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We suggest a scheme for a block cipher which uses only one randomly chosen permutation,F. The key, consisting of two blocks,K 1 andK 2, is used in the following way. The message block is XORed withK 1 before applyingF, and the outcome is XORed withK 2, to produce the cryptogram block. We show that the resulting cipher is secure (when the permutation is(More)
A new type of signature scheme is proposed. It consists of two phases. The first phase is performed off-line, before the message to be signed is even known. The second phase is performed on-line, once the message to be signed is known, and is supposed to be very fast. A method for constructing such on-line/off-line signature schemes is presented. The method(More)
There is given an undirected graph G -(V, E) from which edges are deleted one at a time and about which questions of the type, "Are the vertices u and v in the same connected component?" have to be answered "on-line." There is presented an algorithm which maintains a data structure in which each question is answered in constant time and for which the total(More)
Diverse graph structure models for concurrent processing systems have been suggested and used. The structures differ in generality and scope according to the properties one wishes to model and analyze. In this paper we solve a problem of maximal storage requirements for a simple flowchart model called the Marked Graph Model. Marked Graphs can be derived as(More)