Security proofs in the Random Oracle Model (ROM) often make use of the fact that the queries made by the adversary to the oracle are observable as well as the responses to those queries can be programmed. While, the issue of programmability of query responses has received attention in the literature, to the best of our knowledge, observability of the adversary's queries has not been identified as an artificial artefact of the Random Oracle Model. In this work, we propose a variant of ROM, in which the challenger of the security game cannot "observe" the adversary's queries to the random oracle, but can (possibly) continue to "program" the query responses. We show that this model is separable from ROM by proving that Fischlin's online extractors from [Fis05]) cannot exist when they are Non Observing. At the same time, we also show that reductions/extractors that seem to rely on observability, can sometimes achieve the same effect by programming of the responses. We also show that the schemes RSA-PFDH and Schnorr signatures are still secure with Non Observing reductions.
展开▼
