Skill 3 in course 2.4: Network and Security

SSH Key Authentication

Log in without a password using key pairs, and tighten the SSH server's rules without locking yourself out.

Intermediate2 lessons10 exercises1 h 25 min
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You will be able to

  • Create a key pair, install the public key on another host, and log in without a password.
  • Explain which file and which permissions make key authentication work, and fix them when it fails.
  • Change sshd settings safely using drop-in files, a syntax test and a second session.
  • Forbid root and password logins, restrict users, and run sshd on a different port with SELinux and the firewall updated.

Lessons

  1. 01Key-based SSH loginGenerate a key pair, install the public key on another system, log in without a password, and debug it when it refuses.ssh-keygenssh-copy-id~/.ssh/authorized_keysssh-agentssh-addssh -v0/5 exercises
  2. 02Securing the SSH serverChange sshd's behaviour with drop-in files, forbid root and password logins, limit who may connect, and move the port the right way.sshd -tsshd -T/etc/ssh/sshd_config.dPermitRootLoginPasswordAuthenticationAllowGroups0/5 exercises