Ralph Werchner

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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)
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 diierent worst-case request sequences. The rst is the BIT algorithm that, for each item in the list, alternates between moving it to the(More)
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 well-formed words of parentheses our algorithm establishes communication between all matching pairs in logarithmic time. It can be applied to the membership problem for Dycklan-guages and(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)
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)
In many applications like verification or combinatorial optimization, OBDDs (ordered binary decision diagrams) are used as a representation or data structure for Boolean functions. Efficient algorithms exist for the important operations on OBDDs, and many functions can be represented in reasonable size if a good variable ordering is chosen. In general, it(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) 3 BP(f), BP(f) L (f), L (f) L(f) 2 , and C(f) L(f) ? 1. These estimates(More)