pam_ssh(8) - NetBSD Manual Pages

PAM_SSH(8)              NetBSD 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'' fea-
     tures.

   SSH Authentication Module
     The SSH authentication component provides a function to verify the iden-
     tity 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 pass-
                     word, 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.

   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


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 authenti-
     cation 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 administra-
     tor has no effective means of enforcing SSH passphrase quality, this has
     the potential to expose the system to security risks.

NetBSD 4.0                     February 27, 2005                    NetBSD 4.0