Threshold cryptosystems (TCs), developed to eliminate single points of failure in applications such as key management-as-a-service, signature schemes, encrypted data storage and even blockchain applications, rely on the assumption that an adversary does not corrupt more than a fixed number of nodes in a network. This assumption, once broken, can lead to the entire system being compromised. In this paper, we present a systems-level solution, viz., a reboot-based framework, Groundhog, that adds a layer of resiliency on top of threshold cryptosystems (as well as others); our framework ensures the system can be protected against malicious (mobile) adversaries that can corrupt up all but one device in the network. Groundhog ensures that a sufficient number of honest devices is always available to ensure the availability of the entire system. Our framework is general-izable to multiple threshold cryptosystems - we demonstrate this by integrating it with two well-known TC protocols - the Distributed Symmetric key Encryption system (DiSE) and the Boneh, Lynn and Shacham Distributed Signatures (BLS) system. In fact, Groundhog may have applicability in systems beyond those based on threshold cryptography - we demonstrate this on a simpler cryptographic protocol that we developed named PassAround11In fact, this protocol was suggested by a USENIX Security reviewer that we then refined, implemented and evaluated in conjunction with Groundhog (see §6). . We developed a (generalizable) container-based framework that can be used to combine Groundhog (and its guarantees) with cryptographic protocols and evaluated our system using, ($a$) case studies of real world attacks as well as ($b$) extensive measurements by implementing the aforementioned DiSE, BLS and PassAround protocols on Groundhog. We show that Groundhog is able to guarantee high availability with minimal overheads (less than 7%). In some instances, Groundhog actually improves the performance of the TC schemes!22While it seems counter-intuitive, we explain the reasoning in §5.

With the end of conventional CMOS scaling, efficient resiliency solutions are needed to address the increased likelihood of hardware errors. Silent data corruptions (SDCs) are especially harmful because they can create unacceptable output without the user's knowledge. Several resiliency analysis techniques have been proposed to identify SDC-causing instructions, but they remain too slow for practical use and/or sacrifice accuracy to improve analysis speed. We develop Minotaur, a novel toolkit to improve the speed and accuracy of resiliency analysis. The key insight behind Minotaur is that modern resiliency analysis has many conceptual similarities to software testing; therefore, adapting techniques from the rich software testing literature can lead to principled and significant improvements in resiliency analysis. Minotaur identifies and adapts four concepts from software testing: 1) it introduces the concept of input quality criteria for resiliency analysis and identifies PC coverage as a simple but effective criterion; 2) it creates (fast) minimized inputs from (slow) standard benchmark inputs, using the input quality criteria to assess the goodness of the created input; 3) it adapts the concept of test case prioritization to prioritize error injections and invoke early termination for a given instruction to speed up error-injection campaigns; and 4) it further adapts test case or input prioritization to accelerate SDC discovery across multiple inputs. We evaluate Minotaur by applying it to Approxilyzer, a state-of-the-art resiliency analysis tool. Minotaur's first three techniques speed up Approxilyzer's resiliency analysis by 10.3X (on average) for the workloads studied. Moreover, they identify 96% (on average) of all SDC-causing instructions explored, compared to 64% identified by Approxilyzer alone. Minotaur's fourth technique (input prioritization) enables identifying all SDC-causing instructions explored across multiple inputs at a speed 2.3X faster (on average) than analyzing each input independently for our workloads.

Modern systems are increasingly susceptible to soft errors in the field and traditional redundancy-based mitigation techniques are too expensive to protect against all errors. Recent techniques, such as approximate computing and various low-cost resilience mechanisms, intelligently trade off inaccuracy in program output for better energy, performance, and resiliency overhead. A fundamental requirement for realizing the full potential of these techniques is a thorough understanding of how applications react to errors. Approxilyzer is a state-of-the-art tool that enables an accurate, efficient, and comprehensive analysis of how errors in almost all dynamic instructions in a program's execution affect the quality of the final program output. While useful, its adoption is limited by its implementation using the proprietary Simics infrastructure and the SPARC ISA. We present gem5-Approxilyzer, a re-implementation of Approxilyzer using the open-source gem5 simulator. gem5-Approxilyzer can be extended to different ISAs, starting with x86 in this work. We show that gem5-Approxilyzer is both efficient (up to two orders of magnitude reduction in error injections over a naive campaign) and accurate (average 92% for our experiments) in predicting the program's output quality in the presence of errors. We also compare the error profiles of five workloads under x86 and SPARC to further motivate the need for a tool like gem5-Approxilyzer..

In this work, we examine the resiliency of a state-of-the-art end-to-end video summarization (VS) application that serves as a representative emerging workload in the domain of real time edge computing. The VS application constitutes key video and image analytic elements that are processed by embedded systems aboard unmanned aerial vehicles (UAVs). Real-time performance and energy constraints motivate the consideration of approximations to the VS algorithm. However, mission-critical UAV applications also demand stringent levels of resilience to soft errors that are exacerbated with higher altitude. In this work, we study the effects of three different types of software approximations on the application level resiliency (to soft errors) of the VS algorithm. We show that our approximations yield significant energy savings (up to 68%), with commensurate improvement in performance, without a degradation in the application resilience. Further, by proposing a novel quality metric (appropriate for the UAV vision analytics domain) for the summarized video output, we show that even though the rate of Silent Data Corruptions (SDCs) increases slightly (<2%), the impact of these SDCs on output quality is limited. Thus, we conclude that software approximation can be utilized to achieve significant gains in performance and energy without affecting application resiliency.

Approximate computing environments trade off computational accuracy for improvements in performance, energy, and resiliency cost. For widespread adoption of approximate computing, a fundamental requirement is to understand how perturbations to a computation affect the outcome of the execution in terms of its output quality. This paper presents a framework for approximate computing, called Approxilyzer, that quantifies the quality impact of a single-bit error in all dynamic instructions of an execution with high accuracy (95% on average). We demonstrate two uses of Approxilyzer. First, we show how Approxilyzer can be used to quantitatively tune output quality vs. resiliency vs. overhead to enable ultra-low cost resiliency solutions (with a single bit error model). For example, we show that Approxilyzer determines that a very small loss in output quality (1%) can yield large resiliency overhead reduction (up to 55%) for 99% resiliency coverage. Second, we show how Approxilyzer can be used to provide a first-order estimate of the approximation potential of general-purpose programs. It does so in an automated way while requiring minimal user input and no program modifications. This enables programmers or other tools to focus on the promising subset of approximable instructions for further analysis.

As technology scales, the hardware reliability challenge affects a broad computing market, rendering traditional redundancy based solutions too expensive. Software anomaly based hardware error detection has emerged as a low cost reliability solution, but suffers from Silent Data Corruptions (SDCs). It is crucial to accurately evaluate SDC rates and identify SDC producing software locations to develop software-centric low-cost hardware resiliency solutions.