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Hans Oberschelp

Publications and source records attributed to Hans Oberschelp.

3 recordsLinked to original sources

Mixing Time of the Overlapping Cycles Shuffle

In each step of the overlapping cycles shuffle on $n$ cards, a fair coin is flipped which determines whether the $m$th card or the $n$th card is moved to the top of the deck. Angel, Peres, and Wilson showed the following interesting fact: If $m = \lfloor αn \rfloor$ where $α$ is rational, then the relaxation time of a single card in the overlapping cycles shuffle is $θ(n^2)$. However if $α$ is the golden ratio, then the relaxation time of a single card is $θ(n^\frac{3}{2})$. We show that the mixing time of the entire deck under the overlapping cycles shuffle matches these bounds up to a factor of $\log(n)^3$. That is, the mixing time of the entire deck is $O(n^2 \log(n)^3)$ if $α$ is rational and $O(n^\frac{3}{2} \log(n)^3)$ if $α$ is the golden ratio.

math.PR↗

A Probabilistic Proof of the nCPA to CCA Bound

We provide a new proof of Maurer, Renard, and Pietzak's result that the sum of the nCPA advantages of random permutations $P$ and $Q$ bound the CCA advantage of $P^{-1} \circ Q$. Our proof uses probability directly, as opposed to information theory, and has the advantage of providing an alternate sufficient condition of low CCA advantage. Namely, the CCA advantage of a random permutation can be bounded by its separation distance from the uniform distribution. We use this alternate condition to tighten the best known bound on the security of the swap-or-not shuffle in the special case of having fewer queries than the square root of the number of cards.

cs.CR↗

Format Preserving Encryption in the Bounded Retrieval Model

In the bounded retrieval model, the adversary can leak a certain amount of information from the message sender's computer (e.g., 10 percent of the hard drive). Bellare, Kane and Rogaway give an efficient symmetric encryption scheme in the bounded retrieval model. Their scheme uses a giant key (a key so large only a fraction of it can be leaked.) One property of their scheme is that the encrypted message is larger than the original message. Rogaway asked if an efficient scheme exists that does not increase the size of the message. In this paper we present such a scheme.

cs.CR↗