[CentOS] Low random entropy

Mon May 29 07:13:36 UTC 2017
Rob Kampen <rkampen at kampensonline.com>

On 29/05/17 15:46, Robert Moskowitz wrote:
> On 05/28/2017 06:57 PM, Rob Kampen wrote:
>> On 28/05/17 23:56, Leon Fauster wrote:
>>>> Am 28.05.2017 um 12:16 schrieb 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:
>>>>>> drops back to 30! for a few minutes.  Sigh.
>>>>>>> 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.
>>> /var/lib/random-seed and $HOME/.rnd are approaches to mitigate this 
>>> scenario.
>>> -- 
>>> LF
>> so there are mitigations - the question really is: why hasn't redhat 
>> made these mitigations the default for their enterprise products - 
>> maybe other influences we are unaware of - seems like a huge big 
>> hole. With the advent of SSL/TLS being mandated by google et al, 
>> every device needs access to entropy.
> The challenge is this is so system dependent.  Some are just fine with 
> stock install.  Others need rng-tools.  Still others need haveged.  If 
> Redhat were to do anything, it would be to stop making the default 
> cert during firstboot.  Rather spin off a one-time process that would 
> wait until there was enough entropy and then create the default cert.  
> Thing is I can come up with situations were that can go wrong.
> There are a lot of best practices with certificates and crypto that 
> are not apparent to most admins.  I know some things for the crypto 
> work I do (I am the author of the HIP protocol in the IETF).  There is 
> just not one size fits all here, and people need to collect clues 
> along with random entropy....
OK that makes sense, I've been admin on linux servers for about 18 
years, understand the basics, use certificates for web and email 
servers. This thread has exposed an area that I'm peripherally aware of 
- the need to generate with sufficient entropy the cipher that goes 
across the internet in order to avoid an observer being able to reverse 
engineer the keys used.
I still fail to see why every server and workstation is not set up to do 
this at some minimum level - i guess linux out of the box does this, the 
issue is that the minimum from just the basic kernel on most hardware is 
too little with today's ability to crack ciphers..

Is there some practical guideline out there that puts this in terms that 
don't require a PhD in mathematics to understand and implement.

For instance I have setup and run mail servers for nearly two decades, 
only in the last 10+ years with certificates and mandated SSL/TLS - yet 
the issue of low random entropy is relevant here but until this thread I 
hadn't taken steps to resolve.

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