Commit 9265b52a authored by Nick Mathewson's avatar Nick Mathewson 🎨
Browse files

r15931@catbus: nickm | 2007-10-18 14:34:05 -0400

 Changes to proposal 105 based on recent or-dev exchange with sjmurdoch.


svn:r12031
parent fce82318
......@@ -120,11 +120,12 @@ Proposal:
When a Tor connection is established, both parties normally send a
VERSIONS cell before sending any other cells. (But see below.)
NumVersions [1 byte]
VersionsLen [1 byte]
Versions [NumVersions bytes]
"Versions" is a sequence of NumVersions link connection protocol versions,
each one byte long. Parties should list all of the versions which they
"Versions" is a sequence of NumVersions bytes. Each value between 1 and
127 inclusive represents a single version; current implementations MUST
ignore other bytes. Parties should list all of the versions which they
are able and willing to support. Parties can only communicate if they
have some connection protocol version in common.
......@@ -133,17 +134,23 @@ Proposal:
the other side has sent a VERSIONS cell won't work for these servers:
if the other side sends no cells back, it is impossible to tell
whether they
have sent a VERSIONS cell that has been stalled, or whether they have
dropped our own VERSIONS cell as unrecognized. Thus, immediately after
a TLS connection has been established, the parties check whether the
other side has an obsolete certificate (organizationName equal to "Tor"
or "TOR"). If the other party presented an obsolete certificate,
we assume a v1 connection. Otherwise, both parties send VERSIONS
cells listing all their supported versions. Upon receiving the
other party's VERSIONS cell, the implementation begins using the
highest-valued version common to both cells. If the first cell from
the other party has a recognized command, and is _not_ a VERSIONS cell, we
assume a v1 protocol.
dropped our own VERSIONS cell as unrecognized. Therefore, we'll
change the TLS negotiation parameters so that old parties can still
negotiate, but new parties can recognize each other. Immediately
after a TLS connection has been established, the parties check
whether the other side negotiated the connection in an "old" way or a
"new" way. If either party negotiated in the "old" way, we assume a
v1 connection. Otherwise, both parties send VERSIONS cells listing
all their supported versions. Upon receiving the other party's
VERSIONS cell, the implementation begins using the highest-valued
version common to both cells. If the first cell from the other party
has a recognized command, and is _not_ a VERSIONS cell, we assume a
v1 protocol.
(For more detail on the TLS protocol change, see forthcoming draft
proposals from Steven Murdoch.)
Implementations MUST discard VERSIONS cells that are not the first
recognized cells sent on a connection.
......@@ -159,8 +166,9 @@ Proposal:
A NETINFO cell contains:
Timestamp [4 bytes]
This OR's address [variable]
Other OR's address [variable]
Number of addresses [1 byte]
This OR's addresses [variable]
Timestamp is the OR's current Unix time, in seconds since the epoch. If
an implementation receives time values from many ORs that
......@@ -168,23 +176,32 @@ Proposal:
administrator. (We leave the definition of 'many' intentionally vague
for now.)
Before believing the timestamp in a NETINFO cell, implementations
SHOULD compare the time at which they received the cell to the time
when they sent their VERSIONS cell. If the difference is very large,
it is likely that the cell was delayed long enough that its
contents are out of date.
Each address contains Type/Length/Value as used in Section 6.4 of
tor-spec.txt. The first address is the address of the interface the
party sending the NETINFO cell
used to connect to or accept connections from the other -- we include it
tor-spec.txt. The first address is the one that the party sending
the NETINFO cell believes the other has -- it can be used to learn
what your IP address is if you have no other hints.
The rest of the addresses are the advertised addresses of the party
sending the NETINFO cell -- we include them
to block a man-in-the-middle attack on TLS that lets an attacker bounce
traffic through his own computers to enable timing and packet-counting
attacks.
The second address is the one that the party sending the NETINFO cell
believes the other has -- it can be used to learn what your IP address
is if you have no other hints.
If a party connects to an OR based on an EXTEND cell, and the address
given in the EXTEND cell is not listed in the NETINFO cell, the first
party SHOULD close the connection as a likely MITM attack.
Discussion: Versions versus feature lists
Many protocols negotiate lists of available features instead of (or in
addition to) protocol versions. While it's possible that some amount of
version negotiation could be supported in a later Tor, we should prefer to
feature negotiation could be supported in a later Tor, we should prefer to
use protocol versions whenever possible, for reasons discussed in
the "Anonymity Loves Company" paper.
......@@ -210,9 +227,14 @@ Discussion: Bytes per version, versions per cell
- Decide that if we need to support more versions, we can add a
MOREVERSIONS cell that gets sent before the VERSIONS cell. The spec
above requires Tors to ignore unrecognized cell types that they get
before the first VERSIONS cell, and still allows version negotiation to
before the first VERSIONS cell, and still allows version negotiation
to
succeed.
[Resolution: Reserve the high bit and the v0 value for later use. If
we ever have more live versions than we can fit in a cell, we've made a
bad design decision somewhere along the line.]
Discussion: Reducing round-trips
It might be appealing to see if we can cram more information in the
......@@ -266,7 +288,6 @@ Discussion: Advertising versions in routerdescs and networkstatuses.
unrecognized items; the protocols line should be preceded with an "opt"
until these Tors are obsolete.]
Security issues:
Client partitioning is the big danger when we introduce new versions; if a
......
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