Slackware15.0 ; SSH connect with public key

Contents

Creation of public and private key pairs
Editing SSH Configuration File
Creating a private key using PuTTYgen

Creation of 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 is performed with remote login user 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

JOHN PAUL ELECTED POPE!!

(George and Ringo miffed.)

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):
Created directory '/home/huong/.ssh'.
Enter passphrase (empty for no passphrase): ←パスワード
Enter same passphrase again:　←再度パスワード
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:iUVyHjgxzM3ddeM1CvUJ0pcywF2NKti3O5as/RbBQeA huong@Lepard.korodes.com
The key's randomart image is:
+--[ED25519 256]--+
|     o+=+..=**+==|
|      =*o..o+=B+*|
|       .oo  E++= |
|       o..o o o  |
|      . S  o . . |
|            . .  |
|           . o . |
|           .* .  |
|          .o.+.  |
+----[SHA256]-----+

# su - huong

JOHN PAUL ELECTED POPE!!

(George and Ringo miffed.)

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):

Created directory '/home/huong/.ssh'.

Enter passphrase (empty for no passphrase): ←パスワード

Enter same passphrase again:　←再度パスワード

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:iUVyHjgxzM3ddeM1CvUJ0pcywF2NKti3O5as/RbBQeA huong@Lepard.korodes.com

The key's randomart image is:

+--[ED25519 256]--+

| o+=+..=**+==|

| =*o..o+=B+*|

| .oo E++= |

| o..o o o |

| . S 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 and click "New Session"

Host name : Server IP Address
Port number : SSH port number
User name : Server Login User
Password : Password for the same user
「Save」

Site name : Any name
"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.

Editing SSH Configuration File

Edit the SSH configuration file to disable password authentication.
This time, use su - to become root instead of a normal user.

$ su -
Password:
# vi /etc/ssh/sshd_config
# Line 57 : Changed to no password authentication
PasswordAuthentication no

# /etc/rc.d/rc.sshd restart
WARNING: killing listener process only.  To kill every sshd process, you must
         use 'rc.sshd stop'.  'rc.sshd restart' kills only the parent sshd to
         allow an admin logged in through sshd to use 'rc.sshd restart' without
         being cut off.  If sshd has been upgraded, new connections will now
         use the new version, which should be a safe enough approach.

$ su -

Password:

# vi /etc/ssh/sshd_config

# Line 57 : Changed to no password authentication

PasswordAuthentication no

# /etc/rc.d/rc.sshd restart

WARNING: killing listener process only. To kill every sshd process, you must

use 'rc.sshd stop'. 'rc.sshd restart' kills only the parent sshd to

allow an admin logged in through sshd to use 'rc.sshd restart' without

being cut off. If sshd has been upgraded, new connections will now

use the new version, which should be a safe enough approach.

How to connect with 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 username
Password :Password specified in the creation of a public/private key pair
Under "Use RSA/DSA/ECDSA/ED25519 key to log in", set "Private key file:" to "id_ed25519" that you just saved in Windows.
Click "OK"

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.