Hardware obfuscation is a technique by which the description or the structure of electronic hardware is modified to intentionally conceal its functionality, which makes it significantly more difficult to reverse-engineer. In other words, hardware obfuscation modifies the design in such a away that the resulting architecture becomes un-obvious to an adversary. Hardware Obfuscation can be of two types depending on the hardware platform targeted: (a) DSP Core Hardware Obfuscation - this type of obfuscation performs certain high level transformation on the data flow graph representation of DSP core to convert it into an unknown form that reflects an un-obvious architecture at RTL or gate level. This type of obfuscation is also called 'Structural Obfuscation'. Another type of DSP Core Obfuscation method is called 'Functional Obfuscation' - It uses a combination of AES and IP core locking blocks (ILBs) to lock the functionality of the DSP core using key-bits. Without application of correct key sequence, the DSP core produces either wrong output or no output at all (b) Combinational/Sequential Hardware Obfuscation - this type of obfuscation performs changes to the gate level structure of the circuit itself. In essence, it is different from

digital watermarking A digital watermark is a kind of marker covertly embedded in a noise-tolerant signal such as audio, video or image data. It is typically used to identify ownership of the copyright of such signal. "Watermarking" is the process of hiding digital inf ...

(where the ownership is concealed in the digital content itself), or from hardware

intellectual property Intellectual property (IP) is a category of property that includes intangible creations of the human intellect. There are many types of intellectual property, and some countries recognize more than others. The best-known types are patents, cop ...

(IP) watermarking where the ownership information is embedded and concealed in the description of a

circuit Circuit may refer to: Science and technology Electrical engineering * Electrical circuit, a complete electrical network with a closed-loop giving a return path for current ** Analog circuit, uses continuous signal levels ** Balanced circu ...

. It is also different from cryptography-based hardware IP protection techniques common in the design flow of

Field Programmable Gate Array A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturinghence the term '' field-programmable''. The FPGA configuration is generally specified using a hardware ...

. The importance of

hardware watermarking Hardware watermarking, also known as IP core watermarking is the process of embedding covert marks as design attributes inside a hardware or IP core design itself. Hardware Watermarking can represent watermarking of either DSP Cores (widely used in ...

has increased in the recent years due to widespread adoption of hardware IP based design practices for modern integrated circuits (ICs) such as system on chips (SoCs). Major security issues associated with hardware IPs include: (a) hardware

intellectual property infringement An intellectual is a person who engages in critical thinking, research, and reflection about the reality of society, and who proposes solutions for the normative problems of society. Coming from the world of culture, either as a creator ...

during SoC design; (b)

reverse engineering Reverse engineering (also known as backwards engineering or back engineering) is a process or method through which one attempts to understand through deductive reasoning how a previously made device, process, system, or piece of software accompli ...

the manufactured ICs or the IC design database (in

fabrication Fabrication may refer to: * Manufacturing, specifically the crafting of individual parts as a solo product or as part of a larger combined product. Processes in arts, crafts and manufacturing *Semiconductor device fabrication, the process used t ...

facilities) to produce

counterfeit To counterfeit means to imitate something authentic, with the intent to steal, destroy, or replace the original, for use in illegal transactions, or otherwise to deceive individuals into believing that the fake is of equal or greater value tha ...

or clone ICs; and (c) malicious modifications of an IP through the insertion of

hardware Trojan A Hardware Trojan (HT) is a malicious modification of the circuitry of an integrated circuit. A hardware Trojan is completely characterized by its physical representation and its behavior. The payload of an HT is the entire activity that the ...

to cause in-field functional

failure Failure is the state or condition of not meeting a desirable or intended objective, and may be viewed as the opposite of success. The criteria for failure depends on context, and may be relative to a particular observer or belief system. One ...

. Hardware obfuscation aims at minimizing these threats at IP or chip level by making it difficult for an

adversary An adversary is generally considered to be a person, group, or force that opposes and/or attacks. Adversary may also refer to: * Satan ("adversary" in Hebrew), in Judeo-Christian religion Entertainment Fiction * Adversary (comics), villain fr ...

to comprehend the actual functionality of a design. Hardware obfuscation techniques can be classified into two main categories: (a) the "passive" techniques, which do not directly affect the functionality of the

electronic system Electronic may refer to: *Electronics, the science of how to control electric energy in semiconductor * ''Electronics'' (magazine), a defunct American trade journal *Electronic storage, the storage of data using an electronic device *Electronic co ...

, and (b) the "active" techniques, which directly alter the functionality of the system. Often the active hardware obfuscation techniques are "key-based", such that normal functionality of the obfuscated design can only be enabled by the successful application of a single pre-determined key or a sequence of secret keys at the input; otherwise the circuit operates in a mode, which exhibits incorrect functionality. This can be done by embedding a well-hidden

finite state machine A finite-state machine (FSM) or finite-state automaton (FSA, plural: ''automata''), finite automaton, or simply a state machine, is a mathematical model of computation. It is an abstract machine that can be in exactly one of a finite number o ...

(FSM) in the circuit to control the functional modes based on application of key. The technique of key-based, active hardware obfuscation is similar in principle to private-key cryptographic approaches for

information Information is an abstract concept that refers to that which has the power to inform. At the most fundamental level information pertains to the interpretation of that which may be sensed. Any natural process that is not completely random, ...

protection, since the "key sequence" for the obfuscated design plays a similar role as the cryptographic key. The technique can be applied at different levels of hardware description, namely gate-level or register transfer level (RTL) design and hence can be used to protect soft, firm and hard IP cores.R.S. Chakraborty and S. Bhunia: "RTL hardware IP protection using key-based control and data flow obfuscation", International Conference on Very Large Scale Integration Design (VLSID), 2010. Obfuscation can also help to effectively hide security features in an IC and thus enable protection of ICs from counterfeiting and cloning in fabrication facilities. In contrast, the ''passive'' techniques modify the circuit description in a ''soft'' form (e.g. syntactic changes), such that it becomes difficult for a human reader to understand the functionality of the circuit. These approaches typically employ either string-substitution (including variable name change, comment removal, etc.), or structural change in the

hardware description language In computer engineering, a hardware description language (HDL) is a specialized computer language used to describe the structure and behavior of electronic circuits, and most commonly, digital logic circuits. A hardware description language e ...

(HDL) description of a circuit (including

loop unrolling Loop unrolling, also known as loop unwinding, is a loop transformation technique that attempts to optimize a program's execution speed at the expense of its binary size, which is an approach known as space–time tradeoff. The transformation ...

register renaming In computer architecture, register renaming is a technique that abstracts logical registers from physical registers. Every logical register has a set of physical registers associated with it. When a machine language instruction refers to a partic ...

, etc.). A major shortcoming of the ''passive'' approaches is that they do not modify the

black box In science, computing, and engineering, a black box is a system which can be viewed in terms of its inputs and outputs (or transfer characteristics), without any knowledge of its internal workings. Its implementation is "opaque" (black). The te ...

functionality of a circuit, and hence cannot prevent potential usage of an IP as ''black-box'' in a design. Moreover, the actual strength of such passive obfuscation is debatable, since, in general, ''black-box obfuscation'' does not exist, at least for software programs computing certain

mathematical functions In mathematics, a function from a set to a set assigns to each element of exactly one element of .; the words map, mapping, transformation, correspondence, and operator are often used synonymously. The set is called the domain of the func ...

.B. Barak, O. Goldreich, R. Impagliazzo, S. Rudich, A. Sahai, S.P. Vadhan and K. Yang: "On the (im)possibility of obfuscating programs", Cryptology Conference on Advances in Cryptology (CRYPTO), 2001.

Hardware watermarking Hardware watermarking, also known as IP core watermarking is the process of embedding covert marks as design attributes inside a hardware or IP core design itself. Hardware Watermarking can represent watermarking of either DSP Cores (widely used in ...

can be used in conjunction with hardware obfuscation. In an obfuscated design, watermarking can be effective in providing a second line of defense against unlicensed copying efforts.R.S. Chakraborty and S. Bhunia: "HARPOON: An Obfuscation-Based SoC Design Methodology for Hardware Protection", IEEE Trans. on CAD of Integrated Circuits and Systems (TCAD), 2009.

Historical context

Hardware obfuscation in computing probably has its origins with

mainframe A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterpris ...

CPUs, mainly ones made by IBM during the 1960s and 1970s. IBM, in order to maintain some competitive advantage, implemented secret opcodes that would only be used by the closed source operating system on the mainframe.

References

{{reflist Electronic design automation

Historical context

See also

References