Authors - Masaki Murakami, Atsuhiro Goto Abstract - Post-quantum cryptography (PQC) migration in the financial sector is a resource allocation problem shaped by network interdependence. This study develops a prototype dynamic simulation model that incrementally introduces cyber-risk internalization: starting from a baseline without cyber-risk channels, adding firm-level direct cyber loss, and finally incorporating systemic cyber loss propagated through the financial network. The paper quantifies how the scope of cyber-risk internalization determines migration outcomes under a shared investmentallocation framework. Results show that firm-level internalization accelerates early migration but remains insufficient for full sector-wide coverage, whereas systemic-risk internalization can close the late-stage adoption gap under sufficiently supportive policy conditions. This distinction shows that policy support for PQC migration should not be understood only as cost reduction, but also as a mechanism for internalizing network externalities. Through nested comparisons of these model variants, this study demonstrates how each risk channel distinctly shifts migration outcomes.
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