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We investigate a simple but overlooked folklore approach for searching encrypted documents held at an untrusted service: Just stash an index (with unstructured encryption) at the service and download it for updating and searching. This approach is simple to deploy, enables rich search support beyond unsorted keyword lookup, requires no persistent client state, and (intuitively at least) provides excellent security compared with approaches like dynamic searchable symmetric encryption (DSSE). This work first shows that implementing this construct securely is more subtle than it appears, and that naive implementations with commodity indexes are insecure due to the leakage of the byte-length of the encoded index. We then develop a set of techniques for encoding indexes, called size-locking, that eliminates this leakage. Our key idea is to fix the size of indexes to depend only on features that are safe to leak. We further develop techniques for securely partitioning indexes into smaller pieces that are downloaded, trading leakage for large increases in performance in a measured way. We implement our systems and evaluate that they provide search quality matching plaintext systems, support for stateless clients, and resistance to damaging injection attacks.

Technology plays an increasingly salient role in facilitating intimate partner violence (IPV). Customer support at computer security companies are receiving cases that involve tech-enabled IPV but might not be well equipped to handle these cases. To assess customer support’s existing practices and identify areas for improvement, we conducted five focus groups with professionals who work with IPV survivors (n=17). IPV professionals made numerous suggestions, such as using trauma-informed language, avoiding promises to solve problems, and making referrals to resources and support organizations. To evaluate the practicality of these suggestions, we conducted four focus groups with customer support practitioners (n=11). Support practitioners expressed interest in training agents for IPV cases, but mentioned challenges in identifying potential survivors and frontline agents’ limited capacity to help. We conclude with recommendations for computer security companies to better address tech-enabled IPV through training support agents, tracking the prevalence of these cases, and establishing partnerships with IPV advocates.