Most cities around the world require drivers to pay for the time they occupy a parking spot. In this way, drivers are encouraged to shorten parking time so that other drivers are given a reasonable chance of finding parking. The traditional way, based on moving to a pay station and placing the issued parking ticket on the dashboard of the car, presents several drawbacks like having to predict in advance the duration of parking or the need to move to the car in case the parking time has to be extended. Over the last few years, several applications permitting to pay through the mobile phone have appeared. Such applications manage detailed information about parking operations so that accurate profiles of parking habits of car owners can be created. In this paper we propose a system to pay for parking by phone which preserves the privacy of drivers in the sense that the information managed by the system is proven not to help an attacker with full access to it to do better that she would do by patrolling the city for collecting information about parked cars.

Smart meters inform the electricity suppliers about the consumption of their clients in short intervals. Fine-grained electricity consumption information is highly sensitive as it has been proven to permit to infer people's habits like, for instance, the time they leave or arrive home. Hence, appropriate measures have to be taken to preserve clients' privacy in smart metering systems. In this paper, we first analyze a recent proposal by Busom et al. (2016) and show how a corrupted substation is able to get the individual reading of any arbitrarily chosen smart meter without requiring the collaboration of any other party. After that, we propose a way to fix the mentioned security flaw which is based on adding an additional step in which the substation proves that it has properly followed all the protocol steps. Our solution is analyzed and shown to be computationally feasible for realistic parameter choices.

Given a genus 2 curve [Formula: see text] defined over a finite field [Formula: see text] of odd characteristic such that [Formula: see text], we study the growth of the 2-adic valuation of the cardinality of the Jacobian over a tower of quadratic extensions of [Formula: see text]. In the cases of simpler regularity, we determine the exponents of the 2-Sylow subgroup of [Formula: see text].

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