True random number generator resistant to frequency injection attacks

True random number generators (TRNGs) based on flip-flop (FF) metastability can suffer from sensitivity to frequency injection attacks. A dedicated attack can interfere with a FF´s initial condition and influence the logical state or resolve time. These, in turn might result in significant keyspace reduction. Therefore, a novel TRNG utilising random timing of metastable FF is proposed. In this concept, a programmable delay line driven by a pseudo-random generator with a random seed, changes continuously the phase between triggering signals (data and clock) and the global system clock. Nevertheless, the relative interval of clock and data active slopes remains constant and violates FF timing to ensure metastable (truly random) operation.