When you log in to a new system for the first time with the SSH protocol, the system returns a hostkey fingerprint to you:

The authenticity of host 'submit.grid.fe.up.pt (193.136.38.202)' can't be established.
ED25519 key fingerprint is SHA256:w9YgOJXJmZUzvDuOrAG6sFF2h1dLRYlpP94YF7OvZIQ.
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added 'submit.grid.fe.up.pt' (ED25519) to the list of known hosts.

Before you type “yes” to the question posed to you, you can verify this fingerprint against the list of correct fingerprints for Grid.UP below, to check that you are indeed logged to the correct system.

ED25519
===
SHA256:w9YgOJXJmZUzvDuOrAG6sFF2h1dLRYlpP94YF7OvZIQ
MD5:10:02:f9:23:ad:76:0c:c3:0f:e5:f0:36:8b:73:ba:87

ECDSA
===
SHA256:asY310gAfk8iEh9ZBtvXKZo/oERQG4m6Ajg+S9rdhQk
MD5:aa:97:cc:09:3c:c0:58:d9:3a:61:8c:ab:c6:d5:5d:88

RSA
===
SHA256:GQI2y6zrsyKMqV/wks077hapru7+waIgVvEWTKWox6I
MD5:0a:33:be:a3:da:d5:45:88:71:1a:f9:cd:5a:ff:b4:b7