Pete FreitagSetting up public key authentication over SSH
By Pete Freitag
Every time I want to setup public key authentication over SSH, I have to look it up, and I've never found a simple guide, so here's mine.
Generate key on local machine
ssh-keygen -t rsa
It will ask you for a password, you can leave it blank if you do not want to be prompted for the password every time you login. If you do this, understand that this means the private key file is as good as a password.
You can also specify a key size, like this:
ssh-keygen -t rsa -b 4096
Note you could also pick -t ed25519 which offers better performance, but may not be compatible with older systems.
Ensure that the remote server has a .ssh directory
Make sure the server your connecting to has a .ssh directory in your home directory. If it doesn't exist you can run the ssh-keygen command above, and it will create one with the correct permissions.
Copy your local public key to the remote server
If your remote server doesn't have a file called ~/.ssh/authorized_keys2 then we can create it. If that file already exists, you need to append to it instead of overwriting it, which the command below would do:
scp ~/.ssh/id_rsa.pub remote.server.com:.ssh/authorized_keys2
You should also make sure that the file permissions on the authorized_keys2 file is correct. You can do this by running the command:
chmod 600 ~/.ssh/authorized_keys2
If the file is writable by any user other than the owner it SSH will not use the file, and skip public key authentication.
Now ssh to the remote server
Now you can ssh to the remote server without entering your password.
Security
Now keep in mind that all someone needs to login to the remote server, is the file on your local machine ~/.ssh/id_rsa, so make sure it is secure.
To keep up to date on the latest OpenSSH vulnerabilities, try stack.watch.
Setting up public key authentication over SSH was first published on January 18, 2006.
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Comments
Also, in response to harry who commented that there is no need to secure the file because it's a public key: You absolutely need to make sure this file is at least not writable by any other users (or they can simply append their keys to the file). As for why it shouldn't be readable by other users, that's just the first rule of security. If they don't need access, they don't have access.
scp ~/.ssh/id_rsa.pub remote.server.com:~/.ssh/authorized_keys2
what goes in the /etc/sshd_config file and where does it go please
I have chmod 600 the files in .ssh
thanks
tim
server$ chmod 700 ~/.ssh server$ chmod 600 ~/.ssh/authorized_keys
./ssh - 700
~/.ssh/authorized_keys - 644
regarding authorized_keys or authorized_keys2 .. please check your sshd server config file , i.e. /etc/ssh/sshd_config , prameter AuthorizedKeysFile. It will tell you what file your sshd server is using:)))