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). 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.

— Four digits
You no longer have to invent complex passwords to protect your Yandex account. There are just four digits to memorise: they’ll be used by Yandex.Key to generate a unique one-time password valid for less than a minute.

— Data protection
Yandex.Key safeguards your account from being hacked and your personal information from being stolen. One-time passwords will be available only to you, on your mobile device.

— Easy setup
You can add accounts manually, by entering the data from the service you want to use, or automatically, by scanning a QR-code provided by this service.

— Offline use
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.

— Additional features
The Key can general six- and eight-digit passwords, depending on the service’s requirements. Besides, the Key can update one-time passwords at different intervals, not necessarily once in every 30 seconds (this depends on the service).

— Security standards
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.

— Backing up
Back up the data in Yandex.Key on Yandex's servers, to use in case something happens to your device. It's secure: you backup is encrypted using a password that only you know.

For more detail, please see https://ya.cc/2fa-en