Authentication > google-authenticator

The Google Authenticator project includes implementations of one-time passcode generators for several mobile platforms, as well as a pluggable authentication module (PAM). One-time passcodes are generated using open standards developed by the Initiative for Open Authentication (OATH) (which is unrelated to OAuth). These implementations support the HMAC-Based One-time Password (HOTP) algorithm specified in RFC 4226 and the Time-based One-time Password (TOTP) algorithm specified in RFC 6238. Tutorials: How to set up two-factor authentication for SSH login on Linux