Quantum random number generators use an intrinsically unpredictable quantum
measurement process as the source of randomness, and are therefore less
subject to tampering than algorithmically based random number
generators. Such devices are important for applications in secure
communication, or Monte-Carlo simulations. Physical random number
generators tend to not deliver a clean bit stream. We present a scheme that
generates a raw random input from vacuum fluctuations of the
electromagnetic field, and with very little resources extracts an unbiased,
uncorrelated stream of random bits that passes the usual test suites developed
to discover typical shortcomings of random number generators.