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.
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 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.