code: function convertPublicKey(pk) {
      var z = new Uint8Array(32), x = gf(), a = gf(), b = gf();
      unpack25519(x, pk);
      A(a, x, gf1);
      Z(b, x, gf1);
      inv25519(a, a);
      M(a, a, b);
      pack25519(z, a);
      return z;
  }
docs: Converts Curve25519 public key back to Ed25519 public key. edwardsY = (montgomeryX - 1) / (montgomeryX + 1)