This is a tool that can detect when YubiKey is waiting for your touch. It is designed to be integrated with other UI components to display a visible indicator.

For example, an integration with i3wm and py3status looks like this:

See also: Wiki: Which UI components are already integrated with this app?

This tool only works on Linux. If you want to help implementing (at least partial) support for other OS, pull requests are very welcome!

On Arch Linux, you can install it with pacman -S yubikey-touch-detector

The package also installs a systemd service and socket. If you want the app to launch on startup, just enable the service like so:

$ systemctl --user daemon-reload
$ systemctl --user enable --now yubikey-touch-detector.service

If you want the service to be started only when there is a listener on Unix socket, enable the socket instead like so:

$ systemctl --user daemon-reload
$ systemctl --user enable --now yubikey-touch-detector.socket

Alternatively you can download the latest release from the GitHub releases page. All releases are signed with my PGP key.

Finally you can install the app with go:

• gpgme

sudo apt install libgpgme-dev

• For Go <1.17

$ go get -u github.com/maximbaz/yubikey-touch-detector

• For Go >1.17:

$ go install github.com/maximbaz/yubikey-touch-detector@latest

This places the binary in your $GOPATH/bin folder, as well as the sources in $GOPATH/src for you to use the detection functions in your own code.

To test how the app works, run it in verbose mode to print every event on STDERR:

$ yubikey-touch-detector -v

Now try different commands that require a physical touch and see if the app can successfully detect them.

You can make the app show desktop notifications using libnotify if you run it with corresponding flag:

$ yubikey-touch-detector --libnotify

The app supports the following environment variables and CLI arguments (CLI args take precedence):

You can configure the systemd service by defining any of these environment variables in $XDG_CONFIG_HOME/yubikey-touch-detector/service.conf - see service.conf.example for a configuration example.

First of all, make sure the app is always running (e.g. start a provided systemd user service or socket).

Next, in order to integrate the app with other UI components to display a visible indicator, use any of the available notifiers in the notifier subpackage.

unix_socket notifier allows anyone to connect to the socket $XDG_RUNTIME_DIR/yubikey-touch-detector.socket and receive the following events:

All messages have a fixed length of 5 bytes to simplify the code on the receiving side.

dbus notifier registers a dbus server at the interface name com.github.maximbaz.YubikeyTouchDetector and path /com/github/maximbaz/YubikeyTouchDetector.

Properties on this dbus interface are discoverable through introspection. Properties also emit PropertiesChanged signals to indicate updates and support gobject binding.

Your YubiKey may require a physical touch to confirm these operations:

• sudo request (via pam-u2f)
• WebAuthn
• gpg --sign
• gpg --decrypt
• ssh to a remote host (and related operations, such as scp, rsync, etc.)
• ssh on a remote host to a different remote host (via forwarded ssh-agent)
• HMAC operations

See also: FAQ: How do I configure my YubiKey to require a physical touch?

In order to detect whether a U2F/FIDO2 operation requests a touch on YubiKey, the app is listening on the appropriate /dev/hidraw* device for corresponding messages as per FIDO spec.

See detector/u2f.go for more info on implementation details, the source code is documented and contains relevant links to the spec.

This detection is based on a "busy check" - when the card is busy (i.e. gpg --card-status hangs), it is assumed that it is waiting on a touch. This of course leads to false positives, when the card is busy for other reasons, but it is a good guess anyway.

In order to not run the gpg --card-status indefinitely (which leads to YubiKey be constantly blinking), the check is being performed only after any shadowed private key files inside $GNUPGHOME/private-keys-v1.d/* are opened (the app is thus watching for OPEN events on those files).

If the path to your private-keys-v1.d folder differs, define $GNUPGHOME environment variable, globally or in $XDG_CONFIG_HOME/yubikey-touch-detector/service.conf.

Since v1.11.0 we started using gpgme to perform some operations above:

• we are now using Assuan protocol to query card status, instead of spawning gpg --card-status processes.
• we are now querying path to $GNUPGHOME from gpgme.

The requests performed on a local host will be captured by the gpg detector. However, in order to detect the use of forwarded ssh-agent on a remote host, an additional detector was introduced.

This detector runs as a proxy on the $SSH_AUTH_SOCK, it listens to all communications with that socket and starts a gpg --card-status check in case an event was captured.

This detection is based on the observation that a certain /dev/hidraw* device will disappear when YubiKey will start waiting for a HMAC, and reappear when it stops waiting for a touch.

For sudo requests with pam-u2f, please refer to the documentation on Yubico/pam-u2f and online guides (e.g. official one).

For gpg and ssh operations, install ykman and use the following commands:

$ ykman openpgp keys set-touch sig on   # For sign operations
$ ykman openpgp keys set-touch enc on   # For decrypt operations
$ ykman openpgp keys set-touch aut on   # For ssh operations

If you are going to frequently use OpenPGP operations, cached or cached-fixed may be better for you. See more details here.

Make sure to unplug and plug back in your YubiKey after changing any of the options above.