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WebWatcher: a tour guide for the world wide web
 In Proceedings of International Joint Conference on Artificial Intelligence (IJCAI
, 1997
"... It is well known that n bits of entropy are necessary and sufficient to perfectly encrypt n bits (onetime pad). Even if we allow the encryption to be approximate, the amount of entropy needed doesn’t asymptotically change. However, this is not the case when we are encrypting quantum bits. For the p ..."
Abstract

Cited by 2 (0 self)
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It is well known that n bits of entropy are necessary and sufficient to perfectly encrypt n bits (onetime pad). Even if we allow the encryption to be approximate, the amount of entropy needed doesn’t asymptotically change. However, this is not the case when we are encrypting quantum bits. For the perfect encryption of n quantum bits, 2n bits of entropy are necessary and sufficient (quantum onetime pad), but for approximate encryption one asymptotically needs only n bits of entropy. In this paper, we provide the optimal tradeoff between the approximation measure ǫ and the amount of classical entropy used in the encryption of single quantum bits. Then, we consider nqubit encryption schemes which are a composition of independent singlequbit ones and provide the optimal schemes both in the 2 and the ∞norm. Moreover, we provide a counterexample to show that the encryption scheme of AmbainisSmith [3] based on smallbias sets does not work in the ∞norm.