Modeling and Observing the Jitter in Ring Oscillators Implemented in FPGAs

Abstract : Random number generators represent one of basic cryptographic primitives used to compose cryptographic protocols. While Field Programmable Gate Arrays (FPGAs) are well suited for implementing algorithmic random number generators (pseudo-random number generators), generating fast and secured true random bitstreams inside FPGAs is an open problem. Most of true random number generators in FPGAs employ the timing jitter present in ring oscillator clocks as a source of randomness. The paper analyses the jitter generated in ring oscillators and presents a simple physical model of its sources. The jitter generated in MATLAB in accordance with the proposed model is then used as an input in VHDL simulations. To evaluate the model, we use an embedded technique of jitter measurement. The principle is simulated in VHDL and validated by experiments using different FPGA technologies.