Breach-Resistant Structured Encryption

Motivated by the problem of data breaches, we formalize a notion of security for dynamic structured encryption (STE) schemes that guarantees security against a snapshot adversary; that is, an adversary that receives a copy of the encrypted structure at various times but does not see the transcripts related to any queries. In particular, we focus on the construction of dynamic encrypted multi-maps which are used to build efficient searchable symmetric encryption schemes, graph encryption schemes and encrypted relational databases. Interestingly, we show that a form of snapshot security we refer to as breach resistance implies previously-studied notions such as a (weaker version) of history independence and write-only obliviousness. Moreover, we initiate the study of dual-secure dynamic STE constructions: schemes that are forward-private against a persistent adversary and breach-resistant against a snapshot adversary. The notion of forward privacy guarantees that updates to the encrypted structure do not reveal their association to any query made in the past. As a concrete instantiation, we propose a new dual-secure dynamic multi-map encryption scheme that outperforms all existing constructions; including schemes that are not dual-secure. Our construction has query complexity that grows with the selectivity of the query and the number of deletes since the client executed a linear-time rebuild protocol which can be de-amortized. We implemented our scheme (with the de-amortized rebuild protocol) and evaluated its concrete efficiency empirically. Our experiments show that it is highly efficient with queries taking less than 1 microsecond per label/value pair.

Fracture Analysis for a 2D Prototype of Recycled Aggregate Concrete Using Discrete Cracking Model

Fracture analysis has been made for a 2 dimensional prototype of recycled aggregate concrete using the discrete cracking model. The discrete element method has been developed based on quasi-brittle constitutive law to simulate the behavior of the 2 dimensional recycled aggregate concrete prototype under uniaxial compressive loading. The relationship between stress distribution and failure mechanism of the recycled aggregate concrete plate has been investigated and analyzed. The numerical model proposed in the paper is in the first time used to analyze the mechanical properties of recycled aggregate concrete. Efficiency and accuracy of the numerical model has been demonstrated. It is indicated that this model has potential to be extended for 3 dimensional structural analysis of recycled aggregate concrete.