Configuring SSH Key Authentication in Xshell for Server Access

1. Launch Xshell and navigate to Tools > New User Key Generation Wizard
2. In the key generation wizard, proceed to the next step where you can configure key length. Note that longer keys provide enhanced security
3. After key generation completes, advance to the next screen. Here you may optionally add a password to your key before continuing
4. Continue to the final step and select Save to File, storing the key in an easily accessible location
5. Upload the public key file (with .pub extension) to your server using one of these methods:

Method 1: Using XFTP

Utilize XFTP to directly transfer the public key to the /home/username/.ssh/ directory. XFTP offers a free version for personal use.

Download XFTP from: XFTP - NetSarang Website

Method 2: Using the rz Command

First, verify if the lrzsz package is installed:

rpm -qa | grep lrzsz

If not installed, install it using yum:

sudo yum install -y lrzsz

Navigate to the SSH directory and upload the file:

cd /home/username/.ssh/
# Use the rz command in terminal
rz

Select the public key file when the file transfer window appears.

6. After uploading the public key, append its contents to the authorized_keys file. If this file doesn't exist in the /home/username/.ssh/ directory, create it first:

# Create the file if it doesn't exist
touch authorized_keys

# Append the public key contents
cat your_public_key.pub >> authorized_keys

Note: Using a single > would overwrite the file, while >> appends to it.

7. To complete the setup, double-click the server connection in Xshell's session list. Enter your username and select the previously uploaded private key file when prompted.

Understanding the Authorized_Keys File

The authorized_keys file serves as a database for storing public keys that are permitted to access a server via SSH. When a client attempts to connect, the server uses this file to verify the client's identity by matching the presented public key against those stored in the file.

When you generate a public-private key pair on your client machine, you place the public key in the authorized_keys file on the server. This allows the server to recognize and trust your client for passwordless authentication.

The authentication process involves several security steps:

1. The server receives a connection request and checks the authorized_keys file for a matching public key
2. If found, the server generates a random string and encrypts it with the client's public key
3. The client receives this encrypted string and decrypts it using their private key
4. If the decrypted string matches what the server sent, access is granted without requiring a password

For further details on key-based authentication mechanisms, consult additional SSH documentation resources.