[Cryptography] OpenSSL and random

[Jason Cooper]

On Sun, Dec 04, 2016 at 07:19:04AM +0000, Peter Gutmann wrote:
> Nico Williams <nico at cryptonector.com> writes:
> 
> >For a sufficiently-low number of bits we'd have a number of recognizable SSH
> >host keys and such.  
> 
> That's a good point, but it's conflating entropy with randomisation.  To get
> per-device unique keys, you don't need strong entropy, just a per-device
> unique value to make sure you don't get repeats.  In fact, here's a magic
> trick: A secure SSH key without needing any entropy! [0]
> 
>   seed = HMAC( fixed_secret, time() || MAC address || IP address || kernel version || ... );

It's worth noting here that this will work for individual users with a
simple threat model.  However, this is *not* an acceptable solution for
an OS to ship.

Primarily because there is no current mechanism for putting a
fixed_secret into each download of an OS image.  Which means it will get
dropped, or left the same for everybody for that OS release.

thx,

Jason.