Key Schedule Clause Samples

Key Schedule. The round key is not stored in a bitsliced fashion and the key schedule is computed on the fly. Note that round key precomputation is also a valid implementation option, assuming that the key does not need to be renewed often. Since, key refreshing can act as a side-channel countermeasure, 6 ▇▇▇▇▇://▇▇▇.▇▇▇▇▇▇▇.▇▇▇/security-tools/hardware/pinata (Accessed 24 June 2016). we chose to retain the on-the-fly key updates. Updating the round key requires a push through the Sbox for four bits each round. To that purpose, we use Cortex-M4’s UBFX instruction for extracting a contiguous series of bits from a word in an efficient manner. In addition, we used ARM’s barrel shifter function, which allows the second operand to be shifted with no additional cost before an instruction is performed.