Patent ID: 7814336
Filing Date: 2010-10-12
Classification: G06F

Abstract:
1. A method of limiting operation of a protected circuit, the method comprising: generating first authentication states using a first pseudo-random number (PN) generator of the protected circuit; generating second authentication states using a second PN generator of the protected circuit; wherein the first and second authentication states are generated in pairs, the first and second authentication states in each pair are equivalent in a number of successive pairs, each first authentication state is a function of a previous first authentication state, and each second authentication state is a function of a previous second authentication state; comparing each of the second authentication states to a terminal state, the terminal state providing a time limit on operation of the protected circuit; inverting at least one bit of one of the second authentication states in response to the one of the second authentication states being equal to the terminal state; comparing the first authentication states to the second authentication states; activating the protected circuit for operation in response to a positive comparison between the first and second authentication states; and deactivating the protected circuit for operation in response to a negative comparison between the first and second authentication states.