Ralph Werchner

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We consider a new class of routing requests or partial permutations for which we give optimal on-line routing algorithms on the hypercube and shuffle-exchange network. For wellformed words of parentheses our algorithm establishes communication between all matching pairs in logarithmic time. It can be applied to the membership problem for Dycklanguages and a(More)
An optimal tree contraction algorithm for the boolean hypercube and the constant-degree hypercubic networks, such as the shuffle exchange or the butterfly network, is presented. The algorithm is based on novel routing techniques and, for certain small subtrees, simulates optimal PRAM algorithms. For trees of size n, stored on a p processor hypercube in(More)
We present a randomized on-line algorithm for the list update problem which achieves a competitive factor of 1.6, the best known so far. The algorithm makes an initial random choice between two known algorithms that have different worst-case request sequences. The first is the BIT algorithm that, for each item in the list, alternates between moving it to(More)
In this paper we investigate the security of the server-aided RSA protocols RSA-S1 and RSA-S1M proposed by Matsumoto, Kato and Imai ([MKI89]) and Matsumoto, Imai, Laih and Yen ([MILY93]), respectively. In these protocols a smart card calculates an RSA signature with the aid of an untrusted powerful server. We focus on generic attacks, that is, passive(More)
| In this paper, the OBDD variable ordering problem for functions representable by general fanout-free circuits which may contain EXOR-gates is investigated. It is proved that some depth rst traver-sal of the circuit leads to an optimal variable ordering. The structure and size of optimal OBDDs are characterized. Furthermore, it turns out that optimal(More)
Many Boolean functions have short representations by OBDDs (ordered binary decision diagrams) if appropriate variable orderings are used. For tree-like circuits, which may contain EXOR-gates, it is proved that some depth rst traversal leads to an optimal variable ordering. Moreover, an optimal variable ordering and the resulting OBDD can be computed in time(More)
We study the computational complexity of certain search-hide games on a graph. There are two players, called searcher and hider. The hider is immobile and hides in one of the nodes of the graph. The searcher selects a starting node and a search path of length at most k. His objective is to detect the hider, which he does with certainty if he visits the node(More)
Circuit size, branching program size, and formula size of Boolean functions, denoted by C(f), BP(f), and L(f), are the most important complexity measures for Boolean functions. Often also the formula size L (f) over the restricted basis f_;^;:g is considered. It is well-known that C(f) 3BP(f), BP(f) L (f), L (f) L(f)2, and C(f) L(f) 1. These estimates are(More)