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Limits on the Provable Consequences of Oneway Permutations
, 1989
"... We present strong evidence that the implication, "if oneway permutations exist, then secure secret key agreement is possible" is not provable by standard techniques. Since both sides of this implication are widely believed true in real life, to show that the implication is false requir ..."
Abstract

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We present strong evidence that the implication, "if oneway permutations exist, then secure secret key agreement is possible" is not provable by standard techniques. Since both sides of this implication are widely believed true in real life, to show that the implication is false requires a new model. We consider a world where dl parties have access to a black box or a randomly selected permutation. Being totally random, this permutation will be strongly oneway in provable, informationthevretic way. We show that, if P = NP, no protocol for secret key agreement is secure in such setting. Thus, to prove that a secret key greement protocol which uses a oneway permutation as a black box is secure is as hrd as proving F NP. We also obtain, as corollary, that there is an oracle relative to which the implication is false, i.e., there is a oneway permutation, yet secretexchange is impossible. Thus, no technique which relativizes can prove that secret exchange can be based on any oneway permutation. Our results present a general framework for proving statements of the form, "Cryptographic application X is not likely possible based solely on complexity assumption Y." 1
Black Boxes, Incorporated
, 2012
"... The term “Black Box ” often refers to a device whose functionality we understand, but whose inner workings we don’t, or choose to ignore. This term appears a lot in a large variety of contexts within theoretical computer science, and happens to be extremely convenient to capture computations with re ..."
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The term “Black Box ” often refers to a device whose functionality we understand, but whose inner workings we don’t, or choose to ignore. This term appears a lot in a large variety of contexts within theoretical computer science, and happens to be extremely convenient to capture computations with restricted knowledge about or access to certain information. In its most basic form, a black box (also called an oracle) encodes a function f, to which the computation may issue query x and get the response f(x). We have no knowledge (or interest) on the implementation of f in the black box – indeed, f itself may be computationally hard or even not computable. From a programming perspective, this viewpoint is convenient when solving a problem using a subroutine for f that someone else has implemented and we are given its inputoutput specification only. This simple idea is of wide use in almost any large software development project, as well as in algorithm design. From a theoretical perspective, the ability to efficiently solve a given computational problem g using an oracle to f may constitute a reduction