Re: [Ntp] Mandatory confidentiality for ntpv5

[Martin Burnicki <[e-mail]>]

Hal Murray wrote:
> [e-mail] said:
>> How much of the packet would be encrypted?
>> If it's fully encrypted, how could a NIC find out that an incoming packet is
>> an NTP packet that may need to be timestamped (if timestamping of NTP packets
>> is supported at all)?
> 
> Why not have the NIC timestamp everything and let the driver discard the ones
> that the client software desn't want?

 From what I've yet heard from kernel developers, collecting data in 
which no one is interested would be too expensive.

In my opinion this is similar to multicast: if a consumer is interested, 
it tells in *what* it is interested, and only the requested information 
is provided.

> How does current NIC firmware decide which packets to time stamp?

I#m not familiar with too many different NICs, but I know that some have 
a hard-coded pattern e.g. for PTP packets, and others have a 
configurable packet matcher, to which you can download a specific pattern.

Anyway, as far as I know, you would have problems to detect the network 
packets that are to be timestamped if the packets are fully encrypted.

And, similar to the topic above, IMO it would be too expensive to 
timestamp all packets and drop most of them in which no NTP or PTP 
daemon is interested.

> Are you using "timestamp" in the PTP sense of modify the packet?  I don't know
> how to do that with encrypted data.  I was thinking of "timestamp" in the
> sense of SO_TIMESTAMP.

See above. It would be hard to even *detect* the packets that need to be 
timestamped, regardless whether you try to put the timestamp into the 
encrypted packet (which isn't possible, of course) or make it available 
in a different way.

Lately I haven't been too much involved in the PTP stuff, but from the 
past I remember that it was also important at which point/bit the 
timestamp is taken when it comes in and passes along the packet matcher.


Martin
-- 
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