Fedora 26
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SSH Key-Pair Authentication
2017/07/17
 
Configure SSH server to login with Key-Pair Authentication. Create a private key for client and a public key for server to do it.
[1] Create Key-Pair for each user, so login with a common user and work it like follows.
[fedora@dlp ~]$
ssh-keygen -t ecdsa

Generating public/private ecdsa key pair.
Enter file in which to save the key (/home/fedora/.ssh/id_ecdsa):  
# Enter with default

Created directory '/home/fedora/.ssh'.
Enter passphrase (empty for no passphrase):  
# set passphrase (if set no passphrase, Enter with empty)

Enter same passphrase again:
Your identification has been saved in /home/fedora/.ssh/id_ecdsa.
Your public key has been saved in /home/fedora/.ssh/id_ecdsa.pub.
The key fingerprint is:
SHA256:b4ZG1OZEtWEpxeAVLgRkTlK4tfysA5Y7hkYN14NZ2ZM fedora@localhost.localdomain
The key's randomart image is:
[fedora@dlp ~]$
mv ~/.ssh/id_ecdsa.pub ~/.ssh/authorized_keys

[fedora@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 keys authentication.
[fedora@www ~]$
mkdir ~/.ssh

[fedora@www ~]$
chmod 700 ~/.ssh
# copy the secret key to local ssh directory

[fedora@www ~]$
scp fedora@10.0.0.30:/home/fedora/.ssh/id_ecdsa ~/.ssh/

fedora@10.0.0.30's password:
[fedora@www ~]$
ssh fedora@10.0.0.30

Enter passphrase for key '/home/fedora/.ssh/id_ecdsa':  
# passphrase

Last login: Wed Dec 10 22:23:46 2014 from www.srv.world
[fedora@dlp ~]$  
# just logined
[3] If you set "PasswordAuthentication" no, it's more secure.
[root@dlp ~]#
vi /etc/ssh/sshd_config
# line 65: change to no

PasswordAuthentication
no
[root@dlp ~]#
systemctl restart sshd

SSH Key-Pair Auth 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 input, then answer it. If it's correct passphrase, it's possible to login normally like follows.
 
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