  Random numbers represent an indispensable resource for many applications. A
recent remarkable result is the realization that non-locality in quantum
mechanics can be used to certify genuine randomness through Bell's theorem,
producing reliable random numbers in a device independent way. Here, we explore
the contextuality aspect of quantum mechanics and show that true random numbers
can be generated using only single qutrit (three-state systems) without
entanglement and non-locality. In particular, we show that any observed
violation of the Klyachko-Can-Binicioglu-Shumovsky (KCBS) inequality [Phys.
Rev. Lett. 101, 20403 (2008)] provides a positive lower bound on genuine
randomness. As a proof-of-concept experiment, we demonstrate with photonic
qutrits that at least 5246 net true random numbers are generated with a
confidence level of 99.9%.
