network grows, as it has today. In their seminal work, Dwork, Peleg, Pippenger and Upfal introduced the notion of almost-everywhere secure primitives in an effort to model the reality of large scale global networks and study the impact of limited connectivity on the properties of fundamental fault-tolerant distributed tasks. In this model, the underlying communication network is sparse and hence some nodes may not even be in a position to participate in the protocol (all their neighbors may be corrupt, for instance). A protocol for almost everywhere reliable message transmission, which would guarantee that a large subset of the network can transmit messages to each other reliably, implies a protocol for almost-everywhere agreement where nodes are required to agree on a value despite malicious or byzantine behavior of some subset of nodes, and an almost-everywhere agreement protocol implies a protocol almost-everywhere secure MPC that is unconditionally or information-theoretically secure. The parameters of interest are the degree of the network, the number of corrupted nodes that can be tolerated and the number of nodes that the protocol may give up. Prior work achieves for and for for some fixed constant .
In this work, we first derive message protocols which are efficient with respect to the total number of computations done across the network. We use this result to show an abundance of networks with that are resilient to random corruptions. This randomized result helps us build networks which are resistant to worst-case adversaries.
In particular, we improve the state of the art in the almost everywhere reliable message transmission problem in the worst-case adversary model by showing the existence of an abundance of networks that satisfy for , thus making progress on this question after nearly a decade. Finally, we define a new adversarial model of corruptions that is suitable for networks shared amongst a large group of corporations that: (1) do not trust each other, and (2) may collude,
and construct optimal networks achieving for in this model
A Coordination Language for Databases
We present a coordination language for the modeling of distributed database
applications. The language, baptized Klaim-DB, borrows the concepts of
localities and nets of the coordination language Klaim but re-incarnates the
tuple spaces of Klaim as databases. It provides high-level abstractions and
primitives for the access and manipulation of structured data, with integrity
and atomicity considerations. We present the formal semantics of Klaim-DB and
develop a type system that avoids potential runtime errors such as certain
evaluation errors and mismatches of data format in tables, which are monitored
in the semantics. The use of the language is illustrated in a scenario where
the sales from different branches of a chain of department stores are
aggregated from their local databases. Raising the abstraction level and
encapsulating integrity checks in the language primitives have benefited the
modeling task considerably
Asymptotically Free Broadcast in Constant Expected Time via Packed VSS
Broadcast is an essential primitive for secure computation. We focus in this paper on optimal resilience (i.e., when the number of corrupted parties is less than a third of the computing parties ), and with no setup or cryptographic assumptions.
While broadcast with worst case rounds is impossible, it has been shown [Feldman and Micali STOC\u2788, Katz and Koo CRYPTO\u2706] how to construct protocols with expected constant number of rounds in the private channel model. However, those constructions have large communication complexity, specifically expected number of bits transmitted for broadcasting a message of length . This leads to a significant communication blowup in secure computation protocols in this setting.
In this paper, we substantially improve the communication complexity of broadcast in constant expected time. Specifically, the expected communication complexity of our protocol is . For messages of length , our broadcast has no asymptotic overhead (up to expectation), as each party has to send or receive bits. We also consider parallel broadcast, where parties wish to broadcast bit messages in parallel. Our protocol has no asymptotic overhead for , which is a common communication pattern in perfectly secure MPC protocols. For instance, it is common that all parties share their inputs simultaneously at the same round, and verifiable secret sharing protocols require the dealer to broadcast a total of bits.
As an independent interest, our broadcast is achieved by a packed verifiable secret sharing, a new notion that we introduce. We show a protocol that verifies secrets simultaneously with the same cost of verifying just a single secret. This improves by a factor of the state-of-the-art