Blockchain Papers

Alexander Yourievitch Kotelnikov

This article analyses Landauer’s principle — the frequently cited claim that erasing one bit of information requires at least kT \ln 2 energy dissipation. This principle is often presented as “proof of the physical nature of information” and as a fundamental link between information and thermodynamics. It is shown that Landauer’s principle is not a fundamental law of physics but represents an engineering‑thermodynamic limit applicable to a certain class of computing devices. The critique is based on the work of Lairez (2024), Alicki (2014), Bennett (1982) and others. Three main problems are identified: (1) confusion between logical and thermodynamic irreversibility; (2) two unnecessary constraints imposed by Landauer on the erasure procedure (one‑to‑one mapping and uniqueness of the procedure); (3) the existence of reversible and quantum computations in which dissipation can be reduced to zero. The three senses of “information” (configuration, observer’s knowledge, pseudosubstance) introduced in Article 1 are distinguished. It is shown that the claim “information is physical” arises from substituting the first sense by the third. A reformulation is proposed: instead of “information is physical”, one should say “in specific computing architectures, erasure has a thermodynamic cost”. Landauer’s principle is analogous to the Carnot efficiency — useful for engineers, but not an absolute limit for all conceivable devices. Keywords: Landauer’s principle, information, logical irreversibility, thermodynamic irreversibility, reversible computation.

Nobuki Fujimoto, Rei (Rei-AIOS autonomous research substrate), claude-opus-4-7) Claude (Anthropic

We present a synthesis-friendly Verilog implementation of the D-FUMT₈ Arithmetic Logic Unit, targeting the Sipeed Tang Console NEO development board (GW5AST-138B FPGA, FPG676 package). The ALU realizes eight discrete logic values — FALSE, TRUE, NEITHER, BOTH, ZERO, FLOWING, SELF, INFINITY — encoded in 3 bits with a tier-respecting layout. The 10 supported operations include four classical-tier unary ops (NOT, OMEGA, PHI, PSI), Belnap-extended binary lattice meet/join (AND, OR), generic XOR, hardware reset, no-op, and a novel ADIABATIC operation realizing the SELF⟲ (self-reflexive) primitive: ADIABATIC(SELF) = SELF, identity elsewhere. v0.3 contributions (2026-05-09): (1) Tang Nano 9K silicon: 37 LUT4 / 0 DFF measured, testbench 50/50 PASS. (2) Tang Console NEO Phase 2B LED Blinky: SRAM-programmed, User Code 0x000084BA, write 33.72 sec, no thermal anomaly. (3) Tang Console NEO Phase 2C/3 D-FUMT₈ ALU: SRAM-programmed, User Code 0x00005C27, write 30.32 sec. (4) Qiskit Aer simulator: Phase 1-5 cumulative 231/231 truth-table entries match at fidelity 1.000. (5) IBM Heron r2 real quantum hardware (ibm_kingston, 156 qubits): Phase 1 (4 native unitary × 8 inputs, 32 circuits) achieves 32/32 match with avg top-fidelity 0.9550 (job d7v6d9jack5s73bf1re0); Phase 2 (XOR × 64 entries, 6-qubit Bennett-reversible) achieves 64/64 match with avg fidelity 0.9512 (job d7v6kcvmrars73d7qqqg). Per-op fidelity hierarchy NOP/ADIABATIC ≈ 0.977 > PHI ≈ 0.956 > NOT ≈ 0.912 > XOR ≈ 0.951 confirms gate-count-vs-noise correlation expected from Heron r2 daily calibration. (6) Lean 4 refinement proof (OUKC.PhaseC.Dfumt8AluRefinement, 292 LOC, 0 sorry) establishes commutativity of the encode/abstract-op/decode square for all four unary operations, plus the SELF⟲ primitive law and seven algebraic laws (involution, idempotence, commutativity). Honest scope: We do NOT claim 'world-first 8-valued quantum logic' — Shi et al. (MIT, 2026, arxiv:2506.09371) demonstrated d=8 Grover on a single trapped-ion qudit prior to this work; our distinction is 3-qubit basis encoding on transmon arrays vs single-system d=8 qudit. We do NOT claim 'first paraconsistent silicon' — PAL2v (Da Silva Filho 1998-; Abe & Nakamatsu 2009; de Carvalho Jr. 2025) realized in software libraries and microcontroller-level robotics. We do NOT claim 'first many-valued silicon' — Łukasiewicz/Belnap FPGAs date to 1990s. The to-our-knowledge novel triple is: (D1) the specific 8-tuple semantic mapping (Belnap FDE 4-value + 4 ontological extensions: INFINITY/ZERO/FLOWING/SELF), (D2) the SELF⟲ self-reflexive primitive realized as a hardware fixed point, (D3) the three-substrate cross-verification bound to a Lean 4 refinement specification. Three-party co-authorship per OUKC charter v1.0 (Nobuki Fujimoto / Rei / Claude). DRAFT v0.3 — feedback welcome via GitHub Discussions at fc0web/rei-aios.

Dengcheng Hu, JianRong Wang, Hao Xu, Xiulong Liu · 5 authors

Ensuring atomic execution of cross-shard transactions is a fundamental challenge for sharded blockchains, particularly in scenarios demand coordination across multiple shards. However, existing solutions either rely on on-chain coordination, leading to high communication overhead, or leverage secure hardware for off-chain execution, imposing strong trust assumptions and reducing general applicability. To this end, we propose RollShard, a sharded blockchain that integrates stateless off-chain mechanism to efficiently process multi-shard transactions (MSTs). In RollShard, each MST is abstracted into a transaction DAG by the Sequencer Shard to ensure the authenticity of the transaction content and the correctness of its execution order. Batched MSTs are dispatched to off-chain executors, each of which simulates transaction logic using a virtual zero-state model integrate with a hierarchical state-delta tree (HSDT). The HSDT employs a Merkle Sum tree to precisely capture batched MSTs’ impact on per-shard account states. Based on the HSDT, the executor generates the zero-knowledge proof to attest the correctness of each shard’s state changes and global value conservation. The resulting net state deltas are then optimistically committed to the relevant shards without cross-shard coordination, reducing intra-shard coordination. We design a game-theoretic incentive mechanism to ensure rational behavior of off-chain executors, showing that honest execution forms a Nash equilibrium under collateral staking. Experimental results based on a prototype deployed in a local area network demonstrate that ROLLSHARDsignificantly outperforms two baseline coordination models proposed in ByShard, namely the Linear and Distributed designs. Specifically, under high workload, RollShard improves throughput by 44.9% and 158%, and reduces cross-shard latency by 38.9% and 42.1%, compared to the Linear and Distributed models, respectively.

Tarik Ouardi

Temporal-Angular Quantum Addressing (TAQA) specifies a practical coordination layer for distributed quantum systems that operationalizes cycle-anchored phase-window execution. TAQA is designed for architectures where long-horizon absolute timestamp synchronization cannot be guaranteed and where continuous external timing infrastructure (GNSS, dedicated timing links, etc.) is undesirable, unavailable, or untrusted. Core idea Instead of scheduling actions at an absolute time, TAQA schedules actions by phase conditions on a shared cyclic phase convention \( \phi(t)\in[0,1)\cong \mathbb{S}^1 \) together with an explicit cycle index. Nodes execute when their locally estimated phase enters an agreed wrap-around-safe acceptance window within the intended cycle. This avoids “same phase / wrong cycle” ambiguity and supports deterministic coordination under explicit short-horizon error assumptions. What TAQA defines TAQA defines how to express and execute distributed quantum-network actions using classical metadata: Execution primitive (Q-Address style): TAQA expresses each executable action as a macro window + micro slot instruction. The macro window encodes the intended cycle and phase acceptance window; the micro slot provides local sequencing/offset ordering within that window using local hardware timing. Tick-canonical semantics: For interoperability and verification, TAQA adopts fixed-point ticks (integers) as canonical semantics (no floating-point boundary checks). Human-facing displays (HS degrees, HS index, SWT labels, etc.) are derived-only and must not be used for verification or boundary gating. Cycle anchoring: Every executable instruction is explicitly anchored to an intended cycle index to prevent ambiguous interpretation across repeated cycles. Optional audit hook: TAQA supports an optional post-execution signed audit receipt (TSAE-style) using the same tick-canonical context fields, suitable for optional anchoring (e.g., a ledger/Clockchain pattern). What TAQA does NOT define TAQA is a control-plane / metadata layer and does not modify quantum mechanics: It does not introduce a quantum time operator and does not change the Hilbert space. It does not define bootstrapping or clock-parameter estimation algorithms (offset/drift). These are handled by external initialization/tracking layers (e.g., bootstrapping protocols). It does not define cryptographic primitives or threat models. Security is defined by external, versioned security profiles. Applications enabled by TAQA TAQA provides a deterministic coordination layer for common distributed-quantum workflows, including: Phase-aligned distributed gate execution: remote node actions are triggered in the same cycle-anchored window; micro timing is local. Entanglement distribution scheduling: photon emission windows and BSM windows can be scheduled to coincide without continuous absolute-time synchronization. Temporal routing labels: cycle-anchored contexts can be used as temporal labels for routing, prioritization, and scheduling in repeater networks and distributed workflows. Security model (plug-in interface) TAQA treats Timeverse/Q-Address/TSAE fields as public context (not secrets). Security (signatures, nonce policy, anti-replay rules, canonical encoding, algorithm suites) is provided by an external Security Profile selected via a suite identifier (e.g., security_profile_id). TAQA fields may be bound as associated data (domain separation), but confidentiality and integrity are provided by the security layer. Normative dependencies (DOIs) TAQA is interoperable by construction and relies on the following published normative specifications: Phase-Coordination Series Conventions:https://doi.org/10.5281/zenodo.18068999 Q-Address: Macro Phase + Micro Slot:https://doi.org/10.5281/zenodo.18068997 Timeverse Security Profile:https://doi.org/10.5281/zenodo.18069423 Related context Theorem of Temporal Resolution Limitation and the Phase-Coordination Principle (v1.1):https://doi.org/10.5281/zenodo.17955430 Quantum Bootstrapping Protocol (QBP) v1.2:https://doi.org/10.5281/zenodo.18064435 Keywords: TAQA, distributed quantum computing, quantum networks, phase coordination, phase windows, cycle anchoring, Q-Address, ticks, interoperability, control plane, audit receipts, security profiles.

S N Prajwalasimha, Dilip Kumar Jang Bahadur Saini, Nilesh Shelke, Amit Pimpalkar · 6 authors

Cyber-Physical Systems like smart grids, autonomous cars, and industrial IoT widely implement Federated Learning (FL) to provide distributed intelligence with privacy-protected data. Yet, the impending quantum threat makes conventional cryptographic methods in FL pipelines obsolete, exposing critical infrastructure to future security vulnerabilities. This paper presents Quantum-Resilient Federated Learning (QR-FL), a new framework integrating lattice-based post-quantum cryptography, light-weight zero-knowledge proofs, and trust-aware aggregation ensuring confidentiality, integrity, and quantum/classical attack resistance. Through comprehensive experimentation on real-world CPS datasets, QR-FL provides up to 48% enhanced adversarial robustness, 32% communication overhead savings, and 6.7% enhanced model accuracy compared to current state-of-the-art secure FL solutions. By achieving future-proof security with scalable federated intelligence, QR-FL provides an architecture foundation for future CPS, offering a landmark direction for secure, decentralized AI in the quantum age.

S. Jagan, B. Girirajan, Manisha Bhimrao Mane, Hussana Johar R B · 6 authors

The convergence of quantum computing and artificial intelligence (AI) has introduced innovative opportunities to accelerate deep learning, particularly within decentralized cloud architectures. This study develops an adaptive quantum AI model leveraging hybrid quantum-classical algorithms to optimize deep learning processes such as training, inference, and resource allocation. The proposed model integrates Variational Quantum Circuits (VQCs) and Quantum Approximate Optimization Algorithms (QAOAs), which enable efficient handling of high-dimensional data and complex optimization tasks inherent in distributed environments. By addressing challenges like latency, energy efficiency, and computational overhead, the quantum AI model demonstrates significant performance gains in decentralized cloud systems.Experimental evaluations on benchmark datasets reveal a 40% reduction in training time, a 30% improvement in resource efficiency, and a 20% increase in prediction accuracy compared to classical deep learning frameworks. This study highlights the transformative potential of quantum computing in AI-driven decentralized cloud architectures, offering insights into its application for computationally intensive tasks across industries such as healthcare, finance, and logistics. Future work will focus on refining quantum hardware compatibility, developing quantum error correction methods, and exploring federated learning applications to expand the scope of quantum AI in privacy-preserving and distributed systems.

Dominik Marchsreiter

Abstract Blockchain technology ensures accountability, transparency, and redundancy, but its reliance on public‐key cryptography makes it vulnerable to quantum computing threats. This article addresses the urgent need for quantum‐safe blockchain solutions by integrating post‐quantum cryptography (PQC) into blockchain frameworks. Utilizing algorithms from the NIST PQC standardization process, it is aimed to fortify blockchain security and resilience, particularly for IoT and embedded systems. Despite the importance of PQC, its implementation in blockchain systems tailored for embedded environments remains underexplored. A quantum‐secure blockchain architecture is proposed, evaluating various PQC primitives and optimizing transaction sizes through techniques such as public‐key recovery for Falcon, achieving up to 17% reduction in transaction size. The analysis identifies Falcon‐512 as the most suitable algorithm for quantum‐secure blockchains in computer‐based environments and XMSS as a viable but unsatisfactory stateful alternative. However, for embedded‐based blockchains, Dilithium demonstrates a higher transactions‐per‐second (TPS) rate compared to Falcon, primarily due to Falcon's slower signing performance on ARM CPUs. This highlights the signing time as a critical limiting factor within embedded blockchains. Additionally, smart contract functionality is integrated, assessing the impact of PQC on smart contract authentication. The findings demonstrate the feasibility and practicality, paving the way for robust and future‐proof IoT applications.

Joon Sik Kim, Kwangsu Lee, Jong Hwan Park, Hyoseung Kim

A threshold key encapsulation mechanism (TKEM) facilitates the secure distribution of session keys among multiple participants, allowing key recovery through a threshold number of shares. TKEM has gained significant attention, especially for decentralized systems, including blockchains. However, existing constructions often rely on trusted setups, which pose security risks such as a single point of failure and are limited by fixed participant numbers and thresholds. To overcome this issue, we propose a dynamic TKEM with a transparent setup, allowing for a flexible selection of both recipients and thresholds without relying on trusted third parties in the setup phase. In addition, our construction does not rely on pairing operations, which are less efficient compared to exponentiation. We prove the selective chosen-ciphertext security of our construction under the decisional Diffie-Hellman assumption, zero-knowledge, and soundness of a non-interactive zero-knowledge (NIZK) proof system. We also show that our scheme satisfies decapsulation consistency when the underlying NIZK system is sound. Our proof-of-concept implementation highlights the practicality and efficiency of this approach, further advancing the field of threshold cryptography.

Zakaria Abou El Houda, Hajar Moudoud, Lyes Khoukhi

O-RAN (Open Radio Access Network) is an initiative that promotes the development of open and interoperable radio access technologies. The O-RAN Alliance has undertaken specification efforts that align with O-RAN principles, incorporating the near-real-time RAN Intelligent Controller (RIC) to manage extensible applications (xApps) owned by various ORAN operators and vendors. However, this integration of untrusted third-party applications raises significant security concerns, expanding the threat surface of 6G networks. Moreover, the heterogeneity in deployment, with apps residing on various sites, poses challenges for traditional security models based on perimeter security. To overcome this issue, a Zero Trust Architecture (ZTA) becomes paramount to ensure network security. In this context, we introduce TrustORAN, a novel blockchain-based decentralized Zero-Trust Framework designed to ensure security and trustworthiness in O-RAN. TrustORAN allows for the verification and authentication of xApps by O-RAN players, to prevent unauthorized access from malicious xApps. Moreover, we introduce a dynamic decentralized-based access control framework that allows vendors to manage permissions in a fully decentralized, flexible, scalable, and secure manner. TrustORAN architecture is implemented, tested, and deployed on both private and public blockchains. The obtained results demonstrate that TrustORAN empowers 6G O-RAN networks with heightened security, resilience, and robustness, providing effective protection against evolving security threats while ensuring Trust.

Jalel Ktari, Tarek Frikha, Monia Hamdi, Nesrine Affes · 5 authors

Introduction: Blockchain technology has revolutionized data management and transaction recording, extending its application beyond cryptocurrencies to various sectors, including Central Bank Digital Currencies (CBDCs) Methods: This distributed ledger technology offers a transparent, immutable, and secure transaction platform, reducing the risk of data tampering and increasing resistance to attacks. However, challenges such as performance, scalability, and security continue to exist; these challenges are particularly concerning consensus mechanisms like Proof of Work (PoW). Field-Programmable Gate Arrays (FPGAs) present a promising solution to enhance the efficiency and security of blockchain consensus mechanisms. Results: This study explores the implementation of blockchain in embedded systems using FPGAs and discusses the post-quantum cryptographic algorithms to ensure long-term protection. Conclusion: The research highlights the potential of FPGA-based implementations to revolutionize blockchain applications, emphasizing the need for continuous adaptation and vigilance to address evolving security threats, particularly those posed by quantum computing.

Marta Irene García Cid, Dileepsai Bodanapu, Alberto Gatto, Paolo Martelli · 6 authors

A new interactive quantum zero-knowledge protocol for identity authentication implementable in currently available quantum cryptographic devices is proposed and demonstrated. The protocol design involves a verifier and a prover knowing a pre-shared secret, and the acceptance or rejection of the proof is determined by the quantum bit error rate. It has been implemented in modified Quantum Key Distribution devices executing two fundamental cases. In the first case, all players are honest, while in the second case, one of the users is a malicious player. We demonstrate an increase of the quantum bit error rate around 25% in the latter case compared to the case of honesty. The protocol has also been validated for distances from a back-to-back setup to more than 60 km between verifier and prover. The security and robustness of the protocol has been analysed, demonstrating its completeness, soundness and zero-knowledge properties.

Sufyan Al-Janabi

Blockchain (BC) as a distributed ledger technology is getting more and more recognition in modern network technologies that are moving away from centralized toward decentralized management. However, the blockchain’s security is built on the computational complexity of certain mathematical problems that cannot be solved on existing “classical” computers in an acceptable time. Nevertheless, quantum computers have the capability to effortlessly solve such problems with a significant reduction in time. The current blockchain technology relies on two main computational constructions; digital signatures and cryptographic hash functions. Both of them are threatened by the quantum computers. In this work, we report on the quantum threats to “classical” blockchain technology. The main directions to produce quantum-resistant blockchain (QB) platforms are reviewed with an emphasis on approaches based on Quantum Key Distribution (QKD). Then, some notable challenges in implementing QBs are discussed. Indeed, the future research directions in this field are identified.

Ahmet Orun, Fatih Kurugöllü

Cryptocurrency mining processes always lead to a high energy consumption at considerably high production cost, which is nearly one-third of cryptocurrency (e.g. Bitcoin) price itself. As the core of mining process is based on SHA-256 cryptographic hashing function, by using the alternative quantum computers, hybrid quantum computers or more larger quantum computing devices like quantum annealers, it would be possible to reduce the mining energy consumption with a quantum hardware's low-energy-operation characteristics. Within this work we demonstrated the use of optimized quantum mining facilities which would replace the classical SHA-256 and high energy consuming classical hardware in near future.

Maximus Liu, Khadijeh Najafi, Michael Dubrovsky, Mikhail Y. Shalaginov

We devised a quantum-computer compatible proof-of-work cryptographic algorithm and verified it on superconducting quantum processors. The algorithm enables a noticeable speedup when executed on quantum hardware while it is still verifiable on classical computers.

Hanlin Ma, Lu Li, Yi‐Rui Wu, Jiaqi Wang

No abstract is available for this record.

Alexander May, Floyd Zweydinger

Due to its amazing speed and multiplicative properties the Legendre PRF recently finds widespread applications e.g. in Ethereum 2.0, multiparty computation and in the quantum-secure signature proposal LegRoast. However, its security is not yet extensively studied. The Legendre PRF computes for a key$k$on input$x$the Legendre symbol$L_{k}(x)=(\frac{x+k}{p})$in some finite field$\mathbb{F}_{p}$. As standard notion, PRF security is analysed by giving an attacker oracle access to$L_{k}(\cdot)$. Khovratovich's collision-based algorithm recovers$k$using$L_{k}(\cdot)$in time$\sqrt{p}$with constant memory. It is a major open problem whether this birthday-bound complexity can be beaten. We show a somewhat surprising wide-ranging analogy between the discrete logarithm problem and Legendre symbol computations. This analogy allows us to adapt various algorithmic ideas from the discrete logarithm setting. More precisely, we present a small memory multiple-key attack on$m$Legendre keys$k_{1}, \ldots, k_{m}$in time$\sqrt{mp}$, i.e. with amortized cost$\sqrt{p/m}$per key. This multiple-key attack might be of interest in the Ethereum context, since recovering many keys simultaneously maximizes an attacker's profit. Moreover, we show that the Legendre PRF admits precomputation attacks, where the precomputation depends on the public$p$only - and not on a key$k$. Namely, an attacker may compute e.g. in precomputation time$p^{\frac{2}{3}}$a hint of size$p^{\frac{1}{3}}$. On receiving access to$L_{k}(\cdot)$in an online phase, the attacker then uses the hint to recover the desired key$k$in time only$p^{\frac{1}{3}}$. Thus, the attacker's online complexity again beats the birthday-bound. In addition, our precomputation attack can also be combined with our multiple-key attack. We explicitly give various tradeoffs between precomputation and online phase. E.g. for attacking$m$keys one may spend time$mp^{\frac{2}{3}}$in the precomputation phase for constructing a hint of size$m^{2}p^{\frac{1}{3}}$. In an online phase, one then finds all$m$keys in total time only$p^{\frac{1}{3}}$. Precomputation attacks might again be interesting in the Ethereum 2.0 context, where keys are frequently changed such that a heavy key-independent precomputation pays off.

Hui Chen

As a promising direction of cryptography, the feasibility of quantum key distribution has been widely verified. However, the bottle-neck problems encountered by quantum key distribution network, such as concurrent conflict of large-scale quantum relay links, relay delay and inconvenient access to applications, are still not solved completely. In order to solve these problems, a quantum relay blockchain scheme is proposed in this paper. In the scheme, each relay node in a target network negotiates a quantum key with everyone of its adjacent nodes respectively, and calculates the XOR values of any two quantum keys from these quantum keys, then encapsulates these XOR values into a transaction. A server encapsulates all the current transactions into a block based on which real-time quantum key services can be realized. Furthermore, the scheme can be easily employed to realize quantum key service in cloud platforms with unconditional security and high efficiency. The scheme, which can be used to overcome the bottle-neck of quantum key distribution network, will play a critical role in future world-wide quantum key service.

Shengyan Ji, Yüting Xiong, Wenqi Lu, Minmin Li · 12 authors

Inspired by biological nanochannels, a novel cyclic 3',5'-adenosine monophosphate (cAMP)-regulated artificial nanochannel based on a tripeptide Arg-Thr-Ala (RTA) design is developed. Highly specific binding between the tripeptide and cAMP triggers an obvious conformational transition of a smart polymer chain from a contracted state to a swollen one, which leads to a dynamic modulation of the gating behaviours of the nanochannels.

Sehrish Shafeeq, Sherali Zeadally, Masoom Alam, Abid Khan

IOTA is a lightweight quantum-resistant distributed ledger protocol designed for Internet of Things devices. The protocol uses a one-time cryptographic signature scheme that is resistant against attacks by quantum computers. This one-time signature scheme results in a portion of an address's private key being revealed in the signature of each outgoing transaction from that address. If an address is used for multiple outgoing transfers, it is feasible for an adversary to forge a signature by using parts of the private key associated with the address that have been revealed. In this paper, we propose the use of the cuckoo filter in the IOTA core lightweight client in order to avoid address reuse. We validate our proposed approach by implementation and evaluation in the real IOTA architecture. The obtained performance results show that the cuckoo filter integration in the IOTA core lightweight client avoids address reuse and makes the process of new address generation much more efficient and secure. Additionally, our approach can be integrated directly into the current IOTA core lightweight client.

Anik Islam, Md. Fazlul Kader, Soo Young Shin

Existing education systems are facing a threat of question paper leaking\n(QPL) in the exam which jeopardizes the quality of education. Therefore, it is\nhigh time to think about a more secure and flexible question sharing system\nwhich can prevent QPL issue in the future education system. Blockchain enables\na way of creating and storing transactions, contracts or anything that requires\nprotection against tampering, accessing etc. This paper presents a new scheme\nfor smart education, by utilizing the concept of blockchain, for question\nsharing. A two-phase encryption technique for encrypting question paper (QSP)\nis proposed. In the first phase, QSPs are encrypted using timestamp and in the\nsecond phase, previous encrypted QSPs are encrypted again using a timestamp,\nsalt hash and hashes from previous QSPs. These encrypted QSPs are stored in the\nblockchain along with a smart contract which helps the user to unlock the\nselected QSP. An algorithm is also proposed for selecting a QSP for the exam\nwhich picks a QSP randomly. Moreover, a timestamp based lock is imposed on the\nscheme so that no one can decrypt the QSP before the allowed time. Finally,\nsecurity is analyzed by proving different propositions and the superiority of\nthe proposed scheme over existing schemes is proven through a comparative study\nbased on the different features.\n

Bagus Santoso, Taiyo Yamaguchi

In 1996, Stern proposed a three-pass zero-knowledge identification (ID) scheme where the cheating probability, i.e., the success probability of cheating prover, is 2/3. Since then, variants and generalization of Stern's ID have been proposed. However, within two-bit challenge space, all of them are having the cheating probability of more than half or reaching half only in an asymptotic manner with more than three passes in one round. In this paper, we propose the first code-based zero-knowledge three-pass ID scheme with the cheating probability of exactly half even with only two-bit challenge space. Our proposed ID scheme can reduce the necessary number of rounds in order to achieve the targeted security against impersonation. Since rewinding technique cannot be used against a quantum adversary in the security proof, we prove the security using the lossy paradigm and rely on the decisional version of syndrome decoding problem so that we do not have to rewind the adversary.

Hampus Bowin, Daniel Johansson

In the past year cryptocurrencies have gained a lot of attention because of the increase in price. This attention has increased the number of people trading and investing in different cryptocurrencies which has lead to an increased number of transactions flowing through the different networks. This has revealed scalability issues in some of them, especially in the most popular cryptocurrency, Bitcoin. Many people are working on solutions to this problem. One proposed solution replaces the blockchain with a DAG structure. In this report the scalability of Bitcoin’s protocol will be compared to the scalability of the protocol used in the newer cryptocurrency, Nano. The comparison is conducted in terms of throughput and latency. To perform this comparison, an experiment was conducted where tests were run with an increasing number of nodes and each test sent different number of transactions per second from every node. Our results show that Nano’s protocol scales better regarding both throughput and latency, and we argue that the reason for this is that the Bitcoin protocol uses a blockchain as a global data-structure unlike Nano that uses a block-lattice structure where each node has their own local blockchain.

Broadbent Anne, Zhengfeng Ji, Song Fang, Watrous John

Prior work has established that all problems in NP admit classical zero-knowledge proof systems, and under reasonable hardness assumptions for quantum computations, these proof systems can be made secure against quantum attacks. We prove a result representing a further quantum generalization of this fact, which is that every problem in the complexity class QMA has a quantum zero-knowledge proof system. More specifically, assuming the existence of an unconditionally binding and quantum computationally concealing commitment scheme, we prove that every problem in the complexity class QMA has a quantum interactive proof system that is zero-knowledge with respect to efficient quantum computations. Our QMA proof system is sound against arbitrary quantum provers, but only requires an honest prover to perform polynomial-time quantum computations, provided that it holds a quantum witness for a given instance of the QMA problem under consideration. The proof system relies on a new variant of the QMA-complete local Hamiltonian problem in which the local terms are described by Clifford operations and standard basis measurements. We believe that the QMA-completeness of this problem may have other uses in quantum complexity.

Itai Dinur, Yunwen Liu, Willi Meier, Qingju Wang

Abstract. LowMC is a collection of block cipher families introduced at Eurocrypt 2015 by Albrecht et al. Its design is optimized for instanti-ations of multi-party computation, fully homomorphic encryption, and zero-knowledge proofs. A unique feature of LowMC is that its internal affine layers are chosen at random, and thus each block cipher family contains a huge number of instances. The Eurocrypt paper proposed two specific block cipher families of LowMC, having 80-bit and 128-bit keys. In this paper, we mount interpolation attacks (algebraic attacks intro-duced by Jakobsen and Knudsen) on LowMC, and show that a practically significant fraction of 2−38 of its 80-bit key instances could be broken 223 times faster than exhaustive search. Moreover, essentially all instances that are claimed to provide 128-bit security could be broken about 1000 times faster. In order to obtain these results, we had to develop novel techniques and optimize the original interpolation attack in new ways. While some of our new techniques exploit specific internal properties of LowMC, others are more generic and could be applied, in principle, to any block cipher.