[tor-dev] Proposal 338: Use an 8-byte handshake in NETINFO cells

[Nick Mathewson]

On Mon, Mar 14, 2022 at 3:18 PM Jim Newsome <jnewsome at torproject.org> wrote:

> On 3/14/22 11:44, Nick Mathewson wrote:
>
> <snip>
>
>  > Currently Tor relays use a 4-byte timestamp (in seconds since the Unix
>  > epoch) in their NETINFO cells.  Notoriously, such a timestamp will
>  > overflow on 19 January 2038.
>  >
>  > Let's get ahead of the problem and squash this issue now, by expanding
>  > the timestamp to 8 bytes. (8 bytes worth of seconds will be long enough
>  > to outlast the Earth's sun.)
>
> <snip>
>
> With all those extra bits, would there be any value to using a more
> granular time measure? e.g. microseconds?
>


I don't think so, necessarily.  We aren't doing full NTP here; in fact,
we're just trying to detect clock skew that's big enough to break Tor.
(Like, on the order of hours.)  I don't think we'll get anything useful
out of sub-second observations.


If not, would it be worth saving some bytes and only expanding to 5
> bytes? (I know; it *feels* wrong, but I can't think of much real downside)
>

 Hm, possibly.  One downside is that 5-byte decoder/encoder functions
aren't exactly common, so we'd require everybody to build one.  (Or to do
something like
  u8 ts_high;
  u32 ts_low;
)

Since the extra 3 bytes are only used once per connection attempt, I'm
pretty comfortable letting them be useless until 36812 CE or whenever.
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