pam_ssh(8) - NetBSD Manual Pages

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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.

     nullok          Normally, keys with no passphrase are ignored for authen-
                     tication 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 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 10.1                    December 16, 2011                   NetBSD 10.1