The myths about /dev/urandom page is trying to steer people heavily into using
This guy knows more than I do, so it would be easy for me to nod and accept, but I'd like to post it here so that other people who also know more than I do could comment.
What irks me about myths about /dev/urandom is that:
- The two devices still have a differing behaviour depending on the size of the entropy pool
- There are no use cases given where
/dev/randomis the better choice (which seems unbalanced)
I note that
cryptsetup has an option
NOTES ON RANDOM NUMBER GENERATORS
Using /dev/random on a system without enough entropy sources can cause luksFormat to block until the requested amount of random data is gathered. In a low-entropy situation (embedded system), this can take a very long time and potentially forever. At the same time, using /dev/urandom in a low-entropy situation will produce low-quality keys. This is a serious problem, but solving it is out of scope for a mere man-page. See urandom(4) for more information.
So my question is:
In which practical situations would one want to use
/dev/random in preference to
/dev/urandom, and why?