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I know that private key authentication works, however I'm looking for public key authentication. I'm trying to establish a connection using SSH.NET and a public key. In the Git Bash terminal I can connect and run commands fine using my public key, but when I try connecting to the same host using SSH.NET I. If /.ssh or authorizedkeys is a symbolic link, the canonical path (with symbolic links expanded) is checked. Your /.ssh/authorizedkeys file (on the remote machine) must be readable (at least 400), but you'll need it to be also writable (600) if you will add any more keys to it. With SSH, public key authentication improves security considerably as it frees the users from remembering complicated passwords (or worse yet, writing them down). In addition to security public key authentication also offers usability benefits - it allows users to implement single sign-on across the SSH servers they connect to.
If you have ever worked as a sysadmin (or you want to in the future), you need a good grasp of SSH. I will not run you through the general concept as it has already been hashed out here at Enable Sysadmin. However, I do want to look at a potentially better way to use it. SSH is the single most used remote access protocol in the world. Therefore, it makes sense that we should try to improve its use as much as possible.
I used SSH to remotely connect to thousands of customer machines during my time as a support engineer, and I am sure that others have had a similar experience. With traditional SSH authentication, you need the username and password for the account you want to log in to every time that you wish to access a system. Doesn't sound that bad, right? But, what happens when you need to jump back and forth between systems regularly? Or what if your responsibilities include remote sessions to the same 100 systems throughout the day for health checks? There is another way to accomplish the log in, and with a little upfront investment, it can be far more efficient overall.
It is objectively true that an encrypted key is a much harder target than a username and password for those with ill intentions. Although it can take a little learning, creating and using SSH key-based authentication is worth the investment for every sysadmin.
Here is how it works. You generate a public key and a matching private key. The private key file acts as a password and should be kept safe. However, the public key is copied to the target systems that you connect to regularly. You place the public key in your account home directory on the target server. When you try to log in, the keys are verified, and access is granted.
Now, there are two ways that you can do this. One is more convenient, and the other is a bit tedious but with added protection to you. The convenient way is not to specify a password along with the private key. The result is that you do not have to enter a password when you use your private key for authentication. This means that if someone gets their hands on your private key, they can use it to authenticate, as well. The other method is to password-protect your private key so that you are prompted for the password when authenticating (think two-factor authentication using both the private key and the password).
To generate an SSH key pair, use the following command:
By default, your private and public keys are saved in your
~/.ssh/id_rsa.pub files, respectively.
Creating a password-protected key looks something like this:
-f option to specify the file where the keys will be saved. In the example above, the private and public keys are stored in the
/home/user/.ssh/key-with-pass.pub files, respectively.
During further SSH key pair generation, if you do not specify a unique file name, you are prompted for permission to overwrite the existing
id_rsa.pub files. If you overwrite the existing
id_rsa.pub files, you must then replace the old public key with the new one on ALL of the SSH servers that have your old public key.
Once you have generated the keys, they are stored in the
/user/home/.ssh/ directory with the following permissions:
You aren't done yet. Let's look at the final step in successful SSH key-based authentication.
For all of this to work, you need to share your public key with the remote machines you are trying to SSH to. Use the
ssh-copy-id command to copy your public key over to the destination system. By default, the file path is
/home/user/.ssh/id_rsa.pub. You issue the command, specify the file you are sharing, then the user/host we are sharing it with. It should look like this:
Now that you have shared the public key with the destination host, you can authenticate to the remote server by passing the matching private key. If you specified a file path for your private key, you need to give it here. Otherwise, it defaults to
The advantages of using SSH key-based authentication are clear. Passwords are stolen every day, mainly due to human error but also due to attacker skill and determination. An encrypted key, and more specifically, a password-protected encrypted key, makes your SSH authentication even more difficult to attack. You still need to strike a balance of availability and security, but that is handled differently in every environment.
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