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anotechnology is useful notonly for harnessing physical

techniques in security appli-cations but also to helpresearchers use physics the-

ories to prove applications securitystrength. In a way, this is similar topublic-key cryptography, which usesmathematical theories to build cryp-tographic applications and provetheir cryptographic strength.

Security strength depends on anadversarys inability to perform anoperation that valid users can easily per-

form. Nanotechnology can help resolvethe challenge of devising a means toexecute this principle and accuratelyevaluate the adversarys limitations.

The idea of enlisting physics theo-ries to devise security applications andprove their strength isnt new. Forexample, quantum cryptographywhich many consider to be a revolu-tionary information security tech-nologyfacilitates secure ways toexchange secret keys. Theories from

physics, not mathematics, provide thefoundation to implement the applica-tion and prove its security strength.

FUNDAMENTAL APPLICATIONSA revision of two fundamental

applicationstamper-proofing andfunctionality obfuscationreflectsnanotechnologys ability to deliversecure systems and scientifically estab-lish their security robustness.

Tamper-proofingA secured system is as strong as its

weakest link. Key protection shouldinclude a method to prevent adver-saries from reading the memory thatstores the key from the outside. In

addition, adversaries shouldnt be ableto read the data bus that carries thekey from storage to the processing ele-ment during the circuits dynamicoperation. An additional threat con-cerns probing the secret key at theprocessors initial logic gates. Techni-cal considerations that are more artthan science, however, drive currentapproaches to tamper-proofingforexample, special coating techniquesand clock irregularities. Instead of

providing fundamental proofs, theseapproaches rely on the designersinstincts.

Functionality obfuscationThe possibility of hiding a program

or logic circuits functionality carriesmajor security implications. The hid-den functionality is regarded as a

secret key known only to the designer.When trying to obfuscate a logic cir-cuits functioning, adversaries canshave a circuit layer by layer andcopy the fabrication masks. They canthen reconstruct the circuits logicgates and analyze its functionality.

Analysis leads to the conclusion thatthe discrete structure of programs andlogic circuits inherently prevents trueobfuscation. Yet, security officials con-stantly conduct practical trials intended

to provide functionality obfuscation.

NANOTECHNOLOGY ANDTAMPER-PROOFING

Tamper-proofing should be based ona scientific approach in which probingdestroys the value the probe attemptsto read. The energy the probe radiatesor absorbs during the reading attemptshould disrupt the mechanism thatstores, conducts, or processes a bit,based on established physics laws.

Nanotechnology might provide theright tool because the miniaturizationgets to a level of handling a few elec-trons, increasing the probability of dis-turbing the bits presentation merelyby attempting to probe it.

StorageNonvolatile molecular memory uses

a molecule to store a charge. Appro-priate electrical bias is applied to setand reset a memory cell. In multilevel

molecular memory, the electrical con-ductance in nanowires is adjusted bymolecules that accept or emit elec-trons. Such principles provide amplepossibilities for preventing externalprobing, whereby interaction betweenthe probe and the molecule disruptsthe stored charge or the electrons thatcontrol the nanowire conductance.

An external tampering probe radi-ates or absorbs energy needed for read-ing a stored value. Researchers can use

rules from physics to exactly evaluatethe meaning of the interaction betweenthe probe and the charge or electrons

Enhancing

Security withNanotechnologyBenjamin Arazi, Ben Gurion University

S E C U R I T Y

Nanotechnology can helpresearchers use physics theoriesto build security applicationsand prove their strength.

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In Out In OutB AB

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B A+B

A

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AND OR NOTConducting line

Figure 1.Quantum-dot cellular automata.Encoding a bit causes an interaction that

forces neighboring cells to synchronize their polarization and settle at a minimum

energy-stable state.

the conductors. The force the probeexerts to form a contact with the con-ductor (assuming that the readingcant be based on radiation) exceeds

the strength of the structure, whichwould then collapse. Accurate theo-ries from mechanics can be applied toanalyze this option.

Tamper resistance at initial logic

gates. An alternative is to useCoulomb blockade circuitry, specifi-cally, single-electron transistors, toprovide protection from tampering tothe initial logic that processes thesecret key. Coulomb blockade analy-sis is based on quantum electronics.

NANOTECHNOLOGY ANDFUNCTIONALITY OBFUSCATION

Fundamental studies argue that itsinherently possible to obfuscate soft-ware code or logic hardware func-tionality due to the discrete form ofsuch structures. Based on fundamen-tal observations from physics, thesestudies also point out that nanotech-nology may form the foundations ofhardware obfuscation, in which the

circuits discrete structure is blurred.

QCAIn standard microelectronics, the

transistors and conduction lines aremade of different substances, and dif-ferent masks introduce them into theprocess. Since reverse engineering canrecover the masks, it can also recoverthe logic gates and circuit functionality.

As Figure 1 illustrates, QCA cells arethe building blocks of logic gates as

well as the conduction lines that jointhe gates when forming a logic circuit.Making the gates and conduction lines

that support the memory. Using for-mulas from physics for security analy-sis is comparable to using algebraicformulas to establish the complexity ofbreaking a mathematical code.

Data-bus tamperingData-bus tampering involves tech-

niques such as using an ion beam todrill a hole to the signal line, which theadversary then fills with a conductingmaterial to bring the signal to the sur-face, where its probed. The followingthree possible nanotechnology con-siderations pertain to preventing data-bus readings.

Quantum-dot cellular automata.

A quantum-dot cellular automata(QCA) cell consists of four quantumdots positioned at the vertices of asquare. Two added electrons occupythe cells diagonals. Two possiblepolarizations can encode a bit. Theinteraction forces neighboring cells tosynchronize their polarization and set-tle at a minimum energy-stable state.This forms the basis for a conductionline and logic gates, as Figure 1 shows.

Consider a case in which the system

transfers a stored secret key from stor-age to the processor over a QCA con-duction line. Probing the conductionline from the outside might cause insta-bility in the states of the cells that arebased on single-electron interactions.

Integration of storage and con-

ductance. Findings from a NASAAmes Research Center study of mole-cular memory led to the possibility ofusing a molecule both as a storage ele-ment and a conducting cell. Both uses

involve molecular-level electric charges.We can associate tampering with amolecule-based conduction line withtheories from classical physics, regard-ing an induced change in a charge asthe result of an attempt to use a read-ing probe on the molecule.

Nanomechanics.Researchers havewidely proposed using nanocarbons(and other nanolevel structures) forconducting electric currents, an ideacurrently at various implementation

stages. To prevent external probing ofsuch conductors, one proposal is toapply electromechanical support to

of the same cells obfuscates the dis-crete logic structure. When observingthe production masks, an adversarycant know whether a specific point in

the circuit is part of a gate or part ofthe conduction line that joins the gates.

Chemical or biologicalprocessing

Leading nanotechnology researchfocuses on the fabrication of logic gatesbased on chemical or biologicalprocesses. Based on proved theoriesfrom chemistry and biology, we canexpect to use a combined logic processthat obfuscates internal functionality.

A possible leading component here isthe Fredkin gate, a universal logic gatethat has great potential for being con-structed by chemical or biologicalmeans. It also provides for reversibility,an attractive cryptographic feature.

Its possible to use nanotechnologyprinciples in security applications,based on physics practice and theo-

ries. The practice helps build the appli-cations, while the associated theories

provide a formal means to analyzesecurity robustness. Research activitiesin these and similar directions mightyield fundamental results.

Benjamin Arazi is a professor in the

Department of Electrical and Computer

Engineering at Ben Gurion University.

Contact him at arazi@ee.bgu.ac.il.

Editor: Jack Cole, US Army Research

Laboratorys Information Assurance

Center, jack.cole@ieee.org;

http://msstc.org/cole