Conventional leases protect consistent access to a single unit of state shared among a set of computers. For some types of data, however, this lease exposes too much information, reducing security, and limiting performance by limiting concurrency. We describe a form of lease called a black-box lease that is specialized to the semantics of the data type to which shared access is provided. This specialization exposes between clients only that information required for the given data type, otherwise hiding information to improve concurrency and security.