An electronic circuit includes configurable cells with a test input and an output. The configurable cells are capable of being connected to one another in a chain in a predefined order via the test inputs and the outputs to form a test shift register if they receive a chaining command signal. A connection control module disconnects the test input from at least one configurable cell if the connection control module receives an invalid identification key. The connection control module leaves disconnected the test input from the at least one configurable cell, or applies a constant potential on the test input of the at least one configurable cell, or connects the test input of the at least one configurable cell at an output of a random-data generator.