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Enhancing security of ring oscillator-based trng implemented in FPGA

Random number generators are one of basic cryptographic primitives used in cryptographic protocols. Most of true random number generators in field programmable gate arrays (FPGAs) employ the timing jitter from ring oscillator clocks as a source of randomness. The paper analyses the jitter generated in ring oscillators and it uses a simple physical model of jitter sources to show that the random jitter accumulates slower than the global and manipulable deterministic jitter. This fact, which can be used to attack generators, is not considered even in most recent designs considered to be secure. The paper proposes simple but efficient countermeasure against these attacks. The method is validated using the proposed behavioral VHDL model and it is shown to be efficient also in hardware.