Generating SSH keys (2024)

FAQs

What is the recommended SSH key generation? ›

To generate a robust SSH key, you have two main options: ED25519 and RSA. Both have their advantages, but ED25519 is generally recommended for its security and performance benefits.

We strongly recommend using only the ed25519 algorithm (an ECDSA variant). It is the most secure SSH key type widely available, and is very well supported in the majority of systems. If you are using an client or server without ed25519 support, you should consider upgrading where possible.

ED25519 is generally considered more secure and efficient than RSA, while RSA provides a higher level of security due to its larger key size. The choice between these two algorithms depends on the specific application and the level of security and efficiency required.

If your key has a passphrase and you don't want to enter the passphrase every time you use the key, you can add your key to the SSH agent. The SSH agent manages your SSH keys and remembers your passphrase. If you don't already have an SSH key, you must generate a new SSH key to use for authentication.

Typically a system administrator would first create a key using ssh-keygen and then install it as an authorized key on a server using the ssh-copy-id tool. See also the dedicated page on configuring authorized keys for OpenSSH. We recommend using passphrases for all identity keys used for interactive access.

Generating a SSH key

From the SSH section, select Create SSH Key. In the Create SSH Key dialog, enter a Key Name and then select Create Key. The private and public SSH key pairs generate.

To generate an SSH key on your Linux server, run the command ssh-keygen . The command can take flags if you would like to customize the type of key that is generated and the signing algorithms that are used to generate the key. This example generates a standard 2048-bit RSA key without a passphrase.

In most cases, 2048-bit keys are secure and generally recommended. If you need higher security, such as for critical infrastructure or storing sensitive data, consider using longer keys (3072 or 4096 bits).

What is the strongest key algorithm? ›

arcfour is the fastest cipher, and aes128-cbc is faster than the default aes128-ctr. Note that blowfish-cbc is not particularly fast. ssh is faster than netcat using either the aes128-cbc or arcfour ciphers.

The SSH-RSA is a weak encryption method. It is also already deprecated by OpenSSH and cannot be used unless enabled explicitly. This change impacts you immediately if you are using Azure DevOps Service and are using SSH-RSA keys to connect to repos through SSH.

Key Takeaways

Microsoft is discontinuing Windows RSA keys shorter than 2048 bits to encourage the adoption of more robust encryption techniques for server authentication. Since 2013, internet standards and regulatory bodies have prohibited using 1024-bit keys, recommending 2048 bits or longer RSA keys.

The only downside to Ed25519 is that it will fall to quantum computing before RSA 4096. Except nobody knows when that's gonna really happen. I've personally switched to ed25519-sk wherever I could. Same, the short key looks much nicer and both will fall to quantum anyhow.

EdDSA Keys (Ed25519 & Ed448)

It provides equivalent and usually better security than ECDSA and longer key length RSA keys. Its main advantages are small key sizes, fast key generation times, high performance and is resistance against side-channel attacks. Something to note though is its compatibility.

Only three key sizes are supported: 256, 384, and 521 (sic!) bits. We would recommend always using it with 521 bits, since the keys are still small and probably more secure than the smaller keys (even though they should be safe as well). Most SSH clients now support this algorithm.

The encryption involved in SSH version 1 is weak enough for a middleman to decrypt it, view the contents, and even modify it without both parties knowing about it. Thus, make sure to use SSH version 2 both on the client-side, as well as enforce the same on the server-side.

ssh directory permissions should be 700 (drwx------). The public key (. pub file) should be 644 (-rw-r--r--). The private key (id_rsa) on the client host, and the authorized_keys file on the server, should be 600 (-rw-------).