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<!DOCTYPE html>
<html dir="ltr" lang="en">
<head>
<meta charset='utf-8'>
<title>OpenSSH</title>
</head>
<body>
<a href="index.html">Tools Index</a>
<h1>OpenSSH</h1>
<p>OpenBSD Secure Shell, is a suite of security-related
network-level utilities based on the SSH protocol,
which help to secure network communications via the
encryption of network traffic over multiple authentication
methods and by providing secure tunneling capabilities.</p>
<h2 id="sshd">1. Server</h2>
<p>Crux openssh port install this files to etc;</p>
<pre>
$ pkginfo -l openssh
etc/rc.d/sshd
etc/ssh/moduli
etc/ssh/ssh_config
etc/ssh/sshd_config
</pre>
<p>User commands;</p>
<pre>
usr/bin/scp
usr/bin/sftp
usr/bin/slogin
usr/bin/ssh
usr/bin/ssh-add
usr/bin/ssh-agent
usr/bin/ssh-keygen
usr/bin/ssh-keyscan
</pre>
<p>More information about sshd in man;</p>
<pre>
$ man sshd
</pre>
<h3 id="sshdconf">1.1. Configure Server</h3>
<p>Read OpenSSH server
<a href="http://www.cyberciti.biz/tips/linux-unix-bsd-openssh-server-best-practices.html">Best Security Practices</a>,
This example uses 2222 port to avoid
"default" port, edit /etc/ssh/sshd_config;</p>
<pre>
#Port 22
Port 2222
</pre>
<p>By default ssh will listen on all local addresses, to restrict
to a specific ip edit;</p>
<pre>
#AddressFamily any
AddressFamily inet
#ListenAddress 0.0.0.0
#ListenAddress 192.168.1.254
#ListenAddress ::
</pre>
<pre>
# The default requires explicit activation of protocol 1
Protocol 2
</pre>
<p>Authentication settings;</p>
<pre>
# Authentication:
#LoginGraceTime 2m
LoginGraceTime 1m
#PermitRootLogin prohibit-password
PermitRootLogin no
#StrictModes yes
#MaxAuthTries 6
MaxAuthTries 3
#MaxSessions 10
</pre>
<p>Restrict AllowUsers, AllowGroups that can login;</p>
<pre>
#RSAAuthentication yes
#PubkeyAuthentication yes
AllowGroups admin users gitolite
</pre>
<p>Disable interactive-keyboard and password login;</p>
<pre>
# To disable tunneled clear text passwords, change to no here!
#PasswordAuthentication yes
PasswordAuthentication no
#PermitEmptyPasswords no
# Change to no to disable s/key passwords
#ChallengeResponseAuthentication yes
ChallengeResponseAuthentication no
</pre>
<p>Make sure PAM is disable or above settings can be
overridden. Set banner;</p>
<pre>
# no default banner path
#Banner none
Banner /etc/issue
</pre>
<h3 id="iptables">1.2. Configure iptables</h3>
<p>Iptables;</p>
<p>Example of <a href="scripts/system-iptables.sh">system-iptables.sh</a></p>
<pre>
$IPT -A INPUT -i ${PUB_IF} -p tcp --dport 2222 --sport 1024:65535 -m state --state ESTABLISHED -j ACCEPT
$IPT -A INPUT -i ${PUB_IF} -p tcp --dport 2222 --sport 1024:65535 -m state --state NEW -m limit --limit 3/min --limit-burst 3 -j ACCEPT
$IPT -A OUTPUT -o ${PUB_IF} -p tcp --sport 2222 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT
</pre>
<h3 id="syslogng">1.3. Configure Syslog-ng</h3>
<p>Change SyslogFacility in accordance with <a href="syslog-ng.html#syslog-conf">syslog-ng configuration;</a></p>
<pre>
# Logging
# obsoletes QuietMode and FascistLogging
#SyslogFacility AUTH
SyslogFacility LOCAL1
#LogLevel INFO
LogLevel VERBOSE
</pre>
<p>Example rule for syslog-ng;</p>
<pre>
destination d_sshd { file("/var/log/sshd"); };
filter f_sshd { facility(local1); };
log { source(s_log); filter(f_sshd); destination(d_sshd); };
</pre>
<p>Deny login for root, limit max sessions to 3 if you have limited
resources and only allow 3 failed logins;</p>
<p>Start sshd server;</p>
<pre>
# sh /etc/rc.d/sshd start
# ss -f inet -l -p | grep ssh
</pre>
<h2 id="ssh">2. Client</h2>
<p>To create new key;</p>
<pre>
$ ssh-keygen -t rsa
</pre>
<p>By default this creates two files;</p>
<pre>
~/.ssh/id_rsa : identification (private) key
~/.ssh/id_rsa.pub : public key
</pre>
<p>Default uses id_rsa and id_rsa.pub as output files in
this example we will create keys for gitolite admin so we
name output as gitolte;</p>
<pre>
$ ssh-keygen -t rsa -f ~/.ssh/gitolite
</pre>
<p>Set correct permissions;</p>
<pre>
$ chmod 700 ~/.ssh
$ touch ~/.ssh/authorized_keys
$ chmod 600 ~/.ssh/authorized_keys
$ chmod 600 ~/.ssh/gitolite
</pre>
<h3 id="sshpubkey">2.1. Install Public Keys</h3>
<p>Send gitolite.pub public key to server. In this example
bob (administrator of gitolite) is on same host,
first copy is public key to admin home directory;</p>
<pre>
# install -o admin -g admin /home/bob/.ssh/gitolite.pub /home/admin/.ssh/gitolite.pub
</pre>
<p>If the server is on remote a remote machine;</p>
<pre>
$ scp /home/bob/.ssh/gitolite.pub admin@core.privat-network.net:/home/admin/.ssh/
bob@core.privat-network.net's password:
gitolite.pub 100% 390 0.4KB/s 00:00
</pre>
<p>In case of bob public key for normal ssh login, admin can
add his public key to authorized keys;</p>
<pre>
$ cat bob_rsa.pub >> ~/.ssh/authorized_keys
</pre>
<pre>
$ ssh -P 2222 bob@remote.org
</pre>
<h3 id="sshid">2.2. Configure Identities</h3>
<p>When you have multiple accounts/identities you
can configure ssh client so you dont need to give
-i flag. Create or edit ~/.ssh/config</p>
<pre>
Host admin
Hostname core.privat-network.net
IdentityFile ~/.ssh/id_rsa
Port 2222
User admin
Host gitolite
Hostname core.privat-network.net
IdentityFile ~/.ssh/gitolite
Port 2222
User gitolite
Host box
Hostname core.privat-network.net
IdentityFile ~/.ssh/id_rsa
Port 2222
User bob
Host devbox
Hostname core.privat-network.net
IdentityFile ~/.ssh/id_rsa
Port 2222
User gitolite
</pre>
<p>Now you can just type;</p>
<pre>
$ ssh box
</pre>
<p>On remote start <a href"../systools/tmux.html">tmux</a>
and detach from the session with ctrl + b d</p>
<p>Create alias on ~/.profile;</p>
<pre>
alias boxtmux="ssh servername -t tmux a"
</pre>
<p>Source it and attach to remote;</p>
<pre>
$ boxtmux
</pre>
<p>Logout just detach from session with ctrl + b d </p>
<h2 id="reverse">3. Reverse connection</h2>
<p>This information is inspired by
<a href="http://www.vdomck.org/2005/11/reversing-ssh-connection.html">Reverse SSH connections</a>
and implement the update from <a href="http://www.vdomck.org/2009/11/ssh-all-time.html">SSH all the time</a>,
<p>Simple way, run this command on the machine you want to
access (server);</p>
<pre>
$ ssh -f -N -R 2222:localhost:22 user@laptop
</pre>
<p>This creates a connection from server to client, client will listen
on 2222 port and forward requests to the server as they are on localhost
on port 22.</p>
<pre>
wget http://github.com/mikeymckay/reverse_ssh_tunnel/raw/master/setup_reverse_tunnel.sh
chmod +x ./setup_reverse_tunnel.sh
sudo ./setup_reverse_tunnel.sh
</pre>
<a href="index.html">Tools Index</a>
<p>This is part of the c9-doc Manual.
Copyright (C) 2016
c9 team.
See the file <a href="fdl-1.3-standalone.html">Gnu Free Documentation License</a>
for copying conditions.</p>
</body>
</html>
|