If you don’t see the files in your listing, your will have to generate rsa keys for your ssh sessions: SSH key generation Please don’t generate new keys if you already have a valid keypair!
SSH, or secure shell, is an encrypted protocol used to administer and communicate with servers. When working with a Debian server, chances are you will spend most of your time in a terminal session connected to your server through SSH.
In this guide, we’ll focus on setting up SSH keys for a vanilla Debian 10 installation. SSH keys provide an easy, secure way of logging into your server and are recommended for all users.
The first step is to create a key pair on the client machine (usually your computer):
By default ssh-keygen
will create a 2048-bit RSA key pair, which is secure enough for most use cases (you may optionally pass in the -b 4096
flag to create a larger 4096-bit key).
After entering the command, you should see the following output:
Press enter to save the key pair into the .ssh/
subdirectory in your home directory, or specify an alternate path.
If you had previously generated an SSH key pair, you may see the following prompt:
Warning: If you choose to overwrite the key on disk, you will not be able to authenticate using the previous key anymore. Be very careful when selecting yes, as this is a destructive process that cannot be reversed.
You should then see the following prompt:
OverviewThe APNS certificate is required for Afaria to send requests to the APNS service to send push notifications to a iOS device for connecting to the server to execute a MDM command. PurposeThe intent of this page is to outline the steps needed in order to obtain an Apple Push Notification Services (APNS) certificate for use with Afaria. In order to generate a public and a private key certificate.
Here you optionally may enter a secure passphrase, which is highly recommended. A passphrase adds an additional layer of security to prevent unauthorized users from logging in. To learn more about security, consult our tutorial on How To Configure SSH Key-Based Authentication on a Linux Server.
You should then see the following output:
Nintendo parental controls master key. We would like to show you a description here but the site won’t allow us.
You now have a public and private key that you can use to authenticate. The next step is to place the public key on your server so that you can use SSH-key-based authentication to log in.
The quickest way to copy your public key to the Debian host is to use a utility called ssh-copy-id
. Due to its simplicity, this method is highly recommended if available. If you do not have ssh-copy-id
available to you on your client machine, you may use one of the two alternate methods provided in this section (copying via password-based SSH, or manually copying the key).
ssh-copy-id
The ssh-copy-id
tool is included by default in many operating systems, so you may have it available on your local system. For this method to work, you must already have password-based SSH access to your server.
To use the utility, you simply need to specify the remote host that you would like to connect to and the user account that you have password SSH access to. This is the account to which your public SSH key will be copied.
The syntax is:
You may see the following message:
This means that your local computer does not recognize the remote host. This will happen the first time you connect to a new host. Type “yes” and press ENTER
to continue.
Next, the utility will scan your local account for the id_rsa.pub
key that we created earlier. When it finds the key, it will prompt you for the password of the remote user’s account:
Type in the password (your typing will not be displayed for security purposes) and press ENTER
. The utility will connect to the account on the remote host using the password you provided. It will then copy the contents of your ~/.ssh/id_rsa.pub
key into a file in the remote account’s home ~/.ssh
directory called authorized_keys
.
You should see the following output:
At this point, your id_rsa.pub
key has been uploaded to the remote account. You can continue on to Step 3.
If you do not have ssh-copy-id
available, but you have password-based SSH access to an account on your server, you can upload your keys using a conventional SSH method.
We can do this by using the cat
command to read the contents of the public SSH key on our local computer and piping that through an SSH connection to the remote server.
On the other side, we can make sure that the ~/.ssh
directory exists and has the correct permissions under the account we’re using.
We can then output the content we piped over into a file called authorized_keys
within this directory. We’ll use the >>
redirect symbol to append the content instead of overwriting it. This will let us add keys without destroying previously added keys.
The full command looks like this:
You may see the following message:
This means that your local computer does not recognize the remote host. This will happen the first time you connect to a new host. Type “yes” and press ENTER
to continue.
Afterwards, you should be prompted to enter the remote user account password:
After entering your password, the content of your id_rsa.pub
key will be copied to the end of the authorized_keys
file of the remote user’s account. Continue on to Step 3 if this was successful.
If you do not have password-based SSH access to your server available, you will have to complete the above process manually.
We will manually append the content of your id_rsa.pub
file to the ~/.ssh/authorized_keys
file on your remote machine.
To display the content of your id_rsa.pub
key, type this into your local computer:
You will see the key’s content, which should look something like this:
Access your remote host using whichever method you have available.
Once you have access to your account on the remote server, you should make sure the ~/.ssh
directory exists. This command will create the directory if necessary, or do nothing if it already exists:
Now, you can create or modify the authorized_keys
file within this directory. You can add the contents of your id_rsa.pub
file to the end of the authorized_keys
file, creating it if necessary, using this command:
In the above command, substitute the public_key_string
with the output from the cat ~/.ssh/id_rsa.pub
command that you executed on your local system. It should start with ssh-rsa AAAA..
.
Finally, we’ll ensure that the ~/.ssh
directory and authorized_keys
file have the appropriate permissions set:
This recursively removes all “group” and “other” permissions for the ~/.ssh/
directory.
If you’re using the root
account to set up keys for a user account, it’s also important that the ~/.ssh
directory belongs to the user and not to root
:
In this tutorial our user is named sammy but you should substitute the appropriate username into the above command.
We can now attempt passwordless authentication with our Debian server.
If you have successfully completed one of the procedures above, you should be able to log into the remote host without the remote account’s password.
The basic process is the same:
If this is your first time connecting to this host (if you used the last method above), you may see something like this:
This means that your local computer does not recognize the remote host. Type “yes” and then press ENTER
to continue.
If you did not supply a passphrase for your private key, you will be logged in immediately. If you supplied a passphrase for the private key when you created the key, you will be prompted to enter it now (note that your keystrokes will not display in the terminal session for security). After authenticating, a new shell session should open for you with the configured account on the Debian server.
If key-based authentication was successful, continue on to learn how to further secure your system by disabling password authentication.
If you were able to log into your account using SSH without a password, you have successfully configured SSH-key-based authentication to your account. However, your password-based authentication mechanism is still active, meaning that your server is still exposed to brute-force attacks.
Before completing the steps in this section, make sure that you either have SSH-key-based authentication configured for the root account on this server, or preferably, that you have SSH-key-based authentication configured for a non-root account on this server with sudo
privileges. This step will lock down password-based logins, so ensuring that you will still be able to get administrative access is crucial.
Once you’ve confirmed that your remote account has administrative privileges, log into your remote server with SSH keys, either as root or with an account with sudo
privileges. Then, open up the SSH daemon’s configuration file:
Inside the file, search for a directive called PasswordAuthentication
. This may be commented out. Uncomment the line and set the value to “no”. This will disable your ability to log in via SSH using account passwords:
Save and close the file when you are finished by pressing CTRL
+ X
, then Y
to confirm saving the file, and finally ENTER
to exit nano. To actually implement these changes, we need to restart the sshd
service:
As a precaution, open up a new terminal window and test that the SSH service is functioning correctly before closing this session:
Once you have verified your SSH service, you can safely close all current server sessions.
The SSH daemon on your Debian server now only responds to SSH keys. Password-based authentication has successfully been disabled.
You should now have SSH-key-based authentication configured on your server, allowing you to sign in without providing an account password.
If you’d like to learn more about working with SSH, take a look at our SSH Essentials Guide.
The PuTTYgen program is part of PuTTY, an open source networking client for the Windows platform.
To download PuTTY or PuTTYgen, go to http://www.putty.org/ and click the You can download PuTTY here link.
As the key is being generated, move the mouse around the blank area as directed.
Note:
While a passphrase is not required, you should specify one as a security measure to protect the private key from unauthorized use. When you specify a passphrase, a user must enter the passphrase every time the private key is used.
.ppk
(PuTTY private key).Note:
The.ppk
file extension indicates that the private key is in PuTTY's proprietary format. You must use a key of this format when using PuTTY as your SSH client. It cannot be used with other SSH client tools. Refer to the PuTTY documentation to convert a private key in this format to a different format. Make sure you select all the characters, not just the ones you can see in the narrow window. If a scroll bar is next to the characters, you aren't seeing all the characters.
.pub
extension to indicate that the file contains a public key.ssh
utility on Linux), export the private key:.ppk
format, using an extension such as .openssh
to indicate the file's content.