Private data collection systems such as Prio ensure data privacy by distributing trust among a set of mutually trusted parties, to allow for aggregate data collection without disclosing any single client's data in the clear. While systems like Prio are undergoing widespread interest and adoption, these systems lack efficient mechanisms to provide differential privacy guarantees. In this work, we present a lightweight method that we call DPrio to augment Prio and related systems with differential privacy assurances while ensuring higher data utility than existing noise generation protocols. We compare our results against four related constructions in the literature, and identify how DPrio achieves improved data utility relative to the assumed number of dishonest clients and servers, with only minimal (and batchable) server communication overhead. We present several case studies and discuss considerations for real-world implementations.

Abstract Secret sharing schemes are desirable across a variety of real-world settings due to the security and privacy properties they can provide, such as availability and separation of privilege. However, transitioning secret sharing schemes from theoretical research to practical use must account for gaps in achieving these properties that arise due to the realities of concrete implementations, threat models, and use cases. We present a formalization and analysis, using Ellison’s notion of ceremonies, that demonstrates how simple variations in use cases of secret sharing schemes result in the potential loss of some security properties, a result that cannot be derived from the analysis of the underlying cryptographic protocol alone. Our framework accounts for such variations in the design and analysis of secret sharing implementations by presenting a more detailed user-focused process and defining previously overlooked assumptions about user roles and actions within the scheme to support analysis when designing such ceremonies. We identify existing mechanisms that, when applied to an appropriate implementation, close the security gaps we identified. We present our implementation including these mechanisms and a corresponding security assessment using our framework.