Patent ID: 6985581

Claim:
A circuit comprising: a DES operation unit adapted to perform a circuit operation in a plurality of rounds per clock cycle, the DES operation unit to operate properly under a predetermined range of operating conditions and not to operate if the operating conditions are altered beyond the predetermined range, the DES operation unit adapted to select between receiving an input signal and a test signal and to perform a test round per clock cycle of the circuit operation when the test signal is selected; the circuit adapted to compare a reference value with a result of the test round per clock cycle, the reference value identifying a correct value for the result of the test round per clock cycle when the DES operation unit is operating under the predetermined range of operating conditions; and the DES operation unit further adapted to receive a disable signal to disable the operation unit from performing the circuit operation when the operating conditions of the operating unit have been altered beyond the predetermined range, the disable signal produced when the result of the test round per clock cycle does not match the reference value; wherein the operating conditions include at least one of an operating temperature, an operating voltage or an operating clock frequency.