Yandex Key is an authenticator generating one-time passwords (OTP) for Yandex, Facebook, Google, GitHub, Dropbox, Vk.com, and other services with two-factor authentication (2FA).
Yandex Key doesn’t need internet connection to add accounts and generate one-time passwords, and you don't need to wait for an SMS with your password.
To log in to Yandex, enter this one-time password instead of your regular password, and to sign in to other services, with your normal password.
There are just from 4 to 16 digits to memorise: they’ll be used by Yandex Key to generate a unique one-time password valid for less than a minute.
Yandex Key supports two-factor authentication (or two-step verification) on all services using RFC 6238 and RFC 4226, except for services which only use sms.