Quantum Cyberwar

This book stems from a conviction that has become progressively clearer over the last five years: cyber warfare is about to undergo the most profound transformation in its short history, and that transformation has a name—quantum computing. The reader who holds this work in their hands finds themselves, perhaps unknowingly, at a unique historical moment. Behind the apparent continuity of cybersecurity —the same protocols, the same certifications, the same vocabularies—a revolution is silently developing that will rewrite, within less than a decade, the fundamental rules of digital conflict.

The central thesis defended here is simple in its formulation but radical in its implications: quantum cyberwar is not just another technological vector to join those already existing— ransomware , phishing , exploits , disinformation. It is the new axis around which all modern cyber warfare is reorganized. Where the 20th century articulated power around the atom and space, and where the first decades of the 21st century articulated power around the bit and the network, the next decade will articulate power around the qubit—and who controls it, who fears it, who prepares for its arrival.

The writing of this book was guided by three principles. First, scientific and technical rigor. Every technical statement is based on accessible specialized literature; every reference has been verified; every algorithm discussed has been understood in its mathematical structure and operational implications. Second, clarity of strategic thinking. The work is primarily aimed at senior officers, policymakers, executives of critical organizations, and academic researchers—readers whose role demands multi-dimensional understanding , not just isolated technical knowledge. Third, pre-agreement European Portuguese, with deliberate literary care, avoiding untranslated Anglicisms whenever a precise Portuguese alternative exists.

Throughout these pages, the reader will find a well-argued and, I hope, persuasive defense of the central thesis. They will also find a comparative analysis of state capabilities—the United States, the European Union, China, Russia, and emerging powers—a technical description of the relevant quantum algorithms, a detailed examination of post-quantum alternatives under construction, and, finally, a reflection on the place of Portugal and Europe in this new power architecture.

The work is organized into five parts. Part I establishes the foundations—what cyberspace is as a domain of conflict, what classical cryptography is that protects our communications today, what quantum computing is as an emerging technology, and what is the specific nature of the threat that the latter represents to the former. Part II develops the offensive thesis— quantum cyberwar as a new axis of attack. Part III develops the defensive thesis— quantum cybersecurity as an institutional and technical response. Part IV offers a comparative analysis matrix between the two dimensions. Part V projects the desired evolution until 2040, with particular attention to the Portuguese case and the European architecture.

I hope the reader finds in this work a useful tool for their strategic thinking. If this book contributes, in a modest way, to accelerating Portuguese institutional maturation in the face of the impending quantum transition, it will have fulfilled its purpose. Any remaining errors, whether technical or interpretative, are the sole responsibility of the author.

Sintra Spring 2026
Hermínio Cerqueira