I expose an ssh server to the internet. This allows me to sync up git or hg repositories under a secure connection (without requiring SSL)–but more importantly, keeping the data stored in those repositories under my control.
Since I’m fairly paranoid about security, I chose a random port number (my router routes the random public port to the usual internal port: 22). In addition, I disable password login, which means that I can only log-in using an ssh key. More importantly, other people can’t login using passwords–which means that there’s not possibility of a dictionary (nor simple brute-force) attack.
Here’s the sshd_config file for FreeBSD that does this:
# $OpenBSD: sshd_config,v 1.74 2006/07/19 13:07:10 dtucker Exp $
# $FreeBSD: src/crypto/openssh/sshd_config,v 1.42.2.4 2006/11/11 00:51:28 des Exp $
# This is the sshd server system-wide configuration file. See
# sshd_config(5) for more information.
# This sshd was compiled with PATH=/usr/bin:/bin:/usr/sbin:/sbin
# The strategy used for options in the default sshd_config shipped with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented. Uncommented options change a
# default value.
# Note that some of FreeBSD’s defaults differ from OpenBSD’s, and
# FreeBSD has a few additional options.
#VersionAddendum FreeBSD-20061110
#Port 22
#Protocol 2
#AddressFamily any
#ListenAddress 0.0.0.0
#ListenAddress ::
# HostKey for protocol version 1
#HostKey /etc/ssh/ssh_host_key
# HostKeys for protocol version 2
#HostKey /etc/ssh/ssh_host_dsa_key
# Lifetime and size of ephemeral version 1 server key
#KeyRegenerationInterval 1h
#ServerKeyBits 768
# Logging
# obsoletes QuietMode and FascistLogging
#SyslogFacility AUTH
#LogLevel INFO
# Authentication:
#LoginGraceTime 2m
#PermitRootLogin no
#StrictModes yes
#MaxAuthTries 6
#RSAAuthentication yes
#PubkeyAuthentication yes
#AuthorizedKeysFile .ssh/authorized_keys
# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
#RhostsRSAAuthentication no
# similar for protocol version 2
#HostbasedAuthentication no
# Change to yes if you don’t trust ~/.ssh/known_hosts for
# RhostsRSAAuthentication and HostbasedAuthentication
#IgnoreUserKnownHosts no
# Don’t read the user’s ~/.rhosts and ~/.shosts files
#IgnoreRhosts yes
# Change to yes to enable built-in password authentication.
PasswordAuthentication no
#PermitEmptyPasswords no
# Change to no to disable PAM authentication
ChallengeResponseAuthentication no
# Kerberos options
#KerberosAuthentication no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
#KerberosGetAFSToken no
# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes
# Set this to ‘no’ to disable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication. Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of “PermitRootLogin without-password”.
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to ‘no’.
#UsePAM yes
#AllowTcpForwarding yes
#GatewayPorts no
#X11Forwarding yes
X11Forwarding no
#X11DisplayOffset 10
#X11UseLocalhost yes
#PrintMotd yes
#PrintLastLog yes
#TCPKeepAlive yes
#UseLogin no
#UsePrivilegeSeparation yes
#PermitUserEnvironment no
#Compression delayed
#ClientAliveInterval 0
#ClientAliveCountMax 3
#UseDNS yes
#PidFile /var/run/sshd.pid
#MaxStartups 10
#PermitTunnel no
PermitTunnel no
# no default banner path
#Banner /some/path
# override default of no subsystems
Subsystem sftp /usr/libexec/sftp-server
# restrict users/IP’s
AllowUsers *@192.168.1.* Poojan@*
# Example of overriding settings on a per-user basis
#Match User anoncvs
# X11Forwarding no
# AllowTcpForwarding no
# ForceCommand cvs server
I’ve disabled all authentication types (including PAM)–at least the ones that aren’t disabled by default. Since public key authentication is on by default, I don’t have to change it.
You’ll notice that I’ve disabled tunneling (to disable people from penetrating past the FreeBSD machine into my home network) and chosen not to enable X forwarding (no need for it in this case).
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