Hi!

Today we use OpenSSH and PuTTY to log in remote computers.

• OpenSSH is an open-source version of the Secure Shell (SSH) tools used by administrators of remote systems
• PuTTY is a free implementation of SSH

This blog is built on the following environment:

• Host Machine: OpenSSH_for_Windows_8.1p1, LibreSSL 3.0.2, and PuTTY Release 0.78 on Windows 10 x64.
• Virtual Machine (Server): CentOS 7 Minimal on VMware Player 17 (Intel-VT Virtualization: ON)

Generate Key Pair

SSH requires public/private key pair. The public key is stored on server to authenticate the user who has the corresponding private key. For simplicity, I will use PuTTY to generate public/private key pair:

1. Open PUTTYGEN.EXE of PuTTY installation directory.
2. Click "Generate" to generate public/private key pair
3. Set Key passphase and Confirm the passphase.
4. Click "Save private key", and export to a putty_private_key.ppk file
5. Copy the content of "Public key for pasting into OpenSSH authorized_keys file" (begin with ssh-rsa ...), and paste it in server file (~/.ssh/authorized_keys of CentOS 7).
6. Open PUTTY.EXE of PuTTY installation directory
7. In the left menu, unfold category to find Connection/SSH/Auth/Credentials, and "Browse" to find putty_private_key.ppk
8. In the left menu, click Session, type in the IP address and "Save" this session with a name, like "CentOS7_VM"

Config Server

If we want to log in without password, we will config the server:

1. (Optional) Allow SSH login as root: (find the following item and change its property in /etc/ssh/sshd_config to yes)

   1PermitRootLogin yes
   

2. Ensure the Public key authentication is enabled: (find the following items and change their properties in /etc/ssh/sshd_config to yes)

   1RSAAuthentication yes
   2PubkeyAuthentication yes
   

3. Restrict to use the authorized public keys only: (to disallow password, find the following item and change its property in /etc/ssh/sshd_config to no)

   1PasswordAuthentication no
   

4. Restart SSH service to validate changes: (in terminal)

   1$ service sshd restart
   

Connect

Open PUTTY.EXE, "Load" the saved session called CentOS7_VM, and "Open"

1login as: <Your User Name>
2Authenticating with public key "rsa-key-YYYYMMDD"
3Passphrase for key "rsa-key-YYYYMMDD": <Your Passphrase For private key>

So now we can log in with no passwords in transmission.

However, if you do not want to protect the private key (putty_private_key.ppk) with passphrase at all, you can load your private key with PUTTYGEN.EXE and then override the private key with no passphrase. (Highly unrecommended)