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, pam_ssh 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.
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.

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/id_rsa: SSH2 RSA key
$HOME/.ssh/id_dsa: SSH2 DSA key
$HOME/.ssh/id_ecdsa: SSH2 ECDSA key
$HOME/.ssh/id_ed25519: SSH2 Ed25519 key

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>.