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NetBSD 6.1.5 - man page for pam_ssh (netbsd section 8)

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

     pam_ssh -- authentication and session management with SSH private keys

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

     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 authen-
		     tication 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 pre-
		     viously 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 considera-
		     tion, 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.

     $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

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

     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 Secu-
     rity 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>.

     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.

BSD					December 16, 2011				      BSD

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