Biblio

Found 2955 results

Filters: Keyword is composability  [Clear All Filters]
2020-03-30
2019-01-16
Honggang, Zhao, Chen, Shi, Leyu, Zhai.  Submitted.  Design and Implementation of Lightweight 6LoWPAN Gateway Based on Contiki - IEEE Conference Publication.

6LoWPAN technology realizes the IPv6 packet transmission in the IEEE 802.15.4 based WSN. And 6LoWPAN is regarded as one of the ideal technologies to realize the interconnection between WSN and Internet, which is the key to build the IoT. Contiki is an open source and highly portable multitasking operating system, in which the 6LoWPAN has been implemented. In contiki, only several K Bytes of code and a few hundred bytes of memory are required to provide a multitasking environment and built-in TCP/IP support. This makes it especially suitable for memory constrained embedded platforms. In this paper, a lightweight 6LoWPAN gateway based on Contiki is designed and its designs of hardware and software are described. A complex experiment environment is presented, in which the gateway's capability of accessing the Internet is verified, and its performance about the average network delay and jitter are analyzed. The experimental results show that the gateway designed in this paper can not only realize the interconnection between 6LoWPAN networks and Internet, but also have good network adaptability and stability.

2017-03-20
Dormann, Will.  Submitted.  Google Authentication Risks on iOS. Proceedings of the 1st International Workshop on Mobile Development. :3–5.

The Google Identity Platform is a system that allows a user to sign in to applications and other services by using a Google account. Google Sign-In is one such method for providing one’s identity to the Google Identity Platform. Google Sign-In is available for Android applications and iOS applications, as well as for websites and other devices. Users of Google Sign-In find that it integrates well with the Android platform, but iOS users (iPhone, iPad, etc.) do not have the same experience. The user experience when logging in to a Google account on an iOS application can not only be more tedious than the Android experience, but it also conditions users to engage in behaviors that put the information in their Google accounts at risk.

2020-03-30
Thida, Aye, Shwe, Thanda.  2020.  Process Provenance-based Trust Management in Collaborative Fog Environment. 2020 IEEE Conference on Computer Applications(ICCA). :1–5.
With the increasing popularity and adoption of IoT technology, fog computing has been used as an advancement to cloud computing. Although trust management issues in cloud have been addressed, there are still very few studies in a fog area. Trust is needed for collaborating among fog nodes and trust can further improve the reliability by assisting in selecting the fog nodes to collaborate. To address this issue, we present a provenance based trust mechanism that traces the behavior of the process among fog nodes. Our approach adopts the completion rate and failure rate as the process provenance in trust scores of computing workload, especially obvious measures of trustworthiness. Simulation results demonstrate that the proposed system can effectively be used for collaboration in a fog environment.
2020-04-24
Kim, Chang-Woo, Jang, Gang-Heyon, Shin, Kyung-Hun, Jeong, Sang-Sub, You, Dae-Joon, Choi, Jang-Young.  2020.  Electromagnetic Design and Dynamic Characteristics of Permanent Magnet Linear Oscillating Machines Considering Instantaneous Inductance According to Mover Position. IEEE Transactions on Applied Superconductivity. 30:1—5.
Interior permanent magnet (IPM)-type linear oscillating actuators (LOAs) have a higher output power density than typical LOAs. Their mover consists of a permanent magnet (PM) and an iron core, however, this configuration generates significant side forces. The device can malfunction due to eccentricity in the electromagnetic behavior. Thus, here an electromagnetic design was developed to minimize this side force. In addition, dynamic analysis was performed considering the mechanical systems of LOAs. To perform a more accurate analysis, instantaneous inductance was considered according to the mover's position.
2020-04-17
Gorbenko, Anatoliy, Romanovsky, Alexander, Tarasyuk, Olga, Biloborodov, Oleksandr.  2020.  From Analyzing Operating System Vulnerabilities to Designing Multiversion Intrusion-Tolerant Architectures. IEEE Transactions on Reliability. 69:22—39.
This paper analyzes security problems of modern computer systems caused by vulnerabilities in their operating systems (OSs). Our scrutiny of widely used enterprise OSs focuses on their vulnerabilities by examining the statistical data available on how vulnerabilities in these systems are disclosed and eliminated, and by assessing their criticality. This is done by using statistics from both the National Vulnerabilities Database and the Common Vulnerabilities and Exposures System. The specific technical areas the paper covers are the quantitative assessment of forever-day vulnerabilities, estimation of days-of-grey-risk, the analysis of the vulnerabilities severity and their distributions by attack vector and impact on security properties. In addition, the study aims to explore those vulnerabilities that have been found across a diverse range of OSs. This leads us to analyzing how different intrusion-tolerant architectures deploying the OS diversity impact availability, integrity, and confidentiality.
2020-05-08
Bolla, R., Carrega, A., Repetto, M..  2019.  An abstraction layer for cybersecurity context. 2019 International Conference on Computing, Networking and Communications (ICNC). :214—218.
The growing complexity and diversification of cyber-attacks are largely reflected in the increasing sophistication of security appliances, which are often too cumbersome to be run in virtual services and IoT devices. Hence, the design of cyber-security frameworks is today looking at more cooperative models, which collect security-related data from a large set of heterogeneous sources for centralized analysis and correlation.In this paper, we outline a flexible abstraction layer for access to security context. It is conceived to program and gather data from lightweight inspection and enforcement hooks deployed in cloud applications and IoT devices. We also provide a preliminary description of its implementation, by reviewing the main software components and their role.
2020-06-01
Laranjeiro, Nuno, Gomez, Camilo, Schiavone, Enrico, Montecchi, Leonardo, Carvalho, Manoel J. M., Lollini, Paolo, Micskei, Zoltán.  2019.  Addressing Verification and Validation Challenges in Future Cyber-Physical Systems. 2019 9th Latin-American Symposium on Dependable Computing (LADC). :1–2.
Cyber-physical systems are characterized by strong interactions between their physical and computation parts. The increasing complexity of such systems, now used in numerous application domains (e.g., aeronautics, healthcare), in conjunction with hard to predict surrounding environments or the use of non-traditional middleware and with the presence of non-deterministic or non-explainable software outputs, tend to make traditional Verification and Validation (V&V) techniques ineffective. This paper presents the H2020 ADVANCE project, which aims precisely at addressing the Verification and Validation challenges that the next-generation of cyber-physical systems bring, by exploring techniques, methods and tools for achieving the technical objective of improving the overall efficiency and effectiveness of the V&V process. From a strategic perspective, the goal of the project is to create an international network of expertise on the topic of V&V of cyber-physical systems.
2020-02-17
Chalise, Batu K..  2019.  ADMM-based Beamforming Optimization for Physical Layer Security in a Full-duplex Relay System. ICASSP 2019 - 2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). :4734–4738.
Although beamforming optimization problems in full-duplex communication systems can be optimally solved with the semidefinite relaxation (SDR) approach, its computational complexity increases rapidly when the problem size increases. In order to circumvent this issue, in this paper, we propose an alternating direction of multiplier method (ADMM) which minimizes the augmented Lagrangian of the dual of the SDR and handles the inequality constraints with the use of slack variables. The proposed ADMM is then applied for optimizing the relay beamformer to maximize the secrecy rate. Simulation results show that the proposed ADMM performs as good as the SDR approach.
2020-04-24
Tuttle, Michael, Wicker, Braden, Poshtan, Majid, Callenes, Joseph.  2019.  Algorithmic Approaches to Characterizing Power Flow Cyber-Attack Vulnerabilities. 2019 IEEE Power Energy Society Innovative Smart Grid Technologies Conference (ISGT). :1—5.
As power grid control systems become increasingly automated and distributed, security has become a significant design concern. Systems increasingly expose new avenues, at a variety of levels, for attackers to exploit and enable widespread disruptions and/or surveillance. Much prior work has explored the implications of attack models focused on false data injection at the front-end of the control system (i.e. during state estimation) [1]. Instead, in this paper we focus on characterizing the inherent cyber-attack vulnerabilities with power flow. Power flow (and power flow constraints) are at the core of many applications critical to operation of power grids (e.g. state estimation, economic dispatch, contingency analysis, etc.). We propose two algorithmic approaches for characterizing the vulnerability of buses within power grids to cyber-attacks. Specifically, we focus on measuring the instability of power flow to attacks which manifest as either voltage or power related errors. Our results show that attacks manifesting as voltage errors are an order of magnitude more likely to cause instability than attacks manifesting as power related errors (and 5x more likely for state estimation as compared to power flow).
2020-02-17
de Andrade Bragagnolle, Thiago, Pereira Nogueira, Marcelo, de Oliveira Santos, Melissa, do Prado, Afonso José, Ferreira, André Alves, de Mello Fagotto, Eric Alberto, Aldaya, Ivan, Abbade, Marcelo Luís Francisco.  2019.  All-Optical Spectral Shuffling of Signals Traveling through Different Optical Routes. 2019 21st International Conference on Transparent Optical Networks (ICTON). :1–4.
A recent proposed physical layer encryption technique uses an all-optical setup based on spatial light modulators to split two or more wavelength division multiplexed (WDM) signals in several spectral slices and to shuffle these slices. As a result, eavesdroppers aimed to recover information from a single target signal need to handle all the signals involved in the shuffling process. In this work, computer simulations are used to analyse the case where the shuffled signals propagate through different optical routes. From a security point of view, this is an interesting possibility because it obliges eavesdroppers to tap different optical fibres/ cables. On the other hand, each shuffled signal experiences different physical impairments and the deleterious consequences of these effects must be carefully investigated. Our results indicate that, in a metropolitan area network environment, penalties caused by attenuation and dispersion differences may be easily compensated with digital signal processing algorithms that are presently deployed.
2020-04-13
Cai, Yang, Wang, Yuewu, Lei, Lingguang, Zhou, Quan.  2019.  ALTEE: Constructing Trustworthy Execution Environment for Mobile App Dynamically. 2019 IEEE Symposium on Computers and Communications (ISCC). :1–7.
TEE(Trusted Execution Environment) has became one of the most popular security features for mobile platforms. Current TEE solutions usually implement secure functions in Trusted applications (TA) running over a trusted OS in the secure world. Host App may access these secure functions through the TEE driver. Unfortunately, such architecture is not very secure. A trusted OS has to be loaded in secure world to support TA running. Thus, the code size in secure world became large. As more and more TA is installed, the secure code size will be further larger and larger. Lots of real attack case have been reported [1]. In this paper, we present a novel TEE constructing method named ALTEE. Different from existing TEE solutions, ALTEE includes secure code in host app, and constructs a trustworthy execution environment for it dynamically whenever the code needs to be run.
2020-03-23
Xuewei, Feng, Dongxia, Wang, Zhechao, Lin.  2019.  An Approach of Code Pointer Hiding Based on a Resilient Area. 2019 Seventh International Conference on Advanced Cloud and Big Data (CBD). :204–209.
Code reuse attacks can bypass the DEP mechanism effectively. Meanwhile, because of the stealthy of the operation, it becomes one of the most intractable threats while securing the information system. Although the security solutions of code randomization and diversity can mitigate the threat at a certain extent, attackers can bypass these solutions due to the high cost and coarsely granularity, and the memory disclosure vulnerability is another magic weapon which can be used by attackers to bypass these solutions. After analyzing the principle of memory disclosure vulnerability, we propose a novel code pointer hiding method based on a resilient area. We expatiate how to create the resilient area and achieve code pointer hiding from four aspects, namely hiding return addresses in data pages, hiding function pointers in data pages, hiding target pointers of instruction JUMP in code pages, and hiding target pointers of instruction CALL in code pages. This method can stop attackers from reading and analyzing pages in memory, which is a critical stage in finding and creating ROP chains while executing a code reuse attack. Lastly, we test the method contrastively, and the results show that the method is feasible and effective while defending against ROP attacks.
2020-05-11
Kanimozhi, V., Jacob, T. Prem.  2019.  Artificial Intelligence based Network Intrusion Detection with Hyper-Parameter Optimization Tuning on the Realistic Cyber Dataset CSE-CIC-IDS2018 using Cloud Computing. 2019 International Conference on Communication and Signal Processing (ICCSP). :0033–0036.
One of the latest emerging technologies is artificial intelligence, which makes the machine mimic human behavior. The most important component used to detect cyber attacks or malicious activities is the Intrusion Detection System (IDS). Artificial intelligence plays a vital role in detecting intrusions and widely considered as the better way in adapting and building IDS. In trendy days, artificial intelligence algorithms are rising as a brand new computing technique which will be applied to actual time issues. In modern days, neural network algorithms are emerging as a new artificial intelligence technique that can be applied to real-time problems. The proposed system is to detect a classification of botnet attack which poses a serious threat to financial sectors and banking services. The proposed system is created by applying artificial intelligence on a realistic cyber defense dataset (CSE-CIC-IDS2018), the very latest Intrusion Detection Dataset created in 2018 by Canadian Institute for Cybersecurity (CIC) on AWS (Amazon Web Services). The proposed system of Artificial Neural Networks provides an outstanding performance of Accuracy score is 99.97% and an average area under ROC (Receiver Operator Characteristic) curve is 0.999 and an average False Positive rate is a mere value of 0.001. The proposed system using artificial intelligence of botnet attack detection is powerful, more accurate and precise. The novel proposed system can be implemented in n machines to conventional network traffic analysis, cyber-physical system traffic data and also to the real-time network traffic analysis.
2020-02-17
Liu, Xiaochen, Gao, Yuanyuan, Zang, Guozhen, Sha, Nan.  2019.  Artificial-Noise-Aided Robust Beamforming for MISOME Wiretap Channels with Security QoS. 2019 IEEE 19th International Conference on Communication Technology (ICCT). :795–799.
This paper studies secure communication from a multi-antenna transmitter to a single-antenna receiver in the presence of multiple multi-antenna eavesdroppers, considering constraints of security quality of service (QoS), i.e., minimum allowable signal-to-interference-and-noise ratio (SINR) at receiver and maximum tolerable SINR at eavesdroppers. The robust joint optimal beamforming (RJOBF) of secret signal and artificial noise (AN) is designed to minimize transmit power while estimation errors of channel state information (CSI) for wiretap channels are taken into consideration. The formulated design problem is shown to be nonconvex and we transfer it into linear matrix inequalities (LMIs) along with semidefinite relaxation (SDR) technique. The simulation results illustrate that our proposed RJOBF is efficient for power saving in security communication.
2019-11-25
Pei, Xin, Li, Xuefeng, Wu, Xiaochuan, Zheng, Kaiyan, Zhu, Boheng, Cao, Yixin.  2019.  Assured Delegation on Data Storage and Computation via Blockchain System. 2019 IEEE 9th Annual Computing and Communication Workshop and Conference (CCWC). :0055–0061.
With the widespread of cloud computing, the delegation of storage and computing is becoming a popular trend. Concerns on data integrity, security, user privacy as well as the correctness of execution are highlighted due to the untrusted remote data manipulation. Most of existing proposals solve the integrity checking and verifiable computation problems by challenge-response model, but are lack of scalability and reusability. Via blockchain, we achieve efficient and transparent public verifiable delegation for both storage and computing. Meanwhile, the smart contract provides API for request handling and secure data query. The security and privacy issues of data opening are settled by applying cryptographic algorithms all through the delegations. Additionally, any access to the outsourced data requires the owner's authentication, so that the dat transference and utilization are under control.
2020-01-13
Yugha, R., Chithra, S..  2019.  Attribute Based Trust Evaluation for Secure RPL Protocol in IoT Environment. 2019 International Conference on Vision Towards Emerging Trends in Communication and Networking (ViTECoN). :1–7.
Internet of Things (IoT) is an advanced automation technology and analytics systems which connected physical objects that have access through the Internet and have their unique flexibility and an ability to be suitable for any environment. There are some critical applications like smart health care system, in which the data collection, sharing and routing through IoT has to be handled in sensitive way. The IPv6 Routing Protocol for LL(Low-power and Lossy) networks (RPL) is the routing protocols to ensure reliable data transfer in 6LOWPAN networks. However, RPL is vulnerable to number of security attacks which creates a major impact on energy consumption and memory requirements which is not suitable for energy constraint networks like IoT. This requires secured RPL protocol to be used for critical data transfer. This paper introduces a novel approach of combining a lightweight LBS (Location Based Service) authentication and Attribute Based Trust Evaluation (ABTE). The algorithm has been implemented for smart health care system and analyzed how its perform in the RPL protocol for IoT constrained environments.
2020-04-17
Daniel Albu, Răzvan, Gordan, Cornelia Emilia.  2019.  Authentication and Recognition, Guarantor for on-Line Security. 2019 15th International Conference on Engineering of Modern Electric Systems (EMES). :9—12.
ARGOS is a web service we implemented to offer face recognition Authentication Services (AaaS) to mobile and desktop (via the web browser) end users. The Authentication Services may be used by 3rd party service organizations to enhance their service offering to their customers. ARGOS implements a secure face recognition-based authentication service aiming to provide simple and intuitive tools for 3rd party service providers (like PayPal, banks, e-commerce etc) to replace passwords with face biometrics. It supports authentication from any device with 2D or 3D frontal facing camera (mobile phones, laptops, tablets etc.) and almost any operating systems (iOS, Android, Windows and Linux Ubuntu).
Zollner, Stephan, Choo, Kim-Kwang Raymond, Le-Khac, Nhien-An.  2019.  An Automated Live Forensic and Postmortem Analysis Tool for Bitcoin on Windows Systems. IEEE Access. 7:158250—158263.
Bitcoin is popular not only with consumers, but also with cybercriminals (e.g., in ransomware and online extortion, and commercial online child exploitation). Given the potential of Bitcoin to be involved in a criminal investigation, the need to have an up-to-date and in-depth understanding on the forensic acquisition and analysis of Bitcoins is crucial. However, there has been limited forensic research of Bitcoin in the literature. The general focus of existing research is on postmortem analysis of specific locations (e.g. wallets on mobile devices), rather than a forensic approach that combines live data forensics and postmortem analysis to facilitate the identification, acquisition, and analysis of forensic traces relating to the use of Bitcoins on a system. Hence, the latter is the focus of this paper where we present an open source tool for live forensic and postmortem analysing automatically. Using this open source tool, we describe a list of target artifacts that can be obtained from a forensic investigation of popular Bitcoin clients and Web Wallets on different web browsers installed on Windows 7 and Windows 10 platforms.
2020-04-03
Künnemann, Robert, Esiyok, Ilkan, Backes, Michael.  2019.  Automated Verification of Accountability in Security Protocols. 2019 IEEE 32nd Computer Security Foundations Symposium (CSF). :397—39716.
Accountability is a recent paradigm in security protocol design which aims to eliminate traditional trust assumptions on parties and hold them accountable for their misbehavior. It is meant to establish trust in the first place and to recognize and react if this trust is violated. In this work, we discuss a protocol-agnostic definition of accountability: a protocol provides accountability (w.r.t. some security property) if it can identify all misbehaving parties, where misbehavior is defined as a deviation from the protocol that causes a security violation. We provide a mechanized method for the verification of accountability and demonstrate its use for verification and attack finding on various examples from the accountability and causality literature, including Certificate Transparency and Krollˆ\textbackslashtextbackslashprimes Accountable Algorithms protocol. We reach a high degree of automation by expressing accountability in terms of a set of trace properties and show their soundness and completeness.
2020-04-24
Bettouche, Mohamed Amine, Le Claire, Jean-Claude, Ghedamsi, Kaci, Aouzellag, Djamal, Ahmed, Mourad Ait, Benkhoris, Mohamed Fouad.  2019.  A behavior analysis of Permanent Magnet Synchronous Generator - Vienna rectifier set for marine current energy conversion. 2019 IEEE 2nd International Conference on Renewable Energy and Power Engineering (REPE). :254—259.
This article is dedicated to the study of an innovative architecture for the conversion of renewable marine energy into electrical energy. It consists of a Permanent Magnet Synchronous Generator (PMSG) combined with a three-phase Vienna rectifier. This last converter is not reversible but has the advantage of minimizing the number of active switches. This improves the operational reliability of the chain, which is necessary in the context of marine energy exploitation where access to the installations is not easy. The study focuses on the behavior analysis of electrical chain conversion, and the study of phase and neutral current according to the conduction’s states of the switches of the Vienna rectifier is being investigated. Despite the high non-linearity of this architecture, this control is made possible through to the dynamic performance and control of the maximum switching frequency of the self-oscillating controller called the Phase-Shift Self-Oscillating Current Controller (PSSOCC).
2020-03-30
Bharati, Aparna, Moreira, Daniel, Brogan, Joel, Hale, Patricia, Bowyer, Kevin, Flynn, Patrick, Rocha, Anderson, Scheirer, Walter.  2019.  Beyond Pixels: Image Provenance Analysis Leveraging Metadata. 2019 IEEE Winter Conference on Applications of Computer Vision (WACV). :1692–1702.
Creative works, whether paintings or memes, follow unique journeys that result in their final form. Understanding these journeys, a process known as "provenance analysis," provides rich insights into the use, motivation, and authenticity underlying any given work. The application of this type of study to the expanse of unregulated content on the Internet is what we consider in this paper. Provenance analysis provides a snapshot of the chronology and validity of content as it is uploaded, re-uploaded, and modified over time. Although still in its infancy, automated provenance analysis for online multimedia is already being applied to different types of content. Most current works seek to build provenance graphs based on the shared content between images or videos. This can be a computationally expensive task, especially when considering the vast influx of content that the Internet sees every day. Utilizing non-content-based information, such as timestamps, geotags, and camera IDs can help provide important insights into the path a particular image or video has traveled during its time on the Internet without large computational overhead. This paper tests the scope and applicability of metadata-based inferences for provenance graph construction in two different scenarios: digital image forensics and cultural analytics.
2020-03-27
Jadidi, Mahya Soleimani, Zaborski, Mariusz, Kidney, Brian, Anderson, Jonathan.  2019.  CapExec: Towards Transparently-Sandboxed Services. 2019 15th International Conference on Network and Service Management (CNSM). :1–5.
Network services are among the riskiest programs executed by production systems. Such services execute large quantities of complex code and process data from arbitrary — and untrusted — network sources, often with high levels of system privilege. It is desirable to confine system services to a least-privileged environment so that the potential damage from a malicious attacker can be limited, but existing mechanisms for sandboxing services require invasive and system-specific code changes and are insufficient to confine broad classes of network services. Rather than sandboxing one service at a time, we propose that the best place to add sandboxing to network services is in the service manager that starts those services. As a first step towards this vision, we propose CapExec, a process supervisor that can execute a single service within a sandbox based on a service declaration file in which, required resources whose limited access to are supported by Caper services, are specified. Using the Capsicum compartmentalization framework and its Casper service framework, CapExec provides robust application sandboxing without requiring any modifications to the application itself. We believe that this is the first step towards ubiquitous sandboxing of network services without the costs of virtualization.
2020-05-22
Almashaqbeh, Ghada, Kelley, Kevin, Bishop, Allison, Cappos, Justin.  2019.  CAPnet: A Defense Against Cache Accounting Attacks on Content Distribution Networks. 2019 IEEE Conference on Communications and Network Security (CNS). :250—258.
Peer-assisted content distribution networks (CDNs)have emerged to improve performance and reduce deployment costs of traditional, infrastructure-based content delivery networks. This is done by employing peer-to-peer data transfers to supplement the resources of the network infrastructure. However, these hybrid systems are vulnerable to accounting attacks in which the peers, or caches, collude with clients in order to report that content was transferred when it was not. This is a particular issue in systems that incentivize cache participation, because malicious caches may collect rewards from the content publishers operating the CDN without doing any useful work. In this paper, we introduce CAPnet, the first technique that lets untrusted caches join a peer-assisted CDN while providing a bound on the effectiveness of accounting attacks. At its heart is a lightweight cache accountability puzzle that clients must solve before caches are given credit. This puzzle requires colocating the data a client has requested, so its solution confirms that the content has actually been retrieved. We analyze the security and overhead of our scheme in realistic scenarios. The results show that a modest client machine using a single core can solve puzzles at a rate sufficient to simultaneously watch dozens of 1080p videos. The technique is designed to be even more scalable on the server side. In our experiments, one core of a single low-end machine is able to generate puzzles for 4.26 Tbps of bandwidth - enabling 870,000 clients to concurrently view the same 1080p video. This demonstrates that our scheme can ensure cache accountability without degrading system productivity.
2020-02-24
Dewangan, Ruchi, Altaf, Fahiem, Maity, Soumyadev.  2019.  Certificateless Aggregate Message Authentication for Hierarchical Trusted Authority based VANET. 2019 3rd International Conference on Computing Methodologies and Communication (ICCMC). :429–434.
In VANET, vehicles periodically transmit beacon messages to the neighboring vehicles and the RSU. To establish the authenticity of these messages, a number of digital signature schemes have been proposed in literature. Many of these schemes enable an RSU to perform aggregate verification of the signatures to deal with high vehicle density scenarios. These schemes are either based on traditional PKC concept involving certificate management overhead or identity based cryptography having key escrow problem. Further, these schemes require the existence of OBU device which is resistant to side channel attacks. In this paper, we propose a hierarchical trusted authority privacy preserving certificateless aggregate signature scheme for VANET. In addition to providing message authentication, integrity and non-repudiation, our scheme is resistant to message forgeability attack. The proposed scheme assumes hierarchical organization of network such that vehicles operate under multiple trusted authorities (TA) which in turn are controlled by single root TA. Using our scheme, the entity could verify messages received from vehicles which operate under multiple TAs. The proposed scheme is free from key escrow problem and resistant to side channel attacks on OBU. It also possesses conditional linkability such that originator of a message could be revealed whenever required. Simulations confirm the efficient nature in terms of verification delay as compared to other well known schemes proposed in literature.