Re: [PATCH v6 0/5] /dev/random - a new approach

["H. Peter Anvin" <hpa@linux.intel.com>]

On 08/15/16 22:45, Stephan Mueller wrote:
> Am Montag, 15. August 2016, 13:42:54 CEST schrieb H. Peter Anvin:
> 
> Hi H,
> 
>> On 08/11/16 05:24, Stephan Mueller wrote:
>>> * prevent fast noise sources from dominating slow noise sources
>>>
>>>   in case of /dev/random
>>
>> Can someone please explain if and why this is actually desirable, and if
>> this assessment has been passed to someone who has actual experience
>> with cryptography at the professional level?
> 
> There are two motivations for that:
> 
> - the current /dev/random is compliant to NTG.1 from AIS 20/31 which requires 
> (in brief words) that entropy comes from auditible noise sources. Currently in 
> my LRNG only RDRAND is a fast noise source which is not auditible (and it is 
> designed to cause a VM exit making it even harder to assess it). To make the 
> LRNG to comply with NTG.1, RDRAND can provide entropy but must not become the 
> sole entropy provider which is the case now with that change.
> 
> - the current /dev/random implementation follows the same concept with the 
> exception of 3.15 and 3.16 where RDRAND was not rate-limited. In later 
> versions, this was changed.
> 

I'm not saying it should be *sole*.  I am questioning the value in
limiting it, as it seems to me that it could only ever produce a worse
result.

	-hpa