Protection of authentication tag computation against power and electromagnetic side-channel attacks is described. An example of one or more storage mediums includes instructions for performing a process for calculation of an authentication tag for a data encryption operation, including generating one or more random values; receiving multiple data blocks for calculation, and performing calculation utilizing the received data blocks and the one or more random values to generate intermediate values; performing a data accumulation operation to accumulate random values in calculation of the data blocks; and calculating the authentication tag based at least in part on the generated intermediate values and the accumulated random values.