Communication complexity

About: Communication complexity is a research topic. Over the lifetime, 3870 publications have been published within this topic receiving 105832 citations.

Direct product results and the GCD problem, in old and new communication models

Abstract: This paper contains several results regarding the communication complexity model and the 2-prover games model, which are based on interaction between the two models: 1. We show how to improve the rate of exponential decrease in the parallel repetition theorem of [Ra] in terms of the communication complexity of the verifier's predicate. 2. We apply the improved parallel repetition theorem of 2-prover games to derive, for the first time, a direct product theorem for communication complexity. The second derivation uses a common generalization of the two models, which is independently interesting. We initiate a study of its power by considering the $GCD$ problem, and some variations of it, which exhibit a power gap between the new model and the classical communication complexity model. This gap is partly based on the following upper bounds: Given $n$-bit inputs $x$ and $y$ to Alice and Bob respectively, they can achieve the tasks below with very high probability using only $O(n= log n)$ communication bits: 1. Decide if $GCD(x; y) = 1$ and $b$ (by Bob), satisfying $a _ x + b _ y = 1$. Observe that the outputs in the second task are in general of length $(n)$. A complete analysis of the communication complexity of these two problems (in several models and modes) is given.

Distributed Block Coordinate Descent for Minimizing Partially Separable Functions

Abstract: A distributed randomized block coordinate descent method for minimizing a convex function of a huge number of variables is proposed. The complexity of the method is analyzed under the assumption that the smooth part of the objective function is partially block separable. The number of iterations required is bounded by a function of the error and the degree of separability, which extends the results in Richtarik and Takac (Parallel Coordinate Descent Methods for Big Data Optimization, Mathematical Programming, DOI:10.1007/s10107-015-0901-6) to a distributed environment. Several approaches to the distribution and synchronization of the computation across a cluster of multi-core computer are described and promising computational results are provided.

Computational verifiable secret sharing revisited

Abstract: Verifiable secret sharing (VSS) is an important primitive in distributed cryptography that allows a dealer to share a secret among n parties in the presence of an adversary controlling at most t of them. In the computational setting, the feasibility of VSS schemes based on commitments was established over two decades ago. Interestingly, all known computational VSS schemes rely on the homomorphic nature of these commitments or achieve weaker guarantees. As homomorphism is not inherent to commitments or to the computational setting in general, a closer look at its utility to VSS is called for. In this work, we demonstrate that homomorphism of commitments is not a necessity for computational VSS in the synchronous or in the asynchronous communication model. We present new VSS schemes based only on the definitional properties of commitments that are almost as good as the existing VSS schemes based on homomorphic commitments. Importantly, they have significantly lower communication complexities than their (statistical or perfect) unconditional counterparts. Further, in the synchronous communication model, we observe that a crucial interactive complexity measure of round complexity has never been formally studied for computational VSS. Interestingly, for the optimal resiliency conditions, the least possible round complexity in the known computational VSS schemes is identical to that in the (statistical or perfect) unconditional setting: three rounds. Considering the strength of the computational setting, this equivalence is certainly surprising. In this work, we show that three rounds are actually not mandatory for computational VSS. We present the first two-round VSS scheme for n≥2t+1 and lower-bound the result tightly by proving the impossibility of one-round computational VSS for t≥2 or n≤3t. We also include a new two-round VSS scheme using homomorphic commitments that has the same communication complexity as the well-known three-round Feldman and Pedersen VSS schemes.

On the communication complexity of XOR functions

Abstract: An XOR function is a function of the form g(x;y) = f(x y), for some boolean function f on n bits. We study the quantum and classical communication complexity of XOR functions. In the case of exact protocols, we completely characterise one-way communication complexity for all f. We also show that, when f is monotone, g’s quantum and classical complexities are quadratically related, and that when f is a linear threshold function, g’s quantum complexity is ( n). More generally, we make a structural conjecture about the Fourier spectra of boolean functions which, if true, would imply that the quantum and classical exact communication complexities of all XOR functions are asymptotically equivalent. We give two randomised classical protocols for general XOR functions which are ecient for certain functions, and a third protocol for linear threshold functions with high margin. These protocols operate in the symmetric message passing model with shared randomness.