Patent ID: 8171542

Claim:
A system to control access to a protected device, the system comprising: a test access port operable to communicatively couple with a removable external key device; and an internal key device operable to: generate at least one random number; generate a first plurality of cipher words in response to the at least one random number; communicate the at least one random number to the removable external key device; receive a second plurality of cipher words from the removable external key device and a plurality of test-request signals, wherein each of the plurality of test-request signals is associated with at least one of the second plurality of cipher words, and wherein each of the second plurality of cipher words is synchronized with a corresponding cipher word of the first plurality of cipher words and generated in response to the communicated at least one random number; and for each respective cipher word of the second plurality of cipher words: grant access to at least one of the plurality of test-request signals associated with the respective cipher word of the second plurality of cipher words to input the received at least one of the plurality of test-request signals to the protected device based on comparison of the respective cipher word of the second plurality of cipher words to a synchronized corresponding cipher word of the first plurality of cipher words.