What is a Public SSH Key?

Secure Shell (SSH) is a protocol that enables secure access and management of remote servers. One important feature of SSH is public key authentication, which is a secure alternative to traditional password-based login methods. This article explains what a public SSH key is, how it works, and its benefits.

Understanding Public Key Authentication

Public key authentication allows users to log into a remote server using cryptographic key pairs. These key pairs consist of a public key and a private key. The public key is shared with the SSH server, while the private key remains secure on the user's device.

When logging in, the server sends a challenge to the client. The client uses its private key to encrypt the challenge, and the server verifies the response with the public key. If successful, the user gains access to the server.

This method offers advantages over passwords. It eliminates the need to send passwords over the network, reducing interception risks. Public key authentication also prevents brute-force attacks since the private key is securely stored.

How Does the Public SSH Key Work?

To grasp the functionality of a public SSH key, it helps to understand its components.

Public Key

The public key is generated from the private key through a mathematical algorithm. It is the part shared with the SSH server. In public key cryptography, the public key encrypts data that can only be decrypted by the corresponding private key.

For example, when a user wants to connect to an SSH server, they create a key pair and share the public key with the server.

Private Key

The private key is the counterpart to the public key and is kept secret. It should never be shared. The private key decrypts data encrypted with the public key.

During the login process, when the SSH client receives a challenge from the server, it uses the private key to encrypt this challenge and sends it back. The server then verifies the response using the public key.

Trust and Authorization

When an SSH server receives a public key, it checks its trustworthiness before granting access. This trust is established by adding the public key to the server's authorized_keys file.

Once authorized, the server allows the corresponding private key to log in without additional authentication. This enables automated and passwordless logins, making remote server management more convenient.

Benefits of Public SSH Key Authentication

Public SSH key authentication provides several advantages, making it a popular choice for secure remote access.

Enhanced Security

This method eliminates the need to send passwords over the network, reducing the risk of interception and brute-force attacks. Since the private key is stored securely on the user's device, unauthorized access risk is minimized.

Greater Convenience

Public key authentication simplifies logging into SSH servers, especially when managing multiple servers. Instead of remembering different passwords, users can authenticate without inputting passwords.

Automation and Single Sign-On

Public key authentication is ideal for automated processes and single sign-on for administrators. It allows easy management and authentication across multiple servers without manual input.