OpenSSH is the premier connectivity tool for remote login with the SSH protocol. It encrypts all traffic to eliminate eavesdropping, connection hijacking, and other attacks. In addition, OpenSSH provides a large suite of secure tunneling capabilities, several authentication methods, and sophisticated configuration options.

$ ssh-keygen -f server_ca
Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in server_ca.
Your public key has been saved in server_ca.pub.
The key fingerprint is:
SHA256:IRk7bvTPw7wkFXWVY8BoxxRpedhQ2rUqeBTX2B8V7AU hatterjiang@HatterJiangs-MacBook-Pro.local
The key's randomart image is:
+---[RSA 2048]----+
|      .    .**E=B|
|       +   +o@o@+|
|      * . o.o.+o=|
|     o + .o.  ...|
|      o S..o .   |
|     .   *. .    |
|        . B      |
|         o o     |
|          .      |
+----[SHA256]-----+

$ ls -l
total 16
-rw-------  1 hatterjiang  staff  1675 Jul  8 03:12 server_ca
-rw-r--r--  1 hatterjiang  staff   424 Jul  8 03:12 server_ca.pub


$ ssh-keygen -s server_ca -I host_auth_server -h -n test.example.com -V +52w user_key.pub 
Signed host key user_key-cert.pub: id "host_auth_server" serial 0 for test.example.com valid from 2016-07-08T03:14:00 to 2017-07-07T03:14:59

$ ls -l
total 40
-rw-------  1 hatterjiang  staff  1675 Jul  8 03:12 server_ca
-rw-r--r--  1 hatterjiang  staff   424 Jul  8 03:12 server_ca.pub
-rw-------  1 hatterjiang  staff  1679 Jul  8 03:14 user_key
-rw-r--r--  1 hatterjiang  staff  1377 Jul  8 03:14 user_key-cert.pub
-rw-r--r--  1 hatterjiang  staff   424 Jul  8 03:14 user_key.pub

  1. https://github.com/cloudtools/ssh-cert-authority - ssh-cert-authority
  2. https://github.com/cloudtools/ssh-ca - ssh-ca
  3. https://www.digitalocean.com/community/tutorials/how-to-create-an-ssh-ca-to-validate-hosts-and-clients-with-ubuntu - How To Create an SSH CA to Validate Hosts and Clients with Ubuntu
  4. https://ef.gy/hardening-ssh - How to Harden SSH with Identities and Certificates