commit 55d5de76644522dc9c2bf8f6429006d21d3b2c5f Author: Nick Mathewson <nickm@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]