Patent ID: 8036380

Claim:
An apparatus for generating an authentication code, the apparatus comprising: control and support logic for generating a plurality of control signals; linear feedback shift register (LFSR) circuitry comprising a shift register and feedback circuitry; and additional circuitry connected to the LFSR circuitry, wherein: a first state of the control signals causes the LFSR circuitry and the additional circuitry to function together as a key generator; and a second state of the control signals causes the LFSR circuitry and the additional circuitry to function together as a multiplier; wherein the additional circuitry comprises: multipurpose logic circuitry comprising a shift register and feedback circuitry, wherein: signals to be fed back through the feedback circuitry of the multipurpose logic circuitry are selectively supplied by either one or more output signals supplied by a corresponding one or more stages of the shift register of the LFSR circuitry or by one or more output signals supplied by a corresponding one or more stages of the shift register of the multipurpose logic circuitry; and the feedback circuitry of the multipurpose logic circuitry is configured to generate a feedback signal in accordance with a function specified by one or more of the control signals, and is configured to make the feedback signal available to an input stage of the shift register of the multipurpose logic circuitry; summation circuitry for summing signals supplied by the LFSR circuitry, the multipurpose logic circuitry, and substitution logic circuitry; and the substitution logic circuitry having an input port for receiving one or more signals supplied by the summation circuitry, and an output port for supplying signals to the summation circuitry, and wherein: the key generator is a stream cipher generator; the first state of the control signals causes the LFSR circuitry, the multipurpose logic circuitry, the summation circuitry, and the substitution logic circuitry to function together as the stream cipher generator; and the second state of the control signals causes the LFSR circuitry and the feedback circuitry of the multipurpose logic circuitry to function together as the multiplier.