Abstract: Privacy preserving computational geometry is a new research branch of secure multiparty computation. Be cause of the shortcomings and restraints in existing protocols, in semi-honest, a new protocol based on plumb line algo rithm and oblivious transfer protocol for relative position determination of point and polygon was proposed in this pa per. The correctness,computation efficient and security were analyzed and proved in this paper as well. The new proto col not only can be used in real number field, but also can be used in any polygon with great efficient.

Key words: Seeure multiparty computation, Computational geometry, Polygon, Plumb line algorithm, Oblivious transfer