  Our ability to trust that a random number is truly random is essential for
fields as diverse as cryptography and fundamental tests of quantum mechanics.
Existing solutions both come with drawbacks -- device-independent quantum
random number generators (QRNGs) are highly impractical and standard
semi-device-independent QRNGs are limited to a specific physical implementation
and level of trust. Here we propose a new framework for semi-device-independent
randomness certification, using a source of trusted vacuum in the form of a
signal shutter. It employs a flexible set of assumptions and levels of trust,
allowing it to be applied in a wide range of physical scenarios involving both
quantum and classical entropy sources. We experimentally demonstrate our
protocol with a photonic setup and generate secure random bits under three
different assumptions with varying degrees of security and resulting data
rates.
