Private searching for sensitive file signatures

We consider the problem of privately searching for sensitive or classified file signatures on an untrusted server. Inspired by the private stream searching system of Ostrovsky and Skeith, we propose a new scheme optimized for matching individual file signatures (versus keyword matching in documents). Our optimization stems from the simple observation that a complete list of matching file signatures can be replaced by a much smaller encrypted bitmask. This approach reduces a server´s response overhead from being linear in the number of matched documents to linear with respect to a system robustness parameter.