Aug 19, 2019 Using SSH keys for authentication is highly recommended, as a safer alternative to passwords. This tutorial will guide you through the steps on how to generate and set up SSH keys on CentOS 7. We also cover connecting to a remote server using the keys and disabling password.
This section of Getting Started assumes that:
- You have recently installed Bitvise SSH Server.
- You have configured the SSH Server for access using SFTP, for Git access, or another purpose.
- You have installed Bitvise SSH Client on the computer from which you wish to connect.
- You wish to configure public key authentication between the SSH Server and Client.
Before you configure public key authentication, it is important to understand:
- Public keys, in the way they are commonly used in SSH, are not X.509 certificates.
- Client authentication keys are separate from server authentication keys (host keys).
- A keypair consists of a private key and a public key, which are separate.
- A private key should never be sent to another party. It is private.
If this is the first time you are using public keys, we recommend the page Public keys in SSH.
To use public key authentication, the client from which you are connecting needs to have a public/private keypair. To generate a keypair using Bitvise SSH Client, run the graphical SSH Client, and open the Client key manager:
Press the Generate button to generate a new keypair:
Unless required for compatibility reasons, do not generate a DSA keypair. Only 1024-bit DSA keys are interoperable in SSH, and this key size is no longer considered adequate when using the DSA algorithm. Generate either an ECDSA keypair, or an RSA keypair of size 2048 bits or larger.
If you have saved a named SSH Client profile, the keypair generation interface will offer to store the keypair either in the profile, or globally.
When the keypair is stored globally, it is stored in the Windows registry for the current user, under HKCUSoftwareBitviseKeypairs.
It may be useful to store the keypair in a profile if the profile is going to be used on other computers, or by a job that runs as a different Windows account on the same computer. In SSH Client versions 7.xx and higher, the setting Sensitive information accessibility on the Login tab controls whether a keypair stored in the profile can be read by another Windows user, or on another computer.
You can choose a passphrase with which to protect the keypair. If you enter a passphrase, you will need to provide it every time the keypair is used for authentication.
Before you can use public key authentication, the public key for the keypair you have generated must be configured in the SSH Server. If you are able to connect to the SSH Server using password authentication, you can connect to the server and upload the public key using the Client key manager:
If the SSH Server does not allow you to connect using password authentication, or does not allow you to upload the key, you will need to send the public key to the server administrator using an alternate method of communication. To do this, export the public key using the Client key manager:
Generate Ssh Key For Remote Login
For help with importing the public key into Bitvise SSH Server, check the Public Key Authentication section of our SSH Server Usage FAQ.
Once the public key has been uploaded or imported for your account in the SSH Server, configure the SSH Client to enable public key authentication on the Login tab:
You should now be able to connect to the SSH Server using your public key:
Save the profile to preserve this configuration.
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 Ssh Key For Passwordless Login
- 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.
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):
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:
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.