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A comment on Fixing Getrandom(). Parent comment

Re:Fixing Getrandom() by boring_twenties on Tuesday October 01, 2019 @06:09PM (#21131280)
Well, not really, but before Linux 3.17 there was no way other way to be safe: /dev/urandom was the only other option, and that happily returns data even if the entropy pool isn't (yet) initialized and the CSPRNG can't be properly seeded.

Since then there is get_random(2) which does the right thing for most applications.

The man page also has this to say:

> The /dev/random device is a legacy interface which dates back to a time where the cryptographic primitives used in the implementation of /dev/urandom were not widely trusted.

I must admit though, that I still don't understand why blocking on insufficient entropy is a bad thing for generating long-lived keys. I'm going to use the key for years, why wouldn't I just wait a couple of seconds or minutes?

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Re:Fixing Getrandom() by throwaway2048 on Wednesday October 02, 2019 @09:43AM (#21136314)
Because the entire idea of "insufficient entropy" past an initialization amount is a cargo culted fantasy.

In the Linux kernel view of the world, /dev/random "loses" 1 bit of entropy for every bit that gets read.

That is not how cryptographic and hashing primitives work, if it were it would be dangerous to use an AES key to encrypt more than a few megabytes for example.

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