A method (40) is provided for performing a trustworthiness test on a random number generator, RNG, (20) comprising a physical unclonable function, PUF-module (21). The trustworthiness test is implemented as a known answer test, KAT, and the method (40) comprises: receiving (41), in the PUF-module (21), an input based on test data, T, received from a verifier (11) provided with at least one test data-test result pair, (T, R), providing (42) an output from the PUF-module (21), determining (43) a test result, R′, based on the output from the PUF-module (21), and providing (44) the test result, R′, to the verifier (11). A random number generator (20), computer program and computer program products and a method performed by or in a verifier are also provided.