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Anupam Chattopadhyay

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Published work

14 published item(s)

preprint2026arXiv

Vaporizer: Breaking Watermarking Schemes for Large Language Model Outputs

In this paper, we investigate the recent state-of-the-art schemes for watermarking large language models (LLMs) outputs. These techniques are claimed to be robust, scalable and production-grade, aimed at promoting responsible usage of LLMs. We analyse the effectiveness of these watermarking techniques against an extensive collection of modified text attacks, which perform targeted semantic changes without altering the general meaning of the text content. Our approach encompasses multiple attack strategies, which include lexical alterations, machine translation, and even neural paraphrasing. The attack efficacy is measured with two target criteria - successful removal of the watermark and preservation of semantic content. We evaluate semantic preservation through BERT scores, text complexity measures, grammatical errors, and Flesch Reading Ease indices. The experimental results reveal varying levels of effectiveness among different watermarking models, with the same underlying result that it is possible to remove the watermark with reasonable effort. This study sheds light on the strengths and weaknesses of existing LLM watermarking systems, suggesting how they should be constructed to improve security of available schemes.

preprint2022arXiv

Intermediate Qutrit-based Improved Quantum Arithmetic Operations with Application on Financial Derivative Pricing

In some quantum algorithms, arithmetic operations are of utmost importance for resource estimation. In binary quantum systems, some efficient implementation of arithmetic operations like, addition/subtraction, multiplication/division, square root, exponential and arcsine etc. have been realized, where resources are reported as a number of Toffoli gates or T gates with ancilla. Recently it has been demonstrated that intermediate qutrits can be used in place of ancilla, allowing us to operate efficiently in the ancilla-free frontier zone. In this article, we have incorporated intermediate qutrit approach to realize efficient implementation of all the quantum arithmetic operations mentioned above with respect to gate count and circuit-depth without T gate and ancilla. Our resource estimates with intermediate qutrits could guide future research aimed at lowering costs considering arithmetic operations for computational problems. As an application of computational problems, related to finance, are poised to reap the benefit of quantum computers, in which quantum arithmetic circuits are going to play an important role. In particular, quantum arithmetic circuits of arcsine and square root are necessary for path loading using the re-parameterization method, as well as the payoff calculation for derivative pricing. Hence, the improvements are studied in the context of the core arithmetic circuits as well as the complete application of derivative pricing. Since our intermediate qutrit approach requires to access higher energy levels, making the design prone to errors, nevertheless, we show that the percentage decrease in the probability of error is significant owing to the fact that we achieve circuit robustness compared to qubit-only works.

preprint2022arXiv

Optimal Codeword Construction for DNA-based Finite Automata

Biomolecular computation has emerged as an important area of computer science research due to its high information density, immense parallelism opportunity along with potential applications in cryptography, genetic engineering and bioinformatics. Computational frameworks using DNA molecules have been proposed in the literature to accomplish varied tasks such as simulating logical operations, performing matrix multiplication, and encoding instances of NP-hard problems. In one of the key applications, several studies have proposed construction of finite automata using DNA hybridisation and ligation. The state and symbol encoding of these finite automata are done manually. In this manuscript, we study the codeword construction problem for this approach. We derive exact theoretical bounds on the number of symbols and states in the finite automata and also obtain the complete set of symbols in a specific case. For automatic encoding, two different solutions, based on a heuristic and on Integer Linear Programming (ILP), are proposed. Furthermore, we propose an early simulation-based validation of laboratory experiments. Our proposed flow accepts a finite automaton, automatically encodes the symbols for the actual experiments and executes the simulation step-by-step.

preprint2022arXiv

PA-PUF: A Novel Priority Arbiter PUF

This paper proposes a 3-input arbiter-based novel physically unclonable function (PUF) design. Firstly, a 3-input priority arbiter is designed using a simple arbiter, two multiplexers (2:1), and an XOR logic gate. The priority arbiter has an equal probability of 0's and 1's at the output, which results in excellent uniformity (49.45%) while retrieving the PUF response. Secondly, a new PUF design based on priority arbiter PUF (PA-PUF) is presented. The PA-PUF design is evaluated for uniqueness, non-linearity, and uniformity against the standard tests. The proposed PA-PUF design is configurable in challenge-response pairs through an arbitrary number of feed-forward priority arbiters introduced to the design. We demonstrate, through extensive experiments, reliability of 100% after performing the error correction techniques and uniqueness of 49.63%. Finally, the design is compared with the literature to evaluate its implementation efficiency, where it is clearly found to be superior compared to the state-of-the-art.

preprint2020arXiv

CONTRA: Area-Constrained Technology Mapping Framework For Memristive Memory Processing Unit

Data-intensive applications are poised to benefit directly from processing-in-memory platforms, such as memristive Memory Processing Units, which allow leveraging data locality and performing stateful logic operations. Developing design automation flows for such platforms is a challenging and highly relevant research problem. In this work, we investigate the problem of minimizing delay under arbitrary area constraint for MAGIC-based in-memory computing platforms. We propose an end-to-end area constrained technology mapping framework, CONTRA. CONTRA uses Look-Up Table(LUT) based mapping of the input function on the crossbar array to maximize parallel operations and uses a novel search technique to move data optimally inside the array. CONTRA supports benchmarks in a variety of formats, along with crossbar dimensions as input to generate MAGIC instructions. CONTRA scales for large benchmarks, as demonstrated by our experiments. CONTRA allows mapping benchmarks to smaller crossbar dimensions than achieved by any other technique before, while allowing a wide variety of area-delay trade-offs. CONTRA improves the composite metric of area-delay product by 2.1x to 13.1x compared to seven existing technology mapping approaches.

preprint2020arXiv

FlexWatts: A Power- and Workload-Aware Hybrid Power Delivery Network for Energy-Efficient Microprocessors

Modern client processors typically use one of three commonly-used power delivery network (PDN): 1) motherboard voltage regulators (MBVR), 2) integrated voltage regulators (IVR), and 3) low dropout voltage regulators (LDO). We observe that the energy-efficiency of each of these PDNs varies with the processor power (e.g., thermal design power (TDP) and dynamic power-state) and workload characteristics. This leads to energy inefficiency and performance loss, as modern client processors operate across a wide spectrum of power consumption and execute a wide variety of workloads. We propose FlexWatts, a hybrid adaptive PDN for modern client processors whose goal is to provide high energy-efficiency across the processor's wide range of power consumption and workloads by dynamically allocating PDNs to processor domains. FlexWatts is based on three key ideas. First, it combines IVRs and LDOs in a novel way to share multiple on-chip and off-chip resources. This hybrid PDN is allocated for processor domains with a wide power consumption range and it dynamically switches between two modes: IVR-Mode and LDO-Mode, depending on the power consumption. Second, for all other processor domains, FlexWatts statically allocates off-chip VRs. Third, FlexWatts introduces a prediction algorithm that switches the hybrid PDN to the mode that is the most beneficial. To evaluate the tradeoffs of PDNs, we develop and open-source PDNspot, the first validated architectural PDN model that enables quantitative analysis of PDN metrics. Using PDNspot, we evaluate FlexWatts on a wide variety of SPEC CPU2006, 3DMark06, and battery life workloads against IVR, the state-of-the-art PDN in modern client processors. For a 4W TDP processor, FlexWatts improves the average performance of the SPEC CPU2006 and 3DMark06 workloads by 22% and 25%, respectively. FlexWatts has comparable cost and area overhead to IVR.

preprint2020arXiv

RAPPER: Ransomware Prevention via Performance Counters

Ransomware can produce direct and controllable economic loss, which makes it one of the most prominent threats in cyber security. As per the latest statistics, more than half of malwares reported in Q1 of 2017 are ransomwares and there is a potent threat of a novice cybercriminals accessing ransomware-as-a-service. The concept of public-key based data kidnapping and subsequent extortion was introduced in 1996. Since then, variants of ransomware emerged with different cryptosystems and larger key sizes, the underlying techniques remained same. Though there are works in literature which proposes a generic framework to detect the crypto ransomwares, we present a two step unsupervised detection tool which when suspects a process activity to be malicious, issues an alarm for further analysis to be carried in the second step and detects it with minimal traces. The two step detection framework- RAPPER uses Artificial Neural Network and Fast Fourier Transformation to develop a highly accurate, fast and reliable solution to ransomware detection using minimal trace points. We also introduce a special detection module for successful identification of disk encryption processes from potential ransomware operations, both having similar characteristics but with different objective. We provide a comprehensive solution to tackle almost all scenarios (standard benchmark, disk encryption and regular high computational processes) pertaining to the crypto ransomwares in light of software security.

preprint2016arXiv

Accelerating BLAS on Custom Architecture through Algorithm-Architecture Co-design

Basic Linear Algebra Subprograms (BLAS) play key role in high performance and scientific computing applications. Experimentally, yesteryear multicore and General Purpose Graphics Processing Units (GPGPUs) are capable of achieving up to 15 to 57% of the theoretical peak performance at 65W to 240W respectively for compute bound operations like Double/Single Precision General Matrix Multiplication (XGEMM). For bandwidth bound operations like Single/Double precision Matrix-vector Multiplication (XGEMV) the performance is merely 5 to 7% of the theoretical peak performance in multicores and GPGPUs respectively. Achieving performance in BLAS requires moving away from conventional wisdom and evolving towards customized accelerator tailored for BLAS through algorithm-architecture co-design. In this paper, we present acceleration of Level-1 (vector operations), Level-2 (matrix-vector operations), and Level-3 (matrix-matrix operations) BLAS through algorithm architecture co-design on a Coarse-grained Reconfigurable Architecture (CGRA). We choose REDEFINE CGRA as a platform for our experiments since REDEFINE can be adapted to support domain of interest through tailor-made Custom Function Units (CFUs). For efficient sequential realization of BLAS, we present design of a Processing Element (PE) and perform micro-architectural enhancements in the PE to achieve up-to 74% of the theoretical peak performance of PE in DGEMM, 40% in DGEMV and 20% in double precision inner product (DDOT). We attach this PE to REDEFINE CGRA as a CFU and show the scalability of our solution. Finally, we show performance improvement of 3-140x in PE over commercially available Intel micro-architectures, ClearSpeed CSX700, FPGA, and Nvidia GPGPUs.

preprint2016arXiv

Ancilla-free Reversible Logic Synthesis via Sorting

Reversible logic synthesis is emerging as a major research component for post-CMOS computing devices, in particular Quantum computing. In this work, we link the reversible logic synthesis problem to sorting algorithms. Based on our analysis, an alternative derivation of the worst-case complexity of generated reversible circuits is provided. Furthermore, a novel column-wise reversible logic synthesis method, termed RevCol, is designed with inspiration from radix sort. Extending the principles of RevCol, we present a hybrid reversible logic synthesis framework. The theoretical and experimental results are presented. The results are extensively benchmarked with state-of-the-art ancilla-free reversible logic synthesis methods.

preprint2016arXiv

Reversible Logic Circuit Complexity Analysis via Functional Decomposition

Reversible computation is gaining increasing relevance in the context of several post-CMOS technologies, the most prominent of those being Quantum computing. One of the key theoretical problem pertaining to reversible logic synthesis is the upper bound of the gate count. Compared to the known bounds, the results obtained by optimal synthesis methods are significantly less. In this paper, we connect this problem with the multiplicative complexity analysis of classical Boolean functions. We explore the possibility of relaxing the ancilla and if that approach makes the upper bound tighter. Our results are negative. The ancilla-free synthesis methods by using transformations and by starting from an Exclusive Sum-of-Product (ESOP) formulation remain, theoretically, the synthesis methods for achieving least gate count for the cases where the number of variables $n$ is $< 8$ and otherwise, respectively.

preprint2015arXiv

A Sound and Complete Axiomatization of Majority-n Logic

Manipulating logic functions via majority operators recently drew the attention of researchers in computer science. For example, circuit optimization based on majority operators enables superior results as compared to traditional logic systems. Also, the Boolean satisfiability problem finds new solving approaches when described in terms of majority decisions. To support computer logic applications based on majority a sound and complete set of axioms is required. Most of the recent advances in majority logic deal only with ternary majority (MAJ- 3) operators because the axiomatization with solely MAJ-3 and complementation operators is well understood. However, it is of interest extending such axiomatization to n-ary majority operators (MAJ-n) from both the theoretical and practical perspective. In this work, we address this issue by introducing a sound and complete axiomatization of MAJ-n logic. Our axiomatization naturally includes existing majority logic systems. Based on this general set of axioms, computer applications can now fully exploit the expressive power of majority logic.

preprint2014arXiv

Ancilla-Quantum Cost Trade-off during Reversible Logic Synthesis using Exclusive Sum-of-Products

Emerging technologies with asymptotic zero power dissipation, such as quantum computing, require the logical operations to be done in a reversible manner. In recent years, the problem of synthesizing Boolean functions in the reversible logic domain has gained significant research attention. The efficiency of the synthesis methods is measured in terms of quantum cost, gate cost, garbage lines, logic depth and speed of synthesis. In this paper, we present an approach based on Exclusive sum-of-Products (ESOP), which allows the user to explore the trade-off between quantum cost and garbage lines. The proposed technique adds a new dimension to the reversible logic synthesis solutions. We demonstrate by detailed experiments that controlled improvement in quantum cost and gate count by increasing garbage count can be achieved. In some cases, improved quantum cost and gate count compared to state-of-the-art synthesis methods are reported. Furthermore, we propose a novel rule-based approach to achieve ancilla-free reversible logic synthesis starting from an ESOP formulation.

preprint2014arXiv

Complexity Analysis of Reversible Logic Synthesis

Reversible logic circuit is a necessary construction for achieving ultra low power dissipation as well as for prominent post-CMOS computing technologies such as Quantum computing. Consequently automatic synthesis of a Boolean function using elementary reversible logic gates has received significant research attention in recent times, creating the domain of reversible logic synthesis. In this paper, we study the complexity of reversible logic synthesis. The problem is separately studied for bounded-ancilla and ancilla-free optimal synthesis approaches. The computational complexity for both cases are linked to known/presumed hard problems. Finally, experiments are performed with a shortest-path based reversible logic synthesis approach and a (0-1) ILP-based formulation.

preprint2013arXiv

Designing Parity Preserving Reversible Circuits

Making a reversible circuit fault-tolerant is much more difficult than classical circuit and there have been only a few works in the area of parity-preserving reversible logic design. Moreover, all of these designs are ad hoc, based on some pre-defined parity preserving reversible gates as building blocks. In this paper, we for the first time propose a novel and systematic approach towards parity preserving reversible circuits design. We provide some related theoretical results and give two algorithms, one from reversible specification to parity preserving reversible specification and another from irreversible specification to parity preserving reversible specification. We also evaluate the effectiveness of our approach by extensive experimental results.