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A digital signature is an essential cryptographic tool to offer authentication with public verifiability, non-repudiation, and scalability. However, digital signatures often rely on expensive operations that can be highly costly for low-end devices, typically seen in the Internet of Things and Systems (IoTs). These efficiency concerns especially deepen when post-quantum secure digital signatures are considered. Hence, it is of vital importance to devise post-quantum secure digital signatures that are designed with the needs of such constraint IoT systems in mind. In this work, we propose a novel lightweight post-quantum digital signature that respects the processing, memory, and bandwidth limitations of resource-limited IoTs. Our new scheme, called ANT, efficiently transforms a one-time signature to a (polynomially bounded) many-time signature via a distributed public key computation method. This new approach enables a resource-limited signer to compute signatures without any costly lattice operations (e.g., rejection samplings, matrix multiplications, etc.), and only with a low-memory footprint and compact signature sizes. We also developed a variant for ANT with forward-security, which is an extremely costly property to attain via the state-of-the-art postquantum signatures. 

The lack of authentication protection for bootstrapping messages broadcast by base-stations makes impossible for devices to differentiate between a legitimate and a fake base-station. This vulnerability has been widely acknowledged, but not yet fixed and thus enables law-enforcement agencies, motivated adversaries, and nation-states to carry out attacks against targeted users. Although 5G cellular protocols have been enhanced to prevent some of these attacks, the root vulnerability for fake base-stations still exists. In this paper, we propose an efficient broadcast authentication protocol based on a hierarchical identity-based signature scheme, Schnorr-HIBS, which addresses the root cause of the fake base-station problem with minimal computation and communication overhead. We implement and evaluate our proposed protocol using off-the-shelf software-defined radios and open-source libraries. We also provide a comprehensive quantitative and qualitative comparison between our scheme and other candidate solutions for 5G base-station authentication proposed by 3GPP. Our proposed protocol achieves at least a 6x speedup in terms of end-to-end cryptographic delay and a communication cost reduction of 31% over other 3GPP proposals. 

Certificates ensure the authenticity of users’ public keys, however their overhead (e.g., certificate chains) might be too costly for some IoT systems like aerial drones. Certificate-free cryptosystems, like identity-based and certificateless systems, lift the burden of certificates and could be a suitable alternative for such IoTs. However, despite their merits, there is a research gap in achieving compatible identity-based and certificateless systems to allow users from different domains (identity-based or certificateless) to communicate seamlessly. Moreover, more efficient constructions can enable their adoption in resource-limited IoTs. In this work, we propose new identity-based and certificateless cryptosystems that provide such compatibility and efficiency. This feature is beneficial for heterogeneous IoT settings (e.g., commercial aerial drones), where different levels of trust/control is assumed on the trusted third party. Our schemes are more communication efficient than their public key based counterparts, as they do not need certificate processing. Our experimental analysis on both commodity and embedded IoT devices show that, only with the cost of having a larger system public key, our cryptosystems are more computation and communication efficient than their certificate-free counterparts. We prove the security of our schemes (in the random oracle model) and open-source our cryptographic framework for public testing/adoption. 

Multi-user oblivious storage allows users to access their shared data on the cloud while retaining access pattern obliviousness and data confidentiality simultaneously. Most secure and efficient oblivious storage systems focus on the utilization of the maximum network bandwidth in serving concurrent accesses via a trusted proxy. How- ever, since the proxy executes a standard ORAM protocol over the network, the performance is capped by the network bandwidth and latency. Moreover, some important features such as access control and security against active adversaries have not been thoroughly explored in such proxy settings. In this paper, we propose MOSE, a multi-user oblivious storage system that is efficient and enjoys from some desirable security properties. Our main idea is to harness a secure enclave, namely Intel SGX, residing on the untrusted storage server to execute proxy logic, thereby, minimizing the network bottleneck of proxy-based designs. In this regard, we address various technical design challenges such as memory constraints, side-channel attacks and scalability issues when enabling proxy logic in the secure enclave. We present a formal security model and analysis for secure enclave multi-user ORAM with access control. We optimize MOSE to boost its throughput in serving concurrent requests. We implemented MOSE and evaluated its performance on commodity hardware. Our evaluation confirmed the efficiency of MOSE, where it achieves approximately two orders of magnitudes higher throughput than the state-of-the-art proxy-based design, and also, its performance is scalable proportional to the available system resources. 

An attempt to derive signer-efficient digital signatures from aggregate signatures was made in a signature scheme referred to as Structure-free Compact Rapid Authentication (SCRA) (IEEE TIFS 2017). In this paper, we first mount a practical universal forgery attack against the NTRU instantiation of SCRA by observing only 8161 signatures. Second, we propose a new signature scheme (FAAS), which transforms any single-signer aggregate signature scheme into a signer-efficient scheme. We show two efficient instantiations of FAAS, namely, FAAS-NTRU and FAAS-RSA, both of which achieve high computational efficiency. Our experiments confirmed that FAAS schemes achieve up to 100× faster signature generation compared to their underlying schemes. Moreover, FAAS schemes eliminate some of the costly operations such as Gaussian sampling, rejection sampling, and exponentiation at the signature generation that are shown to be susceptible to side-channel attacks. This enables FAAS schemes to enhance the security and efficiency of their underlying schemes. Finally, we prove that FAAS schemes are secure (in random oracle model), and open-source both our attack and FAAS implementations for public testing purposes. 

Authentication is vital for the Internet of Things (IoT) applications involving sensitive data (e.g., medical and financial systems). Digital signatures offer scalable authentication with non-repudiation and public verifiability, which are necessary for auditing and dispute resolution in such IoT applications. However, digital signatures have been shown to be highly costly for low-end IoT devices, especially when embedded devices (e.g., medical implants) must operate without a battery replacement for a long time. We propose an Energy-aware Signature for Embedded Medical devices (ESEM) that achieves near-optimal signer efficiency. ESEM signature generation does not require any costly operations (e.g., elliptic curve (EC) scalar multiplication/addition), but only a small constant-number of pseudo-random function calls, additions, and a single modular multiplication. ESEM has the smallest signature size among its EC-based counterparts with an identical private key size. We achieve this by eliminating the use of the ephemeral public key (i.e, commitment) in Schnorrtype signatures from the signing via a distributed construction at the verifier without interaction with the signer while permitting a constant-size public key. We proved that ESEM is secure (in random oracle model), and fully implemented it on an 8-bit AVR microcontroller that is commonly used in medical devices. Our experiments showed that ESEM achieves 8.4× higher energy efficiency over its closest counterpart while offering a smaller signature and code size. Hence, ESEM can be suitable for deployment on resource-limited embedded devices in IoT. We 

Efficient authentication is vital for IoT applications with stringent minimum-delay requirements (e.g., energy delivery systems). This requirement becomes even more crucial when the IoT devices are battery-powered, like small aerial drones, and the efficiency of authentication directly translates to more operation time. Although some fast authentication techniques have been proposed, some of them might not fully meet the needs of the emerging delay-aware IoT. In this paper, we propose a new signature scheme called ARIS that pushes the limits of the existing digital signatures, wherein commodity hardware can verify 83,333 signatures per second. ARIS also enables the fastest signature generation along with the lowest energy consumption and end-to-end delay among its counterparts. These significant computational advantages come with a larger storage requirement, which is a favorable trade-off for some critical delay-aware applications. These desirable features are achieved by harnessing message encoding with cover-free families and a special elliptic curve based one-way function. We prove the security of ARIS under the hardness of the elliptic curve discrete logarithm problem in the random oracle model. We provide an open-sourced implementation of ARIS on commodity hardware and an 8-bit AVR microcontroller for public testing and verification. 

Public key Encryption with Keyword Search (PEKS) aims in mitigating the impacts of data privacy versus utilization dilemma by allowing any user in the system to send encrypted files to the server to be searched by a receiver. The receiver can retrieve the encrypted files containing specific keywords by providing the corresponding trapdoors of these keywords to the server. Despite their merits, the existing PEKS schemes introduce a high end-to-end delay that may hinder their adoption in practice. Moreover, they do not scale well for large security parameters and provide no post-quantum security promises. In this paper, we propose novel lattice-based PEKS schemes that offer a high computational efficiency along with better security assurances than that of the existing alternatives. Specifically, our NTRU-PEKS scheme achieves 18 times lower end-to-end delay than the most efficient pairing-based alternatives. Our LWE-PEKS offers provable security in the standard model with a reduction to the worst-case lattice problems. We fully implemented our NTRU-PEKS scheme and benchmarked its performance as deployed on Amazon Web Services cloud infrastructures. 

We introduce a simple, yet efficient digital signature scheme which offers post-quantum security promise. Our scheme, named TACHYON, is based on a novel approach for extending one-time hash-based signatures to (polynomially bounded) many-time signatures, using the additively homomorphic properties of generalized compact knapsack functions. Our design permits TACHYON~to achieve several key properties. First, its signing and verification algorithms are the fastest among its current counterparts with a higher level of security. This allows TACHYON~to achieve the lowest end-to-end delay among its counterparts, while also making it suitable for resource-limited signers. Second, its private keys can be as small as κ bits, where κ is the desired security level. Third, unlike most of its lattice-based counterparts, TACHYON~does not require any Gaussian sampling during signing, and therefore, is free from side-channel attacks targeting this process. We also explore various speed and storage trade-offs for TACHYON, thanks to its highly tunable parameters. Some of these trade-offs can speed up TACHYON signing in exchange for larger keys, thereby permitting TACHYON~to further improve its end-to-end delay. 

Authentication and integrity are fundamental security services that are critical for any viable system. However, some of the emerging systems (e.g., smart grids, aerial drones) are delay-sensitive, and therefore their safe and reliable operation requires delay-aware authentication mechanisms. Unfortunately, the current state-of-the-art authentication mechanisms either incur heavy computations or lack scalability for such large and distributed systems. Hence, there is a crucial need for digital signature schemes that can satisfy the requirements of delay-aware applications. In this paper, we propose a new digital signature scheme that we refer to as Compact Energy and Delay-aware Authentication (CEDA). In CEDA, signature generation and verification only require a small-constant number of multiplications and Pseudo Random Function (PRF) calls. Therefore, it achieves the lowest end-to-end delay among its counterparts. Our implementation results on an ARM processor and commodity hardware show that CEDA has the most efficient signature generation on both platforms, while offering a fast signature verification. Among its delay-aware counter-parts, CEDA has a smaller private key with a constant-size signature. All these advantages are achieved with the cost of a larger public key. This is a highly favorable trade-0ff for applications wherein the verffier is not memory-limited. We open-sourced our implementation of CEDA to enable its broad testing and adaptation.