To answer your questions in order: You can see all authorized keys by running the following script with root privileges. You may use the script above. Improve this answer.
Jakuje 4, 14 14 silver badges 30 30 bronze badges. Liczyrzepa Liczyrzepa 2 2 silver badges 7 7 bronze badges. A robust script should probably verify that setting hasn't been changed and that only OpenSSH is providing sshd. You're right! Barth S. Barth 5, 8 8 gold badges 38 38 silver badges 47 47 bronze badges. Improved code from Liczyrzepa:! Would be helpful to see an example output of running the script. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.
Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Making Agile work for data science. By Justin Ellingwood and Brian Boucheron. SSH, or secure shell, is an encrypted protocol used to administer and communicate with servers.
When working with a Linux server you may often spend much of your time in a terminal session connected to your server through SSH. SSH keys provide an extremely secure way of logging into your server. For this reason, this is the method we recommend for all users. An SSH server can authenticate clients using a variety of different methods.
The most basic of these is password authentication, which is easy to use, but not the most secure. Although passwords are sent to the server in a secure manner, they are generally not complex or long enough to be resistant to repeated, persistent attackers.
Modern processing power combined with automated scripts make brute-forcing a password-protected account very possible. Although there are other methods of adding additional security fail2ban , etc. SSH key pairs are two cryptographically secure keys that can be used to authenticate a client to an SSH server. Each key pair consists of a public key and a private key. The private key is retained by the client and should be kept absolutely secret.
Any compromise of the private key will allow the attacker to log into servers that are configured with the associated public key without additional authentication. As an additional precaution, the key can be encrypted on disk with a passphrase. The associated public key can be shared freely without any negative consequences. The public key can be used to encrypt messages that only the private key can decrypt. This property is employed as a way of authenticating using the key pair.
The public key is uploaded to a remote server that you want to be able to log into with SSH. When a client attempts to authenticate using SSH keys, the server can test the client on whether they are in possession of the private key.
If the client can prove that it owns the private key, a shell session is spawned or the requested command is executed. The first step to configure SSH key authentication to your server is to generate an SSH key pair on your local computer. To do this, we can use a special utility called ssh-keygen , which is included with the standard OpenSSH suite of tools. By default, this will create a bit RSA key pair. The utility will prompt you to select a location for the keys that will be generated.
Usually, it is best to stick with the default location at this stage. If you would like to choose a non-standard path, type that in now, otherwise, press ENTER to accept the default. 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.
Next, you will be prompted to enter a passphrase for the key. This is an optional passphrase that can be used to encrypt the private key file on disk. You may be wondering what advantages an SSH key provides if you still need to enter a passphrase. Some of the advantages are:. Since the private key is never exposed to the network and is protected through file permissions, this file should never be accessible to anyone other than you and the root user.
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