YQVQ
      +---------
GPHQR | UTJRLUNW
       -GPHQR
        =====
        VNXXTU
       -VWJLGR
        ======
         XXPNJN
        -YTWNGZ
         ======
          VMZPNW
         -VWJLGR
          ======
           YZHTG

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: medium