How do I seal and paint over an indoor brick/cement wall?

I am decorating a small room where a small section near the floor used to be covered by tile and just above it the paint and plaster were chipping. I removed the damaged paint and plaster as well as the tile and I am left by this exposed brick/cement area that is cold to the touch and ever so slightly moist. The brick/cement work appears to be slightly flush with the drywall around it and the previous tiles were not flush with the rest of the wall.

How do I seal this area correctly so I can paint over it?

Thanks!