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Re: kaslr: better rng

Le 07/11/2017 à 17:21, Taylor R Campbell a écrit :
Date: Tue, 7 Nov 2017 09:16:25 +0100
From: Maxime Villard <>

Le 06/11/2017 à 19:47, Taylor R Campbell a écrit :
The entropy file is supposed to be rewritten each time it's read, and
on shutdown, or something like that.

Yes, I know that. But what is the point you're trying to make?

The original quotation I was replying to was this:

Well, we could indeed extend /var/db/entropy-file. However, I would really
prefer the random area to be generated from a previous run of the system, and
not from the bootloader taking a seed in the file. Unless there is a
combination of both?

I was trying to point out that the entropy file _does_ come from a
previous run of the system.

Ah alright. But in my mail (that you were answering to) I did understand that
the entropy file comes from the previous run; what I was saying was, I would
prefer the file in question to contain random data right away and not just a
seed. In such a way that whoever wants to get random uints at boot time can
read the file and obtain some, with no generation algorithm whatsoever.

Le 06/11/2017 à 22:31, a écrit :
If you think you need this file, I would argue there should be two: the
current entropy file for the kernel to use, and a separate one generated
from a different chunk of random bit stream, exclusively for the use next
time by the bootloader.

Well yes, my initial plan was two different files.

What's the security goal you hope to achieve by having two different
files that cannot be achieved by using one and deriving two subkeys
from it?

There is no particular security goal behind this. Since I wanted the file not
to be a seed, it made sense to use two different files (one seed, one


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