[CentOS] Low random entropy

Sun May 28 10:16:59 UTC 2017
Robert Moskowitz <rgm at htt-consult.com>

On 05/28/2017 04:24 AM, Tony Mountifield wrote:
> In article <792718e8-f403-1dea-367d-977b157af82c at htt-consult.com>,
> Robert Moskowitz <rgm at htt-consult.com> wrote:
>> On 05/26/2017 08:35 PM, Leon Fauster wrote:
>>>> Am 27.05.2017 um 01:09 schrieb Robert Moskowitz <rgm at htt-consult.com>:
>>>> I am use to low random entropy on my arm boards, not an intel.
>>>> On my Lenovo x120e,
>>>> cat /proc/sys/kernel/random/entropy_avail
>>>> reports 3190 bits of entropy.
>>>> On my armv7 with Centos7 I would get 130 unless I installed rng-tools and then I get ~1300.  SSH into one and it
>> drops back to 30! for a few minutes.  Sigh.
>>>> Anyway on my new Zotac nano ad12 with an AMD E-1800 duo core, I am seeing 180.
>>>> I installed rng-tools and no change.  Does anyone here know how to improve the random entropy?
>>> http://issihosts.com/haveged/
>>> EPEL: yum install haveged
>> WOW!!!
>> installed, enabled, and started.
>> Entropy jumped from ~130 bits to ~2000 bits
>> thanks
>> Note to anyone running a web server, or creating certs.  You need
>> entropy.  Without it your keys are weak and attackable.  Probably even
>> known already.
> Interesting. I just did a quick check of the various servers I support,
> and have noticed that all the CentOS 5 and 6 systems report entropy in
> the low hundreds of bits, but all the CentOS 4 systems and the one old
> FC3 system all report over 3000 bits.
> Since they were all pretty much stock installs, what difference between
> the versions might explain what I observed?

This is partly why so many certs found in the U of Mich study are weak 
and factorable.  So many systems have inadequate entropy for the 
generation of key pairs to use in TLS certs.  Worst are certs created in 
firstboot process where at times there is no entropy, but the firstboot 
still creates its certs.