JULY 2026
Post-Quantum Cryptography: Why the future of digital security depends on the evolution of PKI
In recent years, Post-Quantum Cryptography (PQC) has evolved from a research topic into a key cybersecurity consideration for businesses, public sector organizations and critical infrastructure operators. For many organizations, the question is no longer whether to prepare for the quantum era, but how to plan a transition that will affect digital certificates, digital identities and PKI infrastructures.
Algorithms such as RSA and Elliptic Curve Cryptography (ECC) underpin technologies including TLS, digital certificates, electronic signatures and digital identities. They were designed at a time when the quantum threat was still considered a distant prospect. Today, that landscape has changed.
Although large-scale quantum computers capable of breaking today’s public-key cryptography do not yet exist, the scientific community and international standards bodies have long been working towards the adoption of quantum-resistant algorithms. A major milestone came in August 2024 with the publication of the first NIST standards for post-quantum cryptography—FIPS 203 (ML-KEM), FIPS 204 (ML-DSA) and FIPS 205 (SLH-DSA). These standards now provide the foundation for the evolution of cryptographic ecosystems worldwide.
A challenge that is already here
The need to prepare does not depend solely on the future arrival of sufficiently powerful and reliable quantum computers. A more immediate threat already exists, commonly referred to as Harvest Now, Decrypt Later (HNDL).
Malicious actors can already intercept and store large volumes of encrypted data for future decryption once quantum computing capabilities become sufficiently advanced.
Healthcare records, intellectual property, financial data and government communications may remain valuable for many years, making it essential to protect the most sensitive information today.
For this reason, the transition to quantum-safe algorithms cannot be treated as something that can be postponed. It is a complex process that requires a comprehensive cryptographic inventory, a review of certificate lifecycle management and a well-defined migration strategy—all of which benefit from being started well in advance.
Is Post-Quantum Cryptography just about algorithms?
The most obvious response to the quantum threat is to adopt the new PQC algorithms. However, reducing the transition to a simple algorithm replacement would be an oversimplification.
The new cryptographic primitives have different characteristics from RSA and ECC. In many cases, with lattice-based and hash-based digital signature schemes, public keys, digital signatures and certificates are significantly larger. This can affect the performance of security protocols, TLS connection establishment, PKI management and, more broadly, the scalability of digital trust infrastructures.
The transition to post-quantum cryptography therefore requires a broader approach built around the principles of crypto-agility: the ability to adapt algorithms, protocols and infrastructures quickly as threats evolve and new standards emerge. At this stage of the transition, for example, hybrid deployment models are the most widely adopted approach. These combine classical and post-quantum algorithms to maintain security even if either family of algorithms were to be compromised.
This is also prompting a rethink of how Public Key Infrastructure (PKI) should evolve.
From Certificate Transparency to Merkle Tree Certificates
In recent years, the PKI ecosystem has already undergone a significant transformation with the widespread adoption of Certificate Transparency (CT), the system of public logs that makes it possible to monitor certificates issued by Certification Authorities (CAs) and detect anomalies or unauthorized issuance. As a result, transparency has become a fundamental pillar of digital trust.
Today, the research community is exploring ways to build on this model. Among the most promising proposals are Merkle Tree Certificates (MTCs), which use cryptographic data structures known as Merkle trees. The proposal is currently under discussion within the Internet Engineering Task Force (IETF) and is being developed by an international working group.
This approach differs significantly from traditional PKI architectures. Rather than signing each certificate individually, certificates are organized within a cryptographic tree. The Certification Authority signs only the root of the tree (the Merkle Root), while each certificate is accompanied by a Merkle Proof that demonstrates its inclusion in the published set of certificates.
In practical terms, the goal is to reduce the number of digital signatures required and improve the efficiency of certificate validation—an increasingly important consideration when using post-quantum algorithms with larger keys and signatures.
Why this architecture matters in the post-quantum era
Interest in Merkle Tree Certificates is driven primarily by the need to preserve the efficiency of PKI infrastructures as cryptographic keys and digital signatures become significantly larger.
Because the size of the inclusion proofs grows logarithmically with the number of published certificates, the communication overhead during a connection can remain relatively low even when post-quantum algorithms are used.
There is, however, another equally significant advantage: transparency becomes an intrinsic property of the system. A certificate cannot be added to the tree without leaving a trace that can be verified publicly. As a result, trust is derived not only from the Certification Authority's signature, but also from the ability to verify the state of the infrastructure independently and transparently.
It is important to emphasize that these architectures are still under development and undergoing standardization, and are not intended as an imminent replacement for traditional PKI. Nevertheless, they demonstrate how the transition to post-quantum cryptography is encouraging new approaches to the future of digital trust mechanisms.
Understanding the technologies that could shape tomorrow
Preparing for the post-quantum era begins with understanding the technologies that are emerging today and assessing their benefits, limitations and potential applications.
With this in mind, Actalis—the Certification Authority of the Aruba Group—has launched several initiatives in recent years to raise awareness of and encourage experimentation with post-quantum cryptography. These include the PQC Playground, designed to help professionals and organizations become familiar with the newly standardized algorithms.
The goal is not simply to keep pace with evolving standards, but to foster a culture of crypto-agility and technological preparedness.
Post-Quantum Cryptography represents the first step towards a quantum-safe ecosystem. However, the potential evolution of Public Key Infrastructure (PKI), including innovative approaches such as Merkle Tree Certificates, suggests that the transformation will extend far beyond the adoption of new algorithms,reshaping the very architecture of digital trust on which the internet relies.