When "-tlsServerPreference YES" is set, then one can bring the FTP server with the option -tlsPrioritizeChaCha to prefer ChaCha20 based cipher suites, when the FTP client puts at the head of its cipher suite preference list a ChaCha20 based cipher suite,
With that FTP clients, which don't have hardware support for AES and therefore can encrypt quicker with ChaCha20, can bring the server to select a ChaCha20 cipher suite, even when the server normally prefers AES.
-tlsPrioritizeChaCha |
NO | YES |
NO
The server doesn't prefer ChaCha20 cipher suites. over other ones.
NO is the default.
YES
The server puts ChaCha20 based cipher suites at the top of his cipher suite preference list, if an FTP client signals, that it prefers ChaCha20 cipher suites (e.g. for performance reasons).