Setting up ssh keys for remote server access

how_to_set_up_ssh_keys.md

How to Set up SSH Keys

Create the RSA Key Pair

ssh-keygen -t rsa

Store the Keys and Passphrase

Once you have entered the Gen Key command, you will get a few more questions:

Enter file in which to save the key (/home/demo/.ssh/id_rsa):

You can press enter here, saving the file to the user home (in this case, my example user is called demo).

Enter passphrase (empty for no passphrase):

It's up to you whether you want to use a passphrase.

Entering a passphrase does have its benefits: the security of a key, no matter how encrypted, still depends on the fact that it is not visible to anyone else. Should a passphrase-protected private key fall into an unauthorized users possession, they will be unable to log in to its associated accounts until they figure out the passphrase, buying the hacked user some extra time. The only downside, of course, to having a passphrase, is then having to type it in each time you use the Key Pair.

The entire key generation process looks like this:

ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/demo/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/demo/.ssh/id_rsa.
Your public key has been saved in /home/demo/.ssh/id_rsa.pub.
The key fingerprint is:
4a:dd:0a:c6:35:4e:3f:ed:27:38:8c:74:44:4d:93:67 demo@a
The key's randomart image is:
+--[ RSA 2048]----+
|          .oo.   |
|         .  o.E  |
|        + .  o   |
|     . = = .     |
|      = S = .    |
|     o + = +     |
|      . o + o .  |
|           . o   |
|                 |
+-----------------+

The public key is now located in /home/demo/.ssh/id_rsa.pub

The private key (identification) is now located in /home/demo/.ssh/id_rsa

Copy the Public Key

Once the key pair is generated, it's time to place the public key on the virtual server that we want to use.

You can copy the public key into the new machine's authorized_keys file with the ssh-copy-id command. Make sure to replace the example username and IP address below.

ssh-copy-id [email protected]

Alternatively, you can paste in the keys using SSH:

cat ~/.ssh/id_rsa.pub | ssh [email protected] "cat >> ~/.ssh/authorized_keys"

No matter which command you chose, you should see something like:

The authenticity of host '12.34.56.78 (12.34.56.78)' can't be established.
RSA key fingerprint is b1:2d:33:67:ce:35:4d:5f:f3:a8:cd:c0:c4:48:86:12.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '12.34.56.78' (RSA) to the list of known hosts.
[email protected]'s password:

Now try logging into the machine, with:

ssh [email protected]

and check in:

~/.ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.

Now you can go ahead and log into [email protected] and you will not be prompted for a password. However, if you set a passphrase, you will be asked to enter the passphrase at that time (and whenever else you log in in the future).

Disable the Password for Root Login

Once you have copied your SSH keys unto your server and ensured that you can log in with the SSH keys alone, you can go ahead and restrict the root login to only be permitted via SSH keys.

In order to do this, open up the SSH config file:

sudo nano /etc/ssh/sshd_config

Within that file, find the line that includes PermitRootLogin and modify it to ensure that users can only connect with their SSH key:

PermitRootLogin without-password

Put the changes into effect:

sudo /etc/init.d/ssh restart

@kimleonard you can use your hostname (the name of your device/computer).

I have two laptops, how do I use ssh keys from the 2 laptops on my github account @stormypython

@Phavor set up each laptop with it's own private key and put the public key for both wherever you want to login.

Then if a laptop is stolen or replaced you can just get rid of that public key from the server without affecting the other laptop.

$ ssh-keygen -p

Start the SSH key creation process

Enter file in which the key is (/Users/you/.ssh/id_rsa): [Hit enter]
Key has comment '/Users/you/.ssh/id_rsa'
Enter new passphrase (empty for no passphrase): [Type new passphrase]
Enter same passphrase again: [One more time for luck]
Your identification has been saved with the new passphrase.

I have two laptops, how do I use ssh keys from the 2 laptops on my github account @stormypython

I'm 5 years late — but in case someone is wondering the same:

1. You ought to have already went through the github flow of creating a pair of public/private key. The private key is already installed on one of your labtops. The task now is: How can I use the same private key already installed on labtop A elsewhere?
2. copy the id_rsa private key file from labtop A's ~/.ssh directory to labtop B's ~/.ssh directory.
3. Start the ssh-agent server on labtop B (if you haven't already) with eval `ssh-agent` (include the backticks).
4. On labtop B, run ssh-add ~/.ssh/id_rsa. Should be good now.

tysm
this is the only tutorial that actually worked for me.