arc4random initialization

Mark Murray markm at
Mon Dec 7 08:37:46 UTC 2020


> On 6 Dec 2020, at 23:36, Dave Hayes <dave at> wrote:
> So security-wise, just how bad is it to be improperly seeded? If I cannot get
> a valid entropy stash at boot time, can I delay the need for it until I can get
> a writable filesystem up and running?
> Thanks in advance for any cogent replies.

This means that the random(4) device and relevant infrastructure like
arc4random starts up in an insecure state and is not to be trusted for e.g.
generating SSH keys.

After you have used the machine for a while (exactly how long "depends"),
it will reseed itself and become secure.

Essentially, expect every boot off a DVD on the same hardware to reuse
cryptographic keys and therefore be insecure.

Once you've installed on some R/W medium and rebooted, the necessary
entropy will have been stashed for you, and the first SSH keys will be
generated properly.

Mark R V Murray
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