I cannot try anything before entering my CC number (and paying, no free month or anything), nor finding any detailed information about the setup (apart from 'public/private key client side JS'). But the site/server/data center security probably does matter if the JS is hosted at their site / servers.

Edit: See link below: https://privateforms.net/embed/rNKlzL

So you get jquery, moment, bootstrap + datatimepicker, kbpgp and a few lines of glue to use kbpgp to send and XMLHttpRequest, basically:

    kbpgp.KeyManager.import_from_armored_pgp({
        armored: '-----BEGIN PGP PUBLIC KEY BLOCK-----\n' +
                 /* key */
                 '-----END PGP PUBLIC KEY BLOCK-----'},
        function(err, keyManager) {
            kbpgp.box({msg: '**form=data**', encrypt_for: keyManager},
            function(err, encryptedString, encryptedBuffer) {
                //send result;
            }
        );
    });