SHE based Non Interactive Privacy Preserving Biometric Authentication Protocols

Being unique and immutable for each person, biometric signals are widely used in access control systems. While biometric recognition appeases concerns about password's theft or loss, at the same time it raises concerns about individual privacy. Central servers store several enrolled biometrics, hence security against theft must be provided during biometric transmission and against those who have access to the database. If a server's database is compromised, other systems using the same biometric templates could also be compromised as well. One solution is to encrypt the stored templates. Nonetheless, when using traditional cryptosystem, data must be decrypted before executing the protocol, leaving the database vulnerable. To overcame this problem and protect both the server and the client, biometrics should be processed while encrypted. This is possible by using secure two-party computation protocols, mainly based on Garbled Circuits (GC) and additive Homomorphic Encryption (HE). Both GC and HE based solutions are efficient yet interactive, meaning that the client takes part in the computation. Instead in this paper we propose a non-interactive protocol for privacy preserving biometric authentication based on a Somewhat Homomorphic Encryption (SHE) scheme, modified to handle integer values, and also suggest a blinding method to protect the system from spoofing attacks. Although our solution is not as efficient as the ones based on GC or HE, the protocol needs no interaction, moving the computation entirely on the server side and leaving only inputs encryption and outputs decryption to the client

Perpendicular blade–vortex-interaction over an oscillating airfoil in light dynamic stall

An experimental and numerical study was performed to investigate the effects of perpendicular blade vortex interactions on the aerodynamic performance of an oscillating airfoil. The selected test cases studied the aerodynamic interaction of a stream-wise vortex impacting on a NACA 23012 airfoil oscillating in light dynamic stall regime, representing a typical condition of the retreating blade of a helicopter in forward flight. The analysis of particle image velocimetry surveys and time-accurate simulation results enabled to point out the different effects due to the blade pitching motion on the interacting flow field. Thus, numerical results enabled to achieve a detailed insight about the aerodynamic loads acting on the oscillating airfoil in the interacting cases. In particular, the comparison with the clean airfoil case shows that a severe loss of performance is produced by the interaction of the vortex during the airfoil downstroke motion, as the vortex impact triggers the local stall of the blade section

Experimental Investigation of the Rotor-Wing Aerodynamic Interaction in a Tiltwing Aircraft in Hover

The hovering performance and the lifting capability of tiltrotor aircraft are strongly affected by the aerodynamic interaction between wing and rotors. The tiltwing concept represents a promising technology to increase the hover performance by reducing the wing-rotor interference. The present work describes an experimental activity carried out on a 1/4 scaled tiltwing aircraft half-model to achieve a detailed insight about the main issues characterising the aerodynamic interaction between wing and rotor in hover. The results of the experimental campaign, including both force measurements and Particle Image Velocimetry surveys, enabled to evaluate both the aircraft performance for different configurations of the tilting wing and to achieve a detailed insight about the flow physics of the rotor wake in the interaction with the wing. The test activity provided a comprehensive experimental database that was obtained over a not confidential aircraft configuration

Experimental investigation of a helicopter rotor with Gurney flaps

The present work describes an experimental activity carried out to investigate the performance of Gurney flaps on a helicopter rotor model in hovering. The four blades of the articulated rotor model were equipped with Gurney flaps positioned at 95% of the aerofoil chord, spanning 14% of the rotor radius. The global aerodynamic loads and torque were measured for three Gurney flap configurations characterised by different heights. The global measurements showed an apparent benefit produced by Gurney flaps in terms of rotor performance with respect to the clean blade configuration. Particle image velocimetry surveys were also performed on the blade section at 65% of the rotor radius with and without the Gurney flaps. The local velocity data was used to complete the characterisation of the blade aerodynamic performance through the evaluation of the sectional aerodynamic loads using the the control volume approach

Unsteady Actuating Blade Model for CFD/CSD Analysis of a Tiltrotor

The paper presents an effective method to evaluate the unsteady flow field around a rotor through a Computational Fluid Dynamics model based on the actuator blade approach. The actuator blade extends the classical actuator disk model without the necessity to perform time or azimuth averaging operations. In this way, a time accurate investigation of the influence of the rotor wake on the rotor itself and on other non-rotating parts (fuselage, wings) can be performed. The method exploits the overset grid technique to allow an easy identification of the location of the sources distributed in the flow field to enforce the correct blade loads. The kinematics and the dynamics of the rotating parts is computed thought the coupling with a multibody solver and transmitted to the CFD as movement of the independent surface grids associated with each actuator blade. This allows to keep into account both rigid and elastic movements, including those related to movable surfaces. A comparison with experimental results obtained for a four blade tiltrotor are shown to verify the quality of the prediction of the flow field. Additionally, a comparison with the results obtained through a classical actuator disk allows to quantify the effects of the employment of the time-accurate approach with respect to the time-averaged results of the actuator disk model

Privacy Protection in Biometric-Based Recognition Systems: a marriage between cryptography and signal processing

Systems employing biometric traits for people authentication and identification are witnessing growing popularity due to the unique and indissoluble link between any individual and his/her biometric characters. For this reason, biometric templates are increasingly used for border monitoring, access control, membership verification, and so on. When employed to replace passwords, biometrics have the added advantage that they do not need to be memorized and are relatively hard to steal. Nonetheless, unlike conventional security mechanisms such as passwords, biometric data are inherent parts of a person?s body and cannot be replaced if they are compromised. Even worse, compromised biometric data can be used to have access to sensitive information and to impersonate the victim for malicious purposes. For the same reason, biometric leakage in a given system can seriously jeopardize the security of other systems based on the same biometrics. A further problem associated with the use of biometric traits is that, due to their uniqueness, the privacy of their owner is put at risk. Geographical position, movements, habits, and even personal beliefs can be tracked by observing when and where the biometric traits of an individual are used to identify him/her