Is there any plugin that does this? I know for a fact that the creator of world downloader will not support this in any way. But I find this plugin a little essential when a player can just download the map outside of a persons redstone vault, go into the map on single player, find out the combination, then come back on and steal the persons stuff. Hope to hear back positively about this.
I hate to break it to you, but world downloaders don't actually connect to the server, they just save the cache from the client. The closest you are going to find is Orebfuscator, but even the dev acknowledges that it doesn't stop xray-textures without seriously crippling the server. Given the situation, I think what you're really looking for is chest protection.
give me motivation and I'll bypass any type of your lock. And everyone can bypass that kind of "security" if he really interested with downloading a world.