Circuit for calculating a logic combination of two encrypted input operands recieves first and second dual-rail signals comprising data values in a calculation cycle and precharge values in a precharge cycle, and receives a dual-rail encryption signal comprising encryption values in the calculation cycle and precharge values in the precharge cycle, and outputs a dual-rail result signal comprising encrypted result values in the calculation cycle and precharge values in the precharge cycle. The data and encrypted result values are encrypted with the encryption values of the dual-rail encryption signal according to an encryption rule. A logic circuit determines the encrypted result values according to the logic combination from the data and encryption values, and outputs the encrypted result values in the calculation cycle. A precharge circuit impresses precharge values when precharge values are sensed at a single input, or stops impressing the precharge values only when the first and second dual-rail signals comprise data values and the dual-rail encryption signal comprises encryption values.