Dilip Kumar Krishnappa

Bio: Dilip Kumar Krishnappa is an academic researcher from University of Massachusetts Amherst. The author has contributed to research in topics: Cloud computing & Cache. The author has an hindex of 12, co-authored 18 publications receiving 477 citations. Previous affiliations of Dilip Kumar Krishnappa include Akamai Technologies.

Low-power sub-threshold design of secure physical unclonable functions

Abstract: The unique and unpredictable nature of silicon enables the use of physical unclonable functions (PUFs) for chip identification and authentication. Since the function of PUFs depends on minute uncontrollable process variations, a low supply voltage can benefit PUFs by providing high sensitivity to variations and low power consumption as well. Motivated by this, we explore the feasibility of sub-threshold arbiter PUFs in 45nm CMOS technology. By modeling process variations and interconnect imbalance effects at the post-layout design level, we optimize the PUF supply voltage for the minimum power-delay product and investigate the trade-offs on PUF uniqueness and reliability. Moreover, we demonstrate that such a design optimization does not compromise the security of PUFs regarding modeling attacks and side-channel analysis attacks. Our final 64-stage sub-threshold PUF design only needs 418 gates and consumes 0.047 pJ energy per cycle, which is very promising for low-power wireless sensing and security applications.

Cache-Centric Video Recommendation: An Approach to Improve the Efficiency of YouTube Caches

Abstract: In this article, we take advantage of the user behavior of requesting videos from the top of the related list provided by YouTube to improve the performance of YouTube caches. We recommend that local caches reorder the related lists associated with YouTube videos, presenting the cached content above noncached content. We argue that the likelihood that viewers select content from the top of the related list is higher than selection from the bottom, and pushing contents already in the cache to the top of the related list would increase the likelihood of choosing cached content. To verify that the position on the list really is the selection criterion more dominant than the content itself, we conduct a user study with 40 YouTube-using volunteers who were presented with random related lists in their everyday YouTube use. After confirming our assumption, we analyze the benefits of our approach by an investigation that is based on two traces collected from a university campus. Our analysis shows that the proposed reordering approach for related lists would lead to a 2 to 5 times increase in cache hit rate compared to an approach without reordering the related list. This increase in hit rate would lead to reduction in server load and backend bandwidth usage, which in turn reduces the latency in streaming the video requested by the viewer and has the potential to improve the overall performance of YouTube's content distribution system. An analysis of YouTube's recommendation system reveals that related lists are created from a small pool of videos, which increases the potential for caching content from related lists and reordering based on the content in the cache.

On the feasibility of prefetching and caching for online TV services: a measurement study on hulu

Abstract: Lately researchers are looking at ways to reduce the delay on video playback through mechanisms like prefetching and caching for Videoon-Demand (VoD) services. The usage of prefetching and caching also has the potential to reduce the amount of network bandwidth usage, as most popular requests are served from a local cache rather than the server containing the original content. In this paper, we investigate the advantages of having such a prefetching and caching scheme for a free hosting service of professionally created video (movies and TV shows) named "hulu". We look into the advantages of using a prefetching scheme where the most popular videos of the week, as provided by the hulu website, are prefetched and compare this approach with a conventional LRU caching scheme with limited storage space and a combined scheme of prefetching and caching. Results from our measurement and analysis shows that employing a basic caching scheme at the proxy yields a hit ratio of up to 77.69%, but requires storage of about 236GB. Further analysis shows that a prefetching scheme where the top-100 popular videos of the week are downloaded to the proxy yields a hit ratio of 44% with a storage requirement of 10GB. A LRU caching scheme with a storage limitation of 20GB can achieve a hit ratio of 55% but downloads 4713 videos to achieve such high hit ratio compared to 100 videos in prefetching scheme, whereas a scheme with both prefetching and caching with the same storage yields a hit ratio of 59% with download requirement of 4439 videos. We find that employing a scheme of prefetching along with caching with trade-off on the storage will yield a better hit ratio and bandwidth saving than individual caching or prefetching schemes.

Design and Validation of Arbiter-Based PUFs for Sub-45-nm Low-Power Security Applications

Abstract: Harnessing unique physical properties of integrated circuits to enhance hardware security and IP protection has been extensively explored in recent years. Physical unclonable functions (PUFs) can sense inherent manufacturing variations as chip identifications. To enable the integration of PUFs into low-power and security applications, we study the impacts of process technology and supply voltage scaling on arbiter-based PUF circuit design. A Monte Carlo-based statistical analysis has demonstrated that advanced technologies and reduced supply voltage can improve the PUF uniqueness due to increased delay sensitivity. A linear regression approach has been leveraged to generate PUF delay profile by factoring in device, supply voltage and temperature variations. An accurate SVM-based software modeling analysis is used to verify the PUF additive delay behavior. Finally, postsilicon validation on arbiter-based PUF test chips in 45 nm SOICMOS technology has been correlated to simulation results and the inconsistency has been discussed. The test chips can resist the basic support vector machine attack due to the dynamic circuit effects and the limitation of our delay model.

DASHing YouTube: An analysis of using DASH in YouTube video service

Abstract: Dynamic Adaptive Streaming over HTTP (DASH) is a new streaming standard which adaptively streams video based on the link bandwidth between server and client. DASH encoded videos are chunked in small segments and each segment can have different representations. Switching between these representations enables adaptive streaming, which has the potential to reduce bandwidth consumption in cases where a video is not completely watched. In this paper, we present an analysis on the advantages and disadvantages of using DASH as YouTube's video streaming format. To perform this analysis, we make use of a YouTube video trace and analyze the potential reduction in bandwidth consumption by employing DASH in YouTube, based on user watching patterns. Results from our analysis show that by employing DASH with a segment interval of 2 seconds, we can obtain 95% reduction in bandwidth for low quality videos and up to 83% reduction for HD videos in cases where users do not watch videos completely, which is the case for ~ 42% of all video requests in our trace. Considering all videos requested in the trace the overall bandwidth reduction is 40% for low quality videos and 35% for HD videos.

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

Unreeling netflix: Understanding and improving multi-CDN movie delivery

Abstract: Netflix is the leading provider of on-demand Internet video streaming in the US and Canada, accounting for 29.7% of the peak downstream traffic in US. Understanding the Netflix architecture and its performance can shed light on how to best optimize its design as well as on the design of similar on-demand streaming services. In this paper, we perform a measurement study of Netflix to uncover its architecture and service strategy. We find that Netflix employs a blend of data centers and Content Delivery Networks (CDNs) for content distribution. We also perform active measurements of the three CDNs employed by Netflix to quantify the video delivery bandwidth available to users across the US. Finally, as improvements to Netflix's current CDN assignment strategy, we propose a measurement-based adaptive CDN selection strategy and a multiple-CDN-based video delivery strategy, and demonstrate their potentials in significantly increasing user's average bandwidth.

Physically Unclonable Functions: Constructions, Properties and Applications

Abstract: Physically unclonable functions (PUFs) are innovative physical security primitives that produce unclonable and inherent instance-specific measurements of physical objects; in many ways they are the inanimate equivalent of biometrics for human beings. Since they are able to securely generate and store secrets, they allow us to bootstrap the physical implementation of an information security system. In this book the author discusses PUFs in all their facets: the multitude of their physical constructions, the algorithmic and physical properties which describe them, and the techniques required to deploy them in security applications. The author first presents an extensive overview and classification of PUF constructions, with a focus on so-called intrinsic PUFs. He identifies subclasses, implementation properties, and design techniques used to amplify submicroscopic physical distinctions into observable digital response vectors. He lists the useful qualities attributed to PUFs and captures them in descriptive definitions, identifying the truly PUF-defining properties in the process, and he also presents the details of a formal framework for deploying PUFs and similar physical primitives in cryptographic reductions. The author then describes a silicon test platform carrying different intrinsic PUF structures which was used to objectively compare their reliability, uniqueness, and unpredictability based on experimental data. In the final chapters, the author explains techniques for PUF-based entity identification, entity authentication, and secure key generation. He proposes practical schemes that implement these techniques, and derives and calculates measures for assessing different PUF constructions in these applications based on the quality of their response statistics. Finally, he presents a fully functional prototype implementation of a PUF-based cryptographic key generator, demonstrating the full benefit of using PUFs and the efficiency of the processing techniques described. This is a suitable introduction and reference for security researchers and engineers, and graduate students in information security and cryptography.

Video-aware scheduling and caching in the radio access network

Abstract: In this paper, we introduce distributed caching of videos at the base stations of the Radio Access Network (RAN) to significantly improve the video capacity and user experience of mobile networks. To ensure effectiveness of the massively distributed but relatively small-sized RAN caches, unlike Internet content delivery networks (CDNs) that can store millions of videos in a relatively few large-sized caches, we propose RAN-aware reactive and proactive caching policies that utilize User Preference Profiles (UPPs) of active users in a cell. Furthermore, we propose video-aware backhaul and wireless channel scheduling techniques that, in conjunction with edge caching, ensure maximizing the number of concurrent video sessions that can be supported by the end-to-end network while satisfying their initial delay requirements and minimize stalling. To evaluate our proposed techniques, we developed a statistical simulation framework using MATLAB and performed extensive simulations under various cache sizes, video popularity and UPP distributions, user dynamics, and wireless channel conditions. Our simulation results show that RAN caches using UPP-based caching policies, together with video-aware backhaul scheduling, can improve capacity by 300% compared to having no RAN caches, and by more than 50% compared to RAN caches using conventional caching policies. The results also demonstrate that using UPP-based RAN caches can significantly improve the probability that video requests experience low initial delays. In networks where the wireless channel bandwidth may be constrained, application of our videoaware wireless channel scheduler results in significantly (up to 250%) higher video capacity with very low stalling probability.

PUFs: myth, fact or busted? a security evaluation of physically unclonable functions (PUFs) cast in silicon

Abstract: Physically Unclonable Functions (PUFs) are an emerging technology and have been proposed as central building blocks in a variety of cryptographic protocols and security architectures. However, the security features of PUFs are still under investigation: Evaluation results in the literature are difficult to compare due to varying test conditions, different analysis methods and the fact that representative data sets are publicly unavailable. In this paper, we present the first large-scale security analysis of ASIC implementations of the five most popular intrinsic electronic PUF types, including arbiter, ring oscillator, SRAM, flip-flop and latch PUFs. Our analysis is based on PUF data obtained at different operating conditions from 96 ASICs housing multiple PUF instances, which have been manufactured in TSMC 65 nm CMOS technology. In this context, we present an evaluation methodology and quantify the robustness and unpredictability properties of PUFs. Since all PUFs have been implemented in the same ASIC and analyzed with the same evaluation methodology, our results allow for the first time a fair comparison of their properties.