Implantable medical devices (IMDs) are normally used for monitoring and treating various medical conditions. These days, wireless modules have become an intrinsic part of many modern IMDs. So, doctors can use device programmers wirelessly to configure parameters in the IMDs. However, such a wireless technology exposes the IMDs to security attacks. In this paper, we analyze potential threats faced by the IMDs and discuss security solutions proposed in the existing literature to counter these threats. Securing an IMD involves three design tradeoffs that require a careful consideration. The first one is security versus accessibility in an emergency situation. We compare the IMD security schemes in the literature in terms of their merits and disadvantages. The second one is the tradeoff between the security schemes for supporting emergency access and those for supporting normal check-up access to the IMDs. This normal check-up access to the IMDs should avoid extra resource consumptions, which is different from the requirement in the emergency access. The third one is between the requirements of strong security and limited resources. The IMD, as a tiny wireless device used for medical purposes, has very limited resources when compared with a generic wireless sensor device/node. We analyze various schemes that aim to conserve the underlying resources of an IMD and also counter battery denial of service attacks from different perspectives. Based on the literature review, we analyze general concerns in the IMD security design from the system engineering point of view, and discuss possible future research directions.

Generating random binary sequences (BSes) is a fundamental requirement in cryptography. A BS is a sequence of $N$ bits, and each bit has a value of 0 or 1. For securing sensors within wireless body area networks (WBANs), electrocardiogram (ECG)-based BS generation methods have been widely investigated in which interpulse intervals (IPIs) from each heartbeat cycle are processed to produce BSes. Using these IPI-based methods to generate a 128-bit BS in real time normally takes around half a minute. In order to improve the time efficiency of such methods, this paper presents an ECG multiple fiducial-points based binary sequence generation (MFBSG) algorithm. The technique of discrete wavelet transforms is employed to detect arrival time of these fiducial points, such as P, Q, R, S, and T peaks. Time intervals between them, including RR, RQ, RS, RP, and RT intervals, are then calculated based on this arrival time, and are used as ECG features to generate random BSes with low latency. According to our analysis on real ECG data, these ECG feature values exhibit the property of randomness and, thus, can be utilized to generate random BSes. Compared with the schemes that solely rely on IPIs to generate BSes, this MFBSG algorithm uses five feature values from one heart beat cycle, and can be up to five times faster than the solely IPI-based methods. So, it achieves a design goal of low latency. According to our analysis, the complexity of the algorithm is comparable to that of fast Fourier transforms. These randomly generated ECG BSes can be used as security keys for encryption or authentication in a WBAN system.

Any proposal to provide security for Implantable Medical Devices (IMDs), such as cardiac pacemakers and defibrillators, has to achieve a trade-off between security and accessibility for doctors to gain access to an IMD, especially in an emergency scenario. In this paper, we propose a Finger-to-Heart (F2H) IMD authentication scheme to address this trade-off between security and accessibility. This scheme utilizes a patient's fingerprint to perform authentication for gaining access to the IMD. Doctors can gain access to the IMD and perform emergency treatment by scanning the patient's finger tip instead of asking the patient for passwords/security tokens thereby achieving the necessary trade-off. In the scheme, an improved Minutia Cylinder-Code (MCC) based fingerprint authentication algorithm is proposed for the IMD by reducing the length of each feature vector and the number of query feature vectors. Experimental results show that the improved fingerprint authentication algorithm significantly reduces both the size of messages in transmission and computational overheads in the device, and thus can be utilized to secure the IMD. Compared to existing electrocardiogram signal-based security schemes, the F2H scheme does not require the IMD to capture or process biometric traits in every access attempt since a fingerprint template is generated and stored in the IMD beforehand. As a result, the scarce resources in the IMD are conserved, making the scheme sustainable as well as energy efficient.

Modular analysis using the Design Structure Matrix (DSM) identifies the interactions between groups of components, and clusters them into modules in order to achieve competitive advantages in the product design processes. In this paper, a hybrid approach, based on multidimensional scaling (MDS) and clustering methods, is applied to component DSM for product architecting. The motivation is to facilitate better modularizations that enhance different product attributes in various product lifecycle stages. An experimental framework is developed to evaluate the performance of MDS clustering. Three MDS methods and four ubiquitous clustering methods are compared to reveal the most suitable for DSMs. The experimental results with several examples demonstrate that the effectiveness of MDS clustering, and show the superiority of non-metric MDS, SMACOF (Scaling by MAjorizing a Complicated Function) and hierarchical/cosine methods. These methods are capable of partitioning the product architecture into a set of modules and outperform the Newman-Girven algorithm, which has been extensively applied to DSM clustering. The proposed method is capable of partitioning the product architecture into reasonable modules. In addition, it can produce the optimal modules for any number of clusters, which is favourable especially when the cluster number is a higher managerial decision.

Wearable and Implantable Medical Devices (WIMDs) perform critical health monitoring and therapeutic functions. However, current WIMD products lack security safeguards to protect patients from fatal cyber-attacks. In the recent past, electrocardiogram (ECG) signals based security techniques have been widely explored to secure such devices by using two cryptographic primitives, the fuzzy commitment and the fuzzy vault, respectively. Nonetheless, differences, as well as similarities between these two primitives, have not been well investigated, making it difficult to decide which one would be appropriate for a particular setting. In this paper, we perform a critical analysis on both primitives and discuss their merits and drawbacks in the context of ECG-based key distribution. We analyze the critical challenges within each primitive-based key distribution technique, such as binary sequence generation and polynomial computations. Experimental results show that the technique based on the fuzzy commitment has a better false acceptance rate due to the randomness of ECG binary sequences. On the other hand, the fuzzy vault based scheme can achieve an acceptable false reject rate (5%) with less cost to the WIMDs. Future research is suggested to enhance the precision of ECG signal processing, to improve the efficacy of binary sequence generation process as well as to suggest ways to reduce polynomial computations.

The terms module and modularity are not part of the technical taxonomy in any of the systems engineering standards, which do not regard a module as a part of the formal system breakdown structure. In this paper, we redefine the term module as a unit composed of a set of components with a set of specific interfaces. This unit serves one or more purely nonfunctional goals, such as flexibility, evolvability, manufacturability, testability, and maintainability. According to this definition, a configuration item, a subsystem, an assembly, a subassembly, or a component can all be regarded as modules as they can serve nonfunctional goals. The important assertion here is that a module's boundaries do not necessarily coincide with those dictated by the functional or spatial system decomposition and hierarchy. The aim of this paper is to lay the foundations for the future standardization of various engineering design processes based on modularity for nonfunctional benefits. A clear definition of the terms module and modularity can assist systems designers and developers to optimize the value of a modular system. This research highlights the present inconsistencies in the field of modular system design and puts forward some critical questions, which will shape the future research into this field.