What Is an SSH Key?

An SSH key is a cryptographic authentication method that allows users to securely access a server without using passwords.

SSH key authentication relies on a key pair consisting of a private key and a public key. These keys are mathematically linked and work together to verify identity.

How Does SSH Key Authentication Work?

The SSH key process follows these steps:

• A key pair is generated on the client device
• The public key is added to the server
• The private key remains securely stored on the client
• The server verifies possession of the private key during login

The private key is never transmitted to the server.

Why Use SSH Keys?

Password-based SSH access is vulnerable to brute-force and credential attacks. SSH keys eliminate these risks.

• No password guessing attacks
• Protection against automated login attempts
• Faster and seamless authentication
• Significantly reduced unauthorized access risk

Types of SSH Keys

SSH keys can be generated using different algorithms:

• RSA: Widely supported but requires longer key lengths
• ED25519: Modern, fast, and highly secure
• ECDSA: Used mainly for legacy compatibility

ED25519 is recommended for modern systems.

Hardening SSH with Keys

Using SSH keys alone is not enough. A secure setup should also include:

• Disabling root SSH access
• Turning off password authentication
• Changing the default SSH port
• Restricting access via firewall rules

Common SSH Key Mistakes

• Sharing private keys
• Using keys without passphrases
• Leaving unused keys active
• Reusing the same key across multiple users

From a knowledge base perspective, SSH keys are a core security requirement for modern server access.