no paper faced gypsum board
You said "tub-shower"; that says it all. The wall will get wet every day.
It must be waterproofed. There are many ways to build the right amount of waterproofness.
A vapor barrier behind a CBU is one method; both layers should allow drainage on top of (in front of the edge of) the tub flange.
The other option is to put a membrane directly under the tile, so the CBU itself doesn't ever come in contact with water. Thinset (tile cement, not mastic) goes on this tile-ready membrane. There are three tile-ready membrane options: liquid gunk that hardens, a sheet that you overlap at seams, and an XPS foam board encased in fiberglass fabric and coated with cement. The last one replaces the need for any other board under it, so it saves a lot of time, mess and dust, too. It is very good.
You cannot put paper near that amount of humidity; it'll be eaten by mold, even paper treated to "resist" mold. Even the latest technology that is better than greenboard. No organic matter near permanent humidity. No mastic tile cement either; it gets eaten by mold too! Only portland cement or epoxy cement. When i say "eaten" by mold, i mean that the organic matter will begin to smell very bad, and ultimately get rotten away over the years. The smell is most apparent when you open the walls to demolish them, but the offending micro-organism has been there for years offgassing permanently at the expense of your health and enjoyment.
david