Mind the Gap: Ceremonies for Applied Secret Sharing

Authors: Bailey Kacsmar (University of Waterloo), Chelsea H. Komlo (University of Waterloo), Florian Kerschbaum (University of Waterloo), Ian Goldberg (University of Waterloo)

Volume: 2020
Issue: 2
Pages: 397–415
DOI: https://doi.org/10.2478/popets-2020-0033

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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.

Keywords: secret sharing, applied cryptography, protocol analysis, ceremony analysis

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