SSH

Generate Key

run:

ssh-keygen 

secure algorithm:

ssh-keygen -t ed25519 -C "your_email@example.com"

change passphrase:

ssh-keygen -p -f ~/.ssh/id_ed25519

SSH Config

vim ~/.ssh/config

Host shortname
    HostName 100.100.100.100
    User ubuntu
    IdentityFile ~/.ssh/private-key-filename.key

SSH Agent

save you time with passphrase automation.

check if your ssh agent is running:

eval "$(ssh-agent -s)"

add ssh key:

ssh-add ~/.ssh/id_ed25519

or set timeout period

ssh-add -t 8h ~/.ssh/id_ed25519

check loaded keys:

ssh-add -l

Host SSH

Install SSH Server

sudo apt install ssh-server
systemctl enable ssh

Setup Key Access

scp ~/.ssh/public-key.pub user@100.100.100.100:~
mkdir .ssh/
touch ~/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys
chmod 700 ~/.ssh

Harden your sshd config

(optional: backup your config)

sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak

Search for the line that contains PasswordAuthentication and change it from yes to no and uncomment the line by removing the beginning #

you can edit sshd_config with your favorite text editor:

{% code fullWidth="false" %}

sudo vim /etc/ssh/sshd_config

{% endcode %}

or

you can automate the process by using the sed command:

sudo sed -i 's/^#?PasswordAuthentication .*/PasswordAuthentication yes/' /etc/ssh/sshd_config

then restart ssh demon with

sudo systemctl restart sshd

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