arXiv subjects

Fernando Castillo

Publications and source records attributed to Fernando Castillo.

11 recordsLinked to original sources

arXiv2026

Poled-fibre phase modulator for efficient high-dimensional quantum measurements

Efficient detection of quantum states underpins advanced device-independent quantum-information protocols that provide the ultimate level of security for tasks including quantum random number generation and quantum key distribution (QKD). High-dimensional encoding is a natural route to boost the performance of such protocols, offering enhanced noise resilience and higher information capacity, yet their practical implementation remains challenging. A key experimental bottleneck in higher dimensions is the typical need of active modulators for basis selection, which incur substantial optical losses and polarization-sensitive operation. Poled optical fiber phase modulators (PFPMs) are a fiber-native electro-optic technology that naturally addresses these challenges, combining sub-dB insertion loss, intrinsic polarization independence, and direct compatibility with standard telecommunications fiber. Here we report the first use of a PFPM for active quantum-state measurements in a fully fiber-integrated platform. Basis selection in our receiver for four-dimensional qudits is achieved using a single PFPM, substantially simplifying the receiver architecture. As a benchmark, we perform a four-dimensional QKD session and obtain a finite secret-key rate per pulse that, to the best of our knowledge, surpasses all previously reported QKD demonstrations. Our results establish poled-fiber electro-optic modulation as a broadly applicable platform for high-efficiency detection in fiber-integrated quantum information processing.

quant-ph↗

arXiv2026

An Evidence-driven Protocol for Trustworthy CI Pipelines

Enterprise software supply chains are increasingly vulnerable to infrastructure attacks, resulting in financial and reputational damage. Ensuring the integrity and provenance of software artifacts remains a significant challenge, where re-execution of the build and tests by every consumer to guarantee provenance produces a verification bottleneck and credibility reduction. This paper presents an evidence-driven protocol for trustworthy Continuous Integration (CI) pipelines that combines Deterministic Build Systems (DBS) with Trusted Execution Environments (TEEs). The approach provides cryptographically verifiable guarantees of integrity, authenticity, and attestation for CI artifacts in distributed environments, reducing implicit trust without requiring costly re-execution by consumers. We introduce a protocol that binds deterministic builds with TEE-based attestations, formalizing the evidence life cycle, together with a practical implementation using Nix and Intel TDX. Experimental results show that artifact verification is reduced from redundant computation to lightweight signature and policy checks. These findings demonstrate that evidence-driven CI pipelines establish scalable and verifiable trust in digital infrastructure, effectively amortizing the initial computational overhead introduced by TEEs.

cs.CR↗

arXiv2026

Decentralized Proof-of-Location for Content Provenance: Towards Capture-Time Authenticity

Reliable use of real-world data requires confidence that recorded evidence reflects what actually occurred at the moment of capture. In adversarial or incentive-misaligned cyber-physical settings, device-centric provenance and post-capture verification are insufficient to provide that guarantee. This paper builds on Proof-of-Location (PoL) as a baseline for establishing where and when events take place, and extends it with a witnessing-zone architecture in which multiple independent observers collectively validate physical events. The resulting approach produces auditable evidence artifacts that can support downstream systems in cyber-physical settings, without relying on centralized trust. Through representative scenarios and simulation-based evaluation, this paper shows how such architectures improve sensor data trustworthiness and resilience to fabricated or staged events.

cs.CR↗

arXiv2026

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) IX: Gas-driven origin for the continuum arc in the debris disc of HD 121617

Debris discs were long considered to be largely gas-free environments governed by collisional fragmentation, gravitational stirring, and radiative forces. Recent CO detections show that gas is present, but its abundance and origin remain uncertain. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) revealed a narrow gas and dust ring in the disc HD 121617 with an asymmetric arc 40% brighter than the rest of the ring. We aim to constrain the total gas mass in HD 121617 assuming the dust arc is produced by hydrodynamical gas-dust interactions. We used the Dusty FARGO-ADSG code, modelling dust as Lagrangian particles, including radiation pressure and dust feedback, and varying the total gas mass. Simulations were compared to observations using radiative transfer. An unstable gas ring creates a size-dependent radial and azimuthal dust trap whose efficiency depends on gas mass. Two models, with 50 and 5 Earth masses of gas, reproduce both the ALMA band 7 arc and the outward offset of the VLT/SPHERE scattered-light ring via gas drag and radiation pressure. We infer a conservative gas-mass range of 2.5 to 250 Earth masses. If the ALMA asymmetry is caused by gas drag, the required gas mass compared with the observed CO implies substantial H2, consistent with primordial gas. HD 121617 would then be a hybrid disc between protoplanetary and debris stages. Since a planet could also create an arc, future observations are needed to distinguish these scenarios.

astro-ph.EP↗

arXiv2025

Towards Trusted Service Monitoring: Verifiable Service Level Agreements

Service Level Agreement (SLA) monitoring in service-oriented environments suffers from inherent trust conflicts when providers self-report metrics, creating incentives to underreport violations. We introduce a framework for generating verifiable SLA violation claims through trusted hardware monitors and zero-knowledge proofs, establishing cryptographic foundations for genuine trustworthiness in service ecosystems. Our approach starts with machine-readable SLA clauses converted into verifiable predicates and monitored within Trusted Execution Environments. These monitors collect timestamped telemetry, organize measurements into Merkle trees, and produce signed attestations. Zero-knowledge proofs aggregate Service-Level Indicators to evaluate compliance, generating cryptographic proofs verifiable by stakeholders, arbitrators, or insurers in disputes, without accessing underlying data. This ensures three security properties: integrity, authenticity, and validity. Our prototype demonstrates linear scaling up to over 1 million events per hour for measurements with near constant-time proof generation and verification for single violation claims, enabling trustless SLA enforcement through cryptographic guarantees for automated compliance verification in service monitoring.

cs.CR↗

arXiv2025

A Taxonomy and Methodology for Proof-of-Location Systems

Digital societies increasingly rely on trustworthy proofs of physical presence for services such as supply-chain tracking, e-voting, ride-sharing, and location-based rewards. Yet, traditional localization methods often lack cryptographic guarantees of where and when an entity was present, leaving them vulnerable to spoofing, replay, or collusion attacks. In response, research on Proof-of-Location (PoL) has emerged, with recent approaches combining distance bounding, distributed consensus, and privacy-enhancing techniques to enable verifiable, tamper-resistant location claims. As the design space for PoL systems grows in complexity, this paper provides a unified framework to help practitioners navigate diverse application needs. We first propose a taxonomy identifying four core domains: (1) cryptographic guarantees, (2) spatio-temporal synchronization, (3) trust and witness models, and (4) interaction and overhead. Building on this, we introduce a methodology to map application-specific requirements onto appropriate PoL architectures. We illustrate this process through three use cases (retail e-coupons, supply chain auditing, and physical e-voting), each showing how different constraints shape protocol choices. Overall, this work offers a structured approach to building secure, scalable, and interoperable PoL systems.

cs.CR↗

arXiv2025

Trusted Compute Units: A Framework for Chained Verifiable Computations

Blockchain and distributed ledger technologies (DLTs) facilitate decentralized computations across trust boundaries. However, ensuring complex computations with low gas fees and confidentiality remains challenging. Recent advances in Confidential Computing -- leveraging hardware-based Trusted Execution Environments (TEEs) -- and Proof-carrying Data -- employing cryptographic Zero-Knowledge Virtual Machines (zkVMs) -- hold promise for secure, privacy-preserving off-chain and layer-2 computations. On the other side, a homogeneous reliance on a single technology, such as TEEs or zkVMs, is impractical for decentralized environments with heterogeneous computational requirements. This paper introduces the Trusted Compute Unit (TCU), a unifying framework that enables composable and interoperable verifiable computations across heterogeneous technologies. Our approach allows decentralized applications (dApps) to flexibly offload complex computations to TCUs, obtaining proof of correctness. These proofs can be anchored on-chain for automated dApp interactions, while ensuring confidentiality of input data, and integrity of output data. We demonstrate how TCUs can support a prominent blockchain use case, such as federated learning. By enabling secure off-chain interactions without incurring on-chain confirmation delays or gas fees, TCUs significantly improve system performance and scalability. Experimental insights and performance evaluations confirm the feasibility and practicality of this unified approach, advancing the state of the art in verifiable off-chain services for the blockchain ecosystem.

cs.CR↗

arXiv2025

Trustworthy Decentralized Autonomous Machines: A New Paradigm in Automation Economy

Decentralized Autonomous Machines (DAMs) represent a transformative paradigm in automation economy, integrating artificial intelligence (AI), blockchain technology, and Internet of Things (IoT) devices to create self-governing economic agents participating in Decentralized Physical Infrastructure Networks (DePIN). Capable of managing both digital and physical assets and unlike traditional Decentralized Autonomous Organizations (DAOs), DAMs extend autonomy into the physical world, enabling trustless systems for Real and Digital World Assets (RDWAs). In this paper, we explore the technological foundations, and challenges of DAMs and argue that DAMs are pivotal in transitioning from trust-based to trustless economic models, offering scalable, transparent, and equitable solutions for asset management. The integration of AI-driven decision-making, IoT-enabled operational autonomy, and blockchain-based governance allows DAMs to decentralize ownership, optimize resource allocation, and democratize access to economic opportunities. Therefore, in this research, we highlight the potential of DAMs to address inefficiencies in centralized systems, reduce wealth disparities, and foster a post-labor economy.

cs.MA↗

arXiv2024

TrustOps: Continuously Building Trustworthy Software

Software services play a crucial role in daily life, with automated actions determining access to resources and information. Trusting service providers to perform these actions fairly and accurately is essential, yet challenging for users to verify. Even with publicly available codebases, the rapid pace of development and the complexity of modern deployments hinder the understanding and evaluation of service actions, including for experts. Hence, current trust models rely heavily on the assumption that service providers follow best practices and adhere to laws and regulations, which is increasingly impractical and risky, leading to undetected flaws and data leaks. In this paper, we argue that gathering verifiable evidence during software development and operations is needed for creating a new trust model. Therefore, we present TrustOps, an approach for continuously collecting verifiable evidence in all phases of the software life cycle, relying on and combining already existing tools and trust-enhancing technologies to do so. For this, we introduce the adaptable core principles of TrustOps and provide a roadmap for future research and development.

cs.SE↗

arXiv2024

Advocate -- Trustworthy Evidence in Cloud Systems

The rapid evolution of cloud-native applications, characterized by dynamic, interconnected services, presents significant challenges for maintaining trustworthy and auditable systems, especially in sensitive contexts, such as finance or healthcare. Traditional methods of verification and certification are often inadequate due to the fast-past and dynamic development practices common in cloud computing. This paper introduces Advocate, a novel agent-based system designed to generate verifiable evidence of cloud-native application operations. By integrating with existing infrastructure tools, such as Kubernetes and distributed tracing systems, Advocate captures, authenticates, and stores evidence trails in a tamper-resistant manner. This approach not only supports the auditing process but also allows for privacy-preserving evidence aggregation. Advocate's extensible architecture facilitates its deployment in diverse environments, enabling the verification and adherence to policies and enhance trust in cloud services.

cs.DC↗

arXiv2024

Towards Credential-based Device Registration in DApps for DePINs with ZKPs

Decentralized Physical Infrastructure Networks (DePINS) are secured and governed by blockchains but beyond crypto-economic incentives, they lack measures to establish trust in participating devices and their services. The verification of relevant device credentials during device registration helps to overcome this problem. However, on-chain verification in decentralized applications (dApp) discloses potentially confidential device attributes whereas off-chain verification introduces undesirable trust assumptions. In this paper, we propose a credential-based device registration (CDR) mechanism that verifies device credentials on the blockchain and leverages zero-knowledge proofs (ZKP) to protect confidential device attributes from being disclosed. We characterize CDR for DePINs, present a general system model, and technically evaluate CDR using zkSNARKs with Groth16 and Marlin. Our experiments give first insights into performance impacts and reveal a tradeoff between the applied proof systems.

cs.CR↗