Security through Obscurity: Layout Obfuscation of Digital Integrated Circuits using Don't Care Conditions

Contemporary integrated circuits are designed and manufactured in a globalized environment leading to concerns of piracy, overproduction and counterfeiting. One class of techniques to combat these threats is circuit obfuscation which seeks to modify the gate-level (or structural) description of a circuit without affecting its functionality in order to increase the complexity and cost of reverse engineering. Most of the existing circuit obfuscation methods are based on the insertion of additional logic (called “key gates”) or camouflaging existing gates in order to make it difficult for a malicious user to get the complete layout information without extensive computations to determine key-gate values. However, when the netlist or the circuit layout, although camouflaged, is available to the attacker, he/she can use advanced logic analysis and circuit simulation tools and Boolean SAT solvers to reveal the unknown gate-level information without exhaustively trying all the input vectors, thus bringing down the complexity of reverse engineering. To counter this problem, some ‘provably secure’ logic encryption algorithms that emphasize methodical selection of camouflaged gates have been proposed previously in literature [1,2,3]. The contribution of this paper is the creation and simulation of a new layout obfuscation method that uses don't care conditions. We also present proof-of-concept of a new functional or logic obfuscation technique that not only conceals, but modifies the circuit functionality in addition to the gate-level description, and can be implemented automatically during the design process. Our layout obfuscation technique utilizes don’t care conditions (namely, Observability and Satisfiability Don’t Cares) inherent in the circuit to camouflage selected gates and modify sub-circuit functionality while meeting the overall circuit specification. Here, camouflaging or obfuscating a gate means replacing the candidate gate by a 4X1 Multiplexer which can be configured to perform all possible 2-input/ 1-output functions as proposed by Bao et al. [4]. It is important to emphasize that our approach not only obfuscates but alters sub-circuit level functionality in an attempt to make IP piracy difficult. The choice of gates to obfuscate determines the effort required to reverse engineer or brute force the design. As such, we propose a method of camouflaged gate selection based on the intersection of output logic cones. By choosing these candidate gates methodically, the complexity of reverse engineering can be made exponential, thus making it computationally very expensive to determine the true circuit functionality. We propose several heuristic algorithms to maximize the RE complexity based on don’t care based obfuscation and methodical gate selection. Thus, the goal of protecting the design IP from malicious end-users is achieved. It also makes it significantly harder for rogue elements in the supply chain to use, copy or replicate the same design with a different logic. We analyze the reverse engineering complexity by applying our obfuscation algorithm on ISCAS-85 benchmarks. Our experimental results indicate that significant reverse engineering complexity can be achieved at minimal design overhead (average area overhead for the proposed layout obfuscation methods is 5.51% and average delay overhead is about 7.732%). We discuss the strengths and limitations of our approach and suggest directions that may lead to improved logic encryption algorithms in the future. References: [1] R. Chakraborty and S. Bhunia, “HARPOON: An Obfuscation-Based SoC Design Methodology for Hardware Protection,” IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, vol. 28, no. 10, pp. 1493–1502, 2009. [2] J. A. Roy, F. Koushanfar, and I. L. Markov, “EPIC: Ending Piracy of Integrated Circuits,” in 2008 Design, Automation and Test in Europe, 2008, pp. 1069–1074. [3] J. Rajendran, M. Sam, O. Sinanoglu, and R. Karri, “Security Analysis of Integrated Circuit Camouflaging,” ACM Conference on Computer Communications and Security, 2013. [4] Bao Liu, Wang, B., "Embedded reconfigurable logic for ASIC design obfuscation against supply chain attacks,"Design, Automation and Test in Europe Conference and Exhibition (DATE), 2014 , vol., no., pp.1,6, 24-28 March 2014.

Final Report of the Phase III Archaeological Investigations at the Dr. Upton Scott House (18AP18), Annapolis, Anne Arundel County, Maryland, 1998-1999

In the summers of 1998 and 1999, the Archaeology in Annapolis project carried out archaeological investigation at the eighteenth century Dr. Upton Scott House site (18AP18)located at 4 Shipwright Street in the historic district of Annapolis, Anne Arundel County, Maryland. The Upton Scott House is significant as one of only a few Georgian houses with remnants of its original plantation-inspired landscape still visible (Graham 1998:147). Investigation was completed in agreement with the owners of the historic property, Mr. and Mrs. Paul Christian, who were interested in determining the condition and arrangement of Dr. Upton Scott’s well-documented pleasure gardens. Betty Cosans’ 1972 Archaeological Feasibility Report, the first real archaeological study of the Upton Scott House site, guided the research design and recovery efforts. Cosans determined that testing and survey in the back and side yards of the Scott property would yield important information on the use and history of the property, including that of Scott’s famous gardens. Excavation units and trenches were placed within three separate areas of backyard activity on the site which included Area One: extant brick stables in the southwest of the property; Area Two: the brick foundations of a small outbuilding located in the northwest area of the site; and Area Three: the area of Scott’s formal gardens. The research design included an interest in recovering evidence of African-American spiritual practice and domestic life at the site. Also of significant importance was an analysis of Scott’s garden beds, concerning the order and layout. Also sought was an understanding of the change in perception and use of the backyard by the various owners of the property.

Continuity and Change on an Urban Houselot: Archaeological Excavation at the 22 West Street Backlot (18AP51) of the Annapolis National Historic District, Anne Arundel County, Maryland

Intensive archaeological investigation was undertaken on an urban backlot in Annapolis, Maryland. Fieldwork was conducted on behalf of Historic Annapolis Foundation for the property's owners, King and Cornwall, Inc. Supplemental documentary research, an evaluation of existing conditions on the property, and below-ground excavation of a 35 X 70 ft. urban backlot were conducted. While the project was not a Section 106 compliance effort, the field methods and rationale for the site's investigation are comparable to those of standard Phase II site evaluations. Historical documentation attested to the fact that the 22 West Street Backlot, located along the western most edge of the Historic District of Annapolis, Maryland, had seen development and occupation since the first quarter of the eighteenth century. A substantial brick structure was known to have occupied the property in a series of altered forms for much of that period. This structure served a variety of purposes over time: a private residence in the eighteenth century, a boarding house in the nineteenth century (known as the National Hotel), a duplex in the early twentieth century, half of which remained in use until the structure was entirely razed in the 1970s after destruction by fire. Recovery and analysis of site formation processes (i.e., both cultural and natural transformations of the buried remains) indicated that sections of the site were disturbed to a depth of six feet. In contrast to what initially seemed a poor prognosis for site integrity, other areas of the backlot revealed numerous intact historical features and deposits. Structural remains from the dwelling and its associated outbuildings, additions, and attendant trash deposits were recovered. What was initiated as a program of limited testing evolved into a larger-scale undertaking that made use of largely hand-excavated units in conjunction with machine-assisted stripping of areas demonstrated to contain from four to six-foot deep sterile layers of fill. The current investigations provided a window into a portion of the city and period in its history not documented archaeologically. Moreover, this project provided valuable insight into the archaeology of the homelot within a lightly industrialized, urban context. Evidence was recovered of shifts in the layout and arrangement of the houselot as well as changing relations between individuals and the workplace--all within an urban context--an issue defined elsewhere in the archaeological literature as a significant one. No further investigations are recommended for the site, however, further analysis and interpretation of materials recovered are ongoing. In the event that the site were to undergo development, monitoring of any construction activity is recommended.