Vinayak Salunkhe's team blog

ssh-keygen

Vinayak Salunkhe's photo
Vinayak Salunkhe
·

6 min read

What is the meaning and use case scenarios with example for the following linux command tell me in short and understandable ssh-keygen -t rsa

The command ssh-keygen -t rsa is used to generate a new pair of authentication keys for SSH (Secure Shell), a protocol used for secure remote login and other secure network services over an unsecured network

Here’s a breakdown of the command:

The generated key pair consists of a private key and a public key. The private key is kept secret and secure by the user, while the public key can be shared with anyone. The keys are used to authenticate hosts and users, automating logins and providing a more secure alternative to password-based authentication1.

Here’s an example of how you might use this command:

ssh-keygen -t rsa

When you run this command, it will prompt you for a location to save the keys and a passphrase for additional security. The keys will be stored in your .ssh directory under your home directory1.

This command is commonly used when setting up SSH connections with remote servers, or services like GitHub3. It provides a more secure method of authentication compared to using passwords.

after generating the key what next procedure if I need to access remote linux servers then what will happen and what exactly need to do on those servers ?

\>>>

After generating the SSH key pair, you need to add the public key to the remote server that you want to access. Here are the steps:

  1. Copy the Public Key to the Remote Server: You can use the ssh-copy-id command from your local PC1. The command is as follows:
ssh-copy-id -i path/to/key.pub username@remoteHost

This command adds the public key located at path/to/key.pub with the correct permission to the server at remoteHost using username as login name

  1. Start an SSH Session: After you enter your password, it will copy your public key to the server’s authorized keys file2. This will allow you to log in without the password next time2.

  2. Connect to the Remote Server: Now, you can connect to the remote server using SSH. The most straightforward form of the command is2:

ssh remote_host

The remote_host in this example is the IP address or domain name that you are trying to connect to2.

Remember, it’s important to keep your private key secure on your local machine. Any compromise of the private key will allow an attacker to log into servers that are configured with the associated public key without additional authentication3.

For more detailed instructions, you can refer to these tutorials: How To Configure SSH Key-Based Authentication on a Linux Server and How To Use SSH to Connect to a Remote Server. There are also video tutorials available that can guide you through this process456.

Tell me in a simple and understandable way about How To Configure SSH Key-Based Authentication on a Linux Server and How To Use SSH to Connect to a Remote Server.

Configuring SSH Key-Based Authentication on a Linux Server:

  1. Generate SSH Keys: Use the ssh-keygen command to generate a new SSH key pair1. This will create a 3072 bit RSA key pair by default1.

  2. Install the Public Key on the Server: The public key needs to be added to the remote server that you want to access1. This is done by adding the public key to a special file within the user account you will be logging into called ~/.ssh/authorized_keys1.

  3. Test Authentication: Once the public key is added, you can test the SSH connection. If successful, you should be able to log into the server without entering a password1.

  4. Disable Password-Based Authentication on the Server: For added security, you can disable password-based authentication on the server. This means that only users with the correct SSH key can access the server1.

Using SSH to Connect to a Remote Server:

  1. Use the SSH Command: The ssh command is used to connect to a remote server2. The most straightforward form of the command is ssh remote_host, where remote_host is the IP address or domain name that you are trying to connect to2.

  2. Specify Username if Different: If your username on the remote system is different from your local system, you can specify it using this syntax: ssh remote_username@remote_host2.

  3. Enter Password if Prompted: When you first connect to the server, you may be asked to verify your identity by providing a password2. Once you have set up SSH key-based authentication, you won’t need to enter a password for future logins2.

  4. Exit SSH Session: To exit the SSH session and return back into your local shell session, simply type exit2.

For more detailed instructions, you can refer to these tutorials: How To Configure SSH Key-Based Authentication on a Linux Server and How To Use SSH to Connect to a Remote Server. There are also video tutorials available that can guide you through this process345.

give example file ~/.ssh/authorized_keys of test server when they enter keys in it

The ~/.ssh/authorized_keys file on your server is where you add the public keys of all the machines that will have password-less access to this server. Here’s an example of what it might look like:

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQD3F6+ZXdPEMxGWoeBiht2eX5inVNl3JdeUhC8wRE6VZlO7e5UPaF7JwxN+gDSabzi1M6KyrOrZkaElxYo8C2VR4Pi8h0VnnB4YF1zTc8evCT64yT4rfKoZEnFbCuln+Y+Gz/v0Ibkl/BlXvjojD3sY8w23xn00SQ69/RaPn8v0bbyXjY6OJnbOYvze5FcM/tPPyRoLh6OlYutujCuKLgZIkSNICKRvu1cQctOHpOWNtlu28QBG6DHAHJjsTmyJRuTlFZUfLutqo7slh9b/Hp8SFSuHdd7mSfSzE3h7WQ/LWEszP3U4325Ivl5hdU/kHq8x/i7nGPzj/OhjBEX user1@host1
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCzlJDY9sJ4pB/8B/cBNMOVgP6SOka/6PmC4WVvHuAAZXvDwy2+ZGZ9T9GMCvlgothicXGxdMzH4CzBqVHUKJRa5f6Na5JC+nVkedinAFA+fKc3kvrpq6AsLE5HcIWlOW2GnO3RSPV+hB8H+eCYT6C25qfD0JAfqeeW9DtsoD4Shj9WkZYT2ahvXLAU1h3mAXsLZEPwYZFYwyDbTvA3WteHCp/jCxekIuOE2VZiav0ME82zhrkLn+G2haFPuoUsfLzUXvNRer1MZsfLROcGaLi6ACq7GPgFgG6YA7j/VxTvDVvT50U/rfuU5Xe297ulLC+pjVTxuMb19QHDF user2@host2

Each line in this file represents one key pair, and is formatted like this: KEY_TYPE PUBLIC_KEY COMMENT. In this case, KEY_TYPE is ssh-rsa, PUBLIC_KEY is the long string of characters, and COMMENT is typically the username and hostname from where the key pair was generated.

When a client attempts to authenticate using SSH keys, the server can test whether the client has access to the private key by sending an encrypted message that can only be decrypted with the private key. If the client can decrypt the message and send it back, it proves they have access to the private key and are allowed to log in.

Remember, anyone who has a copy of the public key can add it to their authorized_keys file and grant you (or anyone who holds the corresponding private key) access to their account. So it’s important to keep your private keys secure.

do you mean each linux server used for test or QA or UAT enviornment will have seperate users and depending on the location where our public key is added, we will get access to that server with that perticular users previledges

Yes, you’re correct. Each Linux server, whether it’s used for testing, QA, or UAT environments, can have multiple user accounts. Each user account has its own set of privileges and access controls.

When you add your public key to a specific user’s ~/.ssh/authorized_keys file on a server, you’re granted access to that server with the privileges of that particular user. This means you can log in as that user and perform actions based on the user’s privileges.

For example, if you add your public key to the authorized_keys file of a user named testuser on a server, you can log in as testuser and have the same access rights as testuser.

This is why it’s important to secure your private key. If someone else obtains your private key, they could potentially access any server where your public key is installed.