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some patches on nick's commit
svn:r177
This commit is contained in:
Roger Dingledine
parent
4feda4f5d3
commit
eaf60d09a6
77
tor-spec.txt
77
tor-spec.txt
@ -222,7 +222,7 @@ which reveals the downstream node.
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3. Cell Packet format
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The basic unit of communication between onion routers and onion
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The basic unit of communication for onion routers and onion
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proxies is a fixed-width "Cell." Each Cell contains the following
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fields:
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@ -242,10 +242,10 @@ which reveals the downstream node.
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The interpretation of 'Length' and 'Payload' depend on the type of
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the cell.
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PADDING: Length is 0; Payload is 128 bytes of 0's.
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PADDING: Length is 0; Payload is 120 bytes of 0's.
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CREATE: Length is a value between 1 and 120; the first 'length'
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bytes or payload contain a portion of an onion.
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DATA: Length is a value between 4 [5?] and 120; the first 'length'
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bytes of payload contain a portion of an onion.
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DATA: Length is a value between 4 and 120; the first 'length'
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bytes of payload contain useful data.
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DESTROY: Neither field is used.
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SENDME: Length encodes a window size, payload is unused.
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@ -281,10 +281,12 @@ which reveals the downstream node.
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Key seed material [16 bytes]
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[Total: 28 bytes]
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The value of Version is currently 2.
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The forward and backward ciphers fields can take the following values:
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0: Identity
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1: Single DES in OFB
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2: RC4
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2: RC4
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The port and address field denote the IPV4 address and port of
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the next onion router in the circuit, or are set to 0 for the
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@ -294,8 +296,6 @@ which reveals the downstream node.
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Jan 1970); by default, it is set to the current time plus one
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day.
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The value of OR_VERSION is currently 2.
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When constructing an onion to create a circuit from OR_1,
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OR_2... OR_N, the onion creator performs the following steps:
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@ -305,7 +305,7 @@ which reveals the downstream node.
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A. Create an onion layer L, setting Version=2,
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BackCipher=DES/OFB(1), ForwardCipher=DES/OFB(2),
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ExpirationTime=now + 1 day, and Seed=16 random bytes.
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ExpirationTime=now + 1 day, and Seed=16 random bytes.
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If I=N, set Port=Address=0. Else, set Port and Address to
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the IPV4 port and address of OR_{I+1}.
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@ -330,7 +330,8 @@ which reveals the downstream node.
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2. Choose an ACI not already in use on the connection with the
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first router in the chain. If our address/port pair is
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numerically higher than the
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numerically higher than the address/port pair of the other
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side, then let the high bit of the ACI be 1, else 0.
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3. To send M over the wire, prepend a 4-byte integer containing
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Len(M). Call the result M'. Let N=ceil(Len(M')/120).
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@ -350,9 +351,9 @@ which reveals the downstream node.
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with this ACI, drop the cell.
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Otherwise, if we have no circuit along this connection with
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this ACI, let L = the integer value of the first 4 bytes of
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this ACI, let L = the integer value of the first 4 bytes of
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the payload. Create a half-open circuit with this ACI, and
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begin queueing CREATE cells for this circuit.
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begin queueing CREATE cells for this circuit.
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Otherwise, we have a half-open circuit. If the total
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payload length of the CREATE cells for this circuit is at
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@ -362,15 +363,14 @@ which reveals the downstream node.
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2. Once we have a complete onion, decrypt the first 128 bytes
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of the onion with this OR's RSA private key, and extract
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the outmost onion layer. If the version, back cipher, or
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forward cipher is unrecognized, drop the onion [XXXX then
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what? -NM]. If the expiration time is in the past, then
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drop the onion [XXXX then what? -NM].
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forward cipher is unrecognized, or the expiration time is
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in the past, then tear down the circuit (see section 4.2).
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Compute K1 through K3 as above. Use K1 to decrypt the rest
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of the onion using DES/OFB.
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If we are not the exit node, remove the first layer from the
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decrypted onion, and send it the remainder to the next OR
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decrypted onion, and send the remainder to the next OR
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on the circuit, as specified above. (Note that we'll
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choose a different ACI for this circuit on the connection
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with the next OR.)
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@ -382,16 +382,17 @@ which reveals the downstream node.
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4.2. Tearing down circuits
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Circuits are torn down when an unrecoverable error occurs along
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the circuit, when all topics on a circuit are closed and the
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circuit's intended lifetime is over, or when (.... ?).
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the circuit, or when all topics on a circuit are closed and the
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circuit's intended lifetime is over.
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To tear down a circuit, an OR or OP sends a DESTROY cell with that
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circuit's ACI to every adjacent node on that circuit.
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direction's ACI to the adjacent nodes on that circuit.
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Upon receiving a DESTROY cell, an OR frees resources associated
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with the corresponding circuit, and (if not the start or end of the
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circuit) sends a DESTROY cell for that circuit to the next OR in
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the circuit.
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with the corresponding circuit. If it's not the start or end of the
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circuit, it sends a DESTROY cell for that circuit to the next OR in
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the circuit. If the node is the start or end of the circuit, then
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it tears down any associated edge connections (see section 5.1).
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After a DESTROY cell has been processed, an OR ignores all data or
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destroy cells for the corresponding circuit.
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@ -402,24 +403,24 @@ which reveals the downstream node.
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determines whether it has a corresponding circuit along that
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connection. If not, the OR drops the DATA cell.
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Otherwise, if the OR is not at the edge of the circuit, it
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de/encrypts the length field and the payload with DES/OFB, as
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follows:
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Otherwise, if the OR is not at the OP edge of the circuit (that is,
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either an 'exit node' or a non-edge node), it de/encrypts the length
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field and the payload with DES/OFB, as follows:
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'Forward' data cell (same direction as onion):
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Use K2 as key; encrypt.
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'Back' data cell (opposite direction from onion):
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Use K3 as key; decrypt.
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Otherwise, the OR is at the edge of the circuit, and it generates
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and processes the length and payload fields of DATA cells as
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described in section 5 below. (To encrypt or decrypt DATA cells,
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the OP node de/encrypts the length and payload fields with DES/OFB as
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Otherwise, if the data cell has arrived to the OP edge of the circuit,
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the OP de/encrypts the length and payload fields with DES/OFB as
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follows:
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OP sends data cell:
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For I=1...N, decrypt with K2_I.
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For I=1...N, decrypt with K2_I.
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OP receives data cell:
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For I=N...1, encrypt with K3_I
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)
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For I=N...1, encrypt with K3_I.
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Edge nodes process the length and payload fields of DATA cells as
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described in section 5 below.
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5. Application connections and topic management
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@ -432,14 +433,14 @@ which reveals the downstream node.
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The first 4 bytes of each data cell are reserved as follows:
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Topic command [1 byte]
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Unused, set to 0. [1 byte]
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Topic ID [2 bytes]
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Topic ID [2 bytes]
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The recognized topic commands are:
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1 -- TOPIC_BEGIN
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2 -- TOPIC_DATA
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3 -- TOPIC_END
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4 -- TOPIC_CONNECTED
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5 -- TOPIC_SENDME
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2 -- TOPIC_DATA
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3 -- TOPIC_END
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4 -- TOPIC_CONNECTED
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5 -- TOPIC_SENDME
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All DATA cells pertaining to the same tunneled connection have the
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same topic ID.
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@ -447,7 +448,7 @@ which reveals the downstream node.
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To create a new anonymized TCP connection, the OP sends a
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TOPIC_BEGIN data cell with a payload encoding the address and port
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of the destination host. The payload format is:
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ADDRESS ',' PORT '\000'
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ADDRESS | ',' | PORT | '\000'
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where ADDRESS may be a DNS hostname, or an IPv4 address in
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dotted-quad format; and where PORT is encoded in decimal.
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@ -502,7 +503,7 @@ which reveals the downstream node.
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how many cells it is allowed to send to the next hop in the circuit
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before queueing cells. This 'window' value is initially set to
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1000 cells in each direction. Each edge node on a circuit sends a
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SENDME cell (with length=100) every time it has receives 100 cells
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SENDME cell (with length=100) every time it has received 100 cells
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on the circuit. When a node receives a SENDME cell for a circuit,
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it increases the circuit's window in the corresponding by the value
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of the cell's length field, and (if not an edge node) passes an
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