Ubuntu: SSHOpenSSH Generating RSA Keys

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Generating RSA Keys

The first step involves creating a set of RSA keys for use in authentication.

This should be done on the client.

To create your public and private SSH keys on the command-line:

mkdir ~/.ssh
chmod 700 ~/.ssh
ssh-keygen -t rsa

You will be prompted for a location to save the keys, and a passphrase for the keys. This passphrase will protect your private key while it's stored on the hard drive and be required to use the keys every time you need to login to a key-based system:

Generating public/private rsa key pair.
Enter file in which to save the key (/home/b/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/b/.ssh/id_rsa.
Your public key has been saved in /home/b/.ssh/id_rsa.pub.

Your public key is now available as .ssh/id_rsa.pub in your home folder.

Congratulations! You now have a set of keys. Now it's time to make your systems allow you to login with them

Choosing a good passphrase

Just like with physical keys, you need to change all your locks if your RSA key is stolen. Otherwise, your thief will be able to get access to all your stuff.

An SSH key passphrase is a secondary form of security that gives you a little time when your keys are stolen. If your RSA key has a strong passphrase, it might take your attacker a few hours to guess by brute force. That extra time should be enough to log in to any computers you have an account on, delete your old key from the .ssh/authorized_keys file, and add a new key.

Your SSH key passphrase is only used to protect your private key from thieves. It's never transmitted over the Internet, and the strength of your key has nothing to do with the strength of your passphrase.

You have to choose for yourself whether to use a passphrase with your RSA key. Ultimately, it's a choice between cursing the difficulty every time you have to type it in, or cursing your glibness when someone logs in to all your accounts and changes your password so you can't get in any more.

If you choose to use a passphrase, pick something strong and write it down on a piece of paper that you keep in a safe place. If you choose not to use a password, just press the return key without typing a password - you'll never be asked for one again.


submitted by guest blogger
mary gova ,  Nepal

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