1. A data processing method comprising: applying a transformation to masked input data comprising input data that is masked with an additive mask, wherein said transformation transforms said additive mask into a multiplicative-additive mask comprising an additive component; using a first subset of said masked input data and said additive component of said multiplicative-additive mask in combination to select a lookup table (LUT) from a plurality of LUTs; and using a second subset of said masked input data to select an entry in said LUT corresponding to a transformed version of said input data.