The authorized keys file is a crucial component of secure shell (SSH) protocol-based authentication. It helps ensure secure and authenticated access to remote machines or servers. In simple terms, the authorized keys file on a server contains a list of public keys that are allowed access to that particular server.
Here are the key points to understand about the authorized keys file:
1. Functionality: When a user attempts to connect to a remote server using SSH, the server will check the authorized keys file to verify if the user's public key is listed and authorized. If the public key is found in the file, the server will grant access to the user.
2. Public/Private Key Cryptography: SSH authentication relies on public/private key cryptography. The user possesses a private key that matches the public key stored in the authorized keys file of the SSH server. These keys work together to establish a secure connection and authenticate the user without the need for a password.
3. Use of the File: Typically, users generate a pair of keys—a public key and a private key—on their local machine. The user then adds the public key to the authorized keys file on the server they want to access. This process can be done manually or through automated methods like key-based authentication tools.
4. Format: The authorized keys file usually resides in the user's home directory on the server, specifically in the `~/.ssh/` folder. Each line in the file represents a single authorized key entry.
5. Multiple Authorizations: The authorized keys file can contain multiple entries, allowing different users to access the server using their respective public keys. It enables system administrators to manage access permissions securely and efficiently.
6. Security Considerations: It is essential to protect the authorized keys file from unauthorized modifications or access. Only authorized users should have write access to the file, while others should have read permissions. Additionally, regularly reviewing and managing the contents of the authorized keys file helps maintain a secure environment.
Understanding the role and functionality of the authorized keys file in SSH-based authentication is crucial for maintaining secure remote access to servers and ensuring that only authorized individuals can access sensitive systems.