The U2F 1.0 specification is now being expanded to support the wireless Bluetooth and near-field communications (NFC) protocols. What U2F provides is a second-factor authentication mechanism that can be used to supplement a username and password to provide more secure access to a site or online service. With the initial rollout of U2F, USB-based devices were the primary technology mechanism. USB keys, including those from security vendor Yubico, can be used for U2F to enable secure authentication.
As to why Bluetooth and NFC are being added now to U2F, Sam Srinivas, FIDO Alliance vice president and co-chair of the FIDO U2F Technology Working Group, said FIDO is being pragmatic and incremental in its approach to standardization.