vyos@test1# run generate pki key-pair install rsa-keys
Enter private key type: [rsa, dsa, ec] (Default: rsa)
Enter private key bits: (Default: 2048)
Note: If you plan to use the generated key on this router, do not encrypt the private key.
Do you want to encrypt the private key with a passphrase? [y/N] y
Enter passphrase: vyos
Do you want to install the public key? [Y/n] Y
Do you want to install the private key? [Y/n] Y
Failed to install 2 value(s). Commands to manually install:
set pki key-pair rsa-keys public key 'MIIBIjA......
.........
1 value(s) installed. Use "compare" to see the pending changes, and "commit" to apply.
[edit]
vyos@test1# comp
[pki]
+ key-pair rsa-keys {
+     private {
+         password-protected
+     }
+ }