SSH Keys

• Generate a key pair locally
• Give the public key to the remote server
• Keep the private key yourself

Generate key

1ssh-keygen -t ed25519

Previously, i used to use rsa as the type, but i have since moved on to ed25519. Ed25519 is a newer public-key algorithm which is faster (and safer) than RSA. Ed25519 public-key is also more compact, containing only 68 characters as compared to RSA 3072 that has 544 characters. Ed25519 is supported by OpenSSH so you should be good in almost all cases.

Github recommends passing it your email with -C which is then uses as a label.

1cd ~/.ssh && ssh-keygen -t ed25519 -C "hello@example.com"

Copy .pub file to remote

1scp id_ed25519.pub user@remoteserver:location

On linux you can do

1ssh-copy-id user@123.456.789.123
2
3# ssh-copy-id -i ~/.ssh/mykey -p 1234 user@host

Permissions

The remote server doesn’t like the authorizated_keys file having too many permissions. For better security, change the authorizated_keys file to 600 and the ~/.ssh/ folder to 700. The permissions on .ssh can not be any higher than 755.

1chmod 600 ~/.ssh/authorized_keys
2chmod 700 ~/.ssh

You might even have to change permissions for the /home directory

1chmod go-w ~/

sshd_config

The config file for the ssh daemon is at:

/etc/ssh/sshd_config

You can also use the find command to find the file location:

1find / -name sshd_config

Make a copy of the config file if you are afraid of messing it up

1cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak

Restart SSH

1service sshd restart

If you don’t know what the service name for ssh is, you can list all of the services to find out:

1service --status-all

.ssh/config (local system)

You can create an SSH config file at ~/.ssh/config and save all your SSH connection settings there. You will then be able to run ssh FOO and connect with all the settings defined for the host FOO.

1# My settings for connecting to FOO server
2Host foo
3  #HostName www.myfooserver.com
4  HostName 123.456.789.123
5  User USERNAME
6  Port 22
7  IdentityFile ~/.ssh/MY_SSH_KEY

Start the ssh-agent and load your keys

See if ssh-agent is running:

1ps -e | grep [s]sh-agent

Run ssh-agent:

1ssh-agent /bin/bash

OR

1ssh-agent bash

OR

1eval $(ssh-agent)

Load ssh key:

1ssh-add ~/.ssh/id_ed25519

List loaded ssh keys:

1ssh-add -l

Copy key to clipboard

Copy your key to your clipboard with (Linux only):

1cat ~/.ssh/id_ed25519.pub | pbcopy

Troubleshhoting

Simple as that. Though troubleshooting might be needed.

• make sure the .pub key has been copied to the authorized_keys file, on remote server, in the ~/.ssh folder. If it doesn’t exist, create one.
• make sure that the path you copied to is the path specifies in the ssh config file. The ssh config file is at: sshd_config
• if the error doesn’t make sense try ssh with verbose mode -v.
• make sure you have no extra white space at the end when you copy the key, because that can throw it in a loop.

Resources

• YouTube: Setting Up an SSH Key
• Generating a new SSH key and adding it to the ssh-agent