Debian 9 Stretch
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SSH Key-Pair Authentication
2017/06/21
 
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.
debian@dlp:~$
ssh-keygen

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

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

debian@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.
debian@www:~$
mkdir ~/.ssh

debian@www:~$
chmod 700 ~/.ssh
# copy the secret key to the local ssh directory

debian@www:~$
scp debian@10.0.0.30:/home/debian/.ssh/id_rsa ~/.ssh/

debian@10.0.0.30's password:
id_rsa
debian@www:~$
ssh debian@10.0.0.30

Enter passphrase for key '/home/debian/.ssh/id_rsa':  
# passphrase

Last login: Wed April 18 21:37:19 2017 from www.srv.world
debian@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
no
root@dlp:~#
systemctl restart ssh

SSH Key-Pair Authentication from Windows Client
 
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.
 
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