OpenSSH : SSH Key-Pair Authentication2022/01/07

	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 by each user, so login with a common user on SSH Server Host and work like follows.

# create key-pair

[cent@dlp ~]$

ssh-keygen

Generating public/private rsa key pair.
Enter file in which to save the key (/home/cent/.ssh/id_rsa):   # Enter or input changes if you want
Created directory '/home/cent/.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/cent/.ssh/id_rsa
Your public key has been saved in /home/cent/.ssh/id_rsa.pub
The key fingerprint is:
SHA256:yYOKaIcT25Jd0ZaOOYLa+rgrU0c/M/rVmJx4q4MVZB0 cent@node01.srv.world
The key's randomart image is:
.....
.....

[cent@dlp ~]$

ll ~/.ssh

total 8
-rw-------. 1 cent cent 2655 Jan  7 19:07 id_rsa
-rw-r--r--. 1 cent cent  575 Jan  7 19:07 id_rsa.pub

[cent@dlp ~]$

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

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

[cent@node01 ~]$

mkdir ~/.ssh

[cent@node01 ~]$

chmod 700 ~/.ssh

# transfer the private key to the local ssh directory

[cent@node01 ~]$

scp cent@dlp.srv.world:/home/cent/.ssh/id_rsa ~/.ssh/

cent@dlp.srv.world's password:
id_rsa                                        100% 1876   193.2KB/s   00:00

[cent@node01 ~]$

ssh cent@dlp.srv.world

Enter passphrase for key '/home/cent/.ssh/id_rsa':   # passphrase if you set

[cent@dlp ~]$

# logined

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

[root@dlp ~]#

vi /etc/ssh/sshd_config

# line 65 : change to [no]

PasswordAuthentication

# line 69 : if it's enabled, change it to [no], too

# Change to no to disable s/key passwords
#KbdInteractiveAuthentication yes
KbdInteractiveAuthentication no

[root@dlp ~]#

systemctl restart sshd

SSH Key-Pair Authentication on Windows Client #1

	This is the example to login to SSH server from Windows Client. On this example, it uses Putty. Before it, Transfer a private key to Windows Client.
[4]	Run [Puttygen.exe] that is included in [Putty]. (placed in the same folder with [Putty.exe]) If not included, Download it from the official site (www.chiark.greenend.org.uk/~sgtatham/putty/). After starting [Puttygen.exe], Click [Load] button on the following window.

[5]	Specify the private key that you transferred from SSH server, then passphrase is required like follows, answer it. (if not set passphrase, this step is skipped)

[6]	Click the [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 pane, then specify your private key on the [Private key file] field.

[8]	Back to the [Session] on the left pane and specify your SSH server host to Connect.

[9]	When SSH key-pair is set, the passphrase if it is set is required to login like follows, then answer it.

SSH Key-Pair Authentication on Windows #2

[10]

If you are using Windows 11 like here [8], OpenSSH Client has been implemented as a Windows feature, so it's possible to authenticate with SSH Key-Pair without Putty and other 3rd party softwares. Transfer your private key to your Windows and put it under the [(logon user home).ssh] folder like follows, then it's ready to use Key-Pair authentication.

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