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commit fcfeec23519e9bcbd2e9cb59f26268764824dea4 Author: David Goulet dgoulet@torproject.org AuthorDate: Fri Dec 9 15:45:34 2022 -0500

prop329: Changes after research and discussions

Series of change after discussin with mikeperry the proposal in depth.

Signed-off-by: David Goulet dgoulet@torproject.org --- proposals/329-traffic-splitting.txt | 167 +++++++++++++++++++----------------- tor-spec.txt | 2 + 2 files changed, 90 insertions(+), 79 deletions(-)

diff --git a/proposals/329-traffic-splitting.txt b/proposals/329-traffic-splitting.txt index 9bb72be..6a0d5cb 100644 --- a/proposals/329-traffic-splitting.txt +++ b/proposals/329-traffic-splitting.txt @@ -125,15 +125,23 @@ Status: Draft

2.1. Advertising support for conflux

+2.1.1 Relay + We propose a new protocol version in order to advertise support for circuit linking on the relay side:

- "Relay=4" -- Relay supports an 2 byte sequence number in a RELAY cell - header used for multipath circuit which are linked with the - new RELAY_CIRCUIT_LINK relay cell command. + "Relay=5" -- Relay supports Conflux as in linking circuits together using + the new LINK, LINKED and SWITCH relay command. + +2.1.2 Onion Service + + We propose to add a new line in order to advertise conflux support in the + onion service descriptor:

- XXX: Advertise this in onion service descriptor. - XXX: Onion service descriptor can advertise more than two circuits? + "conflux" SP max-num-circ NL + + The "max-num-circ" value indicate the maximum number of rendezvous + circuits that are allowed to be linked together.

The next section describes how the circuits are linked together.

@@ -148,29 +156,28 @@ Status: Draft All three stages of this handshake are sent on *each* circuit leg to be linked.

- To save round trips, these cells SHOULD be combined with the initial - RELAY_BEGIN cell on the faster circuit leg, using Proposal 325. See - [LINKING_EXIT] and [LINKING_SERVICE] for more details on setup in each - case. + When packed cells are a reality (proposal 340), these cells SHOULD be + combined with the initial RELAY_BEGIN cell on the faster circuit leg. See + [LINKING_EXIT] and [LINKING_SERVICE] for more details on setup in each case.

- There are other ways to do this linking that we have considered, but - they seem not to be significantly better than this method, especially - since we can use Proposal 325 to eliminate the RTT cost of this setup - before sending data. For those other ideas, see [ALTERNATIVE_LINKING] - and [ALTERNATIVE_RTT], in the appendix. + There are other ways to do this linking that we have considered, but they + seem not to be significantly better than this method, especially since we can + use Proposal 340 to eliminate the RTT cost of this setup before sending data. + For those other ideas, see [ALTERNATIVE_LINKING] and [ALTERNATIVE_RTT], in + the appendix.

The first two parts of the handshake establish the link, and enable resumption:

- 16 -- RELAY_CIRCUIT_LINK + 45 -- RELAY_CONFLUX_LINK

- Sent from the OP to the exit/service in order to link - circuits together at the end point. + Sent from the OP to the exit/service in order to link circuits + together at the end point.

- 17 -- RELAY_CIRCUIT_LINKED + 46 -- RELAY_CONFLUX_LINKED

- Sent from the exit/service to the OP, to confirm the circuits - were linked. + Sent from the exit/service to the OP, to confirm the circuits were + linked.

These cells have the following contents:

@@ -201,41 +208,51 @@ Status: Draft The two sequence number fields are 0 upon initial link, but non-zero in the case of a resumption attempt (See [RESUMPTION]).

- If either circuit does not receive a RELAY_CIRCUIT_LINKED response, both + If either circuit does not receive a RELAY_CONFLUX_LINKED response, both circuits MUST be closed.

The third stage of the handshake exists to help the exit/service measure initial RTT, for use in [SCHEDULING]:

- 18 -- RELAY_CIRCUIT_LINKED_RTT_ACK + 47 -- RELAY_CONFLUX_LINKED_ACK

- Sent from the OP to the exit/service, to provide initial RTT - measurement for the exit/service. + Sent from the OP to the exit/service, to provide initial RTT + measurement for the exit/service.

For timeout of the handshake, clients SHOULD use the normal SOCKS/stream timeout already in use for RELAY_BEGIN.

- These three relay commands (RELAY_CIRCUIT_LINK, RELAY_CIRCUIT_LINKED, - and RELAY_CIRCUIT_LINKED_RTT_ACK) are send on *each* leg, to allow each - endpoint to measure the initial RTT of each leg. + These three relay commands are send on *each* leg, to allow each endpoint to + measure the initial RTT of each leg. + + The circuit SHOULD be closed if at least one of these conditions is met: + + - Once a LINK is received, if the next cell relay command is not a + LINKED_ACK. + - Once a LINKED_ACK is received, receiving any other command than these: + * BEGIN, DATA, END, CONNECTED, RESOLVE, RESOLVED, XON, XOFF, SWITCH + - Receiving a LINKED without a LINK. + - Receiving a LINKED_ACK without having sent a LINKED. + + XXX Must define our LINK rate limiting parameters.

2.2. Linking Circuits from OP to Exit [LINKING_EXIT]

To link exit circuits, two circuits to the same exit are built. The client records the circuit build time of each.

- If the circuits are being built on-demand, for immediate use, the - circuit with the lower build time SHOULD use Proposal 325 to append its - first RELAY cell to the RELAY_COMMAND_LINK, on the circuit with the - lower circuit build time. The exit MUST respond on this same leg. After - that, actual RTT measurements MUST be used to determine future - transmissions, as specified in [SCHEDULING]. + If the circuits are being built on-demand, for immediate use, the circuit + with the lower build time SHOULD use Proposal 340 to append its first RELAY + cell to the RELAY_CONFLUX_LINK, on the circuit with the lower circuit build + time. The exit MUST respond on this same leg. After that, actual RTT + measurements MUST be used to determine future transmissions, as specified in + [SCHEDULING].

- The RTT times between RELAY_COMMAND_LINK and RELAY_COMMAND_LINKED are - measured by the client, to determine each circuit RTT to determine - primary vs secondary circuit use, and for packet scheduling. Similarly, - the exit measures the RTT times between RELAY_COMMAND_LINKED and - RELAY_COMMAND_LINKED_RTT_ACK, for the same purpose. + The RTT times between RELAY_CONFLUX_LINK and RELAY_CONFLUX_LINKED are + measured by the client, to determine each circuit RTT to determine primary vs + secondary circuit use, and for packet scheduling. Similarly, the exit + measures the RTT times between RELAY_CONFLUX_LINKED and + RELAY_CONFLUX_LINKED_ACK, for the same purpose.

2.3. Linking circuits to an onion service [LINKING_SERVICE]

@@ -247,9 +264,9 @@ Status: Draft meet the client at two separate rendezvous points. These introduce requests MUST be sent to the same intropoint (due to potential use of onionbalance), and SHOULD be sent back-to-back on the same intro - circuit. They MAY be combined with Proposal 325. + circuit. They MAY be combined with Proposal 340.

- The first rendezvous circuit to get joined SHOULD use Proposal 325 to + The first rendezvous circuit to get joined SHOULD use Proposal 340 to append the RELAY_BEGIN command, and the service MUST answer on this circuit, until RTT can be measured.

@@ -283,50 +300,42 @@ Status: Draft small. It only has to signal that a cell comes after those arriving on another circuit.

- To achieve this, we add a small sequence number to the common relay - header for all relay cells on linked circuits. This sequence number is - meant to signal the number of cells sent on the *other* leg, so that - each endpoint knows how many cells are still in-flight on another leg. - It is different from the absolute sequence number used in - [LINKING_CIRCUITS] and [RESUMPTION], but can be derived from that - number, using relative arithmetic. + To achieve this, we propose a new relay command used to indicate a switch to + another leg:

- Relay command [1 byte] - Recognized [2 bytes] - StreamID [2 bytes] - Digest [4 bytes] - Length [2 bytes] - > LongSeq [1 bit] # If this bit is set, use 31 bits for Seq - > Sequencing [7 or 31 bits] - Data [Remainder] + 48 -- RELAY_CONFLUX_SWITCH

- The sequence number is only set for the first cell after the endpoint - switches legs. In this case, LongSeq is set to 1, and the Sequencing - field is 31 more bits. Otherwise it is a 1 byte 0 value. + Sent from the client to the exit/service when switching leg in an + already linked circuit construction.

- These fields MUST be present on ALL end-to-end relay cells on each leg - that come from the endpoint, following a RELAY_CIRCUIT_LINK command. + The cell payload format is:

- They are absent on 'leaky pipe' RELAY_COMMAND_DROP and - RELAY_COMMAND_PADDING_NEGOTIATED cells that come from middle relays, as - opposed to the endpoint, to support padding. + SeqNum [4 bytes] + + The "SeqNum" value is a relative sequence number which is the number of cells + that was sent on the current leg until the switch. That way, we can always + keep up with the absolute sequence number and learn how many are inflights on + the current leg. + + As an example, if on the first leg we just sent 21 cells after sending 10 + cells (for a total of 31), then the RELAY_CONFLUX_SWITCH cell contains "21" + as the SeqNum then it can compute the absolute number to be 10 + 21 which + means that the first cell coming on the new leg should be considered the 32nd + cell in the sequence for reordering. + + In the rare event that we send more than 2^31 cells (~1TB) on a single leg, + the leg should be switched in order to reset that relative sequence number to + fit within 4 bytes. + + The circuit SHOULD be closed if at least one of these conditions is met:

- When an endpoint switches legs, on the first cell in a new leg, LongSeq - is set to 1, and the following 31 bits represent the *total* number of - cells sent on the *other* leg, before the switch. The receiver MUST wait - for that number of cells to arrive from the previous leg before - delivering that cell. + - The SeqNum value is below the "cwnd_min" which is currently set at 31. + - If immediately after receiving a SWITCH, another one is received.

- XXX: In the rare event that we send more than 2^31 cells (~1TB) on a - single leg, do we force a switch of legs, or expand the field further? + XXX: We should define our rate limiting.

- An alternative method of sequencing, that assumes that the endpoint - knows when it is going to switch, the cell before it switches, is - specified in [ALTERNATIVE_SEQUENCING]. Note that that method requires - only 1 byte for sequence number and switch signaling, but requires that - the sender know that it is planning to switch, the cell before it - switches. (This is possible with [BLEST_TOR], but [LOWRTT_TOR] can - switch based on RTT change, so it may be one cell late in that case). + - If we are NOT an exit circuit. + - If the SeqNum makes our absolute sequence number to overflow.

2.6. Resumption [RESUMPTION]

@@ -636,7 +645,7 @@ Status: Draft [LINKING_CIRCUITS] may be quite noticeable.

As one countermeasure, it may be possible to eliminate the third leg - (RELAY_CIRCUIT_LINKED_RTT_ACK) by computing the exit/service RTT via + (RELAY_CIRCUIT_LINKED_ACK) by computing the exit/service RTT via measuring the time between CREATED/REND_JOINED and RELAY_CIRCUIT_LINK, but this will introduce cross-component complexity into Tor's protocol that could quickly become unwieldy and fragile. @@ -774,7 +783,7 @@ A.2 Alternative Link Handshake [ALTERNATIVE_LINKING]

Additionally, it is not clear that this approach actually saves us anything in terms of setup time, because we can optimize away the - linking phase using Proposal 325, to combine initial RELAY_BEGIN cells + linking phase using Proposal 340, to combine initial RELAY_BEGIN cells with RELAY_CIRCUIT_LINK.

A.3. Alternative RTT measurement [ALTERNATIVE_RTT] diff --git a/tor-spec.txt b/tor-spec.txt index 3f03890..38b8b35 100644 --- a/tor-spec.txt +++ b/tor-spec.txt @@ -1694,6 +1694,8 @@ see tor-design.pdf. 43 -- XON [forward or backward] 44 -- XOFF [forward or backward]

+ 45..48 -- Reserved for Conflux, see prop329. + Commands labelled as "forward" must only be sent by the originator of the circuit. Commands labelled as "backward" must only be sent by other nodes in the circuit back to the originator. Commands marked