[Linux] SSH key pair initiation or copy

Working with SSH Key Pairs

This is to set up the key once, and then don't need to enter the passphrase every single time:

Use an ssh-agent in WSL with your ssh setup from windows 10 | by Philipp Scheit | Medium

Create new key pair

Use the ssh-keygen command to generate a public and private authentication key pair. Authentication keys enable you to connect to a remote system without needing to supply a password each time that you connect. 

To create a public and private SSH2 RSA key pair. To create an SSH key pair by using an algorithm other than the default RSA algorithm, use the -t option. Possible values that you can specify include the following: dsa, ecdsa, ed25519, and rsa. In this case, I use ed25519 algorithm.

ssh-keygen -t ed25519

Generating public/private ed25519 key pair.
Enter file in which to save the key (/home/user/.ssh/id_ed25519):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/user/.ssh/id_ed25519
Your public key has been saved in /home/user/.ssh/id_ed25519.pub

Copy old key pair to new system (new WSL/Ubuntu/laptop)

If you copy the old key pair to the new system, you need to change the permission in order to have it work. 

Run this command:

bash
chmod 600 ~/.ssh/id_rsa

How to check the permissions:

ls -ld ~/.ssh

ls -l ~/.ssh

What the permissions should look like:

File/Folder	Expected Permissions	Command to Fix
~/.ssh/	drwx------ (700)	chmod 700 ~/.ssh
id_rsa	-rw------- (600)	chmod 600 ~/.ssh/id_rsa
id_rsa.pub	-rw-r--r-- (644)	chmod 644 ~/.ssh/id_rsa.pub
authorized_keys (on server)	-rw------- (600)	chmod 600 ~/.ssh/authorized_keys