172 research outputs found
Fast Computation of Sliding Discrete Tchebichef Moments and Its Application in Duplicated Regions Detection
International audienceComputational load remains a major concern when processing signals by means of sliding transforms. In this paper, we present an efficient algorithm for the fast computation of one-dimensional and two-dimensional sliding discrete Tchebichef moments. To do so, we first establish the relationships that exist between the Tchebichef moments of two neighboring windows taking advantage of Tchebichef polynomials’ properties. We then propose an original way to fast compute the moments of one window by utilizing the moment values of its previous window. We further theoretically establish the complexity of our fast algorithm and illustrate its interest within the framework of digital forensics and more precisely the detection of duplicated regions in an audio signal or an image. Our algorithm is used to extract local features of such a signal tampering. Experimental results show that its complexity is independent of the window size, validating the theory. They also exhibit that our algorithm is suitable to digital forensics and beyond to any applications based on sliding Tchebichef moments
An improved fault mitigation strategy for CUDA Fermi GPUs
High computation is a predominant requirement in many applications. In this field, Graphic Processing Units (GPUs) are more and more adopted. Low prices and high parallelism let GPUs be attractive, even in safety critical applications. Nonetheless, new methodologies must be studied and developed to increase the dependability of GPUs. This paper presents an improved fault mitigation strategy against permanent faults for CUDA Fermi GPUs. The proposed approach exploits the reverse engineering of the block scheduling policy in CUDA Fermi GPUs in order to minimize the fault mitigation timing overhead. The graceful performance degradation achieved by the proposed technique outperforms multithreaded CPU implementations and other fault mitigation strategies for CUDA GPU, even in presence of multiple permanent faults
Cybersecurity in implantable medical devices
Mención Internacional en el título de doctorImplantable Medical Devices (IMDs) are electronic devices implanted within
the body to treat a medical condition, monitor the state or improve the
functioning of some body part, or just to provide the patient with a capability
that he did not possess before [86]. Current examples of IMDs
include pacemakers and defibrillators to monitor and treat cardiac conditions;
neurostimulators for deep brain stimulation in cases such as epilepsy
or Parkinson; drug delivery systems in the form of infusion pumps; and a
variety of biosensors to acquire and process different biosignals.
Some of the newest IMDs have started to incorporate numerous communication
and networking functions—usually known as “telemetry”—,
as well as increasingly more sophisticated computing capabilities. This
has provided implants with more intelligence and patients with more autonomy,
as medical personnel can access data and reconfigure the implant
remotely (i.e., without the patient being physically present in medical facilities).
Apart from a significant cost reduction, telemetry and computing
capabilities also allow healthcare providers to constantly monitor the patient’s
condition and to develop new diagnostic techniques based on an
Intra Body Network (IBN) of medical devices [25, 26, 201].
Evolving from a mere electromechanical IMD to one with more advanced
computing and communication capabilities has many benefits but
also entails numerous security and privacy risks for the patient. The majority
of such risks are relatively well known in classical computing scenarios,
though in many respects their repercussions are far more critical in the case
of implants. Attacks against an IMD can put at risk the safety of the patient
who carries it, with fatal consequences in certain cases. Causing an intentional
malfunction of an implant can lead to death and, as recognized by the
U.S. Food and Drug Administration (FDA), such deliberate attacks could
be far more difficult to detect than accidental ones [61]. Furthermore, these
devices store and transmit very sensitive medical information that requires
protection, as dictated by European (e.g., Directive 95/46/ECC) and U.S.
(e.g., CFR 164.312) Directives [94, 204].
The wireless communication capabilities present in many modern IMDs
are a major source of security risks, particularly while the patient is in open
(i.e., non-medical) environments. To begin with, the implant becomes no
longer “invisible”, as its presence could be remotely detected [48]. Furthermore,
it facilitates the access to transmitted data by eavesdroppers who
simply listen to the (insecure) channel [83]. This could result in a major privacy breach, as IMDs store sensitive information such as vital signals,
diagnosed conditions, therapies, and a variety of personal data (e.g., birth
date, name, and other medically relevant identifiers). A vulnerable communication
channel also makes it easier to attack the implant in ways similar
to those used against more common computing devices [118, 129, 156],
i.e., by forging, altering, or replying previously captured messages [82].
This could potentially allow an adversary to monitor and modify the implant
without necessarily being close to the victim [164]. In this regard,
the concerns of former U.S. vice-president Dick Cheney constitute an excellent
example: he had his Implantable Cardioverter Defibrillator (ICD)
replaced by another without WiFi capability [219].
While there are still no known real-world incidents, several attacks on
IMDs have been successfully demonstrated in the lab [83, 133, 143]. These
attacks have shown how an adversary can disable or reprogram therapies
on an ICD with wireless connectivity, and even inducing a shock state to
the patient [65]. Other attacks deplete the battery and render the device
inoperative [91], which often implies that the patient must undergo a surgical
procedure to have the IMD replaced. Moreover, in the case of cardiac
implants, they have a switch that can be turned off merely by applying a
magnetic field [149]. The existence of this mechanism is motivated by the
need to shield ICDs to electromagnetic fields, for instance when the patient
undergoes cardiac surgery using electrocautery devices [47]. However, this
could be easily exploited by an attacker, since activating such a primitive
mechanism does not require any kind of authentication.
In order to prevent attacks, it is imperative that the new generation of
IMDs will be equipped with strong mechanisms guaranteeing basic security
properties such as confidentiality, integrity, and availability. For example,
mutual authentication between the IMD and medical personnel is
essential, as both parties must be confident that the other end is who claims
to be. In the case of the IMD, only commands coming from authenticated
parties should be considered, while medical personnel should not trust any
message claiming to come from the IMD unless sufficient guarantees are
given.
Preserving the confidentiality of the information stored in and transmitted
by the IMD is another mandatory aspect. The device must implement
appropriate security policies that restrict what entities can reconfigure the
IMD or get access to the information stored in it, ensuring that only authorized
operations are executed. Similarly, security mechanisms have to
be implemented to protect the content of messages exchanged through an insecure wireless channel.
Integrity protection is equally important to ensure that information has
not been modified in transit. For example, if the information sent by the
implant to the Programmer is altered, the doctor might make a wrong decision.
Conversely, if a command sent to the implant is forged, modified,
or simply contains errors, its execution could result in a compromise of the
patient’s physical integrity.
Technical security mechanisms should be incorporated in the design
phase and complemented with appropriate legal and administrative measures.
Current legislation is rather permissive in this regard, allowing the
use of implants like ICDs that do not incorporate any security mechanisms.
Regulatory authorities like the FDA in the U.S or the EMA (European
Medicines Agency) in Europe should promote metrics and frameworks for
assessing the security of IMDs. These assessments should be mandatory
by law, requiring an adequate security level for an implant before approving
its use. Moreover, both the security measures supported on each IMD
and the security assessment results should be made public.
Prudent engineering practices well known in the safety and security domains
should be followed in the design of IMDs. If hardware errors are
detected, it often entails a replacement of the implant, with the associated
risks linked to a surgery. One of the main sources of failure when treating
or monitoring a patient is precisely malfunctions of the device itself.
These failures are known as “recalls” or “advisories”, and it is estimated
that they affect around 2.6% of patients carrying an implant. Furthermore,
the software running on the device should strictly support the functionalities
required to perform the medical and operational tasks for what it was
designed, and no more [66, 134, 213].
In Chapter 1, we present a survey of security and privacy issues in
IMDs, discuss the most relevant mechanisms proposed to address these
challenges, and analyze their suitability, advantages, and main drawbacks.
In Chapter 2, we show how the use of highly compressed electrocardiogram
(ECG) signals (only 24 coefficients of Hadamard Transform) is enough
to unequivocally identify individuals with a high performance (classification
accuracy of 97% and with identification system errors in the order of
10−2). In Chapter 3 we introduce a new Continuous Authentication scheme
that, contrarily to previous works in this area, considers ECG signals as
continuous data streams. The proposed ECG-based CA system is intended
for real-time applications and is able to offer an accuracy up to 96%, with
an almost perfect system performance (kappa statistic > 80%). In Chapter 4, we propose a distance bounding protocol to manage access control of
IMDs: ACIMD. ACIMD combines two features namely identity verification
(authentication) and proximity verification (distance checking). The
authentication mechanism we developed conforms to the ISO/IEC 9798-2
standard and is performed using the whole ECG signal of a device holder,
which is hardly replicable by a distant attacker. We evaluate the performance
of ACIMD using ECG signals of 199 individuals over 24 hours,
considering three adversary strategies. Results show that an accuracy of
87.07% in authentication can be achieved. Finally, in Chapter 5 we extract
some conclusions and summarize the published works (i.e., scientific
journals with high impact factor and prestigious international conferences).Los Dispositivos Médicos Implantables (DMIs) son dispositivos electrónicos
implantados dentro del cuerpo para tratar una enfermedad, controlar
el estado o mejorar el funcionamiento de alguna parte del cuerpo, o simplemente
para proporcionar al paciente una capacidad que no poseía antes
[86]. Ejemplos actuales de DMI incluyen marcapasos y desfibriladores
para monitorear y tratar afecciones cardíacas; neuroestimuladores para la
estimulación cerebral profunda en casos como la epilepsia o el Parkinson;
sistemas de administración de fármacos en forma de bombas de infusión; y
una variedad de biosensores para adquirir y procesar diferentes bioseñales.
Los DMIs más modernos han comenzado a incorporar numerosas funciones
de comunicación y redes (generalmente conocidas como telemetría)
así como capacidades de computación cada vez más sofisticadas. Esto
ha propiciado implantes con mayor inteligencia y pacientes con más autonomía,
ya que el personal médico puede acceder a los datos y reconfigurar
el implante de forma remota (es decir, sin que el paciente esté
físicamente presente en las instalaciones médicas). Aparte de una importante
reducción de costos, las capacidades de telemetría y cómputo también
permiten a los profesionales de la atención médica monitorear constantemente
la condición del paciente y desarrollar nuevas técnicas de diagnóstico
basadas en una Intra Body Network (IBN) de dispositivos médicos
[25, 26, 201].
Evolucionar desde un DMI electromecánico a uno con capacidades de
cómputo y de comunicación más avanzadas tiene muchos beneficios pero
también conlleva numerosos riesgos de seguridad y privacidad para el paciente.
La mayoría de estos riesgos son relativamente bien conocidos en los
escenarios clásicos de comunicaciones entre dispositivos, aunque en muchos
aspectos sus repercusiones son mucho más críticas en el caso de los
implantes. Los ataques contra un DMI pueden poner en riesgo la seguridad
del paciente que lo porta, con consecuencias fatales en ciertos casos.
Causar un mal funcionamiento intencionado en un implante puede causar
la muerte y, tal como lo reconoce la Food and Drug Administration (FDA)
de EE.UU, tales ataques deliberados podrían ser mucho más difíciles de
detectar que los ataques accidentales [61]. Además, estos dispositivos almacenan
y transmiten información médica muy delicada que requiere se
protegida, según lo dictado por las directivas europeas (por ejemplo, la Directiva 95/46/ECC) y estadunidenses (por ejemplo, la Directiva CFR
164.312) [94, 204].
Si bien todavía no se conocen incidentes reales, se han demostrado con
éxito varios ataques contra DMIs en el laboratorio [83, 133, 143]. Estos
ataques han demostrado cómo un adversario puede desactivar o reprogramar
terapias en un marcapasos con conectividad inalámbrica e incluso
inducir un estado de shock al paciente [65]. Otros ataques agotan
la batería y dejan al dispositivo inoperativo [91], lo que a menudo implica
que el paciente deba someterse a un procedimiento quirúrgico para reemplazar
la batería del DMI. Además, en el caso de los implantes cardíacos,
tienen un interruptor cuya posición de desconexión se consigue simplemente
aplicando un campo magnético intenso [149]. La existencia de este
mecanismo está motivada por la necesidad de proteger a los DMIs frete
a posibles campos electromagnéticos, por ejemplo, cuando el paciente se
somete a una cirugía cardíaca usando dispositivos de electrocauterización
[47]. Sin embargo, esto podría ser explotado fácilmente por un atacante,
ya que la activación de dicho mecanismo primitivo no requiere ningún tipo
de autenticación.
Garantizar la confidencialidad de la información almacenada y transmitida
por el DMI es otro aspecto obligatorio. El dispositivo debe implementar
políticas de seguridad apropiadas que restrinjan qué entidades
pueden reconfigurar el DMI o acceder a la información almacenada en él,
asegurando que sólo se ejecuten las operaciones autorizadas. De la misma
manera, mecanismos de seguridad deben ser implementados para proteger
el contenido de los mensajes intercambiados a través de un canal inalámbrico
no seguro.
La protección de la integridad es igualmente importante para garantizar
que la información no se haya modificado durante el tránsito. Por ejemplo,
si la información enviada por el implante al programador se altera, el
médico podría tomar una decisión equivocada. Por el contrario, si un comando
enviado al implante se falsifica, modifica o simplemente contiene
errores, su ejecución podría comprometer la integridad física del paciente.
Los mecanismos de seguridad deberían incorporarse en la fase de diseño
y complementarse con medidas legales y administrativas apropiadas.
La legislación actual es bastante permisiva a este respecto, lo que permite
el uso de implantes como marcapasos que no incorporen ningún mecanismo
de seguridad. Las autoridades reguladoras como la FDA en los Estados
Unidos o la EMA (Agencia Europea de Medicamentos) en Europa deberían
promover métricas y marcos para evaluar la seguridad de los DMIs.
Estas evaluaciones deberían ser obligatorias por ley, requiriendo un nivel
de seguridad adecuado para un implante antes de aprobar su uso. Además,
tanto las medidas de seguridad implementadas en cada DMI como los resultados
de la evaluación de su seguridad deberían hacerse públicos.
Buenas prácticas de ingeniería en los dominios de la protección y la
seguridad deberían seguirse en el diseño de los DMIs. Si se detectan errores
de hardware, a menudo esto implica un reemplazo del implante, con
los riesgos asociados y vinculados a una cirugía. Una de las principales
fuentes de fallo al tratar o monitorear a un paciente es precisamente el
mal funcionamiento del dispositivo. Estos fallos se conocen como “retiradas”,
y se estima que afectan a aproximadamente el 2,6 % de los pacientes
que llevan un implante. Además, el software que se ejecuta en el
dispositivo debe soportar estrictamente las funcionalidades requeridas para
realizar las tareas médicas y operativas para las que fue diseñado, y no más
[66, 134, 213].
En el Capítulo 1, presentamos un estado de la cuestión sobre cuestiones
de seguridad y privacidad en DMIs, discutimos los mecanismos más relevantes
propuestos para abordar estos desafíos y analizamos su idoneidad,
ventajas y principales inconvenientes. En el Capítulo 2, mostramos
cómo el uso de señales electrocardiográficas (ECGs) altamente comprimidas
(sólo 24 coeficientes de la Transformada Hadamard) es suficiente para
identificar inequívocamente individuos con un alto rendimiento (precisión
de clasificación del 97% y errores del sistema de identificación del orden
de 10−2). En el Capítulo 3 presentamos un nuevo esquema de Autenticación
Continua (AC) que, contrariamente a los trabajos previos en esta
área, considera las señales ECG como flujos de datos continuos. El sistema
propuesto de AC basado en señales cardíacas está diseñado para aplicaciones
en tiempo real y puede ofrecer una precisión de hasta el 96%,
con un rendimiento del sistema casi perfecto (estadístico kappa > 80 %).
En el Capítulo 4, proponemos un protocolo de verificación de la distancia
para gestionar el control de acceso al DMI: ACIMD. ACIMD combina
dos características, verificación de identidad (autenticación) y verificación
de la proximidad (comprobación de la distancia). El mecanismo de autenticación
es compatible con el estándar ISO/IEC 9798-2 y se realiza utilizando
la señal ECG con todas sus ondas, lo cual es difícilmente replicable
por un atacante que se encuentre distante. Hemos evaluado el rendimiento
de ACIMD usando señales ECG de 199 individuos durante 24 horas, y
hemos considerando tres estrategias posibles para el adversario. Los resultados
muestran que se puede lograr una precisión del 87.07% en la au tenticación. Finalmente, en el Capítulo 5 extraemos algunas conclusiones
y resumimos los trabajos publicados (es decir, revistas científicas con alto
factor de impacto y conferencias internacionales prestigiosas).Programa Oficial de Doctorado en Ciencia y Tecnología InformáticaPresidente: Arturo Ribagorda Garnacho.- Secretario: Jorge Blasco Alís.- Vocal: Jesús García López de Lacall
Transform-based methods for stereo matching and dense depth estimation
Stereo matching is a passive method for estimating depth of a scene from two views from different perspectives. Parallax creates a disparity between the relative positions of scene points on the imaging planes depending on the distance of the points. The principle of stereo matching is to extract those disparities by finding the corresponding points between the images. Although stereo matching has been extensively studied, the existing solutions are still compromises between computational load and achieved quality. In this thesis, advances are made on both fronts. At the core of the matching algorithm is the similarity measure, which directly determines how well correspondences are found and how reliable they are. Traditionally, matching has been done in spatial domain using pixel differences such as sum of absolute differences (SAD). In this thesis, a similarity measure is proposed for use in stereo matching that is based on analysis of coefficient signs of transform domain representations. While originally formulated as an extension of Fourier domain phase-only correlation to the discrete cosine transform (DCT), here the method is developed further by applying it to a number of real-valued abstract harmonic transforms, including type II DCT, integer DCT, Walsh-Hadamard and a modified version of Haar. Results are presented showing that the method in general provides better quality than the reference algorithm SAD, while Haar is shown to be the best performing transform, both in terms of quality and speed.
Furthermore, the approach is adapted to a mobile platform by replacing the transform with an even simpler one, the census transform. An efficient implementation is developed, which utilizes the single instruction, multiple data (SIMD) enabled NEON core included in many ARM processors currently dominating the mobile market. Special attention is paid to the alternate methods of performing a population count on a variable, which is a key component in computing the similarities. Subjective testing along with numerical measurements set the census-based matching slightly under the reference point SAD in terms of quality, but speed-wise SAD is clearly out-performed by the census approach, thus establishing it as a competitive candidate for stereo matching in mobile applications
Three-dimensional block matching using orthonormal tree-structured haar transform for multichannel images
Multichannel images, i.e., images of the same object or scene taken in different spectral bands or with different imaging modalities/settings, are common in many applications. For example, multispectral images contain several wavelength bands and hence, have richer information than color images. Multichannel magnetic resonance imaging and multichannel computed tomography images are common in medical imaging diagnostics, and multimodal images are also routinely used in art investigation. All the methods for grayscale images can be applied to multichannel images by processing each channel/band separately. However, it requires vast computational time, especially for the task of searching for overlapping patches similar to a given query patch. To address this problem, we propose a three-dimensional orthonormal tree-structured Haar transform (3D-OTSHT) targeting fast full search equivalent for three-dimensional block matching in multichannel images. The use of a three-dimensional integral image significantly saves time to obtain the 3D-OTSHT coefficients. We demonstrate superior performance of the proposed block matching
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