Re:Myths about /dev/urandom (2014)
by paavoova on Saturday August 18, 2018 @04:43AM
(#17787528)
entropy_avail returns bits of entropy to a maximum of 4096(?), but this reads 1000 bytes. Why check if it's greater than 1500 if you're going to use it all anyway? Am I missing something here?
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remember that this is for people with external entropy sources, the kernel entropy will refill fast. 1500 is more a measure of "is /dev/random busy at the moment" if it is then it's pulling data from from the external entropy source and /dev/urandom is essentially already being fed with more entropy
The missing mechanism we're trying to emulate used to essentially read N bytes (whatever user space happened to want at the time) every M seconds our experience has been that that can be way more than 1000 bytes, but reduce it if you like