How SSH Works | Authentication Using Public and Private Keys
@onjsdev

@onjsdev

How SSH Works | Authentication Using Public and Private Keys

Oct 02 2024

Check out our video on YouTube, featuring informative animations, to learn about SSH and how SSH authentication works using public and private keys. 😎👇👇

SSH, or Secure Shell is one of the most essential tools for anyone working with remote servers, especially if you’re managing your own infrastructure or deploying applications.

So, what exactly is SSH?

What's SSH?

SSH is a protocol for connecting to a remote computer securely. This connection is established over an encrypted channel, which means all data sent between your machine and the remote server is protected from eavesdropping or interception.

SSH is primarily used for remote command-line access, file transfers, and tunneling traffic. It's often used by system administrators and developers for tasks such as server maintenance, application deployment, and troubleshooting

How SSH Works

To understand how SSH works, let’s break it down into a few key components. There are two main parts: the SSH client and the SSH server. When you initiate an SSH connection from your local machine, that machine is the client, while the remote machine is the server.

The client uses a program called an SSH client, such as ssh in the command line or GUI-based tools like PuTTY. The server must be running an SSH server, often the sshd daemon.

How do you authenticate with SSH?

There are two main methods:

  • Password Authentication: This is the simplest method, where you enter your username and password to access the remote server. However, it’s not the most secure option since passwords can be guessed or intercepted.

  • SSH Key Authentication: This method involves using a public and private key pair. You generate these keys on your local machine and add the public key to the remote server. When you connect, the server uses the public key to create an encrypted message that only your private key can decrypt, thus verifying your identity.

SSH Key Authentication

SSH key authentication is a method used to securely connect to remote servers without using passwords. It uses a pair of cryptographic keys—a public key and a private key—to verify the identity of the client and establish a secure connection.

  • First, the client generates a pair of SSH keys on their local machine: a public key and a private key. The private key is stored securely on the client’s machine, while the public key can is shared freely wit the server.
  • When the client attempts to connect to the server, the server checks if the client has the public key
  • If the public key matches, the server sends an encrypted challenge (a random string) to the client.
  • The client uses its private key to decrypt the challenge sent by the server. The decrypted message is sent back to the server as a response.
  • If the response matches the expected value, the server authenticates the client.
  • Once authenticated, a secure, encrypted SSH session is established between the client and the server. From here, the user can run commands or transfer files securely.

Conclusion

SSH is a versatile and powerful tool that goes beyond just remote login. Whether it’s securely accessing servers, transferring files, or tunneling traffic, understanding SSH fundamentals will help you navigate and manage your server environments more effectively.