“Attribution of cyberattacks requires identifying those responsible for bad acts, prominently including states, and accurate attribution is a crucial predicate in contexts as diverse as criminal indictments, insurance coverage disputes, and cyberwar. But the difficult technical side of attribution is just the precursor to highly contested legal and policy questions about when and how to accuse governments of responsibility for cyberattacks. Although politics may largely determine whether attributions are made public, this Article argues that when cyberattacks are publicly attributed to states, such attributions should be governed by legal standards. Instead of blocking the development of evidentiary standards for attribution, as the United States, United Kingdom, and France are currently doing, states should establish an international law requirement that public attributions must include sufficient evidence to enable cross-checking or corroboration of the accusations. This functionally defined standard harnesses both governmental and non-governmental attribution capabilities to shed light on states’ actions in cyberspace, and understanding state practice is a necessary precondition to establishing norms and customary international law to govern state behavior. Moreover, setting a clear evidentiary standard for attribution in the cybersecurity context has the potential to clarify currently unsettled general international law on evidentiary rules…”