I'll be the fool here since I'm not mathematical: how is it sustainable to mix any potentially flawed source into the entropy pool? For example if my RNG just

I'll be the fool here since I'm not mathematical: how is it sustainable to mix any potentially flawed source into the entropy pool? For example if my RNG just outputs a series of 5s, surely that would weaken the pool even if the other nine sources were lovely lovely entropy? What is the 'threshold' for tolerable degradation? The patch that was finally accepted for the Linux kernel was to mix-in RdRand but not to increment the entropy counter. To me as a layman that suggests that if the other inputs are weak at any time ( e.g. soon after boot ) then RdRand will be dominant.