Quantum Use Case #64: Secure digital signatures for contracts and e-signing

Short answer: This use case addresses the vulnerability of current digital signature standards, such as RSA and ECDSA, to quantum cryptanalysis via Shor’s algorithm. Researchers have proposed post-quantum alternatives, specifically lattice-based schemes like ML-DSA, to ensure long-term authenticity and non-repudiation for electronic contracts. While the mathematical foundations are established in simulation and standardization efforts, operational adoption in commercial e-signing platforms remains a research-stage transition rather than a deployed reality.

The Quantum Threat to Current Standards

Digital signatures underpin the legal validity of electronic documents and the integrity of electronic transactions. Current public key cryptography standards, including Rivest-Shamir-Adleman (RSA) and the Elliptic Curve Digital Signature Algorithm (ECDSA), provide robust security against classical computing capabilities. However, these algorithms were not designed to withstand the emerging threat of quantum computing.

The primary risk arises from Shor’s algorithm. If an attacker possesses a large-enough quantum computer, they can cryptanalyze any RSA or ECC public key. This capability allows an attacker to generate fake digital signatures in seconds, effectively breaking the assurance of authenticity and non-repudiation. If this vulnerability is left unaddressed, digital communications and electronic transactions lose their foundational security guarantees. The threat is particularly acute for long-lived data, such as contracts that must remain verifiable over decades. Existing standards like ECDSA and RSA are considered robust for today’s computing landscape but are fundamentally incompatible with the principles of quantum computation.

Post-Quantum Cryptographic Solutions

To mitigate this risk, researchers have proposed post-quantum digital signing schemes. These new standards are designed to resist attacks from quantum computers. A prominent example is ML-DSA-65, which is associated with FIPS 204. This lattice-based approach offers a path to quantum-resistant signatures that can secure digital agreements without relying on the mathematical assumptions vulnerable to Shor’s algorithm.

The transition to these new standards is not merely about swapping one algorithm for another; it involves ensuring that the entire signature verification process remains secure. Post-quantum signatures must maintain the properties that make digital signatures critical for legal validity, including integrity checks to ensure documents have not been tampered with and authentication to verify the signer’s identity. The goal is to preserve the trust model of electronic transactions while neutralizing the quantum threat.

Integration with Advanced Electronic Signatures

In the context of enterprise and legal compliance, digital signatures often operate within specific frameworks, such as the ETSI Advanced Electronic Signatures (AdES) family. This family includes profiles for various document types, such as PAdES for PDFs, CAdES for binary/CMS, XAdES for XML, and JAdES for JSON/JWS. These profiles support different levels of assurance, including B-B, B-T, B-LT, and B-LTA.

Research-stage implementations have explored integrating post-quantum algorithms like ML-DSA-65 into these frameworks. For instance, concepts for post-quantum digital-signature engines have been described that span the entire AdES family. Such systems are designed not only to produce signatures but also to independently validate them. This includes the verification of long-term archival signatures, which may originate from other vendors or older systems. The ability to verify signatures across different profiles and timeframes is crucial for maintaining the legal validity of electronic documents over long periods.

However, it is important to note that these integrations are largely at the research or proposal stage. While the cryptographic primitives exist, the widespread operational adoption of post-quantum signatures in commercial e-signing platforms is not yet established. Vendors and standards bodies are currently navigating the timelines for migration, acknowledging that different sectors may adopt these changes at different rates.

Challenges and Real-World Constraints

The migration to post-quantum digital signatures presents several challenges. First, there is the issue of interoperability. Existing digital agreements rely on PKC standards that have been in use for decades. Transitioning to new standards requires ensuring that new signatures can be verified alongside or in place of old ones, particularly for archival purposes.

Second, the scale of the quantum computer required to break current standards is a factor in the urgency of the transition. While Shor’s algorithm provides a theoretical path to breaking RSA and ECC, the practical realization of a quantum computer large enough to do so in seconds is still a subject of ongoing research and development. Nevertheless, the consensus among cryptographers is that long-lived data requires protection against this future threat.

Third, the complexity of implementing these schemes in real-world systems is non-trivial. Post-quantum algorithms may have different performance characteristics compared to their classical counterparts, potentially impacting the speed and resource usage of signing and verification processes. Researchers have shown in simulation that these schemes can provide the necessary security, but the practical deployment in high-volume transactional environments requires further validation.

Outlook

The use case of securing digital signatures for contracts and e-signing against quantum threats is a critical area of research. The proposed solutions, such as ML-DSA-65, offer a viable path to quantum-resistant authentication. However, the current state of affairs is one of preparation and standardization rather than widespread operational use. Organizations are advised to monitor developments in post-quantum cryptography and prepare for the eventual migration, but they should not assume that current commercial e-signing platforms are already quantum-secure. The focus remains on ensuring that the mathematical foundations are sound and that the transition can be managed securely when the time comes.

FAQ

Can current digital signatures be broken by quantum computers?

Yes, researchers have shown that Shor’s algorithm can cryptanalyze RSA and ECC public keys on a sufficiently large quantum computer, allowing an attacker to generate fake digital signatures.

What is a post-quantum digital signature?

It is a digital signature scheme designed to withstand attacks from quantum computers. Examples include lattice-based schemes like ML-DSA-65, which are proposed as alternatives to RSA and ECDSA.

Are post-quantum signatures already in commercial use?

No, most use cases are at the research or proposal stage. While standards like FIPS 204 define these algorithms, widespread operational adoption in commercial e-signing platforms has not yet occurred.

How do post-quantum signatures handle long-term archival data?

Research-stage implementations propose integrating post-quantum algorithms into frameworks like the AdES family to support long-term archival profiles (B-LTA). This allows for the verification of signatures over decades, ensuring legal validity.

What is the role of standards bodies in this transition?

Standards bodies are involved in defining the post-quantum algorithms and their integration into existing frameworks. However, the timelines for migration vary, and the transition is not yet complete.