A high-speed oscillator-based truly random number source for cryptographic applications on a smart card IC

The design of a high-speed IC random number source macro-cell, suitable for integration in a smart card microcontroller, is presented. The oscillator sampling technique is exploited and a jittered oscillator which features an amplified thermal noise source has been designed in order to increase the output throughput and the statistical quality of the generated bit sequences. The oscillator feedback loop acts as an offset compensation for the noise amplifier, thus solving one of the major issues in this kind of circuit. A numerical model for the proposed system has been developed which allows us to carry out an analytical expression for the transition probability between successive bits in the output stream. A prototype chip has been fabricated in a standard digital 0.18 μm n-well CMOS process which features a 10 Mbps throughput and fulfills the NIST FIPS and correlation-based tests for randomness. The macro-cell area, excluding pads, is 0.0016 mm² (184 μm × 86 μm) and a 2.3 mW power consumption has been measured.