I've heard that there's a new TI CC3000-type chip out that directly supports HTTPS, so that won't be an issue for Espruino at all.
IMO MD5 implementation would be fine running as a JS module - I really don't see there's much need to swap it in when you need it. It doesn't look too large: http://rosettacode.org/wiki/MD5/Implementation
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
I've heard that there's a new TI CC3000-type chip out that directly supports HTTPS, so that won't be an issue for Espruino at all.
IMO MD5 implementation would be fine running as a JS module - I really don't see there's much need to swap it in when you need it. It doesn't look too large: http://rosettacode.org/wiki/MD5/Implementation