Secure VPS with Certificate SSH #
Generate a new key on the machine that is to access the VPS #
ssh-keygen -a 1000 -b 4096 -C "" -o -t rsa
or
ssh-keygen -a 1000 -C "" -o -t ed25519
-a specifies # of KDF rounds
-b specifies the bit size for RSA keys
-C removes the common comment at the end of the key
-o specifies that we should use the new format provided by OpenSSH
-t specifies the key type (RSA)
Copy key to the VPS #
Copy the public key to the VPS
ssh-copy-id username@remote_host
Check that it worked #
Look at the contents of ~/.ssh/id_rsa.pub
cat ~/.ssh/id_ed25519.pub
and make sure it is the same as the public key on the VPS
cat ~/.ssh/known_hosts
Modify the VPS configuration #
Edit both these files
/etc/ssh/ssh_config
/etc/ssh/sshd_config
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
Should be
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
PasswordAuthentication no
ChallengeResponseAuthentication no
Restart ssh on the VPS #
service ssh restart
Test that SSH is actually using the certs and no passwords #
This happens on the machine you are using to connect TO the VPS
- move the contents of
~/.sshto a backup location - Be careful!!! If you screw this up you won’t be able to get into the server.
- Once the contents of
~/.sshare carefully moved, try to ssh in - Receive the following message
- Permission denied (publickey).
- If you can stil log in with a password, then something is wrong.
TODO #
Change Default port for SSH from 22
- Update firewall
Disable root logon
- Create a new non-root user
- Add user to ???
- Can’t remember how I did this
- PermitRootLogin no
Copy of my sshd_config 20171204 #
# Package generated configuration file
# See the sshd_config(5) manpage for details
# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
#ListenAddress 0.0.0.0
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key
#HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes
# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 1024
# Logging
SyslogFacility AUTH
LogLevel INFO
# Authentication:
LoginGraceTime 120
PermitRootLogin no
StrictModes yes
RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile %h/.ssh/authorized_keys
# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes
# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no
# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no
# Change to no to disable tunnelled clear text passwords
PasswordAuthentication no
# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes
X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no
#MaxStartups 10:30:60
#Banner /etc/issue.net
# Allow client to pass locale environment variables
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server
# Set this to 'yes' to enable 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 yes
# 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
# Added by DigitalOcean build process
ClientAliveInterval 120
ClientAliveCountMax 2
REFERENCES #
https://www.digitalocean.com/community/questions/best-practices-for-hardening-new-sever-in-2017