Structured encryption (STE) schemes allow a client to store sensitive data on a semi-trusted remote server and query the data. STE schemes strike a balance between privacy and efficiency by leaking some information to the server. In particular, many STE schemes leak the volume pattern i.e., response lengths, and the query equality pattern i.e., if any queries are repeated. Recently discovered leakage-abuse attacks demonstrate that leaking the volume pattern can be unsafe; that is, the server can reconstruct parts of the database from this leakage. To address this leakage, Kamara and Moataz proposed a novel multi-map encryption scheme, AVLH, that hides query volumes by padding responses with parts of other responses (Eurocrypt 2019). AVLH was shown to be more storage-efficient than the naive approach to pad responses with dummy values to reach the maximum response length. Subsequently, Patel et al. provided an even more efficient volume-hiding multimap scheme, dprfMM (CCS 2019). Despite these advances, the costs of fully suppressing query volumes are still unclear. In this paper, we provide the first lower bounds on STE schemes for multi-maps that leak at most the query equality pattern. Surprisingly, we find that in many cases, such STE schemes cannot be more storage-efficient than naively padding to the maximum length.

In an onion routing protocol, messages travel through several intermediaries before arriving at their destinations; they are wrapped in layers of encryption (hence they are called "onions"). The goal is to make it hard to establish who sent the message. It is a practical and widespread tool for creating anonymous channels. For the standard adversary models - passive and active - we present practical and provably secure onion routing protocols. Akin to Tor, in our protocols each party independently chooses the routing paths for his onions. For security parameter lambda, our differentially private solution for the active adversary takes O(log^2 lambda) rounds and requires every participant to transmit O(log^{4} lambda) onions in every round.

While proper encryption can protect the confidentiality of messages in network protocols and distributed systems, private contents of messages may still leak from metadata, such as communication paths or message lengths. Many privacy strategies seal leakages by introducing noise into the system, e.g., by injecting dummy messages into the system. These solutions achieve a degree of privacy while introducing an overhead in operational cost, e.g., by transmitting information-less messages. In this paper, we show that randomization is never required for minimizing the operational cost of perfectly secure privacy strategies. While this result is surprising and counterintuitive, it allows for a simplification in the search for optimal solutions and in the analysis of the performance of the selected solutions.

A chaos-based key generation scheme is proposed and its performance analyzed. The method, the logistic map scheme, is applicable for use on wireless networks because it does not require devices to engage in computationally intensive algorithms. In addition, the method achieves reliability from the perspective of the communication agents, as well as randomness and unpredictability from the perspective of an eavesdropper.