Yubico Authenticator is an authenticator application that generates time-based one-time password (TOTP) codes for two-factor authentication. The application stores credentials on YubiKey hardware security keys rather than on mobile devices or computers, providing hardware-backed security for the authentication process. The application works across multiple platforms including Windows, macOS, Linux, iOS, and Android. Users can generate TOTP codes by connecting their YubiKey via USB or NFC tap on supported devices. The credentials are stored in the secure element of the YubiKey and cannot be extracted from the hardware. Users set up accounts by scanning QR codes from services that support TOTP authentication. The application supports all services compatible with standard authenticator apps. Multiple accounts can be secured using a single YubiKey, with credentials remaining separate between services. The application supports biometric unlocking on iOS devices through FaceID or TouchID. Credentials stored on the YubiKey are portable across devices, allowing users to access the same TOTP codes on both desktop and mobile platforms by connecting the same YubiKey. The application is available for download from platform-specific app stores and directly from Yubico's website. It requires a YubiKey hardware device to function.