An apparatus and method authenticate computed results in a public distributed computing environment without the need for fully recomputing the results. The work unit is operated on by client code that computes one or more partial results along with the completed result. When the results are returned to the server, the server may decide to have a trusted computer system process the same work unit to compute the partial result according to a defined acceptance policy. In addition, the work unit name, user identity and current date are encrypted using a time-sensitive key. Should the server detect a problem with the results (e.g., decrypted work unit name does not match, recomputed partial result does not match), the results may be rejected according to a defined rejection policy. In this manner, it becomes very difficult to fool a server into thinking a work unit has been processed when it has not.