SRAM Circuits for True Random Number Generation Using Intrinsic Bit Instability

This paper describes a novel approach to a true random number generator (TRNG) using SRAM circuits. The principles of operation are described in the context of past work on integrated circuit TRNGs. The required modifications to standard SRAM arrays are minor and have little impact on the area. Experimental results from large 1-Mbit SRAM arrays fabricated on a 55-nm process using the foundry supplied SRAM cell layouts show good results. Simple helper functions, suitable for very small hardware implementation, allow improvement, including the ability for the resulting binary strings to pass all of the National Institute of Standards randomness tests. We describe the circuits, their principle of operation and statistical behavior, as well as the underlying physical mechanisms providing the entropy.