Ubuntu Server26.10 : SSH connection with authentication using public key cryptography

SSH connection using authentication with public-key cryptography

 Creation of public and private key pairs

Create a public/private key pair for a user connecting to the Linux server using OpenSSH.
Use ssh-keygen to create key pairs.
This time, we will create a key set using the RSA cipher used in the SSH protocol Version 2.
Creation of public/private key pairs is performed with remote login user privileges (huong).
If you do not specify the destination and file name, id_ed25519,id_ed25519.pub will be created in /home/huong/.ssh/. On the way, enter the password for the key.

# su - huong
huong@Lepard:~$ ssh-keygen -t ed25519
Generating public/private ed25519 key pair.
Enter file in which to save the key (/home/huong/.ssh/id_ed25519):
Enter passphrase for "/home/huong/.ssh/id_ed25519" (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/huong/.ssh/id_ed25519
Your public key has been saved in /home/huong/.ssh/id_ed25519.pub
The key fingerprint is:
SHA256:8i8rQxvDTi5SgSgkk95T5V4NKNZL16T/7KhCzVOGGvg huong@Lepard
The key's randomart image is:
+--[ED25519 256]--+
| .    o...o.     |
|+.   +.+ .+.     |
|+o..o +.oo..     |
|o..o...o...o     |
|.   .oo.S o.     |
|    . *E +  o    |
|   . =.+. .  o   |
|  . . *...  o    |
|   . . oo+o. .   |
+----[SHA256]-----+

$ cat ~/.ssh/id_ed25519.pub >> ~/.ssh/authorized_keys
$ chmod 600 ~/.ssh/authorized_keys
$ chmod 700 ~/.ssh/

Save the generated private key id_ed25519 to the Windows directory c:\USERS\user\.ssh\ using winSCP
Start Winscp
Host name  : Server IP Address
Port number : SSH Port
User name : Server Login User
Password : Password for the same user
and then "Save".

Site name : Any name
Click "OK"

After confirming the server, click "Login".

Click "Update" when the following screen appears

Password of the logged-in user in the Password field

Once connected, the left pane shows the server side, and the right pane shows the PC (Windows) side.
Copy the "id_ed25519" file located in the .ssh directory to the Windows directory[c:\USERS\user\.ssh] on the right side.

Editing SSH Configuration File

Edit the SSH configuration file to disable password authentication.
This time, instead of being an ordinary user, su - to become root.

$ su -
Password:

# vi /etc/ssh/sshd_config
# Around the 80th line: Uncommented and changed password authentication to non-authenticated
PasswordAuthentication no

# systemctl restart ssh

How to connect using Tabby Terminal
Specify the key using the option [-i c:\USERS\xxxxx\.ssh\id_ed25519]

Creating a private key using PuTTYgen

Launch WinSCP, select the relevant server, and then click [Run PuTTYgen] under "Tools."

Click Load

The [ Open File Dialog ] will open, change the file type to [ All Files (. Change the file type to [ All Files (. *) ] and load the private key id_ed25519 that was transferred from the Linux server.

The password is the password set in "Creating a public and private key pair" above

Click on "Save private key"

Save the file with the extension ".ppk" in the same place as "id_ed25519" saved earlier on the Windows side under the name "id_ed25519.ppk".

Select the target server and click "Edit".

Click on "Advanced"

Open the "Authentication" menu and specify "id_ed25519.ppk" saved in Windows for "Private key file

Click "Save"

Click on "Login"

The password is the password set in "Creating a public and private key pair" above

When connecting via Tabby Terminal, do the following:

If you encounter an error like the one below, convert your private key to OpenSSH format.

Launch [WinSCP] > [Run PuTTygen], then import the private key under [Import key] in the [Conversions] tab.

Convert the imported private key to OpenSSH format and save it under a different name
The password specified when creating the public key

Using the [id_ed25519_2.ppk] file converted to OpenSSH format, you can connect as follows: