Systems and methods for determining cryptographic operation masks for improving resistance to external monitoring attacks. An example method may comprise: selecting a first input mask value, a first output mask value, and one or more intermediate mask values; based on the first output mask value and the intermediate mask values, calculating a first transformation output mask value comprising two or more portions, wherein concatenation of all portions of the first transformation output mask value produces the first transformation output mask value, and wherein exclusive disjunction of all portions of the first transformation output mask value is equal to the first output mask value; and performing a first masked transformation based on the first transformation output mask value and the first input mask value.