NIST-Lite: Randomness Testing of RNGs on an Energy-Constrained Platform

Random Number Generators (RNGs) are an essential part of many embedded applications and are used for security, encryption, and built-in test applications. The output of RNGs can be tested for randomness using the well-known NIST statistical test suite. Embedded applications using True Random Number Generators (TRNGs) need to test the randomness of their TRNGs periodically, because their randomness properties can drift over time. Using the full NIST test suite is unpracticed for this purpose, because the full NIST test suite is computationally intensive, and embedded systems (especially real-time systems) often have stringent constraints on the energy and runtime of the programs that are executed on them. In this paper, we propose novel algorithms to select the most effective subset of the NIST test suite, which works within specified runtime and energy budgets. To achieve this, we rank the NIST tests based on multiple metrics, including p-value/Time, p-value/Energy, p-value/Time2 and p-value/Energy2. Based on the total runtime or energy constraint specified by the user, our algorithms proceed to choose a subset of the NIST tests using this rank order. We call this subset of NIST tests as NIST-Lite. Our algorithms also take into account the runtime and energy required to generate the random sequences required (on the same platform) by the NIST-Lite tests. We evaluate the effectiveness of our method against the full NIST test suite (referred to as NIST-Full) and also against a greedily chosen subset of the NIST test suite (referred to as NIST-Greedy). We explore different variants of NIST-Lite. On average, using the same input sequences, the p-value obtained for the 4 best variants of NIST-Lite is 2× and 7× better than the p-value of NIST-Full and NIST-Greedy respectively. NIST-Lite also achieves 158× (204×) runtime (energy) reduction compared to the NIST-Full. Further, we study the performance of NIST-Lite and NIST-Full for deterministic (non-random) input sequences. For such sequences, the pass rate of the NIST-Lite tests is within 16% of the pass rate of NIST-Full on the same sequences, indicating that our NIST-Lite tests have a similar diagnostic ability as NIST-Full.