Analyzing Cryptography in Context: A Cryptography-Native Approach to Threat Modeling

We observe that the existing norms within cryptography do not expect protocol analysts to document the sociotechnical properties that a deployed system should have. To help close this potential gap, we develop a framework that allows bringing sociotechnical dimensions into analyses of cryptographic systems, and in particular facilitates "in-context" analysis of proposed cryptographic deployments on top of widely-accepted cryptographic modeling techniques. To explore the utility of our framework, we use Apple's 2021 CSAM scanning proposal as a case study. We show how our framework naturally surfaces many of the criticisms of Apple's proposal and helps us identify a previously undocumented property of the proposal.