Secure Shell REMOTE HOST IDENTIFICATION HAS CHANGED!


Example

The common error using ssh is to see the error like

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
SHA256:L5ri/Xdgpuals893ej1z5F1wlg1n2YNeBf/tsABX+QQ.
Please contact your system administrator.
Add correct host key in /Users/username/.ssh/known_hosts to get rid of this message.
Offending RSA key in /Users/username/.ssh/known_hosts:12
RSA host key for *IP address* has changed and you have requested strict checking.
Host key verification failed.

This means that you connected to the same server before and it was identified using different host keys. If you are aware you changed the server keys, reinstalled the server or the server administrator announced some changes, it is usually ok to remove the old key and let the ssh to store its new.

The old key can be transparently removed using ssh-keygen:

ssh-keygen -R *IP address*

And next connection should ask you to verify the new fingerprint:

ssh192.168.0.128
The authenticity of host '192.168.0.128 (192.168.0.128)' can't be established.
ECDSA key fingerprint is SHA256:L5ri/Xdgpuals893ej1z5F1wlg1n2YNeBf/tsABX+QQ.
Are you sure you want to continue connecting (yes/no)? 

If you are not aware of any of the above, the best is to contact your server administrator to make sure that everything is ok. If not, the potential attacker would be able to get both your authentication information and all transferred data!