Srinivas Devadas

Bio: Srinivas Devadas is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Sequential logic & Combinational logic. The author has an hindex of 88, co-authored 480 publications receiving 31897 citations. Previous affiliations of Srinivas Devadas include University of California, Berkeley & Cornell University.

Offline Integrity Checking of Untrusted Storage

Abstract: We extend the offline memory correctness checking scheme presented by Blum et. al [BEG91] to develop an offline checker that can detect attacks by active adversaries. We introduce the concept of incremental multiset hashes, and detail one example: MSet-XOR MAC, which uses a secret key, and is efficient as updating the hash costs a few hash and XOR operations. Using multiset hashes as our underlying cryptographic tool, we introduce a primitive, bag integrity checking, to explain offline integrity checking; we demonstrate how this primitive can be used to build cryptographically secure integrity checking schemes for random access memories and disks. Recent papers describe processors, file systems, and databases in which hash trees are used to verify the integrity of data in untrusted storage. Checkers using hash trees are referred to as online checkers, as the trees are used to check, after each operation, whether the storage behaved correctly. The offline checker we describe is designed for checking sequences of operations on an untrusted storage, and, for some applications, performs better and uses less space than a checker using a hash tree. In this paper, we also introduce a hybrid checker, which can capture the best of both the online and offline schemes. The hybrid checker can operate mainly as an online checker when integrity checks need to be performed frequently, and as an offline checker when checks can be performed less frequently. The performance of the checker is expected to be close to the better scheme for every checking period.

Tardis 2.0: Optimized Time Traveling Coherence for Relaxed Consistency Models

Abstract: Cache coherence scalability is a big challenge in shared memory systems. Traditional protocols do not scale due to the storage and traffic overhead of cache invalidation. Tardis, a recently proposed coherence protocol, removes cache invalidation using logical timestamps and achieves excellent scalability. The original Tardis protocol, however, only supports the Sequential Consistency (SC) memory model, limiting its applicability. Tardis also incurs extra network traffic on some benchmarks due to renew messages, and has suboptimal performance when the program uses spinning to communicate between threads. In this paper, we address these downsides of Tardis protocol and make it significantly more practical. Specifically, we discuss the architectural, memory system and protocol changes required in order to implement the TSO consistency model on Tardis, and prove that the modified protocol satisfies TSO. We also describe modifications for Partial Store Order (PSO) and Release Consistency (RC). Finally, we propose optimizations for better leasing policies and to handle program spinning. On a set of benchmarks, optimized Tardis improves on a full-map directory protocol in the metrics of performance, storage and network traffic, while being simpler to implement.

Probabilistic construction and manipulation of free Boolean diagrams

Abstract: We propose a data structure for Boolean functions termed the Free Boolean Diagram (FBD). We extend a previous result to show that the equivalence of two Free Boolean Diagrams can be decided probabilistically in polynomial time. Based on the equivalence checking method, we develop a set of algorithms for the probabilistic construction of Free Boolean Diagrams from multilevel combinational logic circuits, and for their manipulation. These algorithms are modified versions of ordered Binary Decision Diagram manipulation methods. We provide the implementation details of a Free Boolean Diagram package. Results on applying this package to problems in combinational logic verification are presented.

Path-Diverse In-Order Routing

Abstract: We present Path-Diverse In-Order Routing (PDIOR), an oblivious routing method which guarantees network-level inorder delivery for multi-path routing. Based on Exclusive Dynamic Virtual Channel Allocation (EDVCA), which allows single-path efficient inorder delivery with dynamic virtual channel allocation, PDIOR extends the same guarantees to routing schemes where each flow may be routed via more than one path. As with EDVCA, PDIOR avoids the overheads inherent in reordering packets at the destination core, and requires only minor, inexpensive changes to traditional oblivious router architectures: for example, an implementation of PDIOR on 8×8 mesh network with 4 VCs per port requires 492 bytes of memory per node, while inorder packet delivery in a comparable conventional network may requires tens to hundreds of kilobytes of reorder buffer memory at each node.

The Execution Migration Machine: Directoryless Shared-Memory Architecture

Abstract: For certain applications involving chip multiprocessors with more than 16 cores, a directoryless architecture with fine-grained and partial-context thread migration can outperform directory-based coherence, providing lighter on-chip traffic and reduced verification complexity.

TaintDroid: An Information-Flow Tracking System for Realtime Privacy Monitoring on Smartphones

Abstract: Today’s smartphone operating systems frequently fail to provide users with visibility into how third-party applications collect and share their private data. We address these shortcomings with TaintDroid, an efficient, system-wide dynamic taint tracking and analysis system capable of simultaneously tracking multiple sources of sensitive data. TaintDroid enables realtime analysis by leveraging Android’s virtualized execution environment. TaintDroid incurs only 32p performance overhead on a CPU-bound microbenchmark and imposes negligible overhead on interactive third-party applications. Using TaintDroid to monitor the behavior of 30 popular third-party Android applications, in our 2010 study we found 20 applications potentially misused users’ private information; so did a similar fraction of the tested applications in our 2012 study. Monitoring the flow of privacy-sensitive data with TaintDroid provides valuable input for smartphone users and security service firms seeking to identify misbehaving applications.

TaintDroid: an information-flow tracking system for realtime privacy monitoring on smartphones

Abstract: Today's smartphone operating systems frequently fail to provide users with adequate control over and visibility into how third-party applications use their private data. We address these shortcomings with TaintDroid, an efficient, system-wide dynamic taint tracking and analysis system capable of simultaneously tracking multiple sources of sensitive data. TaintDroid provides realtime analysis by leveraging Android's virtualized execution environment. TaintDroid incurs only 14% performance overhead on a CPU-bound micro-benchmark and imposes negligible overhead on interactive third-party applications. Using TaintDroid to monitor the behavior of 30 popular third-party Android applications, we found 68 instances of potential misuse of users' private information across 20 applications. Monitoring sensitive data with TaintDroid provides informed use of third-party applications for phone users and valuable input for smartphone security service firms seeking to identify misbehaving applications.

Symbolic Boolean manipulation with ordered binary-decision diagrams

Abstract: Ordered Binary-Decision Diagrams (OBDDs) represent Boolean functions as directed acyclic graphs. They form a canonical representation, making testing of functional properties such as satisfiability and equivalence straightforward. A number of operations on Boolean functions can be implemented as graph algorithms on OBDD data structures. Using OBDDs, a wide variety of problems can be solved through symbolic analysis. First, the possible variations in system parameters and operating conditions are encoded with Boolean variables. Then the system is evaluated for all variations by a sequence of OBDD operations. Researchers have thus solved a number of problems in digital-system design, finite-state system analysis, artificial intelligence, and mathematical logic. This paper describes the OBDD data structure and surveys a number of applications that have been solved by OBDD-based symbolic analysis.

Physical unclonable functions for device authentication and secret key generation

Abstract: Physical Unclonable Functions (PUFs) are innovative circuit primitives that extract secrets from physical characteristics of integrated circuits (ICs). We present PUF designs that exploit inherent delay characteristics of wires and transistors that differ from chip to chip, and describe how PUFs can enable low-cost authentication of individual ICs and generate volatile secret keys for cryptographic operations.