modules/pam_ssh/pam_ssh.8

.\" $NetBSD: pam_ssh.8,v 1.8 2014/03/18 18:20:38 riastradh Exp $
.\" Copyright (c) 2001 Mark R V Murray
.\" All rights reserved.
.\" Copyright (c) 2001-2003 Networks Associates Technology, Inc.
.\" All rights reserved.
.\"
.\" This software 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.
.\"
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.\" $FreeBSD: src/lib/libpam/modules/pam_ssh/pam_ssh.8,v 1.13 2004/07/02 23:52:18 ru Exp $
.\"
.Dd December 16, 2011
.Dt PAM_SSH 8
.Os
.Sh NAME
.Nm pam_ssh
.Nd authentication and session management with SSH private keys
.Sh SYNOPSIS
.Op Ar service-name
.Ar module-type
.Ar control-flag
.Pa pam_ssh
.Op Ar options
.Sh DESCRIPTION
The
SSH
authentication service module for PAM
provides functionality for two PAM categories:
authentication
and session management.
In terms of the
.Ar module-type
parameter, they are the
.Dq Li auth
and
.Dq Li session
features.
.Ss SSH Authentication Module
The
SSH
authentication component
provides a function to verify the identity of a user
.Pq Fn 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.
.Pp
The following options may be passed to the authentication module:
.Bl -tag -width ".Cm use_first_pass"
.It Cm 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.
.It Cm try_first_pass
This option is similar to the
.Cm use_first_pass
option,
except that if the previously obtained password fails,
the user is prompted for another password.
.It Cm 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.
.El
.Ss SSH Session Management Module
The
SSH
session management component
provides functions to initiate
.Pq Fn pam_sm_open_session
and terminate
.Pq Fn pam_sm_close_session
sessions.
The
.Fn 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
.Fn pam_sm_close_session
function kills the previously started SSH agent
by sending it a
.Dv SIGTERM .
.Pp
The following options may be passed to the session management module:
.Bl -tag -width ".Cm want_agent"
.It Cm want_agent
Start an agent even if no keys were decrypted during the
authentication phase.
.El
.Sh FILES
.Bl -tag -width ".Pa $HOME/.ssh/identity" -compact
.It Pa $HOME/.ssh/identity
SSH1 RSA key
.It Pa $HOME/.ssh/id_rsa
SSH2 RSA key
.It Pa $HOME/.ssh/id_dsa
SSH2 DSA key
.It Pa $HOME/.ssh/id_ecdsa
SSH2 ECDSA key
.El
.Sh SEE ALSO
.Xr ssh-agent 1 ,
.Xr pam.conf 5 ,
.Xr pam 8
.Sh AUTHORS
The
.Nm
module was originally written by
.An -nosplit
.An "Andrew J. Korty" Aq Mt ajk@iu.edu .
The current implementation was developed for the
.Fx
Project by
ThinkSec AS and NAI Labs, the Security Research Division of Network
Associates, Inc.\& under DARPA/SPAWAR contract N66001-01-C-8035
.Pq Dq CBOSS ,
as part of the DARPA CHATS research program.
This manual page was written by
.An "Mark R V Murray" Aq Mt markm@FreeBSD.org .
.Sh SECURITY CONSIDERATIONS
The
.Nm
module implements what is fundamentally a password authentication scheme.
Care should be taken to only use this module over a secure session
.Po
secure TTY, encrypted session, etc.
.Pc ,
otherwise the user's SSH passphrase could be compromised.
.Pp
Additional consideration should be given to the use of
.Nm 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.