Beyond Single Signatures: Building Resilience into Digital Agreements

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Author: Denis Avetisyan

A new concept, QoeSiGN, proposes a collaborative approach to qualified electronic signatures, mitigating risks and enhancing user control.

This paper details QoeSiGN, a system leveraging privacy-preserving collaborative computation to create more robust and agile Qualified Electronic Signatures (QES) compliant with eIDAS.

Despite the increasing reliance on electronic signatures for data authenticity and legal validity, current Qualified Electronic Signature (QES) systems-as defined by regulations like eIDAS-present a centralized point of failure. This paper introduces QoeSiGN: Towards Qualified Collaborative eSignatures, a novel concept leveraging privacy-preserving collaborative computations to distribute trust and enhance the robustness, agility, and user involvement in QES creation. By exploring architectures like multi-party hardware security modules and secure multi-party computation, QoeSiGN offers viable pathways towards a more resilient and adaptable QES ecosystem. Could this approach unlock new possibilities for secure and user-centric digital signing in the future?

Unveiling the Cracks in Centralized Trust

The foundation of many Qualified Electronic Signature (QES) systems, exemplified by initiatives like ID Austria, rests on centralized infrastructure. This architecture, while seemingly efficient, inherently introduces single points of failure and potential compromise. Critical signing keys and essential processes are concentrated within a limited number of servers and facilities, making them attractive targets for malicious actors. A successful attack on this central authority could invalidate a vast number of signatures, disrupting essential services and eroding public trust. Furthermore, reliance on a single provider creates dependencies that can be exploited through denial-of-service attacks or internal vulnerabilities. This centralization contrasts with emerging decentralized technologies and highlights a growing need for more resilient and distributed approaches to digital trust.

Despite the stringent security requirements outlined in the eIDAS Regulation, reliance on traditional Hardware Security Modules (HSMs) introduces vulnerabilities in the face of increasingly sophisticated cyber threats. While designed to safeguard cryptographic keys, HSMs represent centralized points of failure, susceptible to both physical compromise and remote exploitation via evolving attack vectors. The fixed architecture of many HSMs hinders rapid adaptation to new threats, demanding costly and time-consuming upgrades or replacements. Furthermore, the complexity of managing and maintaining these devices, coupled with a shortage of skilled personnel, increases the risk of misconfiguration and operational errors. Consequently, organizations must actively reassess their reliance on traditional HSMs and explore more agile, distributed security solutions to effectively mitigate risk and maintain compliance within the dynamic threat landscape.

Qualified Trust Service Providers, the backbone of secure digital identities and transactions, face increasing pressure to fortify their cybersecurity posture to align with the stringent demands of the NIS-2 Directive. This legislation necessitates a significant elevation of risk management practices and incident handling capabilities, pushing beyond conventional security measures. Centralized infrastructure, while historically prevalent in establishing trust, presents a considerable challenge in meeting these heightened standards due to its inherent vulnerability to large-scale attacks and systemic failures. The Directive’s emphasis on supply chain security and proactive threat mitigation requires providers to demonstrate resilience not only within their own systems, but also across the entire ecosystem of interconnected services they rely upon, demanding continuous monitoring, rigorous testing, and substantial investment in advanced threat detection and response technologies.

QoeSiGN: Architecting Trust Beyond the Centralized Model

QoeSiGN addresses the limitations of traditional Qualified Electronic Signature (QES) creation by implementing a distributed trust architecture. This approach moves away from centralized Hardware Security Modules (HSMs) and relies on Distributed Service Robustness, where cryptographic operations are performed collaboratively across multiple independent parties. By distributing the signing process and key management, QoeSiGN eliminates single points of failure that could compromise signature validity or availability. The system leverages collaborative computation to ensure that a minimum number of participating parties are required to generate a valid signature, while preventing any single entity from unilaterally creating or invalidating signatures, as detailed in the referenced paper.

QoeSiGN’s foundational security relies on distributing cryptographic key management and digital signing processes via Threshold Cryptography and Multi-Party Hardware Security Modules (HSMs). Threshold Cryptography necessitates a quorum of participating parties to collectively perform a cryptographic operation, preventing any single entity from unauthorized access or control. Multi-Party HSMs further enhance this by ensuring that the private key is never fully reconstructed in any single location; instead, key shares are distributed and held by independent parties. A digital signature then requires contributions from these shares, assembled only during the signing process and eliminating single points of failure or compromise. This distributed approach mitigates risks associated with traditional centralized key management systems and enhances overall system resilience.

QoeSiGN facilitates Agile Crypto Deployment through a modular architecture enabling independent updates to cryptographic algorithms and key lengths without requiring system-wide disruptions. This is achieved by isolating the cryptographic core within Multi-Party HSMs and utilizing a distributed key management system. Consequently, organizations can rapidly integrate post-quantum cryptography or respond to newly discovered vulnerabilities by updating individual components without impacting overall system availability. The distributed nature also minimizes the blast radius of potential compromises, enhancing long-term security posture and reducing the costs associated with large-scale cryptographic rollouts or emergency patching.

Deconstructing Risk: Validating QoeSiGN Through Rigorous Analysis

QoeSiGN’s security validation employs STRIDE Threat Modeling – a systematic approach identifying potential vulnerabilities within the Quantum Encryption Standard (QES) creation process. STRIDE categorizes threats across six areas: Spoofing, Tampering, Repudiation, Information Disclosure, Denial of Service, and Elevation of Privilege. By analyzing each stage of QES generation – including key derivation, encryption, and distribution – through these threat categories, the process reveals specific attack vectors. This methodology allows for proactive identification of weaknesses in the system’s design and implementation, facilitating targeted mitigation strategies before deployment. The resulting threat model provides a documented, prioritized list of vulnerabilities to address, enhancing the overall security posture of QoeSiGN.

DREAD risk assessment is employed to quantitatively prioritize threats identified during the STRIDE threat modeling phase of QoeSiGN security validation. This methodology assigns scores based on Damage potential, Reproducibility, Exploitability, Affected users, and Discoverability; each factor is rated on a scale of 1-10. The cumulative DREAD score allows for objective ranking of vulnerabilities, enabling the security team to concentrate mitigation efforts on the highest-risk items first. This focused approach optimizes resource allocation and ensures the most critical security concerns are addressed efficiently within the QES creation process.

QoeSiGN incorporates advanced cryptographic techniques to bolster security and operational flexibility within its distributed architecture. Homomorphic Encryption allows for computations to be performed directly on encrypted data, eliminating the need for decryption and subsequent re-encryption, thereby minimizing exposure of sensitive information. Complementing this, Multi-Party Computation – Virtual Secret Sharing Mechanism (MPC-VSM) enables distributed computation of a function over inputs held by multiple parties, without any party revealing their individual input. This combination reduces single points of failure and enhances data confidentiality by distributing cryptographic operations and key management across the network, increasing resilience against compromise and supporting agile data processing.

Beyond Resilience: Towards a Future Forged in Distributed Trust

QoeSiGN represents a significant advancement in securing Qualified Electronic Signatures (QES) by fundamentally shifting away from architectures reliant on single points of failure. Traditional QES infrastructure often concentrates trust in centralized Hardware Security Modules (HSMs) or trusted service providers, creating vulnerabilities to attack and disruption. This design instead distributes trust across a network, eliminating the risks associated with these dependencies. By removing centralized components, QoeSiGN bolsters the resilience of critical digital processes – from financial transactions to legally binding agreements – ensuring continued operation even in the face of compromise or outage. This isn’t merely mitigation; it’s actively safeguarding the very integrity and availability of digital trust mechanisms, forging a more robust foundation for the digital economy.

The architecture is purposefully aligned with the stringent requirements of both the eIDAS regulation and the NIS-2 directive, bolstering confidence in digital interactions. By adhering to these frameworks, the system establishes a robust foundation for legally valid electronic signatures and secure digital identities across Europe. This commitment to regulatory compliance isn’t merely procedural; it actively mitigates risks associated with fraud, data breaches, and unauthorized access, ultimately fostering a higher degree of trust among users and institutions. Consequently, the design facilitates seamless cross-border transactions and strengthens the integrity of online services, creating a more secure and reliable digital ecosystem for individuals and businesses alike.

The proposed architecture unlocks next-generation electronic signature solutions by prioritizing both security and scalability, ultimately fostering innovation and economic expansion within the digital economy. Recognizing that a one-size-fits-all approach is naive, the design details two distinct implementation pathways: MP-HSM and VSM-MPC. MP-HSM leverages established hardware security modules for robust key protection, prioritizing security and established trust, while VSM-MPC employs multi-party computation to distribute signing operations, enhancing agility and potentially minimizing single points of failure. These instantiations represent deliberate tradeoffs; MP-HSM offers heightened security and robustness, whereas VSM-MPC prioritizes flexibility and user control, allowing organizations to select the optimal balance based on their specific requirements and risk tolerance, and ensuring a future-proof approach to digital trust.

The pursuit of QoeSiGN, as detailed in the paper, embodies a spirit of challenging established norms within the realm of digital signatures. The concept deliberately dismantles the traditional, centralized Qualified Electronic Signature (QES) creation process, recognizing its inherent vulnerability. This isn’t merely about improving security; it’s about fundamentally rethinking how trust is established in a digital world. As Vinton Cerf aptly stated, “The Internet is not about technology; it’s about people.” QoeSiGN mirrors this sentiment by shifting signature creation towards a more distributed, collaborative model, ultimately placing greater control and resilience in the hands of the users themselves – a deliberate inversion of the status quo, born from a desire to understand and overcome limitations.

Beyond the Seal: Charting Future Directions

QoeSiGN’s proposition-distributing trust in qualified electronic signatures-reveals a fundamental tension. Current systems, built upon centralized authorities, offer a comforting illusion of control. Yet, that control becomes a single, glaring vulnerability. The paper rightly exposes this, but the pursuit of absolute resilience is a paradoxical game. Each layer of redundancy introduces new failure modes, new avenues for subtle compromise. The true challenge isn’t eliminating risk, but shifting the cost of failure, making it more inconvenient than catastrophic.

Future work must confront the practical implications of truly decentralized QES. The cryptographic overhead of privacy-preserving collaborative computation isn’t merely a technical hurdle; it’s a fundamental limitation on scalability. Can a system designed for ultimate security also accommodate the mundane demands of everyday transactions? Furthermore, the integration with existing eIDAS frameworks presents a knotty problem. Compliance isn’t a bug to be fixed, but a constraint that shapes the very architecture of trust.

Ultimately, QoeSiGN nudges the field toward a necessary, if uncomfortable, question: what does ‘qualified’ even mean in a world where identity and authority are fluid concepts? The pursuit of unbreakable signatures may be a fool’s errand. Perhaps the most valuable outcome of this research will be a clearer understanding of where, and why, those seals should be broken.

Original article: https://arxiv.org/pdf/2512.13613.pdf

Contact the author: https://www.linkedin.com/in/avetisyan/

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2025-12-16 19:08