Split Manufacturing Research Articles

Assessing the Impact of IOS Scanning Accuracy on Additively Manufactured Occlusal Splints.

Introduction: Digital workflow and intraoral scanners (IOSs) are used to clinically obtain data for a wide range of applications in restorative dentistry. The study aimed to compare two different IOSs with inexperienced users in the digital workflow of oral split manufacturing. Material and Methods: Anonymous stone models of upper and lower dentate patients were used. Both models were scanned with a desktop 3D scanner 3Shape D2000 to obtain the reference models (STLR). Ten inexperienced operators scanned each model three times with each IOS system (3Shape TRIOS 3 and Carestream CS 3800). Finally, 20 intraoral scanners were randomly chosen from the obtained dataset (10 per IOS system) to design and manufacture 20 nightguards. All the nightguards were scanned. Trueness and precision were calculated and compared between the two IOS systems. Results: All the mean errors both for trueness and precision were below 40 µm, more than acceptable for the design and manufacturing of intraoral devices such as nightguards. All the mean errors (except one) for trueness between the inner part of the nightguards and the upper control model were below 100 µm, less than a printed layer height. For inexperienced operators, both IOSs are suitable for a digital workflow of manufacturing occlusal splints.

Hardware Trojan prevention using memristor technology

The design of modern integrated circuits includes many steps and different entities providing opportunities to adversaries for Trojan injection or IP (intellectual property) piracy at different design levels. Hardware Trojans and IP piracy are the new realities that must be taken into consideration for trustworthy integrated circuit design. In this work, a new method utilizing memristor technology is presented to implement a configurable layout to obfuscate the design. In the proposed solution, the main design is divided into clusters of sub-circuits in which interconnects between the clusters are not known to anyone other than the designer. The clusters are then connected through configurable memristor switches. In the proposed solution, split manufacturing is not needed, and the integrated circuit/IP core can be fabricated by an untrusted foundry without compromising the security. Moreover, the clustering technique provides direct access to the sub-circuits through the network of configurable switches. This will increase the observability and controllability in the test phase and assists the detection and isolation of possible Trojans.

FSM Inspired Unconventional Hardware Watermark Using Field-Assisted SOT-MTJ

The globalization of the Integrated Circuits supply chain has increased threats from untrusted entities involved in the process. Several mechanisms, such as logic locking, watermarking and split manufacturing, are widely used to ensure hardware security. This study describes a novel method for creating hardware watermarks inspired by finite-state machines. It makes use of the unique physical property of magnetic tunnel junctions that are based on spin-orbit torque. The design strategy is described in detail, including the use of an EDA tool to analyze and take advantage of the unique switching properties of MTJ, their non-volatility, and their reliance on an external magnetic field to direct information through a predetermined order of states in a manner akin to an FSM. Furthermore, the performance prospects are analyzed using Monte Carlo simulations. For the 5% and 10% of process variation in the key MTJ parameters, the accuracy of 100% and 99.80%, respectively, are achieved. In control signal voltage variation, a tolerance of 9% (0.91V) is observed. The required state transition is not altered, demonstrating a tolerable sensitivity to temperature variation from 250K to 350K. The security aspects and methodology for the approach are explained to ensure a more robust and practical application, and finally, a comparison is made with other FSM-based watermarks.

ObfusX: Routing obfuscation with explanatory analysis of a machine learning attack

This is the first work that incorporates recent advancements in “explainability” of machine learning (ML) to build a routing obfuscator called ObfusX. We adopt a recent metric—the SHAP value—which explains to what extent each layout feature can reveal each unknown connection for a recent ML-based split manufacturing attack model. The unique benefits of SHAP-based analysis include the ability to identify the best candidates for obfuscation, together with the dominant layout features which make them vulnerable. As a result, ObfusX can achieve better hit rate (97% lower) while perturbing significantly fewer nets when obfuscating using a via perturbation scheme, compared to prior work. When imposing the same wirelength limit using a wire lifting scheme, ObfusX performs significantly better in performance metrics (e.g., 2.2 times more reduction on average in percentage of netlist recovery).

A New Paradigm in Split Manufacturing: Lock the FEOL, Unlock at the BEOL

Split manufacturing was introduced as a countermeasure against hardware-level security threats such as IP piracy, overbuilding, and insertion of hardware Trojans. However, the security promise of split manufacturing has been challenged by various attacks which exploit the well-known working principles of design tools to infer the missing back-end-of-line (BEOL) interconnects. In this work, we define the security of split manufacturing formally and provide the associated proof, and we advocate accordingly for a novel, formally secure paradigm. Inspired by the notion of logic locking, we protect the front-end-of-line (FEOL) layout by embedding secret keys which are implemented through the BEOL in such a way that they become indecipherable to foundry-based attacks. At the same time, our technique is competitive with prior art in terms of layout overhead, especially for large-scale designs (ITC’99 benchmarks). Furthermore, another concern for split manufacturing is its practicality (despite successful prototyping). Therefore, we promote an alternative implementation strategy, based on package-level routing, which enables formally secure IP protection without splitting at all, and thus, without the need for a dedicated BEOL facility. We refer to this as “poor man’s split manufacturing” and we study the practicality of this approach by means of physical-design exploration.

A Modern Approach to IP Protection and Trojan Prevention: Split Manufacturing for 3D ICs and Obfuscation of Vertical Interconnects

Split manufacturing (SM) and layout camouflaging (LC) are two promising techniques to obscure integrated circuits (ICs) from malicious entities during and after manufacturing. While both techniques enable protecting the intellectual property (IP) of ICs, SM can further mitigate the insertion of hardware Trojans (HTs). In this paper, we strive for the "best of both worlds," that is we seek to combine the individual strengths of SM and LC. By jointly extending SM and LC techniques toward 3D integration, an up-and-coming paradigm based on stacking and interconnecting of multiple chips, we establish a modern approach to hardware security. Toward that end, we develop a security-driven CAD and manufacturing flow for 3D ICs in two variations, one for IP protection and one for HT prevention. Essential concepts of that flow are (i) "3D splitting" of the netlist to protect, (ii) obfuscation of the vertical interconnects (i.e., the wiring between stacked chips), and (iii) for HT prevention, a security-driven synthesis stage. We conduct comprehensive experiments on DRC-clean layouts of multi-million-gate DARPA and OpenCores designs (and others). Strengthened by extensive security analysis for both IP protection and HT prevention, we argue that entering the third dimension is eminent for effective and efficient hardware security.

Concerted Wire Lifting: Enabling Secure and Cost-Effective Split Manufacturing

In this work, we advance the security promise of split manufacturing through judicious handling of interconnects. First, we study the cost-security tradeoffs underlying for split manufacturing, which are limiting its adoption. Next, aiming to resolve these concerns, we propose three effective and efficient strategies to dedicatedly lift nets to higher metal layers. Toward this end, we design custom “elevating cells” and devise procedures for routing blockages. All our techniques are employed in a commercial-grade computer-aided design (CAD) framework. For our security analysis, we leverage various state-of-the-art attacks (network flow-based attack, routing-congestion-aware attack, and deep learning-based attack), established metrics (correct connection rate, output error rate, and Hamming distance), and advanced metrics (percentage of netlist recovery and mutual information). Our extensive experiments show that our scheme provides superior protection. Simultaneously, we induce reasonably low and controllable overheads on power and performance, without any silicon area costs. Besides, we support higher split layers, which helps to alleviate concerns on the practicality of split manufacturing.

On the Effect of the Gap of End Seals on Force Coefficients of a Test Integral Squeeze Film Damper: Experiments and Predictions

Abstract An integral squeeze film damper (ISFD) offers the advantages of a lower number of parts, a shorter axial span, a lighter weight, a split manufacturing, and high precision on its film clearance construction. An ISFD does not only add damping to reduce shaft vibration amplitudes and to enhance the stability of a rotor-bearing system but also can be used to tune a rotor-bearing system natural frequency, and thus increasing the operational safety margin between the running shaft speed and the system critical speed. In spite of the numerous commercial applications, the archival literature is scant as per the experimental quantification of force coefficients for ISFDs. This paper details the results of an experimental and analytical endeavor to quantify and to predict the dynamic force coefficients of an ISFD, hence bridging the gap between theory and practice. With an axial length of 76 mm, the test damper element has four arcuate film lands, 73 deg in arc extent at a diameter of 157 mm, and each with a clearance (c) equaling to 0.353 mm. As is customary, the damper has its axial ends sealed with end plates produced by a set of installed shims giving an axial gap (d) equal to 1.5c, 1.21c, and 0.8c. A baseline configuration, namely, open ends, is also tested without the end seals in place. In the test rig, the ISFD and its housing are flexibly mounted while the rotor is rigid and stationary (no spinning). The lubricant is an ISO VG46 oil supplied at a low pressure, 1 to 2 bar(g) and ∼47 °C inlet temperature, typical of compressor applications. The test procedure applies static loads on the ISFD and records the bearing static offset or eccentricity to verify the structure stiffness, and meanwhile, individual hydraulic shakers deliver dynamic loads along two orthogonal directions to produce motions over a set frequency range, 10 Hz to 160 Hz. The ISFD produces direct damping and inertia that increase with the journal static eccentricity albeit at a lower rate than predictions from a computational squeeze film flow model that includes lubricant compressibility. The end seals are effective in significantly raising the damping coefficient while reducing the oil through flow rate. The damper with the tightest sealed ends (d = 0.8c) shows nearly 20 times more damping that the open ends ISFD albeit also revealing a significant stiffness hardening (negative virtual mass) as the excitation frequency increases. On the contrary, the open ends ISFD and the sealed-ends configurations with gaps d = 1.21c and 1.5c produce a (positive) virtual mass that exceeds the test element physical mass and thus softens the test element direct dynamic stiffness. For the configurations with loose end seals (d = 1.21c or larger to open ends), the model predicts well the damping coefficients but under predicts the added masses by 50% or more. Note this virtual mass coefficient, largely ignored in practice, can make the test element either extremely stiff as with the sealed damper configuration with the smallest gap d = 0.8c, or very soft as with the ISFD with end seals gap = 1.21c or 1.5c. Hence, designers are cautioned not to pursue overly tight end sealed dampers as the mineral lubricant, nearly incompressible though always having a small amount of entrapped gas, may behave distinctly when confined to a squeezed film volume and having no adequate routes to escape or flow through.

Games, Dollars, Splits: A Game-Theoretic Analysis of Split Manufacturing

Split manufacturing has been proposed as a defense to prevent threats like intellectual property (IP) piracy and illegal overproduction of integrated circuits (ICs). Over the last few years, researchers have developed a plethora of attack and defense techniques, creating a cat-and-mouse game between defending designers and attacking foundries. In this paper, we take an orthogonal approach to this ongoing research in split manufacturing; rather than developing an attack or a defense technique, we propose a means to analyze different attack and defense techniques. To that end, we develop a game-theoretic framework that helps researchers evaluate their new and existing attack and defense techniques. We model two attack scenarios using two different types of games and obtain the optimal defense strategies. We perform extensive simulations with our proposed framework, using nine different attacks and a class of placement and routing-based defense techniques on various benchmarks to gain deeper insights into split manufacturing. For instance, our framework indicates that the optimal defense techniques in the two attack scenarios are the same. Moreover, larger benchmarks are secure by naive split manufacturing and do not require any additional defense technique under our cost model and considered attacks. We also uncover a counter-intuitive finding—an attacker using the network-flow attack should not use all the hints; instead, she should use only a subset.

Deep Learning Analysis for Split-Manufactured Layouts With Routing Perturbation

Split manufacturing of integrated circuits means to delegate the front-end-of-line (FEOL) and back-end-of-line (BEOL) parts to different foundries, in order to prevent overproduction, intellectual property (IP) piracy, or targeted insertion of hardware Trojans (i.e., threats arising from adversaries in the FEOL foundry). This article challenges the security promise of split manufacturing by formulating various layout-level placement and routing hints as vector-based and image-based features that enable a sophisticated deep neural network (DNN), which can infer the missing BEOL connections with high accuracy. Compared with the network-flow attack (Wang et al. , 2018), we achieve on average $1.21 \times $ and $1.12 \times $ of their correct connection rate (CCR; the higher, the better) when splitting after M1 and M3, respectively, with less than 1% of their runtime (across the same set of ISCAS-85 and ITC-99 benchmarks). Compared with Zeng et al. (2019), ours reduces the candidate list (the smaller, the better) by 47% with only 1% loss of accuracy, and we further achieve an average CCR of $2.2 \times $ of that of Zeng et al. (2019). Aside from these superior results, we propose a randomized, routing-blockage-centric defense strategy to escalate the resilience against our and other attacks. Our defense strategy, which can be integrated into any commercial design flow, leads on average to $22.78~pp$ (percentage points) degradation in CCR when compared with unprotected layouts, while inducing only 3.3% and 3.2% overheads on power and timing, respectively, within the same die outlines (i.e., zero area cost). The source code of our heterogeneous feature extraction is available at https://github.com/cuhk-eda/split-extract , and the source code of our DNN is available at https://github.com/cuhk-eda/split-attack .

Comparison of umbilical cord tissue-derived mesenchymal stromal cells isolated from cryopreserved material and extracted by explantation and digestion methods utilizing a split manufacturing model

Background aimsUmbilical cord (UC) tissue is recognized as an advantageous source of mesenchymal stromal cells (MSCs), whose therapeutic properties are being actively evaluated in pre-clinical and clinical trials. In recognition of its potential value, storage of UC tissue or cells from UC tissue in newborn stem cell banks is now commonplace; however, strategies for isolating UC-derived MSCs (UCMSCs) from UC tissue have not been standardized. The majority of newborn stem cell banks take one of two approaches to cord tissue processing and cryopreservation: enzymatic digestion of the fresh tissue with cryopreservation of the subsequent cell suspension or cryopreservation of the tissue as a composite whole with later, post-thaw isolation of cells by explantation. Evaluation of UCMSCs derived by these two principal preparation and cryopreservation strategies is important to understanding whether the methods currently employed by newborn stem cell banks retain the desirable clinical attributes of UC cells. MethodsUCMSCs were isolated from 10 UC tissue samples by both explantation and enzymatic digestion methods to allow for comparison of cells from the same donor. Cell isolates from both methods were compared pre- and post-cryopreservation as well as after serial passaging. Cell viability, morphology, growth kinetics, immunophenotype, cytokine secretion and differentiation capacity were evaluated. ResultsUCMSCs could be derived from fresh UC tissue by both explantation and digestion methods and from thawed UC tissue by explantation. Initial cell populations isolated by digestion were heterogeneous and took longer to enrich for UCMSCs in culture than populations obtained by explantation. However, once isolated and enriched, UCMSCs obtained by either method showed no significant difference in viability, morphology, rate of proliferation, surface marker expression, levels of cytokine secretion or differentiation capacity. ConclusionsDerivation of UCMSCs by explantation after thawing UC cryopreserved as a composite tissue may be favorable in terms of initial purity and number of cells achievable by a specific passage. However, we observed no evidence of functional difference between UCMSCs derived by explanation or digestion, suggesting that cells isolated from cryopreserved material obtained by either method maintain their therapeutic properties.

Opening the Doors to Dynamic Camouflaging: Harnessing the Power of Polymorphic Devices

The era of widespread globalization has led to the emergence of hardware-centric security threats throughout the IC supply chain. Prior defenses like logic locking, layout camouflaging, and split manufacturing have been researched extensively to protect against intellectual property (IP) piracy at different stages. In this work, we present dynamic camouflaging as a new technique to thwart IP reverse engineering at all stages in the supply chain, viz., the foundry, the test facility, and the end-user. Toward this end, we exploit the multi-functionality, post-fabrication reconfigurability, and run-time polymorphism of spin-based devices, specifically the magneto-electric spin-orbit (MESO) device. Leveraging these unique properties, dynamic camouflaging is shown to be resilient against state-of-the-art analytical SAT-based attacks and test-data mining attacks. Such dynamic reconfigurability is not afforded in CMOS owing to fundamental differences in operation. For such MESO-based camouflaging, we also anticipate massive savings in power, performance, and area over other spin-based camouflaging schemes, due to the energy-efficient electric-field driven reversal of the MESO device. Based on thorough experimentation, we outline the promises of dynamic camouflaging in securing the supply chain end-to-end along with a case study, demonstrating the efficacy of dynamic camouflaging in securing error-tolerant image processing IP.

Comparison of functional attributes of mscs isolated by explant and digestion umbilical cord tissue using a split manufacturing model

Background & Aim Umbilical cord tissue (CT) is a rich source of mesenchymal stromal cells (MSCs) and many newborn stem cell banks have established programs for cryopreservation of CT as a source material for future clinical use. Here we utilize a split manufacturing model to compare MSCs isolated after thawing cord tissue cryopreserved as composite cord tissue (c-CT MSCs) and MSCs isolated from previously-cryopreserved, heterogeneous, single-cell suspensions of enzymatically-digested cord tissue (d-CT MSCs) to determine if growth kinetics and differentiation capacity are impacted by the two predominant CT storage strategies adopted by the banking industry. Methods, Results & Conclusion Methods: 10 umbilical cords were obtained for research from consenting mothers. Each CT was divided in half with one half cut into small pieces cryopreserved as whole, composite material, and the other half enzymatically digested to obtain a heterogeneous cell suspension that was cryopreserved. After at least 1 week, thawed composite tissue was explanted in MSC-selective medium for 2 weeks while cells from digested tissue were seeded directly into culture. Cells from both methods were expanded to the end of the third passage (P3) and assessed by flow cytometry, viability, and differentiation capacity. Results Cell yield/gr41 and post-thaw recovery were greater for explanted material (Table 1). Initial heterogeneity of d-CT is addressed by serial culture; P3 d-CT populations are enriched for MSCs, with no differences between CD73, CD90, and CD34/45 compared to c-CT populations (Figure 1). Viabilities and doubling times at P3 were similar (Table 2). Similar qualitative adipo-, and chondrogenic differentiation capabilities were observed for c-CT and d-CT cells while osteogenic capacity was confirmed with calcium deposition as well as an increase in ALP activity (2.7 and 2.9 fold increase for c-CT and d-CT, p=0.8). Conclusion The processes for cryopreservation and isolation of c-CT and d-CT MSCs differ, but once a purified population is obtained, MSCs from the same donor are indistinguishable with regards to growth kinetics and tri-lineage differentiation potential. These results build on our previous report that cells from the same donor are not notably different in secreted factors. While these studies highlight that either CT cryopreservation strategy is suitable for maintaining MSC properties, storage of composite tissue is advantageous due to the greater purity of cells and higher per-gram yield.

Obfuscating the Interconnects: Low-Cost and Resilient Full-Chip Layout Camouflaging

Layout camouflaging can protect the intellectual property of modern circuits. Most prior art, however, incurs excessive layout overheads and necessitates customization of active-device manufacturing processes, i.e., the front-end-of-line (FEOL). As a result, camouflaging has typically been applied selectively, which can ultimately undermine its resilience. Here, we propose a low-cost and generic scheme---full-chip camouflaging can be finally realized without reservations. Our scheme is based on obfuscating the interconnects, i.e., the back-end-of-line (BEOL), through design-time handling for real and dummy wires and vias. To that end, we implement custom, BEOL-centric obfuscation cells, and develop a CAD flow using industrial tools. Our scheme can be applied to any design and technology node without FEOL-level modifications. Considering its BEOL-centric nature, we advocate applying our scheme in conjunction with split manufacturing, to furthermore protect against untrusted fabs. We evaluate our scheme for various designs at the physical, DRC-clean layout level. Our scheme incurs a significantly lower cost than most of the prior art. Notably, for fully camouflaged layouts, we observe average power, performance, and area overheads of 24.96%, 19.06%, and 32.55%, respectively. We conduct a thorough security study addressing the threats (attacks) related to untrustworthy FEOL fabs (proximity attacks) and malicious end-users (SAT-based attacks). An empirical key finding is that only large-scale camouflaging schemes like ours are practically secure against powerful SAT-based attacks. Another key finding is that our scheme hinders both placement- and routing-centric proximity attacks; correct connections are reduced by 7.47X, and complexity is increased by 24.15X, respectively, for such attacks.

How Secure Is Split Manufacturing in Preventing Hardware Trojan?

With the trend of outsourcing fabrication, split manufacturing is regarded as a promising way to both acquire the high-end nodes in untrusted external foundries and protect the design from potential attackers. However, in this article, we show that split manufacturing is not inherently secure, that a hardware Trojan attacker can still recover necessary information with a proximity-based or a simulated-annealing-based mapping approach together with a probability-based or net-based pruning method at the placement level. We further propose a defense approach by moving the insecure gates away from their easily attacked candidate locations. Results on benchmark circuits show the effectiveness of our proposed methods.

A Comprehensive Review on Plant derived Natural products for Diabetes and its complication as nephropathyExtraction and Quantitative Estimation of Chrysophanol From Cassia tora Meal Powder by High-Performance Liquid Chromatography

An isocratic reverse phase HPLC method were described to determined chrysophanol contain in cassia tora meal powder obtained during the split manufacturing process of cassia tora seed husk and germs which are used as a valuable cattle feed and poultry feed as they are quite rich in protein. The method involves methanol: water (90:10) with 0.05% Ortho-Phosphoric acid as solvent system and chromatogram detection was done on 254 nm using photodiode array detector. Chrysophanol were extracted using methanol, 70% methanol, acid hydrolysis and Oxidative hydrolysis by different concentration of the Hydrochloric acid and ferric chloride respectively. An average chrysophanol content was observed in cassia tora meal powder was 0.066 percent. In an efforts to develop an improved method for the determination of content of chrysophanol which is important marker compound in cassia tora meal and also improve method of an extraction methods. The solvents for extraction of chrysophanol from cassia tora were examined in order to increase the chrysophanol contents in cassia tora meal powder. It was found that 70% methanol, 20% HCL (v/v) and 3% FeCl3 (v/v) was capable of increasing the chrysophanol contain up to 0.099 percent.
 Keywords: HPLC, Chrysophanol, Extraction, Cassia tora meal powder

A Survey on Split Manufacturing: Attacks, Defenses, and Challenges

In today's integrated circuit (IC) ecosystem, owning a foundry is not economically viable, and therefore most IC design houses are now working under a fabless business model. In order to overcome security concerns associated with the outsorcing of IC fabrication, the Split Manufacturing technique was proposed. In Split Manufacturing, the Front End of Line (FEOL) layers (transistors and lower metal layers) are fabricated at an untrusted high-end foundry, while the Back End of Line (BEOL) layers (higher metal layers) are manufactured at a trusted low-end foundry. This approach hides the BEOL connections from the untrusted foundry, thus preventing overproduction and piracy threats. However, many works demonstrate that BEOL connections can be derived by exploiting layout characteristics that are introduced by heuristics employed in typical floorplanning, placement, and routing algorithms. Since straightforward Split Manufacturing may not afford a desirable security level, many authors propose defense techniques to be used along with Split Manufacturing. In our survey, we present a detailed overview of the technique, the many types of attacks towards Split Manufacturing, as well as possible defense techniques described in the literature. For the attacks, we present a concise discussion on the different threat models and assumptions, while for the defenses we classify the studies into three categories: proximity perturbation, wire lifting, and layout obfuscation. The main outcome of our survey is to highlight the discrepancy between many studies -- some claim netlists can be reconstructed with near perfect precision, while others claim marginal success in retrieving BEOL connections. Finally, we also discuss future trends and challenges inherent to Split Manufacturing, including the fundamental difficulty of evaluating the efficiency of the technique.

Security Promises and Vulnerabilities in Emerging Reconfigurable Nanotechnology-Based Circuits

Emerging nanotechnologies based reconfigurable field-effect transistors (RFETs) allow switching between p-type and n-type behavior at runtime upon application of different bias potentials. While prior works have mainly focused on security schemes using RFETs, here we revisit the underlying security promises, and furthermore, showcase certain circuit vulnerabilities which can lead to adversarial scenarios. More specifically, first, we explore how transistor-level reconfigurability can be leveraged for logic locking and split manufacturing in the pretext of RFET-based modeling of the ITC-99 circuits. We find that with only 30% reconfigurable logic gates, we can induce 100% output error rate (OER) and 31% Hamming distance(HD) on split-manufacturing schemes. Second, which is arguably more disruptive, we explore how the very reconfigurability can be exploited to induce either short-circuit or open-circuit configurations, essentially destroying the reliability, electrical, or functional characteristics of the chip. By means of fault modeling for such exploitation, 100% OER (across all benchmarks) as well as 36.5%, 40.02%, and 6.34% HD, respectively, can be expected for the MCNC, EPFL, and ITC-99 benchmarks. The novelty and severity of such disruptive scenario lies in the fact that they can be readily realized in an actual on-field RFET-based chip, either as an adversarial or a fail-safe measure.

Reverse Engineering for 2.5-D Split Manufactured ICs

Integrated circuit (IC) split manufacturing has been shown to be one of the most effective protection schemes to prevent reverse engineering from malicious foundries. Among the existing split manufacturing approaches, the 2.5-D split manufacturing using silicon interposer has much less fabrication and testing costs compared to layer splitting approaches. In this article, we propose a Boolean satisfiability (SAT)-based attack to reconstruct the wire connections of the 2.5-D split manufacturing netlists. Our SAT-based attack can fully reconstruct the missing wires between modules with 100% correctness and therefore the functionality of the chip can be completely reverse engineered. In addition, we show that the runtime of attack is significantly reduced compared to existing 2.5-D split manufacturing SAT attacks by applying grouping hints obtained from a satisfiability modulo theories (SMTs)-based grouping algorithm, which is purely depending on the circuit functionality, so no physical defensive mechanisms can prevent such attack. In our experiments, we show that our grouping algorithm can speed up the existing SAT attack runtime by more than $1000\times $ and can successfully reverse engineer reasonable size benchmarks even when the split nets contains more than one fanouts and the total cut size is close to 1000.

Analysis of Security of Split Manufacturing Using Machine Learning

This paper is the first to analyze the security of split manufacturing using machine learning (ML), based on data collected from layouts provided by industry, with eight routing metal layers and significant variation in wire size and routing congestion across the layers. Many types of layout features are considered in our ML model, including those obtained from placement, routing, and cell sizes. Since the runtime cost of our basic ML procedure becomes prohibitively large for lower layers, we propose novel techniques to make it scalable with little sacrifice in the effectiveness of the attack. Moreover, we further improve the performance in the top routing layer by making use of higher quality training samples and by exploiting the routing convention. We also propose a validation-based proximity attack procedure, which generally outperforms our recent prior work. In the experiments, we analyze the ranking of the features used in our ML model and show how features vary in importance when moving to the lower layers. We provide comprehensive evaluation and comparison of our model with different configurations and demonstrate dramatically better performance of attacks compared to the prior work.