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Nick Mathewson 2018-08-08 14:20:53 -04:00
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62
tor-spec.txt
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@ -1179,15 +1179,12 @@ see tor-design.pdf.
Once both parties have X and Y, they derive their shared circuit keys
and 'derivative key data' value via the KDF-TOR function in 5.2.1.
If an OR sees a circuit created with CREATE_FAST, the OR is sure to be the
first hop of a circuit. ORs SHOULD reject attempts to create streams with
RELAY_BEGIN exiting the circuit at the first hop: letting Tor be used as a
single hop proxy makes exit nodes a more attractive target for compromise.
The CREATE_FAST handshake is currently deprecated whenever it is not
necessary; the migration is controlled by the "usecreatefast"
networkstatus parameter as described in dir-spec.txt.
[Tor 0.3.1.1-alpha and later disable CREATE_FAST by default.]
5.2. Setting circuit keys
5.2.1. KDF-TOR
@ -1247,13 +1244,15 @@ see tor-design.pdf.
When creating a circuit through the network, the circuit creator
(OP) performs the following steps:
1. Choose an onion router as an exit node (R_N), such that the onion
router's exit policy includes at least one pending stream that
needs a circuit (if there are any).
1. Choose an onion router as an end node (R_N):
* N MAY be 1 for non-anonymous directory mirror, introduction point,
or service rendezvous connections.
* N SHOULD be 3 or more for anonymous connections.
Some end nodes accept streams (see 6.1), others are introduction
or rendezvous points (see rend-spec-{v2,v3}.txt).
2. Choose a chain of (N-1) onion routers
(R_1...R_N-1) to constitute the path, such that no router
appears in the path twice.
2. Choose a chain of (N-1) onion routers (R_1...R_N-1) to constitute
the path, such that no router appears in the path twice.
3. If not already connected to the first router in the chain,
open a new connection to that router.
@ -1332,8 +1331,24 @@ see tor-design.pdf.
Circuits are torn down when an unrecoverable error occurs along
the circuit, or when all streams on a circuit are closed and the
circuit's intended lifetime is over. Circuits may be torn down
either completely or hop-by-hop.
circuit's intended lifetime is over.
ORs SHOULD also tear down circuits which attempt to create:
* streams with RELAY_BEGIN, or
* rendezvous points with ESTABLISH_RENDEZVOUS,
ending at the first hop. Letting Tor be used as a single hop proxy makes
exit and rendezvous nodes a more attractive target for compromise.
ORs MAY use multiple methods to check if they are the first hop:
* If an OR sees a circuit created with CREATE_FAST, the OR is sure to be
the first hop of a circuit.
* If an OR is the responder, and the initiator:
* did not authenticate the link, or
* authenticated with a key that is not in the consensus,
then the OR is probably the first hop of a circuit (or the second hop of
a circuit via a bridge relay).
Circuits may be torn down either completely or hop-by-hop.
To tear down a circuit completely, an OR or OP sends a DESTROY
cell to the adjacent nodes on that circuit, using the appropriate
@ -1479,11 +1494,16 @@ see tor-design.pdf.
6.1. Relay cells
Within a circuit, the OP and the exit node use the contents of
Within a circuit, the OP and the end node use the contents of
RELAY packets to tunnel end-to-end commands and TCP connections
("Streams") across circuits. End-to-end commands can be initiated
by either edge; streams are initiated by the OP.
End nodes that accept streams may be:
* exit relays (RELAY_BEGIN, anonymous),
* directory servers (RELAY_BEGIN_DIR, anonymous or non-anonymous),
* onion services (RELAY_BEGIN, anonymous via a rendezvous point).
The payload of each unencrypted RELAY cell consists of:
Relay command [1 byte]
'Recognized' [2 bytes]
@ -1509,7 +1529,7 @@ see tor-design.pdf.
14 -- RELAY_EXTEND2 [forward] [control]
15 -- RELAY_EXTENDED2 [backward] [control]
32..40 -- Used for hidden services; see rend-spec.txt.
32..40 -- Used for hidden services; see rend-spec-{v2,v3}.txt.
Commands labelled as "forward" must only be sent by the originator
of the circuit. Commands labelled as "backward" must only be sent by
@ -1644,6 +1664,12 @@ see tor-design.pdf.
connection to its directory port. RELAY_BEGIN_DIR cells ignore exit
policy, since the stream is local to the Tor process.
Directory servers may be:
* authoritative directories (RELAY_BEGIN_DIR, usually non-anonymous),
* bridge authoritative directories (RELAY_BEGIN_DIR, anonymous),
* directory mirrors (RELAY_BEGIN_DIR, usually non-anonymous),
* onion service directories (RELAY_BEGIN_DIR, anonymous).
If the Tor relay is not running a directory service, it should respond
with a REASON_NOTDIRECTORY RELAY_END cell.
@ -1708,9 +1734,9 @@ see tor-design.pdf.
Because TCP connections can be half-open, we follow an equivalent
to TCP's FIN/FIN-ACK/ACK protocol to close streams.
An exit connection can have a TCP stream in one of three states:
'OPEN', 'DONE_PACKAGING', and 'DONE_DELIVERING'. For the purposes
of modeling transitions, we treat 'CLOSED' as a fourth state,
An exit (or onion service) connection can have a TCP stream in one of
three states: 'OPEN', 'DONE_PACKAGING', and 'DONE_DELIVERING'. For the
purposes of modeling transitions, we treat 'CLOSED' as a fourth state,
although connections in this state are not, in fact, tracked by the
onion router.