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PAM_SSH(8)                  System Manager's Manual                 PAM_SSH(8)

NAME
     pam_ssh - authentication and session management with SSH private keys

SYNOPSIS
     [service-name] module-type control-flag pam_ssh [options]

DESCRIPTION
     The SSH authentication service module for PAM provides functionality for
     two PAM categories: authentication and session management.  In terms of
     the module-type parameter, they are the "auth" and "session" features.

   SSH Authentication Module
     The SSH authentication component provides a function to verify the
     identity of a user (pam_sm_authenticate()), by prompting the user for a
     passphrase and verifying that it can decrypt the target user's SSH key
     using that passphrase.

     The following options may be passed to the authentication module:

     use_first_pass      If the authentication module is not the first in the
                         stack, and a previous module obtained the user's
                         password, that password is used to authenticate the
                         user.  If this fails, the authentication module
                         returns failure without prompting the user for a
                         password.  This option has no effect if the
                         authentication module is the first in the stack, or
                         if no previous modules obtained the user's password.

     try_first_pass      This option is similar to the use_first_pass option,
                         except that if the previously obtained password
                         fails, the user is prompted for another password.

     nullok              Normally, keys with no passphrase are ignored for
                         authentication purposes.  If this option is set, keys
                         with no passphrase will be taken into consideration,
                         allowing the user to log in with a blank password.

   SSH Session Management Module
     The SSH session management component provides functions to initiate
     (pam_sm_open_session()) and terminate (pam_sm_close_session()) sessions.
     The pam_sm_open_session() function starts an SSH agent, passing it any
     private keys it decrypted during the authentication phase, and sets the
     environment variables the agent specifies.  The pam_sm_close_session()
     function kills the previously started SSH agent by sending it a SIGTERM.

     The following options may be passed to the session management module:

     want_agent      Start an agent even if no keys were decrypted during the
                     authentication phase.

FILES
     $HOME/.ssh/identity      SSH1 RSA key
     $HOME/.ssh/id_rsa        SSH2 RSA key
     $HOME/.ssh/id_dsa        SSH2 DSA key
     $HOME/.ssh/id_ecdsa      SSH2 ECDSA key

SEE ALSO
     ssh-agent(1), pam.conf(5), pam(8)

AUTHORS
     The pam_ssh module was originally written by Andrew J. Korty
     <ajk@iu.edu>.  The current implementation was developed for the FreeBSD
     Project by ThinkSec AS and NAI Labs, the Security Research Division of
     Network Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035
     ("CBOSS"), as part of the DARPA CHATS research program.  This manual page
     was written by Mark R V Murray <markm@FreeBSD.org>.

SECURITY CONSIDERATIONS
     The pam_ssh module implements what is fundamentally a password
     authentication scheme.  Care should be taken to only use this module over
     a secure session (secure TTY, encrypted session, etc.), otherwise the
     user's SSH passphrase could be compromised.

     Additional consideration should be given to the use of pam_ssh.  Users
     often assume that file permissions are sufficient to protect their SSH
     keys, and thus use weak or no passphrases.  Since the system
     administrator has no effective means of enforcing SSH passphrase quality,
     this has the potential to expose the system to security risks.

NetBSD 10.99                   December 16, 2011                  NetBSD 10.99