!!! Overview[1][2]
[{$pagename}] ([U2F])  [protocol] is a [FIDO protocol] is an open [authentication] standard that strengthens and simplifies [Multi-Factor Authentication] using specialized [USB] or [NFC] devices based on similar security technology found in [Smart Cards].

[{$pagename}] initially developed by [Google] and [Yubico], with contribution from [NXP Semiconductors], the standard is now hosted by the [FIDO] Alliance.

[{$pagename}] allows online services to augment the security of their existing [password] infrastructure by requiring a [Hard token] using a [FIDO Authenticator]. 

The [authenticator] provides an additional [Authentication Factor] to augment user login. 

!! [{$pagename}] [Authentication] process
In a [U2F] deployment the [Authentication] process is similar to 
* the user logs in to an [Service Provider] as usual (ie using [Password Authentication])
* the [user] is presented with a Challenge [user] "unlocks" the [U2F device] by using a [Personal Entity] [presence].
* [U2F device] proves possession of the [Private Key] to the [Service Provider] by signing the challenge.

!! [Universal Second Factor Challenges]
There are some [Universal Second Factor Challenges] that need to be considered.

!! More Information
There might be more information for this subject on one of the following:
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* [#1] - [Universal_2nd_Factor|Wikipedia:Universal_2nd_Factor|target='_blank'] - based on information obtained 2017-04-02
* [#2] - [Smart Card Technology and the FIDO Protocols|https://www.securetechalliance.org/wp-content/uploads/FIDO-and-Smart-Card-Technology-FINAL-April-2016.pdf|target='_blank'] - based on information obtained 2016-05-21
* [#2] - [USB-Dongle Authentication|http://www.dongleauth.info/|target='_blank'] - based on information obtained 2017-03-21