Universal Second Factor Security Keys are supported by Google Chrome since version 40 and Opera since version 40. Universal Second Factor security keys can be used as an additional method of two-step verification on online services that support the U2F protocol, including
However, several of these only support is currently only available for the Chrome browser. Universal Second Factor Challenges is not widely supported in general.[3]The issues with the a set of one-time backup authentication codes is that either the person is unwilling or unable to save the codes in a Secure location or they are unable to obtain access or find them when needed. To store them in a secure place, requires some tool similar to a Password Management Application, which is the kind of thing we are trying to eliminate.