Create an SSH key

What are SSH keys?

SSH keys are cryptographic keys that are used in secure data transmission. They enable an encrypted connection between a client and a server, allowing data to be transferred securely. Unlike traditional passwords, SSH keys provide a more robust authentication method that is not only more secure but also more user-friendly. When using SSH keys, authentication is performed by a mathematical algorithm that ensures that only authorized users have access to sensitive information.

Definition and functionality

The functionality of SSH keys is based on asymmetric cryptography, which comprises two keys: a public and a private key. The public key can be freely distributed, while the private key is kept secret. During a connection, the public key is stored on the server, while the private key remains in the possession of the client. When the client connects to the server, a challenge is generated that can only be answered with the private key. This ensures that only the legitimate user has access to the server.

Areas of application for SSH keys

SSH keys are used in many areas, especially in IT security and remote access. They are indispensable for administrators who need to access servers to make configurations or install software. Developers also often use SSH keys to securely access repositories such as GitHub and manage their code changes. Furthermore, they are crucial for securing data transfers in cloud technologies where sensitive information needs to be exchanged between different services. At a time when cyberattacks are becoming increasingly sophisticated, SSH keys are an essential tool for ensuring data security.

The next stage in our article will look at the process of creating an SSH key and show you how to successfully implement this important step to improve your IT security.

Difference between public and private keys

SSH keys consist of a public and a private key that fulfill different functions. The public key is stored on the server and is accessible to everyone, while the private key remains secret and is only known to the user. This separation ensures that even if an attacker has access to the public key, they will not be able to connect to the server without the private key. In addition, multiple public keys for different users can be stored on a server, allowing flexible management of access rights.

The next steps cover the requirements for creating an SSH key, where it is important to consider certain software tools and system requirements.

Types of SSH keys

There are different types of SSH keys, each offering different levels of security. The most common types are RSA, DSA, ECDSA and Ed25519. RSA is the most widely used type and offers a good balance between security and performance. DSA is less commonly used and has some limitations in terms of key length. ECDSA is more efficient and uses elliptic curves for cryptography, which means that shorter keys are sufficient for comparable security levels. Ed25519 is a more recent development and is considered particularly secure and fast. When choosing an SSH key type, you should consider your specific requirements and compatibility with the systems you want to access.

Requirements for creating an SSH key

Before you create an SSH key, some basic requirements should be met. These prerequisites include both the necessary software and the system requirements to ensure that the process runs smoothly.

Software and tools

To create SSH keys, you need certain software tools that are available on most operating systems. Usually, the terminal or command prompt is your main tool. Here are some common tools you can use:

• OpenSSH: This is the most widely used software for SSH communication. It is pre-installed in most Unix-based systems and can also be used on Windows via the Windows Subsystem for Linux (WSL) or as a separate installation.

• PuTTY: A popular SSH client tool for Windows that provides a graphical user interface. It is particularly useful if you are not familiar with the command line.

• Git Bash: If you have Git installed on your Windows machine, you also get access to a bash environment where you can generate SSH keys.

Make sure you choose the right tool for your operating system. For example, if you are a Linux or macOS user, you can work directly in the terminal. Windows users should consider PuTTY or Git Bash.

System requirements

Make sure that your system fulfills the necessary requirements to successfully generate SSH keys. The basic requirements are:

• Operating system: your operating system should be up-to-date. Most modern versions of Windows, macOS and Linux support the creation of SSH keys.

• Storage space: Make sure that you have sufficient storage space on your hard disk. Generating an SSH key only requires a small amount of space, but it is always good to have some free space.

• Access rights: Make sure that you have the necessary authorizations to install software and generate keys. This can be particularly important for enterprise systems.

Check these points thoroughly before proceeding. Once all requirements are met, you can start creating your SSH key.

The next steps include a detailed step-by-step guide to creating an SSH key, where we will look at the key pair generation process.

Step-by-step guide to creating an SSH key

Creating an SSH key is done in several simple steps. This guide will walk you through the process so that you can generate your own keys securely and efficiently. It is important that you follow each step carefully to ensure that your connection to servers is protected.

Generating the key pair

To generate an SSH key, use the command ‘ssh-keygen’ in your terminal. To do this, open your terminal or the command prompt and enter the following command:

ssh-keygen -t rsa -b 4096 -C "your_email@example.com"

Here the parameter -t specifies the type of key (in this case RSA), -b the size in bits (4096 is a recommended size for increased security), and -C adds a comment, which is often your e-mail address, to make it easier to identify the key later. After executing the command, you will be prompted to specify a location for the key. By default, the key is stored in the ~/.ssh/ directory. If you simply press Enter, the default path will be used.

Selecting the storage location and passphrase

During generation, you have the option of specifying the storage location of the key and an optional passphrase. A passphrase significantly increases the security of your private key. You will be prompted to enter a passphrase and re-enter it for confirmation. Choose a strong passphrase that consists of a combination of letters, numbers and special characters.

If you do not specify a special location or passphrase, your key will be stored in the default directory without any additional protection. This can be risky, especially if other users have access to your system. Make sure that you do not forget the passphrase, as it is required to access your private key.

After you have made all the entries, the key pair will be created. You should see two files: the private key (idrsa by default) and the public key ( id_rsa.pub ). The private key remains secret and should never be passed on. The public key, on the other hand, can be distributed without any problems.

Checking the key generation

To ensure that your SSH keys have been created correctly, you can display the content of the public key with the following command:

Copy the displayed content to your clipboard. This public key is the one you need to add on the servers you want to access.

Now you are ready for the next steps in using your SSH keys. It’s important to know how to use and manage them effectively. The next sections will cover adding the public key to servers as well as managing multiple SSH keys to ensure a clear structure and maximize the security of your connections.

Using and managing SSH keys

Once you have successfully created your SSH keys, it is crucial to understand how to use and manage them effectively. Careful handling of your keys not only ensures a smooth connection to servers, but also contributes significantly to the security of your data. In this section, we’ll take a detailed look at public key integration with servers, managing multiple SSH keys, and practical tips for optimizing your security strategy.

Add the public key to servers

The public key must be added to the servers you want to access. This process is crucial to enable authentication. Here are the steps you should follow:

• Access the server: make sure you have the necessary permissions to make changes to the user accounts or the server’s SSH settings.

• Copy public key: You can view the contents of your public key with the following command:

cat ~/.ssh/id_rsa.pub

Copy the entire text displayed to your clipboard

• Establish an SSH connection to the server: Use your terminal or an SSH client tool to connect to the server:

ssh username@server_ip_address

• Add public key: Once logged in, add your public key to the ~/.ssh/authorized_keys file. Use the following command to do this:

echo “your_public_key” >> ~/.ssh/authorized_keys

Alternatively, you can also use the nano or vim editor to edit the file manually.

• Check authorizations: Make sure that the permissions for the .ssh directories and the authorized_keys file are set correctly. The folders should be set to 700 and the file to 600:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys

These steps ensure that your public key is stored correctly on the server and that you can authenticate yourself securely.

Copy public key to the server

The next step is to transfer your public key to the server you want to connect to. You can do this manually or using the ssh-copy-id command:

ssh-copy-id username@serveraddress

This command adds your public key to the ~/.ssh/authorized_keys file of the target server. After the transfer, you can connect to the server without a password request.

Administration of multiple SSH keys

Several SSH keys can be managed for different projects or servers, which requires a clear structure. Here are some tips for effective management:

• Key naming: Use meaningful names for your SSH keys to make them easier to identify. For example, you could name your key for a specific server like this: id_rsa_project_name.

• Port: It’s important to note that when using SSH keys, you can also use different options and parameters to customize your connection. For example, you can specify the port if the SSH service is running on a non-standard port.

• Use the SSH configuration file: You can create a configuration file ( ~/.ssh/config ) to define different SSH keys for different hosts. Here is an example of the contents of this file:

Host server1
    HostName server1.example.com
    User username
    IdentityFile ~/.ssh/id_rsa_project1
    Port 2222
Host server2
    HostName server2.example.com
    User username
    IdentityFile ~/.ssh/id_rsa_project2
    Port 4321

With this configuration, you can simply connect to ssh server1 or ssh server2 without having to enter the full command each time.

• Regular check: Check your SSH keys regularly and remove keys that are no longer required from the configuration file and from the servers. This minimizes the risk of unauthorized access.

• Create a backup: Create regular backups of your SSH keys and keep them in a safe place. This is particularly important for the private key, as the loss of this key jeopardizes access to all servers connected to it.

Proper management of your SSH keys contributes significantly to the security of your connections and enables efficient use in various projects.

With these instructions, you will be well equipped to use and manage your SSH keys effectively. In the next section, we will look at security tips for handling SSH keys to prevent unauthorized access and further protect the integrity of your data.

Security tips for dealing with SSH keys

The security of your SSH keys is of utmost importance to prevent unauthorized access. To ensure your keys are protected at all times, there are some best practices you should follow. These tips will help you ensure the integrity of your data transmissions and minimize potential security risks.

Remember that it is important to manage your SSH keys securely. Never store your private key in an insecure location and do not share it with others. If you use multiple SSH keys, it’s helpful to clearly name and document them to avoid confusion.

Using strong passphrases

A strong passphrase protects your private key from unauthorized access. It is crucial that you choose a passphrase that is not easy to guess. Use a combination of upper and lower case letters, numbers and special characters. For example, a good passphrase could consist of a sentence that you enrich with numbers and symbols. Instead of “MyDogIsSweet”, you could use “M2D0g!s$weet”. Make sure that you save this passphrase in a safe place or memorize it well, as you will need it to access your private key.

You should also make sure that your passphrase is not stored in written form on your computer or near your workplace. If necessary, use a password manager to securely store your passwords and passphrases. These tools can help you generate complex passphrases and manage them securely.

Regular key rotation

Regular key rotation is a proven method for increasing the security of your SSH connections. It is recommended to change your SSH keys at regular intervals, for example every six to twelve months. This process minimizes the risk of a compromised key being used over a longer period of time.

To perform the key rotation, you should first generate a new SSH key and then update it on the servers. Don’t forget to remove the old key from the authorized_keys file on the servers to ensure that only the current keys have access. The process of key rotation can be automated by using scripts that facilitate the creation of new keys and their distribution to the appropriate servers.

In addition to regular rotation, you should also take immediate action if you suspect that a key has been compromised. Immediately remove the affected key from all servers and generate a new one.

Restricting access

Another important aspect of the security of your SSH keys is restricting access to the systems on which they are stored. Make sure that your private key is only accessible to you and that it is stored in a protected directory. Use file system level permissions to restrict access to your .ssh folder and the files it contains. The private key should be secured with permissions of 600 (read and write only for the owner).

You should also make sure that your systems are updated regularly. Keep both the operating system and all relevant software applications up to date. Security updates often close known vulnerabilities and help protect your system from attacks.

Back up your SSH keys

Make regular backups of your SSH keys and keep them in a safe place. This is particularly important for the private key, as the loss of this key jeopardizes access to all servers connected to it. You can back up your SSH keys to an external storage device or to encrypted cloud storage.

Make sure that the backups are also protected by strong passphrases. If possible, use additional security measures such as two-factor authentication (2FA) to access your backup system.

By following these security tips, you can significantly reduce the risk of unauthorized access and strengthen the integrity of your SSH connections.

Conclusion

The creation and management of SSH keys is an essential part of IT security for computer scientists working in an increasingly networked world. You have now learned that SSH keys are not only a secure authentication method, but also a user-friendly alternative to traditional passwords. The advantages of these keys are undeniable: they protect your data from unauthorized access and make it easy to manage your server connections. In the previous sections, you learned the basic requirements for creating an SSH key, identified the necessary tools and received step-by-step instructions on how to generate your key pair. We also explained how you can add your public key to servers and manage multiple SSH keys to ensure a clear structure in your projects. Security is a key issue - so the tips on using strong passphrases, regular key rotations and restricting access to your keys are crucial. Remember that the integrity of your data transfers depends largely on the care you take with your SSH keys.

To deepen your knowledge, you can use additional resources, such as the instructions for creating an SSH key on heise.de or the official GitHub documentation on connecting to GitHub via SSH at docs.github.com. The University of Bremen also offers helpful information on creating SSH keys, which you can find here: uni-bremen.de. Put what you have learned into practice and optimize your security strategy - you will be well equipped to navigate the digital world safely.