[openssl-project] FW: [openssl/openssl] VMS: lower the entropy demand for this platform specifically (#5904)

[Kurt Roeckx]

On Sun, Apr 08, 2018 at 10:31:58AM +0200, Richard Levitte wrote:
> In message <20180408080942.GB3653 at roeckx.be> on Sun, 8 Apr 2018 10:09:42 +0200, Kurt Roeckx <kurt at roeckx.be> said:
> 
> kurt> On Sun, Apr 08, 2018 at 07:39:30AM +0200, Richard Levitte wrote:
> kurt> > In message <20180407190250.GA27401 at roeckx.be> on Sat, 7 Apr 2018 21:02:51 +0200, Kurt Roeckx <kurt at roeckx.be> said:
> kurt> > 
> kurt> > kurt> On Sat, Apr 07, 2018 at 06:49:50PM +0200, Richard Levitte wrote:
> kurt> > kurt> > Hmmmm...  case 4 shouldn't pose too much problems unless you restart
> kurt> > kurt> > the application more than once every second or so (for a 1 second
> kurt> > kurt> > resolution).  On VMS, the system time is kept with 100 nanosecond
> kurt> > kurt> > granularity...  this doesn't mean that it's actually updated every 100
> kurt> > kurt> > nanosecond, but the possibility is there when VMS runs on fast enough
> kurt> > kurt> > hardware (a VAX is decidedly not in that range, Alpha has a minimum
> kurt> > kurt> > update rate of 1ms, Itaniums are faster than most Alphas...).  Either
> kurt> > kurt> > way, the timestamp is 64 bits, it seems that then, we'd add a 64-bit
> kurt> > kurt> > counter to match the 128 bit nonce requirement, do I get that right?
> kurt> > kurt> 
> kurt> > kurt> The requirement is not to have it 128 bit. Just that it doesn't
> kurt> > kurt> repeat as often as a 128 random number. You're most likely not
> kurt> > kurt> going to instantiate it 2^64 times. As long as the combination is
> kurt> > kurt> unique, it should be fine.
> kurt> > 
> kurt> > "The requirements" depend on where you look.  Looking at the code, or
> kurt> > more specifically drbg_ctr_init in drbg_ctr.c, about line 421, I see
> kurt> > this:
> kurt> > 
> kurt> >         drbg->min_noncelen = drbg->min_entropylen / 2;
> kurt> > 
> kurt> > So the DRBG CTR code currently requires 128 bits minimum by default,
> kurt> > unconditionally.
> kurt> 
> kurt> The standard does not require this 128 bit. This 128 bit is only
> kurt> required for the random value. The example even has a nonce of 32
> kurt> bit.
> 
> So then maybe the code in drbg_ctr_init() shouldn't set such a high
> minimum when drbg->get_nonce is defined?  That, or RAND_DRBG_instantiate()
> shouldn't try to check against drbg->min_noncelen, i.e. the latter
> should only be used when drbg->get_nonce is undefined.

Yes, after what I all said previously, it's clear the code could
use improvements. I think at least Matthias and I assumed the code
about the minimum size was correct and that there was a minimum
requirement of 128 bit.


Kurt