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Abstract-Using Cloud Storage, users can remotely store their data and enjoy the on-demand high quality applications and services from a shared pool of configurable computing resources, without the burden of local data storage and maintenance. However, the fact that users no longer have physical possession of the outsourced data makes the data integrity protection in Cloud Computing a formidable task, especially for users with constrained computing resources. Moreover, users should be able to just use the cloud storage as if it is local, without worrying about the need to verify its integrity. Thus, enabling public auditability for cloud storage is of critical importance so that users can resort to a third party auditor (TPA) to check the integrity of outsourced data and be worry-free. To securely introduce an effective TPA, the auditing process should bring in no new vulnerabilities towards user data privacy, and introduce no additional online burden to user. In this paper, we propose a secure cloud storage system supporting privacy-preserving public auditing. We further extend our result to enable the TPA to perform audits for multiple users simultaneously and efficiently. Extensive security and performance analysis show the proposed schemes are provably secure and highly efficient.

Abstract-Using cloud storage, users can remotely store their data and enjoy the on-demand high-quality applications and services from a shared pool of configurable computing resources, without the burden of local data storage and maintenance. However, the fact that users no longer have physical possession of the outsourced data makes the data integrity protection in cloud computing a formidable task, especially for users with constrained computing resources. Moreover, users should be able to just use the cloud storage as if it is local, without worrying about the need to verify its integrity. Thus, enabling public auditability for cloud storage is of critical importance so that users can resort to a third-party auditor (TPA) to check the integrity of outsourced data and be worry free. To securely introduce an effective TPA, the auditing process should bring in no new vulnerabilities toward user data privacy, and introduce no additional online burden to user. In this paper, we propose a secure cloud storage system supporting privacy-preserving public auditing. We further extend our result to enable the TPA to perform audits for multiple users simultaneously and efficiently. Extensive security and performance analysis show the proposed schemes are provably secure and highly efficient. Our preliminary experiment conducted on Amazon EC2 instance further demonstrates the fast performance of the design.

Abstract. Cloud Computing has been envisioned as the next-generation architecture of IT Enterprise. It moves the application software and databases to the centralized large data centers, where the management of the data and services may not be fully trustworthy. This unique paradigm brings about many new security challenges, which have not been well understood. This work studies the problem of ensuring the integrity of data storage in Cloud Computing. In particular, we consider the task of allowing a third party auditor (TPA), on behalf of the cloud client, to verify the integrity of the dynamic data stored in the cloud. The introduction of TPA eliminates the involvement of client through the auditing of whether his data stored in the cloud is indeed intact, which can be important in achieving economies of scale for Cloud Computing. The support for data dynamics via the most general forms of data operation, such as block modification, insertion and deletion, is also a significant step toward practicality, since services in Cloud Computing are not limited to archive or backup data only. While prior works on ensuring remote data integrity often lacks the support of either public verifiability or dynamic data operations, this paper achieves both. We first identify the difficulties and potential security problems of direct extensions with fully dynamic data updates from prior works and then show how to construct an elegant verification scheme for seamless integration of these two salient features in our protocol design. In particular, to achieve efficient data dynamics, we improve the Proof of Retrievability model [1] by manipulating the classic Merkle Hash Tree (MHT) construction for block tag authentication. Extensive security and performance analysis show that the proposed scheme is highly efficient and provably secure.

Abstract-CloudComputing has been envisioned as the next-generation architecture of IT Enterprise. It moves the application software and databases to the centralized large data centers, where the management of the data and services may not be fully trustworthy. This unique paradigm brings about many new security challenges, which have not been well understood. This work studies the problem of ensuring the integrity of data storage in Cloud Computing. In particular, we consider the task of allowing a third party auditor (TPA), on behalf of the cloud client, to verify the integrity of the dynamic data stored in the cloud. The introduction of TPA eliminates the involvement of the client through the auditing of whether his data stored in the cloud is indeed intact, which can be important in achieving economies of scale for Cloud Computing. The support for data dynamics via the most general forms of data operation, such as block modification, insertion and deletion, is also a significant step toward practicality, since services in Cloud Computing are not limited to archive or backup data only. While prior works on ensuring remote data integrity often lacks the support of either public auditability or dynamic data operations, this paper achieves both. We first identify the difficulties and potential security problems of direct extensions with fully dynamic data updates from prior works and then show how to construct an elegant verification scheme for the seamless integration of these two salient features in our protocol design. In particular, to achieve efficient data dynamics, we improve the existing proof of storage models by manipulating the classic Merkle Hash Tree construction for block tag authentication.To support efficient handling of multiple auditing tasks, we further explore the technique of bilinear aggregate signature to extend our main result into a multi-user setting, where TPA can perform multiple auditing tasks simultaneously. Extensive security and performance analysis show that the proposed schemes are highly efficient and provably secure.

We examine whether corporate governance mechanisms, especially the market for corporate control, affect the profitability of firm acquisitions. We find that acquirers with more antitakeover provisions experience significantly lower announcementperiod abnormal stock returns. This supports the hypothesis that managers at firms protected by more antitakeover provisions are less subject to the disciplinary power of the market for corporate control and thus are more likely to indulge in empire-building acquisitions that destroy shareholder value. We also find that acquirers operating in more competitive industries or separating the positions of CEO and chairman of the board experience higher abnormal announcement returns.FOLLOWING A STRING OF CORPORATE SCANDALS in the United States, legislators and regulators rushed to enact corporate governance reforms, which resulted in the passage of the Sarbanes-Oxley Act of 2002. Yet, these reforms were instituted with little scientific evidence to support their purported benefits. As the impact of these reforms continues to be strongly felt, with further reforms likely in the future, it is of great economic import to understand how major corporate governance mechanisms affect shareholder wealth. A series of recent studies by Gompers, Ishii, and Metrick (GIM, 2003), Bebchuk, Cohen, and Ferrell (BCF, 2004), Bebchuk and Cohen (2005), and Cremers and Nair (2005) examine one important dimension of corporate governance, namely, the market for corporate control. They document negative relations between various indices of antitakeover provisions (ATPs) and both firm value and * Ronald W. Masulis is from the Owen Graduate School of Management, Vanderbilt University; Cong Wang is from the Faculty of Business Administration, Chinese University of Hong Kong; and Fei Xie is from the School of Management, George Mason University. We thank an associate editor, an anonymous referee, George Benston, Margaret Blair, Paul Chaney, Bill Christie, Harry DeAngelo, Mara Faccio, Amar Gande, Sreeni Kamma, Veronika Krepely, Craig Lewis, Xi Li, Micah Officer, Hans Stoll, René Stulz, Randall Thomas, Robert Thompson, and seminar participants at the Accounting and Finance Research Camp at the Australian Graduate School of Management, the American Finance Association annual meetings in Boston, the Conference on International Markets and Corporate Governance at Georgetown University Law School, the JFI/CRES Corporate Governance Conference at Washington University, Chinese University of Hong Kong, Emory University, Hong Kong University of Science and Technology, University of New South Wales, and Vanderbilt University for helpful comments, and Martijn Cremers and Vinay Nair for providing institutional ownership data. Fei Xie also thanks Haibo Tang from Yale University for his assistance in conducting early analyses on this topic. 1852The Journal of Finance long-run stock return performance.1, 2 However, it remains unclear exactly how or through what channels antitakeover provisions negatively affect sh...

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