In the case of Google Authenticator, the TOTP are generated using a software (soft) token on a mobile device. A TOTP is a single-use code with a finite lifetime that can be calculated by two parties (client and server) using a shared secret and a synchronized clock (see RFC 4226 for additional information).
Earlier this year Google released their time-based one-time password (TOTP) solution named Google Authenticator.
