  As sensors become ever more prevalent, more and more information will be
collected about each of us. A longterm research question is how best to support
beneficial uses while preserving individual privacy. Presence systems are an
emerging class of applications that support collaboration. These systems
leverage pervasive sensors to estimate end-user location, activities, and
available communication channels. Because such presence data are sensitive, to
achieve wide-spread adoption, sharing models must reflect the privacy and
sharing preferences of the users. To reflect users' collaborative relationships
and sharing desires, we introduce CollaPSE security, in which an individual has
full access to her own data, a third party processes the data without learning
anything about the data values, and users higher up in the hierarchy learn only
statistical information about the employees under them. We describe simple
schemes that efficiently realize CollaPSE security for time series data. We
implemented these protocols using readily available cryptographic functions,
and integrated the protocols with FXPAL's myUnity presence system.
