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If you decided not to create a passphrase with your key, you're essentially setting up 
authentication without a password, meaning you won't be asked to enter anything 
when authenticating.
Utilizing an SSH agent
When we created our SSH key earlier, it was mentioned that having a passphrase 
is optional but is a good idea. Using passphrases with OpenSSH key-pairs boosts 
their security. If an OpenSSH key falls into the wrong hands, it will be useless if the 
person attempting to utilize it doesn't know the passphrase. However, we lose a 
bit of convenience because we need to enter the passphrase for a key each time we 
want to use it. An OpenSSH key without a passphrase will allow us to connect to 
a server and be logged in without entering anything at all. With an 
SSH agent
, you 
can actually cache your passphrase the first time you use it, so you won't be asked 
for it with every connection. This essentially allows you to benefit from the added 
security of a passphrase, and still maintain at least some convenience. Best of all, if 
your laptop or desktop is able to utilize the OpenSSH client for connecting to remote 
systems, you should have an SSH agent on your system already. If we're using a 
flavor of Linux or macOS on our workstation or laptop, for example, we will have 
the 
ssh-agent
 command available to us.
The 
ssh-agent
 is used by starting it in the background in our terminal. We can then 
"unlock" our keys with our passphrase, and then the unlocked key will be stored 
in memory and will be automatically used when we attempt to connect to a server 
we've copied our public key to. To start it, enter the following command as your 
normal user account on the machine you're starting your connections from (that is, 
your workstation):
eval $(ssh-agent) 
This command will start an SSH agent, which will continue to run in the background 
of your shell. But it's not adding any value to us yet—so we will need to add an SSH 
key to the now running agent. The 
ssh-add
 command allows us to add an SSH key to 
our running 
ssh-agent
. To do so, we can give the 
ssh-add
 command the path to our 
public key as an argument:
ssh-add ~/.ssh/id_rsa 
At this point, you'll be asked for your passphrase. As long as you enter it properly, 
your key will remain open and you won't need to enter it again for future 
connections, until you close that shell or log out. Now that you have the 
ssh-
agent
 running in the background with your unlocked key, utilizing a key with a 
passphrase becomes much easier and you'll end up typing a lot less.

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