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  1. Digital Twins (DT) virtually model cyber-physical objects via sensory inputs by simulating or monitoring their behavior. Therefore, DTs usually harbor vast quantities of Internet of Things (IoT) components (e.g., sensors) that gather, process, and offload sensitive information (e.g., healthcare) to the cloud. It is imperative to ensure the trustworthiness of such sensitive information with long-term and compromise-resilient security guarantees. Digital signatures provide scalable authentication and integrity with non-repudiation and are vital tools for DTs. Post-quantum cryptography (PQC) and forward-secure signatures are two fundamental tools to offer long-term security and breach resiliency. However, NIST-PQC signature standards are exorbitantly costly for embedded DT components and are infeasible when forward-security is also considered. Moreover, NIST-PQC signatures do not admit aggregation, which is a highly desirable feature to mitigate the heavy storage and transmission burden in DTs. Finally, NIST recommends hybrid PQ solutions to enable cryptographic agility and transitional security. Yet, there is a significant gap in the state of the art in the achievement of all these advanced features simultaneously. Therefore, there is a significant need for lightweight digital signatures that offer compromise resiliency and compactness while permitting transitional security into the PQ era for DTs.

    We create a series of highly lightweight digital signatures called Hardware-ASisted Efficient Signature (HASES) that meets the above requirements. The core ofHASES is a hardware-assisted cryptographic commitment construct oracle (CCO) that permits verifiers to obtain expensive commitments without signer interaction. We created threeHASES schemes:PQ-HASES is a forward-secure PQ signature,LA-HASES is an efficient aggregate Elliptic-Curve signature, andHY-HASES is a novel hybrid scheme that combinesPQ-HASES andLA-HASES with novel strong nesting and sequential aggregation.HASES does not require a secure-hardware on the signer. We prove thatHASES schemes are secure and implemented them on commodity hardware and and 8-bit AVR ATmega2560. Our experiments confirm thatPQ-HASES andLA-HASES are two magnitudes of times more signer efficient than their PQ and conventional-secure counterparts, respectively.HY-HASES outperforms NIST PQC and conventional signature combinations, offering a standard-compliant transitional solution for emerging DTs. We open-sourceHASES schemes for public-testing and adaptation.

     
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    Free, publicly-accessible full text available December 21, 2024
  2. The Internet of Things (IoT) harbors a large number of resource-limited devices (e.g., sensors) that continuously generate and offload sensitive information (e.g., financial, health, personal). It is imperative the ensure the trustworthiness of this data with efficient cryptographic mechanisms. Digital signatures can offer scalable authentication with public verifiability and nonrepudiation. However, the state-of-the-art digital signatures do not offer the desired efficiency and are not scalable for the connected resource-limited IoT devices. This is without considering long term security features such as post-quantum security and forward security. In this paper, we summarize the main challenges to an energy-aware and efficient signature scheme. Then, we propose new scheme design improvements that uniquely embed different emerging technologies such as Mutli-Party Computation (MPC) and secure enclaves (e.g., Intel SGX) in order to secret-share confidential keys of low-end IoT devices across multiple cloud servers. We also envision building signature schemes with Fully Homomorphic Encryption (FHE) to enable verifiers to compute expensive commitments under encryption. We provide evaluation metrics that showcase the feasibility and efficiency of our designs for potential deployment on embedded devices in IoT. 
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    Free, publicly-accessible full text available November 7, 2024
  3. Digital signatures provide scalable authentication with non-repudiation and therefore are vital tools for the Internet of Things (IoT). IoT applications harbor vast quantities of low-end devices that are expected to operate for long periods with a risk of compromise. Hence, IoT needs post-quantum cryptography (PQC) that respects the resource limitations of low-end devices while offering compromise resiliency (e.g., forward security). However, as seen in NIST PQC efforts, quantum-safe signatures are extremely costly for low-end IoT. These costs become prohibitive when forward security is considered. We propose a highly lightweight post-quantum digital signature called HArdware-Supported Efficient Signature (HASES) that meets the stringent requirements of resource-limited signers (processor, memory, bandwidth) with forward security. HASES transforms a key-evolving one-time hash-based signature into a polynomial unbounded one by introducing a public key oracle via secure enclaves. The signer is non-interactive and only generates a few hashes per signature. Unlike existing hardware-supported alternatives, HASES does not require secure-hardware on the signer, which is infeasible for low-end IoT. HASES also does not assume non-colluding servers that permit scalable verification. We proved that HASES is secure and implemented it on the commodity hardware and the 8-bit AVR ATmega2560 microcontroller. Our experiments confirm that HASES is 271  and 34  faster than (forward-secure) XMSS and (plain) Dilithium. HASES is more than twice and magnitude more energy-efficient than (forward-secure) ANT and (plain) BLISS, respectively, on an 8-bit device. We open-source HASES for public testing and adaptation. 
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  4. Internet of Things (IoT) and Storage-as-a-Service (STaaS) continuum permit cost-effective maintenance of security-sensitive information collected by IoT devices over cloud systems. It is necessary to guarantee the security of sensitive data in IoT-STaaS applications. Especially, log entries trace critical events in computer systems and play a vital role in the trustworthiness of IoT-STaaS. An ideal log protection tool must be scalable and lightweight for vast quantities of resource-limited IoT devices while permitting efficient and public verification at STaaS. However, the existing cryptographic logging schemes either incur significant computation/signature overhead to the logger or extreme storage and verification costs to the cloud. There is a critical need for a cryptographic forensic log tool that respects the efficiency requirements of the IoT-STaaS continuum. In this paper, we created novel digital signatures for logs called Optimal Signatures for secure Logging (OSLO), which are the first (to the best of our knowledge) to offer both small-constant signature and public key sizes with near-optimal signing and batch verification via various granularities. We introduce new design features such as one-time randomness management, flexible aggregation along with various optimizations to attain these seemingly conflicting properties simultaneously. Our experiments show that OSLO offers 50× faster verification (for 235 entries) than the most compact alternative with equal signature sizes, while also being several magnitudes of more compact than its most logger efficient counterparts. These properties make OSLO an ideal choice for the IoT-STaaS, wherein lightweight logging and efficient batch verification of massive-size logs are vital for the IoT edge and cold storage servers, respectively. 
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  5. Storage-as-a-service (STaaS) permits the client to outsource her data to the cloud, thereby reducing data management and maintenance costs. However, STaaS also brings significant data integrity and soundness concerns since the storage provider might not keep the client data intact and retrievable all the time (e.g., cost saving via deletions). Proof of Retrievability (PoR) can validate the integrity and retrievability of remote data effectively. This technique can be useful for regular audits to monitor data compromises, as well as to comply with standard data regulations. In particular, cold storage applications (e.g., MS Azure, Amazon Glacier) require regular and frequent audits with less frequent data modification. Yet, despite their merits, existing PoR techniques generally focus on other metrics (e.g., low storage, fast update, metadata privacy) but not audit efficiency (e.g., low audit time, small proof size). Hence, there is a need to develop new PoR techniques that achieve efficient data audit while preserving update and retrieval performance. In this paper, we propose Porla, a new PoR framework that permits efficient data audit, update, and retrieval functionalities simultaneously. Porla permits data audit in both private and public settings, each of which features asymptotically (and concretely) smaller audit-proof size and lower audit time than all the prior works while retaining the same asymptotic data update overhead. Porla achieves all these properties by composing erasure codes with verifiable computation techniques which, to our knowledge, is a new approach to PoR design. We address several challenges that arise in such a composition by creating a new homomorphic authenticated commitment scheme, which can be of independent interest. We fully implemented Porla and evaluated its performance on commodity cloud (i.e., Amazon EC2) under various settings. Experimental results demonstrated that Porla achieves two to four orders of magnitude smaller audit proof size with 4x–18000x lower audit time than all prior schemes in both private and public audit settings at the cost of only 2x–3x slower update. 
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  6. End-to-end encrypted file-sharing systems enable users to share files without revealing the file contents to the storage servers. However, the servers still learn metadata, including user identities and access patterns. Prior work tried to remove such leakage but relied on strong assumptions. Metal (NDSS '20) is not secure against malicious servers. MCORAM (ASIACRYPT '20) provides confidentiality against malicious servers, but not integrity. Titanium is a metadata-hiding file-sharing system that offers confidentiality and integrity against malicious users and servers. Compared with MCORAM, which offers confidentiality against malicious servers, Titanium also offers integrity. Experiments show that Titanium is 5x-200x faster or more than MCORAM. 
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  7. 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. 
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  8. Proof of Work (PoW) protocols, originally proposed to circumvent DoS and email spam attacks, are now at the heart of the majority of recent cryptocurrencies. Current popular PoW protocols are based on hash puzzles. These puzzles are solved via a brute force search for a hash output with particular properties, such as a certain number of leading zeros. By considering the hash as a random function, and fixing a priori a sufficiently large search space, Grover’s search algorithm gives an asymptotic quadratic advantage to quantum machines over classical machines. In this paper, as a step towards a fuller understanding of post-quantum blockchains, we propose a PoW protocol for which quantum machines have a smaller asymptotic advantage. Specifically, for a lattice of rank n sampled from a particular class, our protocol provides as the PoW an instance of the Hermite Shortest Vector Problem (Hermite-SVP) in the Euclidean norm, to a small approximation factor. Asymptotically, the best known classical and quantum algorithms that directly solve SVP type problems are heuristic lattice sieves, which run in time 20.292n+o(n) and 2 0.265n+o(n) respectively. We discuss recent advances in SVP type problem solvers and give examples of where the impetus provided by a lattice-based PoW would help explore often complex optimization spaces. 
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  9. 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. 
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