[tor-commits] [torspec/master] prop#249: Add recommendation on equal number of cells in each direction.

[isis at torproject.org]

commit 21e79aec731e068c0ba92c50f5fa5d3f5132b003
Author: Isis Lovecruft <isis at torproject.org>
Date:   Wed Dec 13 23:51:21 2017 +0000

    prop#249: Add recommendation on equal number of cells in each direction.
---
 proposals/249-large-create-cells.txt | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/proposals/249-large-create-cells.txt b/proposals/249-large-create-cells.txt
index b1967f3..c08b596 100644
--- a/proposals/249-large-create-cells.txt
+++ b/proposals/249-large-create-cells.txt
@@ -77,6 +77,14 @@ Status: Open
    If any intervening cells are received, the receiver SHOULD destroy
    the circuit.
 
+   Protocols which make use of CREATE(D)2V cells SHOULD send an equal number
+   of cells in either direction, to avoid trivially disclosing information
+   about the direction of the circuit: for example a relay might use the
+   fact that it saw five EXTEND2 cells in one direction and three in the
+   other to easily determine whether it is the middle relay on the onion
+   service-side or the middle relay on the client-side of a rendezvous
+   circuit.
+
 4. Interacting with RELAY_EARLY cells
 
    The first EXTEND2 cell in a batch must arrive in a RELAY_EARLY cell.