pam_ssh - authentication and session management with SSH private keys
The SSH authentication service module for PAM, pam_ssh provides
functionality for two PAM categories: authentication and session
SSH Authentication Module
The SSH authentication component verifies the identity of a user by
prompting the user for a passphrase and verifying that it can decrypt at
least one of the user’s SSH login keys using that passphrase.
The following options may be passed to the authentication module:
debug syslog(3) debugging information at LOG_DEBUG
use_first_pass If the authentication module is not the first in
the stack, and a previous module obtained the
user’s password, then that password is used to
decrypt the user’s SSH login keys. If this
fails, then the authentication module returns
failure without prompting the user for a
try_first_pass Similar to the use_first_pass option, except that
if the previously obtained password fails to
decrypt any of the SSH login keys, then the user
is prompted for an SSH passphrase.
try_first_pass has no effect if pam_ssh is the
first module on the stack, or if no previous
modules obtained the user’s password.
allow_blank_passphrase Allow SSH keys with no passphrase.
If neither use_first_pass nor try_first_pass is specified, pam_ssh will
unconditionally ask for an SSH passphrase.
In addition to the above authentication procedure, all standard SSH keys
(identity, id_rsa, id_dsa) for which the obtained password matches will
SSH Session Management Module
The SSH session management component initiates sessions by starting an
SSH agent, passing it any SSH login keys it decrypted during the
authentication phase, and sets the environment variables accordingly.
The SSH session management component terminates the session by killing
the previously started SSH agent by sending it a SIGTERM.
The following options may be passed to the session management module:
debug syslog(3) debugging information at LOG_DEBUG level.
Be careful with the using the try_first_pass option when pam_ssh is the
first authentication module because it will then leak information about
existing users without login keys: such users will not be asked for a
specific SSH passphrase, whereas non-existing users and existing users
with login keys will be asked for a passphrase.
$HOME/.ssh/id_dsa OpenSSH DSA/RSA keys decrypted by pam_ssh.
$HOME/.ssh/login-keys.d/ Location of (possibly symbolic links to)
OpenSSH DSA/RSA keys used for authentication
and decrypted by pam_ssh.
/var/log/auth.log Usual log file for syslog(3)
ssh-agent(1), syslog(3), pam.conf(5), pam(8).
Andrew J. Korty 〈email@example.com〉 wrote pam_ssh. Dag-Erling Smorgrav wrote
the original OpenPAM support code. Mark R V Murray wrote the original
version of this manual page. Jens Peter Secher introduced the login-key