Retiming and Resynthesis with Sweep Are Complete for Sequential Transformation

Abstract-There is a long history of investigations and debates on whether a sequence of retiming and resynthesis is complete for all sequential transformations (on steady states). It has been shown that the sweep operation, which adds or removes registers not used by any output, is necessary for some sequential transformations. However, it is an open question whether retiming and resynthesis with sweep are complete. This paper proves that the operations are complete, but with one caveat: at least one resynthesis operation needs to look through the register boundary into the logic of previous cycle. We showed that this one-cycle reachability is required for retiming and resynthesis to be complete for re-encodings with different code length. This requirement comes from the fact that Boolean circuit is used for a discrete function thus its range needs to be computed by a traversal of the circuit. In theory, five operations in the order of sweep, resynthesis, retiming, resynthesis, and sweep are already complete. However, some practical limitations on resynthesis must be considered. The complexity of retiming and resynthesis verification is also discussed

Active hardware metering for intellectual property protection and security

Abstract We introduce the first active hardware metering scheme that aims to protect integrated circuits (IC) intellectual property (IP) against piracy and runtime tampering. The novel metering method simultaneously employs inherent unclonable variability in modern manufacturing technology, and functionality preserving alternations of the structural IC specifications. Active metering works by enabling the designers to lock each IC and to remotely disable it. The objectives are realized by adding new states and transitions to the original finite state machine (FSM) to create boosted finite state machines(BFSM) of the pertinent design. A unique and unpredictable ID generated by an IC is utilized to place an BFSM into the power-up state upon activation. The designer, knowing the transition table, is the only one who can generate input sequences required to bring the BFSM into the functional initial (reset) state. To facilitate remote disabling of ICs, black hole states are integrated within the BFSM. We introduce nine types of potential attacks against the proposed active metering method. We further describe a number of countermeasures that must be taken to preserve the security of active metering against the potential attacks. The implementation details of the method with the objectives of being low-overhead, unclonable, obfuscated, stable, while having a diverse set of keys is presented. The active metering method was implemented, synthesized and mapped on the standard benchmark circuits. Experimental evaluations illustrate that the method has a low-overhead in terms of power, delay, and area, while it is extremely resilient against the considered attacks

A Robust FSM Watermarking Scheme for IP Protection of Sequential Circuit Design

Finite state machines (FSMs) are the backbone of sequential circuit design. In this paper, a new FSM watermarking scheme is proposed by making the authorship information a non-redundant property of the FSM. To overcome the vulnerability to state removal attack and minimize the design overhead, the watermark bits are seamlessly interwoven into the outputs of the existing and free transitions of state transition graph (STG). Unlike other transition-based STG watermarking, pseudo input variables have been reduced and made functionally indiscernible by the notion of reserved free literal. The assignment of reserved literals is exploited to minimize the overhead of watermarking and make the watermarked FSM fallible upon removal of any pseudo input variable. A direct and convenient detection scheme is also proposed to allow the watermark on the FSM to be publicly detectable. Experimental results on the watermarked circuits from the ISCAS'89 and IWLS'93 benchmark sets show lower or acceptably low overheads with higher tamper resilience and stronger authorship proof in comparison with related watermarking schemes for sequential functions

N-variant Hardware Design

The emergence of lightweight embedded devices imposes stringent constraints on the area and power of the circuits used to construct them. Meanwhile, many of these embedded devices are used in applications that require diversity and flexibility to make them secure and adaptable to the fluctuating workload or variable fabric. While field programmable gate arrays (FPGAs) provide high flexibility, the use of application specific integrated circuits (ASICs) to implement such devices is more appealing because ASICs can currently provide an order of magnitude less area and better performance in terms of power and speed. My proposed research introduces the N-variant hardware design methodology that adds the sufficient flexibility needed by such devices while preserving the performance and area advantages of using ASICs. The N-variant hardware design embeds different variants of the design control part on the same IC to provide diversity and flexibility. Because the control circuitry usually represents a small fraction of the whole circuit, using multiple versions of the control circuitry is expected to have a low overhead. The objective of my thesis is to formulate a method that provides the following advantages: (i) ease of integration in the current ASIC design flow, (ii) minimal impact on the performance and area of the ASIC design, and (iii) providing a wide range of applications for hardware security and tuning the performance of chips either statically (e.g., post-silicon optimization) or dynamically (at runtime). This is achieved by adding diversity at two orthogonal levels: (i) state space diversity, and (ii) scheduling diversity. State space diversity expands the state space of the controller. Using state space diversity, we introduce an authentication mechanism and the first active hardware metering schemes. On the other hand, scheduling diversity is achieved by embedding different control schedules in the same design. The scheduling diversity can be spatial, temporal, or a hybrid of both methods. Spatial diversity is achieved by implementing multiple control schedules that use various parts of the chip at different rates. Temporal diversity provides variants of the controller that can operate at unequal speeds. A hybrid of both spatial and temporal diversities can also be implemented. Scheduling diversity is used to add the flexibility to tune the performance of the chip. An application of the thermal management of the chip is demonstrated using scheduling diversity. Experimental results show that the proposed method is easy to integrate in the current ASIC flow, has a wide range of applications, and incurs low overhead

On the Optimization Power of Retiming and Resynthesis Transformations

Retiming and resynthesis transformations can be used for optimizing the area, power, and delay of sequential circuits. Even though this technique has been known for more than a decade, its exact optimization capability has not been formally established. We show that retiming and resynthesis can exactly implement 1-step equivalent state transition graph transformations. This result is the strongest to date. We also show how the notions of retiming and resynthesis can be moderately extended to achieve more powerful state transition graph transformations. Our work will provide theoretical foundation for practical retiming and resynthesis based optimization and verification. 1 Introduction In combinational synthesis [1, 8], the positions of the latches are fixed and the logic is optimized for area, delay, or power. In retiming [5], the latches are moved across combinational gates. Retiming can change the number of latches (and hence the area) and the minimum cycle time (i.e., the clock ra..