Computer Science Department
School of Computer Science, Carnegie Mellon University


Security for a High Performance Commodity Storage Subsystem

Howard B. Gobioff

July 1999

Ph.D. Thesis

Keywords: Computer security, network attached storage, network attached secure disks, NASD, capability system

How do we incorporate security into a high performance commodity storage subsystem? Technology trends and the increasing importance of I/O bound workloads are driving the development of commodity network attached storage devices which deliver both increased functionality and increased performance to end-users. In the network attached world, storage devices co-exist on the network with their clients, application file-managers, and malicious adversaries who seek to bypass system security policies. As storage devices move from behind the protection of a server and become first-class net-work entities in their own right, they must become actively involved in protecting themselves from network attacks. They must do this while cooperating with higher level applications, such as distributed file systems or database systems, to enforce the application's security policies over storage resources. In this dissertation, I address this problem by proposing a cryptographic capability system which enables application filemanagers to asynchronously make policy decisions while the commodity storage devices synchronously enforce these decisions.

This dissertation analyzes a variety of access control schemata that exist in current distributed storage systems. Motivated by the analysis, I propose a basic cryptographic capability system that is flexible enough to efficiently meet the requirements of many distributed storage systems. Next, I explore how a variety of different mechanisms for describing a set of NASD objects can be used to improve the basic capability system. The result is a new design based on remote execution techniques. The new design places more access control processing at the drive in order to deliver increased performance and functional advantages. Based on the performance limitations of software cryptography demonstrated in a prototype implementation of a network attached storage device, I propose and evaluate an alternative to standard message authentication codes. This allows storage devices to pre-compute some security information and reduces the amount of request-time computation required to protect the integrity of read operations. Finally, I discuss the availability of cryptographic hardware, how much is required for a network attached storage device, and the implications of adding tamper-resistant hardware to a storage device.

212 pages

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