CityFlow removes the need for central server storage and enables secure, hands-free authentication for both identity verification and payment. Users complete authentication and payment quickly and reliably through biometrics alone—without launching an app, tapping a device, or presenting a card. This seamless flow applies across diverse offline environments such as public transit, hospitals, financial services, and retail, unifying verification and payment into one effortless action. Biometric data is stored only on the user’s smartphone through a decentralized structure and never transmitted externally. Encrypted, tiered data transmission ensures that only the minimum required information is shared per institution, preventing overexposure. If a device is lost, CI-value deletion permanently erases the original biometric data, blocking misuse and unauthorized use. CityFlow ensures compliance with global privacy and authentication regulations while delivering a next-generation experience that balances security and convenience.