AlmaLinux 9.1 : Authenticated SSH connection with key pair

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SSH connection with authentication using public key cryptography

SSH connection with authentication using public key cryptography

Create public and private key pairs

Create a public/private key pair for a user connecting to a Linux server using OpenSSH.
Use ssh-keygen to create the key pair.
The creation of a public/private key pair must be done as a user with remote login privileges.
If you do not specify the destination and file name, id_ed25519 and id_ed25519.pub will be created in /home/(user name)/.ssh/. On the way, enter the password for the key.

# su - huong
[huong@Alma~]$ 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 (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:jkWIZvNhc5fHRioH3nTrTz7CLlbjVaOMmmkuKFaW1tY huong@Alma
The key's randomart image is:
+--[ED25519 256]--+
|        . . o    |
|     . o + * .   |
|    = = = * =    |
|   o + = + +   ..|
|      + S   + o..|
|     = * E oo*.  |
|    + + . +ooo+  |
|   o . . =o... . |
|  . .   +o ..    |
+----[SHA256]-----+

# su - huong

[huong@Alma~]$ 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 (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:jkWIZvNhc5fHRioH3nTrTz7CLlbjVaOMmmkuKFaW1tY huong@Alma

The key's randomart image is:

+--[ED25519 256]--+

| . . o |

| . o + * . |

| = = = * = |

| o + = + + ..|

| + S + o..|

| = * E oo*. |

| + + . +ooo+ |

| o . . =o... . |

| . . +o .. |

+----[SHA256]-----+

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

$ cat ~/.ssh/id_ed25519.pub >> ~/.ssh/authorized_keys

$ chmod 600 ~/.ssh/authorized_keys

$ chmod 700 ~/.ssh/

Save the created private key id_ed25519 to an appropriate location on windows using winSCP.
Start Winscp
Host name : Server IP Address
Port number : SSH Port
User name : Server Login User
Password : Password for the above user
Click "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

When connected, the right column is the server side and the left column is the PC (Windows) side.
Save the file "id_ed25519" in the .ssh directory to an appropriate location on Windows in the left column.

Edit SSH configuration file

Edit the SSH configuration file to disable password authentication.

$ su -
Password:
# vi /etc/ssh/sshd_config
# Line 66 : Changed to password authentication disabled
PasswordAuthentication no

# systemctl restart sshd

How to connect using Tera Term

Start Tera Term, and select "File" menu "New connection"

Host : Server IP Address
TCP port : SSH Port number

If you get the following security warning "Replace...." and click "Continue".

User name : Login User Name
Password :Password specified in the creation of a public/private key pair
Use RSA/DSA/ECDSA/ED25519 key to log in Private key file: "id_ed25519" saved in Windows.

Creating a private key using PuTTYgen

Start Winscp and launch Run Puttygen from "Tools".
Select the appropriate server

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.