This proposal is developing theoretical foundations as well as algorithms and software for secrecy-preserving reasoning. The key novel idea, rather different from existing work, is to exploit the indistinguishability (as far as the querying agent is concerned) between secret information, on one hand, and incomplete information, on the other hand, under the open world semantics. The Principal Investigator utilizes his ideas of for computing small secrecy envelopes so that answering "Unknown" to queries inside the envelope while answering queries outside the envelope truthfully, constitutes a secrecy-preserving query-answering algorithm. The Principal Investigator plans to integrate this research into education and to enhance interdisciplinary collaborations within and beyond Iowa State University. In addition, he plans to advance collaborations with industrial partners (Boeing in the high-tech area and Mayo Clinic in the health care area) as well as applications in the areas of information assurance and national security.