Updated: Heads up: Deployment with newly generated SSH key (using ED25519) might fail

Changes

If you use a newer SSH key generated with the ED25519 algorithm instead of RSA (see [Create a new SSH key pair](https://makandracards.com/makandra-orga/599-create-a-new-ssh-key-pair)), the deployment with Capistrano may fail with the following message:
```raw
The deploy has failed with an error: unsupported key type `ssh-ed25519'
net-ssh requires the following gems for ed25519 support:
 * ed25519 (>= 1.2, < 2.0)
 * bcrypt_pbkdf (>= 1.0, < 2.0)
See https://github.com/net-ssh/net-ssh/issues/565 for more information
Gem::LoadError : "ed25519 is not part of the bundle. Add it to your Gemfile."
```
+## Solution
+
As described in the error message, the `ed25519` and `bcrypt_pbkdf` gems must be added to the Gemfile to solve the problem. Now, the deployment should work faultlessly again.
-After changing to ed25519, existing hostname fingerprints might no longer match. If you see an error like this when deploying to a server, you can remove your old (e.g. RSA based) fingerprints from ` ~/.ssh/known_hosts`:
+
+## Fixing a (consecutive) fingerprint mismatch
+
+After changing to ed25519, existing hostname fingerprints might no longer match and you will see an error like this:
> Exception while executing as USER@HOSTNAME: fingerprint SHA256:HASH does not match for "HOSTNAME,IP" (SSHKit::Runner::ExecuteError)
+
+This is generally an indicator of a man-in-the-middle attack. You can test this: if an SSH shell (e.g. `geordi shell production`) opens without fingerprint error, you should be fine. You may then proceed to remove your old (e.g. RSA based) fingerprints from ` ~/.ssh/known_hosts`. [Here are instructions](/operations/485199-ssh-fix-host-key-verification-error-makandra-servers).