SecuCode: Intrinsic PUF Entangled Secure Wireless Code Dissemination for Computational RFID Devices

The simplicity of deployment and perpetual operation of energy harvesting devices provides a compelling proposition for a new class of edge devices for the Internet of Things. In particular, Computational Radio Frequency Identification (CRFID) devices are an emerging class of battery-free, computational, sensing enhanced devices that harvest all of their energy for operation. Despite wireless connectivity and powering, secure wireless firmware updates remains an open challenge for CRFID devices due to: intermittent powering, limited computational capabilities, and the absence of a supervisory operating system. We present, for the first time, a secure wireless code dissemination (SecuCode) mechanism for CRFIDs by entangling a device intrinsic hardware security primitive Static Random Access Memory Physical Unclonable Function (SRAM PUF) to a firmware update protocol. The design of SecuCode: i) overcomes the resource-constrained and intermittently powered nature of the CRFID devices; ii) is fully compatible with existing communication protocols employed by CRFID devices in particular, ISO-18000-6C protocol; and ii) is built upon a standard and industry compliant firmware compilation and update method realized by extending a recent framework for firmware updates provided by Texas Instruments. We build an end-to-end SecuCode implementation and conduct extensive experiments to demonstrate standards compliance, evaluate performance and security.Comment: Accepted to the IEEE Transactions on Dependable and Secure Computin

An Efficient Authentication Protocol for Smart Grid Communication Based on On-Chip-Error-Correcting Physical Unclonable Function

Security has become a main concern for the smart grid to move from research and development to industry. The concept of security has usually referred to resistance to threats by an active or passive attacker. However, since smart meters (SMs) are often placed in unprotected areas, physical security has become one of the important security goals in the smart grid. Physical unclonable functions (PUFs) have been largely utilized for ensuring physical security in recent years, though their reliability has remained a major problem to be practically used in cryptographic applications. Although fuzzy extractors have been considered as a solution to solve the reliability problem of PUFs, they put a considerable computational cost to the resource-constrained SMs. To that end, we first propose an on-chip-error-correcting (OCEC) PUF that efficiently generates stable digits for the authentication process. Afterward, we introduce a lightweight authentication protocol between the SMs and neighborhood gateway (NG) based on the proposed PUF. The provable security analysis shows that not only the proposed protocol can stand secure in the Canetti-Krawczyk (CK) adversary model but also provides additional security features. Also, the performance evaluation demonstrates the significant improvement of the proposed scheme in comparison with the state-of-the-art

Secure Code Updates for Smart Embedded Devices based on PUFs

Code update is a very useful tool commonly used in low-end embedded devices to improve the existing functionalities or patch discovered bugs or vulnerabilities. If the update protocol itself is not secure, it will only bring new threats to embedded systems. Thus, a secure code update mechanism is required. However, existing solutions either rely on strong security assumptions, or result in considerable storage and computation consumption, which are not practical for resource-constrained embedded devices (e.g., in the context of Internet of Things). In this work, we propose to use intrinsic device characteristics (i.e., Physically Unclonable Functions or PUF) to design a practical and lightweight secure code update scheme. Our scheme can not only ensure the freshness, integrity, confidentiality and authenticity of code update, but also verify that the update is installed correctly on a specific device without any malicious software. Cloned or counterfeit devices can be excluded as the code update is bound to the unpredictable physical properties of underlying hardware. Legitimate devices in an untrustworthy software state can be restored by filling suspect memory with PUF-derived random numbers. After update installation, the initiator of the code update is able to obtain the verifiable software state from device, and the device can maintain a sustainable post-update secure check by enforcing a secure call sequence. To demonstrate the practicality and feasibility, we also implement the proposed scheme on a low-end MCU platform (TI MSP430) by using onboard SRAM and Flash resources

A Survey on Lightweight Entity Authentication with Strong PUFs

Physically unclonable functions (PUFs) exploit the unavoidable manufacturing variations of an integrated circuit (IC). Their input-output behavior serves as a unique IC \u27fingerprint\u27. Therefore, they have been envisioned as an IC authentication mechanism, in particular the subclass of so-called strong PUFs. The protocol proposals are typically accompanied with two PUF promises: lightweight and an increased resistance against physical attacks. In this work, we review nineteen proposals in chronological order: from the original strong PUF proposal (2001) to the more complicated noise bifurcation and system of PUFs proposals (2014). The assessment is aided by a unied notation and a transparent framework of PUF protocol requirements

Multi-factor Physical Layer Security Authentication in Short Blocklength Communication

Lightweight and low latency security schemes at the physical layer that have recently attracted a lot of attention include: (i) physical unclonable functions (PUFs), (ii) localization based authentication, and, (iii) secret key generation (SKG) from wireless fading coefficients. In this paper, we focus on short blocklengths and propose a fast, privacy preserving, multi-factor authentication protocol that uniquely combines PUFs, proximity estimation and SKG. We focus on delay constrained applications and demonstrate the performance of the SKG scheme in the short blocklength by providing a numerical comparison of three families of channel codes, including half rate low density parity check codes (LDPC), Bose Chaudhuri Hocquenghem (BCH), and, Polar Slepian Wolf codes for n=512, 1024. The SKG keys are incorporated in a zero-round-trip-time resumption protocol for fast re-authentication. All schemes of the proposed mutual authentication protocol are shown to be secure through formal proofs using Burrows, Abadi and Needham (BAN) and Mao and Boyd (MB) logic as well as the Tamarin-prover

Modeling attack resistant strong physical unclonable functions : design and applications

Physical unclonable functions (PUFs) have great promise as hardware authentication primitives due to their physical unclonability, high resistance to reverse engineering, and difficulty of mathematical cloning. Strong PUFs are distinguished by an exponentially large number of challenge-response pairs (CRPs), in contrast with weak PUFs that have a smaller CRP set. Because the adversary cannot create an enumeration clone by recording all CRPs even when in physical possession of a PUF, strong PUFs enable secure direct authentication, that does not require cryptography and are thus attractive to low-energy and IoT applications. The first contribution of this dissertation is the design of a strong silicon PUF resistant to machine learning (ML) attacks. For a strong PUF to be an effective security primitive, the CRPs need to be unpredictable: given a set of known CRPs, it should be difficult to predict the unobserved CRPs. Otherwise, an adversary can succeed in an attack based on building a model of the PUF. Early strong PUFs have shown vulnerability to ML based attacks. We take advantage of the strongly nonlinear I -- V property of MOSFETs operating in subthreshold region to introduce a highly unpredictable PUF. The PUF, termed the subthreshold current array PUF (SCA-PUF), consists of a pair of two-dimensional transistor arrays, a circuit stabilizing the PUF output, and a low-offset comparator. The proposed 65-bit SCA-PUF is fabricated in a 130nm process and allows 2⁶⁵ CRPs. It consumes 68nW and 11pJ/bit while exhibiting high uniqueness, uniformity, and randomness. It achieves bit error rate (BER) of 5.8% for the temperature range of -20 to +80°C and supply voltage variation of ±10%. A calibration-based CRP selection method is developed to improve BER to 0.4% with a 42% loss of CRPs. When subjected to ML attacks, the prediction error stays over 40% on 10⁴ training points, which shows negligible loss in PUF unpredictability and about 100X higher resilience than the 65-bit arbiter PUF, 3-XOR PUF, and 3-XOR lightweight PUF. The second contribution is the application of a strong PUF in a secure key update scheme. Side-channel attacks on cryptographic implementations threaten system security via the loss of the secret key. The adversary can recover the key by analyzing side-channel analog behavior of a cryptographic device, such as power consumption. Fresh re-keying techniques aim to mitigate these attacks by regularly updating the key, so that the side-channel exposure of each key is minimized. Existing key update schemes generate fresh keys by processing a root key using arithmetic operations. Unfortunately, such techniques have been demonstrated to also be vulnerable to side-channel attacks. We propose a novel approach to fresh re-keying that replaces the arithmetic key update function with a strong PUF. We show that the security of our scheme hinges on the resilience of the PUF to a power side-channel attack and propose a realization based on the SCA-PUF. We show that the SCA-PUF is resistant to simple power analysis and a modeling attack that uses ML on the power side-channel. We target an insecure device and secure server encryption scenario for which we provide an efficient and scalable method of PUF enrollment. Finally, we develop an end-to-end encryption system with PUF-based fresh re-keying, using a reverse fuzzy extractor construction. The third contribution is the implementation of a strong PUF provably secure against ML attacks. The security is derived from cryptographic hardness of learning decryption functions of semantically secure public-key cryptosystems within the probably approximately correct framework. The proposed PUF, termed the lattice PUF, compactly realizes the decryption function of the learning-with-errors (LWE) public-key cryptosystem as the core block. The lattice PUF is lightweight and fully digital. It is constructed using a weak PUF, as a physically obfuscated key (POK), an LWE decryption function block, a pseudo-random number generator in the form of a linear-feedback shift register (LFSR), a self-incrementing counter, and a control block. The POK provides the secret key of the LWE decryption function. A fuzzy extractor is utilized to ensure stability of the POK. The proposed lattice PUF significantly improves upon a direct implementation of LWE decryption function in terms of challenge transfer cost by exploiting distributional relaxations allowed by recent work in space-efficient LWEs. Specifically, only a small challenge-seed is transmitted while the full-length challenge is re-generated by the LFSR resulting in a 100X reduction of communication cost. To prevent an active attack in which arbitrary challenges can be submitted, the value of a self-incrementing counter is embedded into the challenge seed. We construct a lattice PUF that realizes a challenge-response pair space of size 2¹³⁶, requires 1160 POK bits, and guarantees 128-bit ML resistance. Assuming a bit error rate of 5% for SRAM-based POK, 6.5K SRAM cells are needed. The PUF shows excellent uniformity, uniqueness, and reliability. We implement the PUF on a Spartan 6 FPGA. It requires only 45 slices for the lattice PUF proper and 233 slices for the fuzzy extractorElectrical and Computer Engineerin

On Improving Robustness of Hardware Security Primitives and Resistance to Reverse Engineering Attacks

The continued growth of information technology (IT) industry and proliferation of interconnected devices has aggravated the problem of ensuring security and necessitated the need for novel, robust solutions. Physically unclonable functions (PUFs) have emerged as promising secure hardware primitives that can utilize the disorder introduced during manufacturing process to generate unique keys. They can be utilized as \textit{lightweight} roots-of-trust for use in authentication and key generation systems. Unlike insecure non-volatile memory (NVM) based key storage systems, PUFs provide an advantage -- no party, including the manufacturer, should be able to replicate the physical disorder and thus, effectively clone the PUF. However, certain practical problems impeded the widespread deployment of PUFs. This dissertation addresses such problems of (i) reliability and (ii) unclonability. Also, obfuscation techniques have proven necessary to protect intellectual property in the presence of an untrusted supply chain and are needed to aid against counterfeiting. This dissertation explores techniques utilizing layout and logic-aware obfuscation. Collectively, we present secure and cost-effective solutions to address crucial hardware security problems