[tor-commits] [torspec/master] Merge 4-byte circids (prop 214) into the spec.
nickm at torproject.org
nickm at torproject.org
Thu Mar 14 16:43:12 UTC 2013
commit 55d5de76644522dc9c2bf8f6429006d21d3b2c5f
Author: Nick Mathewson <nickm at torproject.org>
Date: Wed Mar 13 14:00:24 2013 -0400
Merge 4-byte circids (prop 214) into the spec.
---
proposals/214-longer-circids.txt | 3 +-
tor-spec.txt | 62 +++++++++++++++++++++++--------------
2 files changed, 40 insertions(+), 25 deletions(-)
diff --git a/proposals/214-longer-circids.txt b/proposals/214-longer-circids.txt
index 3277a9c..9494984 100644
--- a/proposals/214-longer-circids.txt
+++ b/proposals/214-longer-circids.txt
@@ -2,7 +2,8 @@ Filename: 214-longer-circids.txt
Title: Allow 4-byte circuit IDs in a new link protocol
Author: Nick Mathewson
Created: 6 Nov 2012
-Status: Finished
+Status: Closed
+Implemented-In: 0.2.4.11-alpha
0. Overview
diff --git a/tor-spec.txt b/tor-spec.txt
index 6831744..9aea142 100644
--- a/tor-spec.txt
+++ b/tor-spec.txt
@@ -57,7 +57,10 @@ see tor-design.pdf.
PAYLOAD_LEN -- The longest allowable cell payload, in bytes. (509)
- CELL_LEN -- The length of a Tor cell, in bytes.
+ CELL_LEN(v) -- The length of a Tor cell, in bytes, for link protocol
+ version v.
+ CELL_LEN(v) = 512 if v is less than 4;
+ = 514 otherwise.
0.3. Ciphers
@@ -117,10 +120,6 @@ see tor-design.pdf.
see Goldberg's PET2006 paper for details. We will add a MAC to this
scheme one day. -RD]
-0.4. Other parameter values
-
- CELL_LEN=512
-
1. System overview
Tor is a distributed overlay network designed to anonymize
@@ -274,11 +273,11 @@ see tor-design.pdf.
Once a TLS connection is established, the two sides send cells
(specified below) to one another. Cells are sent serially. Standard
- cells are CELL_LEN bytes long, but variable-length cells also exist; see
- Section 3. Cells may be sent embedded in TLS
- records of any size or divided across TLS records, but the framing
- of TLS records MUST NOT leak information about the type or contents
- of the cells.
+ cells are CELL_LEN(link_proto) bytes long, but variable-length cells
+ also exist; see Section 3. Cells may be sent embedded in TLS records
+ of any size or divided across TLS records, but the framing of TLS
+ records MUST NOT leak information about the type or contents of the
+ cells.
TLS connections are not permanent. Either side MAY close a connection
if there are no circuits running over it and an amount of time
@@ -357,14 +356,14 @@ see tor-design.pdf.
On a version 1 connection, each cell contains the following
fields:
- CircID [2 bytes]
+ CircID [CIRCID_LEN bytes]
Command [1 byte]
Payload (padded with 0 bytes) [PAYLOAD_LEN bytes]
- On a version 2 or 3 connection, all cells are as in version 1 connections,
- except for variable-length cells, whose format is:
+ On a version 2 or higher connection, all cells are as in version 1
+ connections, except for variable-length cells, whose format is:
- CircID [2 octets]
+ CircID [CIRCID_LEN octets]
Command [1 octet]
Length [2 octets; big-endian integer]
Payload [Length bytes]
@@ -374,6 +373,10 @@ see tor-design.pdf.
higher connection, variable-length cells are indicated by a command
byte equal to 7 ("VERSIONS"), or greater than or equal to 128.
+ CIRCID_LEN is 2 for link protocol versions 1, 2, and 3. CIRCID_LEN
+ is 4 for link protocol version 4 or higher. The VERSIONS cell itself
+ always has CIRCID_LEN == 2 for backward compatibility.
+
The CircID field determines which circuit, if any, the cell is
associated with.
@@ -493,6 +496,13 @@ see tor-design.pdf.
used, implementations MUST NOT list any version before 3, and SHOULD
list at least version 3.
+ Link protocols differences are:
+ 1 -- The "certs up front" handshake.
+ 2 -- Uses the renegotiation-based handshake. Introduces
+ varible-length cells.
+
+
+
4.2. CERTS cells
The CERTS cell describes the keys that a Tor instance is claiming
@@ -710,20 +720,24 @@ see tor-design.pdf.
5.1.1. Choosing circuit IDs in create cells
- The CircID for a CREATE cell is an arbitrarily chosen nonzero 2-byte
- integer, selected by the node (OP or OR) that sends the CREATE cell.
+ The CircID for a CREATE cell is an arbitrarily chosen nonzero integer,
+ selected by the node (OP or OR) that sends the CREATE cell. In link
+ protocol 3 or lower, CircIDs are 2 bytes long; in protocol 4 or
+ higher, CircIDs are 4 bytes long.
+
To prevent CircID collisions, when one node 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 node has a lower
- key, it chooses a CircID with an MSB of 0; otherwise, it chooses a
- CircID with an MSB of 1.
- [XXXX fix this when documenting link protocol 4.]
+ on the ORs' public identity keys. In link protocol version 3 or
+ lower, if the sending node 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.)
+
+ In link protocol version 4 or higher, whichever node initiated the
+ connection sets its MSB to 0, and whichever node didn't initiate the
+ connection sets its MSB to 1.
(An OP with no public key MAY choose any CircID it wishes, since an OP
never needs to process a CREATE cell.)
- [XXXX fix this when documenting link protocol 4.]
-
- Public keys are compared numerically by modulus.
5.1.2. EXTEND and EXTENDED cells
@@ -1183,7 +1197,7 @@ see tor-design.pdf.
StreamID [2 bytes]
Digest [4 bytes]
Length [2 bytes]
- Data [CELL_LEN-14 bytes]
+ Data [PAYLOAD_LEN-11 bytes]
The relay commands are:
1 -- RELAY_BEGIN [forward]
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