Generating Key Pairs Using the ssh-keygen Command

Use the ssh-keygen command to generate a public and private authentication key pair. Authentication keys enable you to connect to a remote system without needing to supply a password each time that you connect. Each user must generate their own pair of keys.

Running ssh-keygen

To create a public and private SSH2 key pair, run the following command:

ssh-keygen

The command output and default key names are as follows:

• On Oracle Linux 8 and Oracle Linux 9, the ssh-keygen utility generates RSA keys with base name id_rsa by default. The command output is similar to the following sample output:

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

• On Oracle Linux 10, the ssh-keygen utility generates ed25519 keys with base name id_ed25519 by default. The command output is similar to the following sample output:

  Generating public/private ed25519 key pair.
  Enter file in which to save the key (/home/opc/.ssh/id_ed25519): 
  Enter passphrase (empty for no passphrase): 
  Enter same passphrase again: 
  Your identification has been saved in /home/guest/.ssh/id_ed25519
  Your public key has been saved in /home/guest/.ssh/id_ed25519.pub

To create an SSH key pair by using an algorithm other than the default algorithm, use the -t option. Possible values that you can specify include ecdsa, ed25519, and rsa.

For security, in case an attacker gains access to the private key, you can specify a passphrase to encrypt the private key. If you encrypt the private key, you must enter this passphrase each time that you use the key. If you don't specify a passphrase, you're not prompted for a passphrase.

For more information, see the ssh-keygen(1) manual page.

Location of key files

ssh-keygen generates a private key file and a public key file in $HOME/.ssh (unless you specify an different directory for the private key file). To see the keys on a server, run the following command:

ls -l $HOME/.ssh

...
-rw-------. 1 guest guest 1743 Apr 13 12:07 id_sshkey
-rw-r--r--. 1 guest guest  397 Apr 13 12:07 id_sshkey.pub
...

Note:

In the preceding output example, the placeholder id_sshkey has the following default values on Oracle Linux instances:

• id_rsa on Oracle Linux 8 and Oracle Linux 9 instances.

• id_ed25519 on Oracle Linux 10 instances.