SSH clients by default store the key fingerprint of the SSH servers that it has connected to. This is to establish a list of known hosts and for the server's key fingerprint to be checked against the stored copy of the fingerprint every time a connection is to be established.

You'll get a warning if the server's key fingerprint does not match the one locally stored and you will not be able to log in to the server. For this you'll have to update stored known host's SSH key fingerprint.

OpenSSH clients on Linux and other Unix-based operating systems store the key fingerprints in ~/.ssh/known_hosts file while PuTTY in Windows store these information in the system registry.

Steps to update or delete known host fingerprint for PuTTY on Windows:

  1. Launch Registry Editor by running regedit from the search bar.
  2. Click Yes to allow registry editor to make changes to the system.
  3. Navigate to ComputerHKEY_CURRENT_USERSoftwareSimonTathamPuTTYSshHostKeys from the tree list.
  4. Double-click on the key from the list to see more details.
  5. Edit key value to update as necessary and click OK to save.
  6. Right click on the key from the list and click on Delete to delete the host key fingerprint.
  7. Click Yes to confirm the deletion.
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