openssl on windows isn't more complicated than using gettext in windows.
I didn't do a windows build or edit a cmake file before an got it built within an hour.
But I know you don't like to add library dependencys to minetest that's why i didn't even expect you to add it upstream. It's just a proof of concept.
The reason I added openssl is i required a reliable hash algorithm to decide if a texture within the client cache matches the one present on server. If anyone does want to implement md5 or any other hash algorithm himself it it wouln't be much of an effort to switch to that algorithm.
I personaly don't like reinventing the wheel, especially if its something critical as an hash algorithm.
On the other hand, having some sort of cryptographic library available in minetest wouldn't be that bad in my opinion. At least it would reduce the amount of work to add a secure password system.
EDIT1:
The changes i did to build on windows (additional to downloading openssl windows build)
http://www.mediafire.com/?57n7c552787s9q7