[ntpwg] Antw: Re: call for adoption (draft-dfranke-ntp-data-minimization)

["Ulrich Windl" <[e-mail]>]

>>> Greg Dowd <[e-mail]> schrieb am 29.03.2017 um 17:37 in Nachricht
<[e-mail]>:
> IIRC, there is a randomizer of a second or two attached to the calculation of 
> the next poll in ntpd?

Actually I think this isn't needed considering the fact that today's timers all have sub-second resolution. So it would be enough to distribute the polls within aone second.

Regards,
Ulrich

> 
> 
> -----Original Message-----
> From: ntpwg [mailto:ntpwg-bounces+gdowd=[e-mail]] On 
> Behalf Of Miroslav Lichvar
> Sent: Wednesday, March 29, 2017 2:41 AM
> To: Daniel Franke <[e-mail]>
> Cc: [e-mail] 
> Subject: Re: [ntpwg] call for adoption (draft-dfranke-ntp-data-minimization)
> 
> EXTERNAL EMAIL
> 
> 
> On Mon, Mar 27, 2017 at 04:50:42PM -0400, Daniel Franke wrote:
>> Regardless of your opinion of OpenNTPD design choices, the facts 
>> remain that it's in wide deployment and sets the precision field to 
>> zero.  Those facts alone make it a good choice for standardization
>> since:
>>
>> 1. Matching an existing implementation leads to one less opportunity 
>> for fingerprinting.
> 
> I'm not sure how much that really helps. Even if other implementations sent 
> packets looking exactly like those from openntpd, the timing of the packets 
> would still be different. An observer can easily tell if it's openntpd, 
> busybox (which is based on openntpd), ntpd, chrony, or something else, 
> without actually looking at the values in the packets.
> 
> The fixed one-second timer in ntpd not only helps with fingerprinting the 
> implementation, it can be also very useful for fingerprinting individual ntpd 
> instances as they send requests at the same sub-second fraction.
> 
> A specification on how exactly should the timing for a given poll interval 
> look like (e.g. its distribution and granularity) might help.
> However, adjustments of the polling interval that clients normally do to 
> adapt to the stability of the clock and network could still be useful for 
> fingerprinting. Suggesting a constant polling interval for all NTP clients on 
> the Internet would probably not be a good idea.
> 
>> 2. Existing widespread use of this value means we can be confident it 
>> won't break anything.
> 
> 32 is not as common as 0, but it is used too. Another large precision that I 
> often see is 118. I've no idea where that comes from.
> 
> --
> Miroslav Lichvar
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