What is SSH Key Authentication
SSH is a command line application similar to Telnet that allows you to log in to one server from another. Where Telnet submitted user passwords over the network in plain text, SSH provides a layer of encryption that prevents nefarious actors from sniffing passwords during transit on the local network.
However, whilst passwords are generally more secure to use with SSH, the protocol provides a more secure alternative option in the form of SSH Key Authentication. With SSH Key authentication, the user must possess a private key file to log in. In contrast to password authentication, anyone who knows the password can gain access.
Private keys provide a higher level of security than passwords, as the key uses a cryptographic algorithm rather than a defined string of characters. And unlike passwords, private keys are much more difficult to guess or crack by hackers, making them highly secure online.
How to use SSH Key Authentication
Using the ssh-keygen command, users generate a key pair on the client machine to create the public and private keys. The private key must be kept secure on the client and protected with permissions to prevent read access from other users. A passphrase can further protect the private key, encrypting the contents so that only the user with the passphrase can read it.
The user then distributes the public key to the SSH server to which they want to log in and places the public key content into their .ssh/authorized_keys file. By performing this action, the user is instructing the SSH server that the key is acceptable for authentication and that the user authorizes anyone logging in with this key to access their account.
To log in using the key, the user passes the private key file to the ssh command, which uses the private key to generate a unique cryptographic signature that the ssh server can verify with the public key. Successful execution of these operations proves that the user logging in possesses the private key and should be allowed access to the system.
Benefits of SSH Key Authentication
Increase Security
The main benefit of SSH Key Authentication is the increased security of privileged accounts. When using private keys to authenticate, there is no need to transmit passwords over the network. And because the private key is kept on your local machine, it is less vulnerable to interception or attack. An SSH server configured only to accept SSH Key Authentication is more secure and prevents bots from attempting to brute force access by repeated attempts to authenticate with random passwords.
Better Access Control
SSH keys can control access to servers and applications by restricting access only to authorized users with the corresponding private key.
For example, when logging into a device to perform privileged operations without a separate sudo configuration, multiple administrators do not need to share the root password. Each user should use a unique key, making it easier to revoke as existing users can continue to use their keys, and no passwords need to be changed.
Convenience
SSH keys can be more convenient and increase users’ productivity when properly configured and used. Whilst the recommended practice is to encrypt keys with a unique passphrase, tools like ssh-agent will hold keys in memory, allowing access to the ssh client to save users from having to enter the passphrase repeatedly and reduce the risk of mistakes when entering passwords.
Automation
SSH keys can be used in scripts and automation tools to automate tasks that require logging into a remote server. This can make managing and maintaining servers and applications easier and reduces the risk of a password being exposed.
Conclusion
In conclusion, SSH key authentication provides a secure and convenient way to authenticate remote access to servers and applications. By using an SSH key pair, you can increase the security of your connections by eliminating the need for passwords and reducing the risk of brute-force attacks. SSH keys also provide better access control, automation, and auditing capabilities, making them ideal for managing and maintaining remote servers and applications. While there may be a learning curve to get started with SSH keys, their benefits are well worth the investment of time and effort.
Overall, SSH key authentication is a reliable and effective solution for securing remote server access and protecting sensitive information. Using SSH keys provides a more secure, convenient, and flexible way to access remote servers than passwords.