OpenSSH : SSH Key-Pair Authentication2018/04/28

	Configure SSH server to login with Key-Pair Authentication. Create a private key for client and a public key for server.
[1]	Create Key-Pair for each user, so login with a user you'd like to set Key-Pair Auth and work it like follows.

# create key pair

ubuntu@dlp:~$

ssh-keygen -t rsa

Generating public/private rsa key pair.
Enter file in which to save the key (/home/ubuntu/.ssh/id_rsa):

# Enter if you don't need to change the default

Enter passphrase (empty for no passphrase):

# set passphrase (if not set, Enter with empty)

Enter same passphrase again:

Your identification has been saved in /home/ubuntu/.ssh/id_rsa.
Your public key has been saved in /home/ubuntu/.ssh/id_rsa.pub.
The key fingerprint is:
30:ee:f0:47:38:9d:8a:24:5e:01:c8:13:df:15:40:b4 ubuntu@dlp
The key's randomart image is:

ubuntu@dlp:~$

mv ~/.ssh/id_rsa.pub ~/.ssh/authorized_keys

ubuntu@dlp:~$

chmod 600 ~/.ssh/authorized_keys

[2]	Transfer the secret key created on the Server to a Client, then it's possbile to login with Key-Pair authentication.

ubuntu@www:~$

mkdir ~/.ssh

ubuntu@www:~$

chmod 700 ~/.ssh

# copy the secret key to the local ssh directory

ubuntu@www:~$

scp ubuntu@10.0.0.30:/home/ubuntu/.ssh/id_rsa ~/.ssh/

ubuntu@10.0.0.30's password:
id_rsa

ubuntu@www:~$

ssh ubuntu@10.0.0.30

Enter passphrase for key '/home/ubuntu/.ssh/id_rsa':

# passphrase

Last login: Sat Apr 28 20:30:53 2018 from www.srv.world
ubuntu@dlp:~$

# just logined

[3]	If you set "PasswordAuthentication no", it's more secure.

root@dlp:~#

vi /etc/ssh/sshd_config

# line 56: uncomment and turn to [no]

PasswordAuthentication

root@dlp:~#

systemctl restart ssh

SSH Key-Pair Authentication from Windows Client #1

	It's the example to login to SSH server from Windows Client. It uses Putty on here. Transfer a secret key to Windows Client first.
[4]	Download [Puttygen.exe] from Putty Site and save it under the Putty directory. Next execute it and click [Load] button.

[5]	Specify the secret key which you downloaded, then passphrase is required like follows, answer it.

[6]	Click [Save private key] button to save it under a folder you like with any file name you like.

[7]	Start Putty and open [Connection] - [SSH] - [Auth] on the left menu, then select the [private_key] which was just saved above.

[8]	Back to the [Session] on the left menu and connect to the SSH server.

[9]	The passphrase is required to login, then answer it. If it's correct, it's possible to login normally like follows.

SSH Key-Pair Authentication from Windows Client #2

[10]

If your Windows is Windows 10 Version 1803 like here, OpenSSH Client has been implemented as a Windows feature, so it's possbile to authenticate with SSH Key-Pair without Putty and others. Transfer the secret key to your Windows 10 and put it uder the [(logon user home)\.ssh] folder like follows, then it's ready to use Key-Pair login.

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