NAME

       pam_u2f - Module for U2F authentication

SYNOPSIS

       pam_u2f [...]

DESCRIPTION

       The module provides U2F authentication against Yubikeys and other compliant
       authenticators.

OPTIONS

       debug
           Enables debug output

       debug_file
           Filename to write debugging messages to.  If this file is missing, nothing will be
           logged. This regular file has to be created by the user or must exist and be a regular
           file for anything getting logged to it. It is not created by pam-u2f on purpose (for
           security considerations). This filename may be alternatively set to "stderr"
           (default), "stdout", or "syslog".

       origin=origin
           Set the origin for the FIDO authentication procedure. If no value is specified, the
           origin "pam://$HOSTNAME" is used.

       appid=appid
           Set the application ID for the U2F authentication procedure. If no value is specified,
           the same value used for origin is taken ("pam://$HOSTNAME" if also origin is not
           specified).

       authfile=file
           Set the location of the file that holds the mappings of user names to keyHandles and
           user keys. The format is username:keyHandle1,public_key1:keyHandle2,public_key2:...
           the default location of the file is $XDG_CONFIG_HOME/Yubico/u2f_keys. If the
           environment variable is not set, $HOME/.config/Yubico/u2f_keys is used. An individual
           (per user) file may be configured relative to the users' home dirs, i.e.
           ".ssh/u2f_keys".

       authpending_file=file
           Set the location of the file that is used for touch request notifications. This file
           will be opened when pam-u2f starts waiting for a user to touch the device, and will be
           closed when it no longer waits for a touch. Use inotify to listen on these events, or
           a more high-level tool like yubikey-touch-detector. Default value:
           /var/run/user/$UID/pam-u2f-authpending. Set an empty value in order to disable this
           functionality, like so: "authpending_file=".

       nouserok
           Set to enable authentication attempts to succeed even if the user trying to
           authenticate is not found inside authfile or if authfile is missing/malformed.

       openasuser
           Setuid to the authenticating user when opening the authfile. Useful when the user’s
           home is stored on an NFS volume mounted with the root_squash option (which maps root
           to nobody which will not be able to read the file). Note that after release 1.0.8 this
           is done by default when no global authfile or XDG_CONFIG_HOME environment variable has
           been set.

       alwaysok
           Set to enable all authentication attempts to succeed (aka presentation mode).

       max_devices=n_devices
           Maximum number of devices allowed per user (default is 24). Devices specified in the
           authentication file that exceed this value will be ignored.

       interactive
           Set to prompt a message and wait before testing the presence of a U2F device.
           Recommended if your device doesn’t have tactile trigger.

       [prompt=your prompt here]
           Set individual prompt message for interactive mode. Watch the square brackets around
           this parameter to get spaces correctly recognized by PAM.

       manual
           Set to drop to a manual console where challenges are printed on screen and response
           read from standard input. Useful for debugging and SSH sessions without U2F-support
           from the SSH client/server. If enabled, interactive mode becomes redundant and has no
           effect.

       cue
           Set to prompt a message to remind to touch the device.

       [cue_prompt=your prompt here]
           Set individual prompt message for the cue option. Watch the square brackets around
           this parameter to get spaces correctly recognized by PAM.

       nodetect
           Skip detecting if a suitable key is inserted before performing a full authentication.
           See NOTES below.

       userpresence=int
           If 1, require user presence during authentication. If 0, do not request user presence
           during authentication. Otherwise, fallback to the authenticator’s default behaviour.

       userverification=int
           If 1, require user verification during authentication. If 0, do not request user
           verification during authentication. Otherwise, fallback to the authenticator’s default
           behaviour.

       pinverification=int
           If 1, require PIN verification during authentication. If 0, do not request PIN
           verification during authentication. Otherwise, fallback to the authenticator’s default
           behaviour.

       sshformat
           Use credentials produced by versions of OpenSSH that have support for FIDO devices. It
           is not possible to mix native credentials and SSH credentials. Once this option is
           enabled all credentials will be parsed as SSH.

EXAMPLES

       auth sufficient pam_u2f.so debug origin=pam://$HOSTNAME appid=pam://$HOSTNAME

       auth required pam_u2f.so origin=http://example.com appid=http://example.com
       authfile=/etc/yubikey_mappings

CAVEATS

       By default the mapping file inside a home directory will be opened as the target user,
       whereas the central file will be opened as "root". If the "XDG_CONFIG_HOME" variable is
       set, privileges will not be dropped unless the "openasuser" configuration setting is set.

       Using pam-u2f to secure the login to a computer while storing the mapping file in an
       encrypted home directory, will result in the impossibility of logging into the system. The
       partition is decrypted after login and the mapping file can not be accessed.

NOTES

       The "nodetect" option should be used with caution. pam_u2f checks that a key configured
       for the user is inserted before performing the full tactile authentication. This detection
       is done by sending a "check-only" authentication request to all inserted tokens to so see
       if at least one of them responds affirmatively to one or more of the keyhandles configured
       for the user. By doing this, pam_u2f can avoid emitting the "cue" prompt (if configured),
       which can cause some confusing UI issues if the cue is emitted followed by the underlying
       library immediately failing the tactile authentication. This option is also useful to
       avoid an unintended 1-second delay prior to the tactile authentication caused by versions
       of libu2f-host <= 1.1.5.

       If pam_u2f is configured to "cue" and "nodetect", an attacker can determine that pam_u2f
       is part of the authentication stack by inserting any random U2F token and performing an
       authentication attempt. In this scenario, the attacker would see the cue message followed
       by an immediate failure, whereas with detection enabled, the U2F authentication will fail
       silently. Understand that an attacker could choose a U2F token that alerts him or her in
       some way to the "check-only" authentication attempt, so this precaution only pushes the
       issue back a step.

       In summary, the detection feature was added to avoid confusing UI issues and to prevent
       leaking information about the authentication stack in very specific scenario when "cue" is
       configured. The "nodetect" option was added to avoid buggy sleep behavior in older
       versions of libu2f-host and for hypothetical tokens that do not tolerate the double
       authentication. Detection is performed, and likewise "nodetect" honored, regardless of
       whether "cue" is also specified.

BUGS

       Report pam-u2f bugs in the issue tracker: https://github.com/Yubico/pam-u2f/issues

SEE ALSO

       pam(7)

       The pam-u2f home page: https://developers.yubico.com/pam-u2f/

       YubiKeys can be obtained from Yubico: http://www.yubico.com/