Taking a brief look for SSL or TLS in Racket, I see http://docs.racket-lang.org/openssl/ .[1]
In particular, ports->ssl-ports looks like it might be a big help here. In fact, it has an option for TLS, so I guess this is the right place to look. :)
[1] I also see "Using HTTPS" at (http://docs.racket-lang.org/continue/#(part._.Using_.H.T.T.P...) but that's for Racket's own continuation-based server framework, not a library Arc can easily use.