Hard disk drives have multiple layers of fault tolerance mechanisms that protect against data loss. However, a few failures occasionally breach the entire set of mechanisms. To prevent such scenarios, we rely on failure prediction mechanisms to raise alarms with sufficient warning to allow the at-risk data to be copied to a safe location. A common failure prediction technique monitors the occurrence of soft errors and triggers an alarm when the soft error rate exceeds a specified threshold. This study uses data collected from a population of over 50,000 customer deployed disk drives to examine the relationship between soft errors and failures, in particular failures manifested as hard errors. The data analysis shows that soft errors alone cannot be used as a reliable predictor of hard errors. However, in those cases where soft errors do accurately predict hard errors, sufficient warning time exists for preventive actions.

Secure Real-time Transport Protocol (SRTP) provides confidentiality, authentication, integrity and replay protection for secure media transport in VoIP. However, the overhead of HMAC-SHA1 incurred per packet makes SRTP susceptible to flooding based Denial-of-Service attack. In this paper, we present a class of schemes to increase the DoS tolerance in SRTP. The central idea is to add a light-weight authentication mechanism on top of SRTP. This mechanism is used to efficiently discard illegitimate packets early on in the face of a DoS attack. Analysis shows that substantially larger traffic flood can be handled with the proposed enhancements.

Voice-over-IP (VoIP) systems are gaining in popularity as the technology for transmitting voice traffic over IP networks. As the popularity of VoIP systems increases, they are being subjected to different kinds of intrusions some of which are specific to such systems and some of which follow a general pattern. VoIP systems pose several new challenges to intrusion detection system (IDS) designers. First, these systems employ multiple protocols for call management (e.g., SIP) and data delivery (e.g., RTP). Second, the systems are distributed in nature and employ distributed clients, servers and proxies. Third, the attacks to such systems span a large class, from denial of service to billing fraud attacks. Finally, the systems are heterogeneous and typically under several different administrative domains. In this paper, we propose the design of an intrusion detection system targeted to VoIP systems, called SCIDIVE (pronounced "Skydive"). SCIDIVE is structured to detect different classes of intrusions, including, masquerading, denial of service, and media stream-based attacks. It can operate with both classes of protocols that compose VoIP systems - call management protocols (CMP), e.g., SIP, and media delivery protocols (MDP), e.g., RTP. SCIDIVE proposes two abstractions for VoIP IDS - stateful detection and cross-protocol detection. Stateful detection denotes assembling state from multiple packets and using the aggregated state in the rule-matching engine. Cross protocol detection denotes matching rules that span multiple protocols. SCIDIVE is demonstrated on a sample VoIP system that comprises SIP clients and SIP proxy servers with RTP as the data delivery protocol. Four attack scenarios are created and the accuracy and the efficiency of the system evaluated with rules meant to catch these attacks.

Libsafe is a practical solution that protects against the most common forms of buffer overflow attacks. Such attacks often result in granting the attacker full privileges on the target system. Libsafe is implemented as a shared library that intercepts calls to vulnerable standard library functions. Based on an inspection of the process stack and the function arguments, Libsafe ensures that no return addresses can be overwritten, thus preventing the most common form of buffer overflow attack.

The DTS (Dependability Test Suite) fault injection tool can be used to (1) obtain fault injection-based evaluation of system reliability, (2) compare the reliability of different applications, fault tolerance middleware, and platforms, and (3) provide feedback to improve the reliability of the target applications, fault tolerance middleware, and platforms. This paper describes the architecture of the tool as well as the procedure for using the tool. Data from experiments with the DTS tool used on the Apache web server, the Microsoft IIS web server and the Microsoft SQL Server, along with the Microsoft Cluster Server (MSCS) and Bell Labs watched (part of NT-SwiFT) fault tolerance packages is presented to demonstrate the utility of the tool. The observations drawn from the data also illustrate the strengths and weaknesses of the tested applications and fault tolerance packages with respect to their reliability.

The objective of fault injection is to mimic the existence of faults and to force the exercise of the fault tolerance mechanisms of the target system. To maximize the efficacy of each injection, the locations, timing, and conditions for faults being injected must be carefully chosen. Faults should be injected with a high probability of being accessed. This paper presents two fault injection methodologies-stress-based injection and path-based injection; both are based on resource activity analysis to ensure that injections cause fault tolerance activity and, thus, the resulting exercise of fault tolerance mechanisms. The difference between these two methods is that stress-based injection validates the system dependability by monitoring the run-time workload activity at the system level to select faults that coincide with the locations and times of greatest workload activity, while path-based injection validates the system from the application perspective by using an analysis of the program flow and resource usage at the application program level to select faults during the program execution. These two injection methodologies focus separately on the system and process viewpoints to facilitate the testing of system dependability. Details of these two injection methodologies are discussed in this paper, along with their implementations, experimental results, and advantages and disadvantages.