2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/30949This paper has been withdrawn by the author(s), due to the existence of a much better paper in http://arxiv.org/abs/cs.CR/0207027Paper withdrawalCryptography and SecurityComputational ComplexityG.3; G.2.1; D.4.6text