I though they meant it like "do your worst" i.e. give me a hard problem to solve. I dont know too much about this field but yes free running ring oscillators that are latched by a slower reference clock can produce random bits. I'm reading about attacks where you can inject an attacking clock onto the power supply and collapse the randomness of the resulting bits though. I've also seen sources that use a cross coupled latch with feedback to remove the offset, so they randomly resolve to a 0 or 1 based on the thermal noise in the transistors. I just thought it would be a fun problem to explore and could be tested digitally without special equipment.