Re: [tor-dev] Much-revised draft, RFC: removing current obsolete clients from the network

On 8 Jan 2016, at 04:12, Nick Mathewson <nickm@xxxxxxxxxxxxxx> wrote:
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2. Some ideas that don't work.

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2.2. Blocking circuit creation under certain circumstances

  In tor 0.2.5.1-alpha, we began ignoring the UseNTorHandshake option,
  and always preferring the ntor handshake where available.

  Unfortunately, we can't simply drop all TAP handshakes, since clients
  and relays can still use them in the hidden service protocol. But
  we could detect these versions by:

       Looking for use of a TAP handshake from an IP not associated
       with with any known relay, or on a connection where the client
       did not authenticate. (This could be from a bridge, but clients
       don't build circuits that go to an IntroPoint or RendPoint
       directly after a bridge.)

I wonder how this affects existing Tor2web clients (as they make

one-hop client intro and rendezvous connections), and the

upcoming rendezvous single onion services, which make one-hop

intro and rendezvous server connections. (I also wonder about

single onion service extends, but I think they're ok.)

  This would still result in clients not having directories, however,
  and retrying once an hours.

3. Ideas that might work

3.1. Move all authorities to new ports

  We could have each authority known to older clients start listening
  for connections at a new port P. We'd forward the old port to the new
  port. Once sufficiently many clients were using the new ports, we
  could disable the forwarding.

  This would result in the old clients turning into zombies as above,
  but they would only be scrabbling at nonexistent ports, causing less
  load on the authorities.

  [This proposal would probably be easiest to implement.]

This might not work for clients that are always on:

Changing authority ports would only affect clients that have yet to

bootstrap, or clients that are off for long enough for their consensus

to expire. Otherwise, they can continue to contact directory mirrors in

their current consensus to obtain their next consensus.

For similar reasons, changing ports only works for tor versions

*without* default Fallback Directory mirrors, which likely means 0.2.7

and earlier.

This might have unintended consequences:

Some clients have FascistFirewall set, which restricts the initial

directory connection (to the authorities) to port 80. If we switched

some authorities away from DirPort 80, we'd need to switch a similar

number to DirPort 80. (Or make sure a sufficient number of default

Fallback Directory mirrors are on DirPort 80 from 0.2.8 onwards.)

(FascistFirewall also restricts OR connections to port 443, but by the

time a client makes an OR connection, it has the full consensus.)

3.2. Start disabling old link protocols on relays

  We could have new relays start dropping support for the old link
  protocols, while maintaining support on the authorities and older
  relays.

  The result here would be a degradation of older client performance
  over time. They'd still behave zombieishly if the authorities
  dropped support, however.

If a relay fails to support a client's protocol, does the client continue to

contact relays until it is successful?

If so, does this place extra load on (new) relays as the proportion of new

relays increases? (Or extra load on old relays which still support the old

protocols?)

3.3. Changing the consensus format.

  We could allow 'f' (short for "flag") as a synonym for 's' in
  consensus documents. Later, if we want to disable all Tor versions
  before today, we can change the consensus algorithm so that the
  consensus (or perhaps only the microdesc consensus) is spelled with
  'f' lines instead of 'f' lines. This will create a consensus which
  older clients and relays parse as having all nodes down, which will
  make them not connect to the network at all.

  We could similarly replace "r" with "n", or replace Running with
  Online, or so on.

  In doing this, we could also rename fresh-until and valid-until, so
  that new clients would have the real expiration date, and old clients
  would see "this consensus never expires". This would prevent them
  from downloading new consensuses.

  [This proposal would result in the quietest shutdown.]