Patent ID: 7702100

Claim:
Apparatus for generating round-key words in accordance with a Rijndael algorithm, the apparatus comprising: (a) a key expansion register block comprising a key expansion shift register adapted to receive a first cipher key of a key expansion schedule in accordance with the Rijndael algorithm, wherein the key expansion register block is adapted to shift the contents of the key expansion shift register; (b) a round constant generator adapted to generate a current round constant based on a seed value and in response to a first control signal; (c) a first XOR adder adapted to add a first word of the key expansion shift register to a second word to generate and provide a first sum to the key expansion register block, wherein: the first word of the key expansion shift register is a round-key word provided as an output of the apparatus; and the first sum comprises a first-sum first byte, a first-sum second byte, a first-sum third byte, and a first-sum fourth byte; (d) a transformation block adapted to generate a transformed word based on the first sum and the current round constant over four counts of a first cyclical counter; and (e) a second XOR adder adapted to add the transformed word to the first word of the key expansion shift register to generate and provide a second sum to the key expansion register block; wherein the round constant generator comprises: a round constant register adapted to store 9 bits and to refresh in response to the first control signal; and a third XOR adder, adapted to add the value of the contents of the round constant register to a first generated number, and to provide a portion of the resultant fourth sum to the round constant register.