Subsequently, when the user opens the Authenticator app, it calculates an HMAC- SHA1 hash value using this secret key. This is transferred to the Authenticator app as a 16, 26, or 32-character base32 string, or as a QR code. Technical description ĭuring setup, the service provider generates an 80-bit secret key for each user (whereas RFC 4226 §4 requires 128 bits and recommends 160 bits). An alternative route of attack is a man-in-the-middle attack: if the device used for the login process is compromised by malware, the credentials and one-time password can be intercepted by the malware, which then can initiate its login session to the site, or monitor and modify the communication between the user and the site. With this kind of two-factor authentication, mere knowledge of username and password is insufficient to break into a user's account - the attacker also needs knowledge of the shared secret key or physical access to the device running the Authenticator app. The user runs the Authenticator app, which independently computes and displays the same password, which the user types in, authenticating their identity. The site then computes (but does not display) the required six-digit one-time password and asks the user to enter it. To log into a site or service that uses two-factor authentication and supports Authenticator, the user provides a username and password to the site. This secret key will be used for all future logins to the site. It must be set up for each site with which it is to be used: the site provides a shared secret key to the user over a secure channel, to be stored in the Authenticator app. The app is first installed on a smartphone to use Authenticator. Ĭurrent software releases are proprietary freeware. However, this fork was archived in and is now read only. Google provides Android, Wear OS, BlackBerry, and iOS versions of Authenticator.Īn official open-source fork of the Android app is available on GitHub. When logging into a site supporting Authenticator (including Google services) or using Authenticator-supporting third-party applications such as password managers or file hosting services, Authenticator generates a six- to eight-digit one-time password which users must enter in addition to their usual login details.

It implements multi-factor authentication services using the time-based one-time password (TOTP specified in RFC 6238) and HMAC-based one-time password (HOTP specified in RFC 4226), for authenticating users of software applications. Google Authenticator is a software-based authenticator by Google. Proprietary freeware (some versions were under Apache License 2.0)

Google authenticator hotp or totp