[or-cvs] Resolve a FIXME: use identity comparison, not nickname comp...

[Nick Mathewson]

Update of /home/or/cvsroot/doc
In directory moria.mit.edu:/tmp/cvs-serv19477/doc

Modified Files:
	tor-spec.txt 
Log Message:
Resolve a FIXME: use identity comparison, not nickname comparison, to
choose circuit ID types.  This is important because our view of "the
nickname of the router on the other side of this connection" is
skewed, and depends on whether we think the other rotuer is
verified--and there's no way to know whether another router thinks you
are verified.

For backward compatibility, we notice when the other router chooses
the same circuit ID type as us (because it's running an old version),
and switch our type to be polite.


Index: tor-spec.txt
===================================================================
RCS file: /home/or/cvsroot/doc/tor-spec.txt,v
retrieving revision 1.68
retrieving revision 1.69
diff -u -d -r1.68 -r1.69
--- tor-spec.txt	10 Nov 2004 01:20:17 -0000	1.68
+++ tor-spec.txt	10 Nov 2004 20:14:37 -0000	1.69
@@ -198,13 +198,19 @@
          DH data (g^y)                 [128 bytes]
          Derivative key data (KH)      [20 bytes]   <see 4.2 below>
 
-   The CircID for a CREATE cell is an arbitrarily chosen 2-byte
-   integer, selected by the node (OP or OR) that sends the CREATE
-   cell.  To prevent CircID collisions, when one OR sends a CREATE
-   cell to another, it chooses from only one half of the possible
-   values based on the ORs' nicknames: if the sending OR has a
-   lexicographically earlier nickname, it chooses a CircID with a high
-   bit of 0; otherwise, it chooses a CircID with a high bit of 1.
+   The CircID for a CREATE cell is an arbitrarily chosen 2-byte integer,
+   selected by the node (OP or OR) that sends the CREATE cell.  To prevent
+   CircID collisions, when one OR sends a CREATE cell to another, it chooses
+   from only one half of the possible values based on the ORs' public
+   identity keys: if the sending OR has a lower key, it chooses a CircID with
+   an MSB of 0; otherwise, it chooses a CircID with an MSB of 1.
+
+   Public keys are compared numerically by modulus.
+
+   (Older versions of Tor compared OR nicknames, and did it in a broken and
+   unreliable way.  To support versions of Tor earlier than 0.0.9pre6,
+   implementations should notice when the other side of a connection is
+   sending CREATE cells with the "wrong" MSG, and switch accordingly.)
 
 4.2. Setting circuit keys