NAME¶
pam_ssh —
authentication and session
management with SSH private keys
DESCRIPTION¶
The SSH authentication service module for PAM,
pam_ssh
provides functionality for two PAM categories: authentication and session
management.
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 level.
- 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
passphrase.
- 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 be
decrypted.
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.
FILES¶
- $HOME/.ssh/identity
-
- $HOME/.ssh/id_rsa
-
- $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)
SEE ALSO¶
ssh-agent(1),
syslog(3),
pam.conf(5),
pam(8).
AUTHORS¶
Andrew J. Korty ⟨ajk@iu.edu⟩ 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 concept.
