Google Authenticator OpenSource

Google Authenticator is the open-source counterpart of Google’s one-time passcode apps, implementing industry-standard OATH algorithms such as TOTP (time-based) and HOTP (counter-based) for two-factor authentication. The repository historically hosts code for mobile platforms like iOS and BlackBerry, demonstrating how to generate numeric codes locally without needing network access. Its core purpose is to help services and users add a second factor that’s simple to deploy yet resistant to password reuse and phishing. The app flow revolves around enrolling secrets via QR codes or manual entry, storing them securely on-device, and rendering rotating codes synchronized by time. Because it uses open standards, it interoperates with virtually any service that supports TOTP/HOTP, not just Google properties. The project also serves as a reference for implementers who want to understand enrollment UX, secret provisioning, and code generation at the application layer.