How Do I Generate Ed25519 SSH Keys ?

There are several reasons why one might choose to use an Ed25519 key over an RSA key:

Security: Ed25519 is a more modern and secure algorithm compared to RSA. It is resistant to several types of attacks that can be used against RSA, such as side-channel attacks and attacks based on certain types of mathematical properties of RSA. Ed25519 is also faster and requires shorter key lengths for equivalent security compared to RSA.
Key generation: Generating Ed25519 keys is faster and less resource-intensive than generating RSA keys. This makes it more suitable for applications where keys need to be generated frequently or where resources are limited.
Signature size: Signatures generated using Ed25519 are smaller than those generated using RSA. This makes it more efficient in terms of bandwidth and storage.
Key management: Ed25519 keys are simpler to manage compared to RSA keys. There is no need to worry about key sizes or key strength, and key rotation is less frequent.
Resistance to quantum attacks: RSA is vulnerable to attacks from quantum computers, which can factor large numbers much faster than classical computers. Ed25519, on the other hand, is believed to be quantum-resistant, meaning it will remain secure even if quantum computers become a reality.
Simplified implementation: Ed25519 has a simpler implementation compared to RSA, which makes it less prone to implementation errors that could compromise security.
Interoperability: Ed25519 is a widely adopted standard for digital signatures and is supported by many popular libraries and platforms. This makes it easier to integrate into existing systems and use in a variety of applications.
Adoption by major tech companies: Many major tech companies, such as Google and Cloudflare, have adopted Ed25519 for their security protocols, which demonstrates its reliability and suitability for modern applications.
Key exchange: RSA can be used for key exchange as well as digital signatures, while Ed25519 is primarily used for digital signatures. If key exchange is a critical requirement for your application, RSA may be a better choice.
Hardware support: RSA has been widely implemented in hardware and has hardware acceleration support on many platforms, while Ed25519 hardware support is less common. If hardware acceleration is important for your application, RSA may be a better choice.
Existing infrastructure: If your organization already has existing infrastructure and processes in place that are based on RSA, switching to Ed25519 may require significant effort and resources. In this case, RSA may be a more practical choice.
Regulatory requirements: Some industries and jurisdictions may have regulatory requirements that mandate the use of specific cryptographic algorithms or key sizes. Before choosing Ed25519 or RSA, it's important to ensure that your choice complies with any relevant regulations.

Overall, Ed25519 offers a modern, secure, and efficient alternative to RSA for applications that require public-key cryptography. However, it's important to note that RSA is still widely used and remains a valid choice for many applications. The choice of which algorithm to use ultimately depends on the specific requirements of the application and the tradeoffs between security, performance, and key management.

To generate an ECDSA key for use with SSH, you can use the `ssh-keygen` command-line tool, which is included with most SSH implementations. Here are the steps to generate an ECDSA key with `ssh-keygen`:

1. Open a terminal or command prompt on your local machine.

2. Run the following command to generate a new ECDSA key:

```

ssh-keygen -t ecdsa

```

This will start the key generation process and prompt you for a file name and passphrase.

3. Enter a file name for the key, or press Enter to accept the default.

4. Enter a passphrase for the key, or press Enter to create a key without a passphrase. Note that adding a passphrase can provide additional security but may also make the key less convenient to use.

5. The `ssh-keygen` tool will generate two files: a private key file and a public key file. By default, the files are stored in the `.ssh` directory in your home directory, with the private key named `id_ecdsa` and the public key named `id_ecdsa.pub`.

6. Copy the contents of the public key file (`id_ecdsa.pub`) and add it to the `authorized_keys` file on the remote server you wish to access. This will allow you to use the private key to authenticate with the server using SSH.

That's it! You now have an ECDSA key that can be used to authenticate with SSH. Note that some SSH clients and servers may have specific requirements for ECDSA key sizes or other parameters, so you may need to consult the documentation for your specific implementation to ensure compatibility.

`ssh-keygen -t ed25519 -a 100 -f ~/.ssh/id_ed25519-$(date +%d-%m-%Y) -C "Connect To Server"` is a command that generates a new Ed25519 SSH key with a custom file name, comment, and passphrase. Here's a breakdown of what each option does:

- `-t ed25519`: specifies that the key type to be generated is Ed25519, which is a type of elliptic curve cryptography key.

- `-a 100`: specifies the number of KDF (key derivation function) rounds used when generating the key. A higher number of rounds can make it more difficult for an attacker to crack the passphrase. The default value is 16, and a value of 100 is considered a good balance between security and performance.

- `-f ~/.ssh/id_ed25519-$(date +%d-%m-%Y)`: specifies the file name and location for the new key. The `%d-%m-%Y` format string in the file name uses the `date` command to insert the current day, month, and year, which can be helpful for keeping track of multiple keys. The `~/.ssh` directory is the default location for SSH keys on Unix-like systems.

- `-C "Connect To Server"`: specifies a comment to be associated with the key. The comment can be used to identify the key, for example, when managing multiple keys or when viewing the key in the `authorized_keys` file on a remote server.

After running the `ssh-keygen -t ed25519 -a 100 -f ~/.ssh/id_ed25519-$(date +%d-%m-%Y) -C "Connect To Server"` command, you will be prompted to enter a passphrase for the new key. The passphrase adds an extra layer of security to the key and is required whenever the key is used to authenticate with a remote server.

Once the key is generated, you will have two files: a private key file (with a `.pub` file extension) and a public key file (with the specified file name and no file extension). The public key can be copied to the remote servers you wish to access, while the private key should be kept secure on your local machine.

Note that the `~/.ssh` directory should have the appropriate file permissions (i.e., only readable by the user) for SSH to use the key. Additionally, not all SSH clients and servers support Ed25519 keys, so you should check the documentation for your specific implementation to ensure compatibility.

More about : SSH-KEYGEN , SSH-COPY-ID , RSA , DSA & ECDSA