.\" Copyright (c) 2001 Mark R V Murray .\" All rights reserved. .\" Copyright (c) 2001 Networks Associates Technology, Inc. .\" All rights reserved. .\" .\" This software 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. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. The name of the author may not be used to endorse or promote .\" products derived from this software without specific prior written .\" permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" $Id: pam_ssh.8,v 1.7 2008/05/12 18:57:12 rosenauer Exp $ .\" .\".Dd November 26, 2001 .Dd July 7, 2013 .Dt PAM_SSH 8 .Os Debian .Sh NAME .Nm pam_ssh .Nd authentication and session management with SSH private keys .Sh SYNOPSIS .Op Ar service-name .Ar module-type .Ar control-flag .Pa pam_ssh .Op Ar options .Sh DESCRIPTION The SSH authentication service module for PAM, .Nm provides functionality for two PAM categories: authentication and session management. In terms of the .Ar module-type parameter, they are the .Dq Li auth and .Dq Li session features. It also provides null functions for the remaining categories. .Ss 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. .Pp The following options may be passed to the authentication module: .Bl -tag -width ".Cm use_first_pass" .It Cm debug .Xr syslog 3 debugging information at .Dv LOG_DEBUG level. .It Cm 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 decrypt the user's SSH login keys. If this fails, then the authentication module returns failure without prompting the user for a passphrase. .\"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. .It Cm try_first_pass Similar to the .Cm 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 a SSH passphrase. .\".It Cm keyfiles .\"Specify the comma-separated list of files in .\".Pa $HOME/.ssh .\"to check for SSH keys. .\"The default is .\".Dq id_dsa,id_rsa,identity . .It Cm nullok Allow SSH keys with no passphrase. .El .Pp If neither .Cm use_first_pass nor .Cm try_first_pass is specified, .Nm pam_ssh will unconditionally ask for an SSH passphrase. .Pp In addition to the above authentication procedure, all standard SSH keys (identity, id_rsa, id_dsa, id_ecdsa) for which the obtained password matches will be decrypted. .Pp The now deprecated name .Cm allow_blank_passphrase for .Cm nullok is kept for compatibility reasons. .Ss 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 environment variable TMPDIR, which can be set through the pam_tmpdir module for example, is also honoured by being passed to the SSH agent. .Pp The SSH session management component terminates the session by killing the previously started SSH agent by sending it a .Dv SIGTERM . .Pp The following options may be passed to the session management module: .Bl -tag -width ".Cm use_first_pass" .It Cm debug .Xr syslog 3 debugging information at .Dv LOG_DEBUG level. .El .Sh INFORMATION LEAKS Be careful with the using the .Cm try_first_pass option when .Nm 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. .Sh FILES .Bl -tag -width ".Pa $HOME/.ssh/login-keys.d" -compact .It Pa $HOME/.ssh/identity standard SSH1/SSH RSA key decrypted by pam_ssh .It Pa $HOME/.ssh/id_rsa standard SSH RSA key decrypted by pam_ssh .It Pa $HOME/.ssh/id_dsa standard SSH DSA key decrypted by pam_ssh .It Pa $HOME/.ssh/id_ecdsa standard SSH ECDSA key decrypted by pam_ssh .It Pa $HOME/.ssh/login-keys.d location of (possibly symbolic links to) SSH RSA1/RSA/DSA/ECDSA keys .\"used for authentication and decrypted by pam_ssh (keys with .disabled or .frozen as suffix are ignored) .It Pa /var/log/auth.log usual log file for .Xr syslog 3 .El .Sh SEE ALSO .Xr ssh-agent 1 , .Xr syslog 3 , .Xr pam.conf 5 , .Xr pam 8 , .Xr pam_tmp .Sh AUTHORS .Pp .An -nosplit .An "Andrew J. Korty" wrote .Nm . .An "Dag-Erling Smorgrav" wrote the original OpenPAM support code. .An "Mark R V Murray" wrote the original version of this manual page. .An "Jens Peter Secher" introduced the login-key concept.