Libu2f-host provides a C library and command-line tool that implements the host-side of the U2F protocol. There are APIs to talk to a U2F device and perform the U2F Register and U2F Authenticate operations. For the server-side aspect, see our libu2f-server project.

This project is deprecated and is no longer being maintained. libfido2 is a new project with support for U2F and FIDO2.


The library and command-line tool is licensed under the LGPLv2+ license. Some other files are licensed under the GPLv3+ license. The license for each file should be clear from the comments at the top of it. See the files COPYING (for GPLv3) and COPYING.LGPLv2 for complete license texts. If you have a desire to use this package under another license, please contact us to discuss the reason. For any copyright year range specified as YYYY-ZZZZ in this package note that the range specifies every single year in that closed interval.


The library usage is documented in the API manual, see gtk-doc/html/ after you built with ./configure --enable-gtk-doc.

There is a command-line utility that is useful for debugging or testing. We describe how you could use it here.


First get a register challenge JSON blob somehow. You could use the Yubico U2F demo server interactively in a browser (with the U2F extension disabled). Alternatively, use the WSAPI or our server-side library. For example:

curl '' > foo

For reference, a blob looks like this:

{"challenge": "6l8aRM6f35hwrramrt7sKt7gDkvTamt2rYrMgMYE9ro", "version": "U2F_V2", "appId": ""}

Then invoke the u2fhost command, like this:

u2f-host -aregister -o < foo > bar

Your U2F device should start to blink, and you should touch it to proceed. For reference, the output blob is:

{ "registrationData": "BQQOtd__bgnv8V6_T-E4914xE-Pb6ji1YMUoP0LDLDCGtzCHPwbkMLlxlo6C6fawnQ7671o85nSbek9v0m3_fK7fQBLviOeAdzHiknazlys7eXtC9DBraClKAhYO-2SuxHnyFS9Jfk2nNrib1dtJJNcfRJrOBGILWIIlXzSt5xV4VBgwggIbMIIBBaADAgECAgRAxBIlMAsGCSqGSIb3DQEBCzAuMSwwKgYDVQQDEyNZdWJpY28gVTJGIFJvb3QgQ0EgU2VyaWFsIDQ1NzIwMDYzMTAgFw0xNDA4MDEwMDAwMDBaGA8yMDUwMDkwNDAwMDAwMFowKjEoMCYGA1UEAwwfWXViaWNvIFUyRiBFRSBTZXJpYWwgMTA4NjU5MTUyNTBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABK2iSVV7KGNEdPE-oHGvobNnHVw6ZZ6vB3jNIYB1C4t32OucHzMweHqM5CAMSMDHtfp1vuJYaiQSk7jb6M48WtejEjAQMA4GCisGAQQBgsQKAQEEADALBgkqhkiG9w0BAQsDggEBAVg0BoEHEEp4LJLYPYFACRGS8WZiXkCA8crYLgGnzvfKXwPwyKJlUzYxxv5xoRrl5zjkIUXhZ4mnHZVsnj9EY_VGDuRRzKX7YtxTZpFZn7ej3abjLhckTkkQ_AhUkmP7VuK2AWLgYsS8ejGUqughBsKvh_84uxTAEr5BS-OGg2yi7UIjd8W0nOCc6EN8d_8wCiPOjt2Y_-TKpLLTXKszk4UnWNzRdxBThmBBprJBZbF1VyVRvJm5yRLBpth3G8KMvrt4Nu3Ecoj_Q154IJpWe1Dp1upDFLOG9nWCRQk25Y264k9BDISfqs-wHvUjIo2iDnKl5UVoauTWaT7M6KuEwl4wRAIgU5qU72pCVD-bq68tETIKZ8aw7FRKviPVyFZc5Q8BlC0CICTc7_QuTWZFHwxGIotQO639WIllrPf1QqtvHCyzzKg_", "clientData": "eyAiY2hhbGxlbmdlIjogIjZsOGFSTTZmMzVod3JyYW1ydDdzS3Q3Z0RrdlRhbXQycllyTWdNWUU5cm8iLCAib3JpZ2luIjogImh0dHA6XC9cL2RlbW8ueXViaWNvLmNvbSIsICJ0eXAiOiAibmF2aWdhdG9yLmlkLmZpbmlzaEVucm9sbG1lbnQiIH0=" }

Then finish the U2F registration against the server:

curl -d "username=jas&password=foo&data=`cat bar`"

The output from that web service is JSON with some information.

{"username": "jas", "origin": "", "attest_cert": "-----BEGIN CERTIFICATE-----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\npeVFaGrk1mk+zOirhMJe\n-----END CERTIFICATE-----\n"}


To authenticate (aka sign), you should acquire a challenge somehow. Our demo server provides them.

curl '' > foo

For reference the challenge is:

{"challenge": "Pa3eucFQrH-5c9CAEdGESJiIW9po_Sozs6EfPeYN3nM", "version": "U2F_V2", "keyHandle": "Eu-I54B3MeKSdrOXKzt5e0L0MGtoKUoCFg77ZK7EefIVL0l-Tac2uJvV20kk1x9Ems4EYgtYgiVfNK3nFXhUGA", "appId": ""}

You invoke the u2f-host command as before, again your U2F device should blink up and wait for touch.

u2f-host -aauthenticate -o < foo > bar

For reference the response is:

{ "signatureData": "AQAAAAIwRAIgPIlfE6dsRykM5M_KG88hHjRh2ZdiyMakVUIKG9Q2w9QCIBcQYTOhD-D2McYQ2MK0xvoonqNnA0G_WEGNaHtttX32", "clientData": "eyAiY2hhbGxlbmdlIjogIlBhM2V1Y0ZRckgtNWM5Q0FFZEdFU0ppSVc5cG9fU296czZFZlBlWU4zbk0iLCAib3JpZ2luIjogImh0dHA6XC9cL2RlbW8ueXViaWNvLmNvbSIsICJ0eXAiOiAibmF2aWdhdG9yLmlkLmdldEFzc2VydGlvbiIgfQ==", "challenge": "Eu-I54B3MeKSdrOXKzt5e0L0MGtoKUoCFg77ZK7EefIVL0l-Tac2uJvV20kk1x9Ems4EYgtYgiVfNK3nFXhUGA" }

To use our demo server to verify it, you may use this call:

curl -d "username=jas&password=foo&data=`cat bar`"

On success, the output contains a counter and whether touch was asserted:

{"touch": "\u0001", "counter": 2}

That’s it!



  • Pkg-config simplifies finding other dependencies.

  • The JSON-C library is needed.

  • You will also need HIDAPI installed.

All of the above can be installed in Debian via:

apt-get install pkg-config libjson0-dev libhidapi-hidraw0 libhidapi-dev


This project uses autoconf, automake and libtool to achieve portability and ease of use. If you downloaded a tarball, build it as follows:

./configure --enable-gtk-doc
make check && sudo make install

Building from Git

You may check out the sources using Git with the following command:

git clone

This will create a directory libu2f-host. Enter the directory:

cd libu2f-host

Autoconf, automake and libtool must be installed. Help2man is used to generate the manpages. GTK-DOC is used to generated API documentation. Gengetopt is needed for command line parameter handling. HIDAPI developer files are also required. All of the above can be installed in Debian via:

apt-get install gtk-doc-tools gengetopt help2man

Generate the build system using:


See for some settings.


The main development platform is Debian GNU/Linux and it should be well supported. Windows and Mac OS X are important platforms and we support them fully as well.

Building Mac binaries can be done using The resulting binaries have been tested successfully on Mac OS X 10.7 and 10.9.

make -f VERSION=X.Y.Z

Windows binaries can be cross-compiled using For this to work the packages wine, mingw-w64 and mingw-w64-dev are required. The resulting binaries have been tested successfully on Windows 7 Pro 32-bit.

make -f VERSION=X.Y.Z

Both of these require that a release tarball of the project exists in the current directory. The value of the VERSION variable must match the version on that tarball.

Building from Git works on FreeBSD (excluding documentation), using gmake. Dependencies may be installed via:

pkg install gengetopt help2man hidapi json-c u2f-devd

And then configure and build using:

./configure --disable-gtk-doc


Project name: Yubico Universal 2nd Factor (U2F) Host C Library
Short name: libu2f-host
Symbol prefix: u2fh_
Tool: u2f-host
Pkg-config: u2f-host