Mirosław Kutyłowski

Efficient algorithms for leader election in radio networks

We present energy efficient algorithms for leader election in single channel single-hop radio networks with no collision detection. We present a deterministic solution with sublogarithmic energy cost (the best previous result was O(log n)) and show a double logarithmic lower bound. We prove that this lower bound holds in a randomized case, in a certain sense.For the case, when the number n of active stations can be approximated in advance, we show a randomized algorithm with energy consumption O(log* n) that yields a result with high probability (the best previous result was O(log log n)).

Mathematical Foundations of Computer Science 1999

Let /? be a real number > 1. Addition and multiplication by a fixed positive integer of real numbers represented in bsise /3 cire shown to be computable by an on-line algorithm, and thus are continuous functions. When /? is a Pisot number, these functions cire computable by an on-line finite automaton.

Energy-Efficient Size Approximation of Radio Networks with No Collision Detection

Algorithms for radio networks are studied in two scenarios: (a) the number of active stations is known (or approximately known) (b) the number of active stations is unknown. In the second (more realistic) case it is much harder to design efficient algorithms. For this reason, we design an efficient randomized algorithm for a single-hop radio network that approximately counts the number of its active stations. With probability higher than 1 - 1/n, this approximation is within a constant factor, the algorithm runs in poly-logarithmic time and its energy cost is o(log log n). This improves the previous O(log n) bound for energy. In particular, our algorithm can be applied to improve energy cost of known leader election and initialization protocols (without loss of time efficiency).

Onions based on universal re-encryption – anonymous communication immune against repetitive attack

Encapsulating messages in onions is one of the major techniques providing anonymous communication in computer networks. To some extent, it provides security against traffic analysis by a passive adversary. However, it can be highly vulnerable to attacks by an active adversary. For instance, the adversary may perform a simple so–called repetitive attack: a malicious server sends the same massage twice, then the adversary traces places where the same message appears twice – revealing the route of the original message. A repetitive attack was examined for mix–networks. However, none of the countermeasures designed is suitable for onion–routing. In this paper we propose an “onion-like” encoding design based on universal re-encryption. The onions constructed in this way can be used in a protocol that achieves the same goals as the classical onions, however, at the same time we achieve immunity against a repetitive attack. Even if an adversary disturbs communication and prevents processing a message somewhere on the onion path, it is easy to identify the malicious server performing the attack and provide an evidence of its illegal behavior.

Rapid mixing and security of Chaum's visual electronic voting

Recently, David Chaum proposed an electronic voting scheme that combines visual cryptography and digital processing. It was designed to meet not only mathematical security standards, but also to be accepted by voters that do not trust electronic devices.

Kleptographic attacks on e-voting schemes

We analyze electronic voting schemes and show that in many cases it is quite easy to implement a kleptographic channel, which is a profound danger for electronic voting systems. We show serious problems with Neffs scheme. We present also attacks on Chaums visual voting scheme and some related schemes, which work at least when implementation is not careful enough.

Fast Generation of Random Permutations via Networks Simulation

We consider the classical problem of generating random permutations with the uniform distribution. That is, we require that for an arbitrary permutation π of n elements, with probability 1/n! the machine halts with the ith output cell containing π(i), for 1≤i≤n. We study this problem on two models of parallel computations: the CREW PRAM and the EREW PRAM.

Exact time bounds for computing boolean functions on PRAMs without simultaneous writes

The time complexity of Boolean functions on abstract parallel random access machines without simultaneous writes is considered. Improving upon results of COOK, DWORK, and REISCHIJK (1986), and extending work of KUTYLOWSKI (1989), who proved a lower time bound for the OR function on such machines that equals the upper bound, we provide a general means for obtaining exact (i.e., correct up to an additive constant) lower bounds, which works for many Boolean functions, in particular all symmetric functions. The new approach is based on the fact observed by SMOLENSKY (1987) that the Boolean functions can be regarded as polynomials, thus have a degree. For some functions, e.g., AND and PARITY, the exact time bound also holds for nondeterministic machines. For probabilistic machines, we obtain exact lower time bounds for PARITY in the unbounded error model and, utilizing results by SZECEDY (1989), prove a general lower bound valid for all Boolean functions in the bounded error model, which implies, by results by NISAN (1989) that the (b ounded error) probabilistic time complexity of Boolean functions on CREW PRAMS differs at most by a factor of 8 from the deterministic time complexity. We also obtain exact bounds for machines that allow a few processors to try to write to the same cell simultaneously. No tight bounds for this model were known before. For PARITY and other balanced Boolean formulas upper time bounds that match the lower time bounds up to a small additive term are realized by CREW and EREW algorithms that use a linear or slightly superpolynomial number of processors. 1 Introduct ion This paper studies the time complexity of Boolean functions on abstract concurrent-read exclusive-write parallel random access machines (CREW PRAMS). A PRAM consists of processors PI, Pz, Mz, and a common random access memory consisting of cells Mr, . . . . The input is given in the first n cells; at the end of the computation the output is the content of the first memory cell. We are mainly interested in the CREW model, in which several processors may simultaneously read a common memory cell, but never more than one processor is allowed to write to a common memory *Note: This paper was put together from two technical reports, which contain independent work of the first author ([Diego]) and the second and third author ([KRSO]). The upper bounds are from (KRSO]. Lower bounds, inspired by (Kut891, were proved in both papers. For presenting the lower bounds, the more general approach of [DieSO] is chosen. tpartially supported by DFG grant ME 872/l-3 rpart of this work was done while visiting the TH Darmstadt supported by the Alexander-van-Humboldt-Stiftung 5 partially supported by the International Computer Science Institute, Berkeley, California Permission to copy without fee all or part of this material is granted provided that the copies arc not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission.

Adversary Immune Leader Election in ad hoc Radio Networks

Recently, efficient leader election algorithms for ad hoc radio networks with low time complexity and energy cost have been designed even for the no-collision detection, (no-CD), model. However, these algorithms are fragile in the sense that an adversary may disturb communication at low energy cost so that more than one station may regard itself as a leader. This is a severe fault since the leader election is intended to be a fundamental subroutine used to avoid collisions and to make it reliable.

Privacy Protection for RFID with Hidden Subset Identifiers

We propose very simple and cheap but nevertheless effective protection against privacy threats for RFID-tags. For the hidden subsetRFID-tags proposed in this paper, the ID string presented by an RFID-tag evolves rapidly. It is is not the bit value that enables one to recognize a tag. Instead, a reader detects some invariant properties that are hard to be recognized by a curious illegitimate reader. The solution is not based on any cryptographic primitive, it relies only on properties of random sets and on linear mappings between vector spaces. The solution proposed is well suited for low-end devices, since all mechanisms can be easily implemented by circuits of a small size.