Oct 29, 2012 Linux / Unix ssh-keygen: Create A Host Key File. Ssh-keygen will generate an RSA key for use in SSH protocol 2 connections. Why create a new host key files? Notice that the knownhosts file by itself is not very useful without having verified the host fingerprints first. The following caution is straight from the ssh-keyscan man page: SECURITY If an sshknownhosts file is constructed using ssh-keyscan without veri- fying the keys. A host key is a cryptographic key used for authenticating computers in the SSH protocol. Host keys are key pairs, typically using the RSA, DSA, or ECDSA algorithms. Public host keys are stored on and/or distributed to SSH clients, and private keys are stored on SSH servers. Jul 29, 2019 Step 1- Generate the SSH Key Pair. On your client system – the one you’re using to connect to the server – you need to create a pair of key codes. To generate a pair of SSH key codes, enter the commands: This will create a hidden directory to store. Jul 17, 2017 Create a file /.ssh/authorizedkeys if already exist ignore this step $ vim /.ssh/authorizedkeys Changes are made in file /.ssh/authorizedkeys such as copy the pub in file /.ssh/authorizedkeys on the machine to which you want to connect, appending it to its end if the file.
How do I regenerate OpenSSH sshd server host keys stored in /etc/ssh/ssh_host_* files? Can I safely regenerate ssh host keys using remote ssh session as my existing ssh connections shouldn’t be interrupted on Debian or Ubuntu Linux? How do I regenerate new ssh server keys? How to regenerate new host keys on a Debian or Ubuntu Linux?[donotprint][/donotprint]To regenerate keys you need to delete old files and reconfigure openssh-server. It is also safe to run following commands over remote ssh based session. Your existing session shouldn’t be interrupted.
Why regenerate new ssh server keys?
Most Linux and Unix distribution create ssh keys for you during the installation of the OpenSSH server package. But it may be useful to be able re-generate new server keys from time to time. For example, when you duplicate VM (KVM or container) which contains an installed ssh package and you need to use different keys from cloned KVM VM guest/machine.
Steps to regenerate OpenSSH host keys on Linux
Let us see all steps
Step 1 – Delete old ssh host keys
Login as the root and type the following command to delete files on your SSHD server:# /bin/rm -v /etc/ssh/ssh_host_*
Sample outputs:
Step 2 – Debian or Ubuntu Linux Regenerate OpenSSH Host Keys
Remove Ssh Host Key
Now create a new set of keys on your SSHD server, enter:# dpkg-reconfigure openssh-server
Sample output:
You just regenerated new ssh server keys. You need to restart ssh server:$ sudo systemctl restart ssh
OR$ /etc/init.d/ssh restart
Step 3 – Update all ssh client(s) known_hosts files
Finally, you need to update ~/.ssh/known_hosts files on client computers, otherwise everyone will see an error message that read as follows:
Either remove host fingerprint or update the file using vi text editor (command must be typed on client machine):$ ssh-keygen -R remote-server-name-here
Now login using the ssh command:$ ssh [email protected]
Conclusion
You just regenerated OpenSSH Host Keys on a Debian or Ubuntu Linux using the dpkg-reconfigure command. For more info see the man page or this wiki page here:$ man dpkg-reconfigure
$ man sshd
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Overview
Public key authentication is a way of logging into an SSH/SFTP account using a cryptographic key rather than a password.
If you use very strong SSH/SFTP passwords, your accounts are already safe from brute force attacks. However, using public key authentication provides many benefits when working with multiple developers. For example, with SSH keys you can
- allow multiple developers to log in as the same system user without having to share a single password between them;
- revoke a single developer's access without revoking access by other developers; and
- make it easier for a single developer to log in to many accounts without needing to manage many different passwords.
How Public Key Authentication Works
Keys come in pairs of a public key and a private key. Each key pair is unique, and the two keys work together.
These two keys have a very special and beautiful mathematical property: if you have the private key, you can prove you have it without showing what it is. It's like proving you know a password without having to show someone the password.
Public key authentication works like this:
- Generate a key pair.
- Give someone (or a server) the public key.
- Later, anytime you want to authenticate, the person (or the server) asks you to prove you have the private key that corresponds to the public key.
- You prove you have the private key.
You don't have to do the math or implement the key exchange yourself. The SSH server and client programs take care of this for you.
Generate an SSH Key Pair
You should generate your key pair on your laptop, not on your server. All Mac and Linux systems include a command called ssh-keygen that will generate a new key pair.
If you're using Windows, you can generate the keys on your server. Just remember to copy your keys to your laptop and delete your private key from the server after you've generated it.
To generate an SSH key pair, run the command ssh-keygen.
It will look like this when you run it:
You'll be prompted to choose the location to store the keys. The default location is good unless you already have a key. Press Enter to choose the default location.
Next, you'll be asked to choose a password. Using a password means a password will be required to use the private key. It's a good idea to use a password on your private key.
After you choose a password, your public and private keys will be generated. There will be two different files. The one named id_rsa is your private key. The one named id_rsa.pub is your public key.
You'll also be shown a fingerprint and 'visual fingerprint' of your key. You do not need to save these.
Configure an SSH/SFTP User for Your Key
Method 1: Using ssh-copy-id
Now that you have an SSH key pair, you're ready to configure your app's system user so you can SSH or SFTP in using your private key.
To copy your public key to your server, run the following command. Be sure to replace 'x.x.x.x' with your server's IP address and SYSUSER with the name of the the system user your app belongs to.
Method 2: Manual Configuration
If you don't have the ssh-copy-id command (for example, if you are using Windows), you can instead SSH in to your server and manually create the .ssh/authorized_keys file so it contains your public key.
First, run the following commands to make create the file with the correct permissions.
Next, edit the file .ssh/authorized_keys using your preferred editor. Copy and paste your id_rsa.pub file into the file.
Log In Using Your Private Key
You can now SSH or SFTP into your server using your private key. From the command line, you can use:
If you didn't create your key in the default location, you'll need to specify the location:
If you're using a Windows SSH client, such as PuTTy, look in the configuration settings to specify the path to your private key.
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Granting Access to Multiple Keys
The .ssh/authorized_keys file you created above uses a very simple format: it can contain many keys as long as you put one key on each line in the file.
If you have multiple keys (for example, one on each of your laptops) or multiple developers you need to grant access to, just follow the same instructions above using ssh-copy-id or manually editing the file to paste in additional keys, one on each line.
When you're done, the .ssh/authorized_keys file will look something like this (don't copy this, use your own public keys):
Additional Information
Retrieve Your Public Key from Your Private Key
The following command will retrieve the public key from a private key:
This can be useful, for example, if your server provider generated your SSH key for you and you were only able to download the private key portion of the key pair.
Note that you cannot retrieve the private key if you only have the public key.
Correcting Permissions on the .ssh Directory
The instructions in this article will create your server's .ssh directory and .ssh/authorized_keys file with the correct permissions. However, if you've created them yourself and need to fix permissions, you can run the following commands on your server while SSH'd in as your app's system user.
Disabling Password Authentication
NOTE: When changing anything about the way SSH is accessed(ports, authentication methods, et cetera), it is very strongly recommended to leave an active root SSH session open until everything is working as intended. This ensures you have a way to revert changes in the event something goes wrongand logins are not working properly.
As an extra security precaution, once you have set up SSH keys, you may wish to disable password authentication entirely. This will mean no users will be able to log into SSH or SFTP without SSH keys. Anyone entering a password will receive a message like:
Or:
Disabling password authentication is an excellent way to improve server security. Please see our guide here for the steps to accomplish this goal.
Then, test whether you're able to log in with a password by opening a new SSH or SFTP session to the server. Passwords should not be able to be used and, if everything has been done correctly, an error will be issued when someone tries to use a password. Unless this setting is changed back to allow password authentication, no users will be able to log in without an SSH key set up.