Customary International Law Formation in the Digital Age: Rethinking State Practice and Opinio Juris in the Context of Cyber Norms

This dissertation theoretically and empirically examines the formation of customary international law in the digital age, focusing on whether state practice in cyberspace and opinio juris expressed through national cyber policy documents, GGE reports, and UN resolutions constitute a legally coherent body of emerging cyber customary international law. The traditional sources doctrine of customary international law, requiring the two-element showing of general state practice and accepted legal obligation (opinio juris), faces significant conceptual challenges in the cyber context where practice is largely covert, attribution is disputed, and formal legal statements are strategically ambiguous. Drawing on the ILC's 2018 Conclusions on the Identification of Customary International Law, the Tallinn Manual methodology, and a comprehensive analysis of state cyberspace practice documentation and policy statements, this research develops an original digital state practice framework for identifying and verifying custom formation in cyberspace. It fills a fundamental gap in the sources doctrine literature by providing the first systematic theoretical framework for evaluating cyber norms as customary international law, informed by digital state practice analysis. The dissertation applies this framework to assess the customary law status of key cyber norms including the prohibition of attacks on critical civilian infrastructure, the peacetime cyber espionage rule, and the due diligence obligation. Original contributions include the digital state practice framework and an empirical assessment of the customary status of major cyber norms. Findings indicate that few cyber norms have yet achieved customary law status under a rigorous analytical framework. Keywords: customary international law, cyber norms, state practice, opinio juris, digital age.