pam_ssh(8) - NetBSD Manual Pages

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PAM_SSH(8)              NetBSD System Manager's Manual              PAM_SSH(8)

pam_ssh -- authentication and session management with SSH private keys
[service-name] module-type control-flag pam_ssh [options]
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'' fea- tures. SSH Authentication Module The SSH authentication component provides a function to verify the iden- tity 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 pass- word, 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 authen- tication 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.
$HOME/.ssh/identity SSH1 RSA key $HOME/.ssh/id_rsa SSH2 RSA key $HOME/.ssh/id_dsa SSH2 DSA key $HOME/.ssh/id_ecdsa SSH2 ECDSA key
ssh-agent(1), pam.conf(5), pam(8)
The pam_ssh module was originally written by Andrew J. Korty <>. 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 <>.
The pam_ssh module implements what is fundamentally a password authenti- cation 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 administra- tor has no effective means of enforcing SSH passphrase quality, this has the potential to expose the system to security risks. NetBSD 10.0 December 16, 2011 NetBSD 10.0
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