SSH connection to know host still needs authorization

I am trying to setup a backup server using duply and a secure connection. I have created the ~/.ssh/config file with the following content: Host backup IdentityFile ~/.ssh/id_ed25519_backup Hostname Port 22 User Furthermore, I have also defined the known_hosts file, by copy-pasting in it the server public key (found in /etc/ssh/ssh_host_ed25519_key.pub) All seems to work properly when using the ssh -v backup command: Authenticated to ([]:22) However, when launching duply backup routine, I see that the server is not recognized: The authenticity of host '[]:22' can't be established. SSH-ED25519 key fingerprint is c3:06:95:f8:5f:d3:76:7f:c6:9d:19:ef:e5:23:9a:14. Are you sure you want to continue connecting (yes/no)? Why is this happening? ---------- **Update** It seems that duply is computing the MD5 hash of the public key, while ssh the SHA256 one: in fact, as mentioned here , ssh-keygen -l -E md5 -f /etc/ssh/ssh_host_ed25519_key.pub returns the same hexadecimal stated above. Since they are two different hash of the same key, why a connection confirmation is still asked? Is it possible to oblige SSH to use only a single hash algorithm? **Further update:** ssh -o FingerprintHash=md5 -v backup does not require confirmation, so I suppose that the issue is limited to duply. Maybe, does it not refer to the user known_hosts file?