Re: [PATCH v5 0/7] /dev/random - a new approach

On Mon, Jun 20, 2016 at 09:00:49PM +0200, Stephan Mueller wrote:

The time stamp maintenance is the exact cause for the correlation: one HID 
event triggers:

- add_interrupt_randomness which takes high-res time stamp, Jiffies and some 
pointers

- add_input_randomness which takes high-res time stamp, Jiffies and HID event 
value

The same applies to disk events. My suggestion is to get rid of the double 
counting of time stamps for one event.

And I guess I do not need to stress that correlation of data that is supposed 
to be entropic is not good :-)

What is your concern, specifically?  If it is in the entropy
accounting, there is more entropy in HID event interrupts, so I don't
think adding the extra 1/64th bit of entropy is going to be problematic.

If it is that there are two timestamps that are closely correleated
being added into the pool, the add_interrupt_randomness() path is
going to mix that timestamp with the interrupt timings from 63 other
interrupts before it is mixed into the input pool, while the
add_input_randomness() mixes it directly into the pool.  So if you
think there is a way this could be leveraged into attack, please give
specifics --- but I think we're on pretty solid ground here.

Cheers,

						- Ted