commit 6136c48d95d3e6ffb1fef8c9f918038e5bcf6c9b Author: Karsten Loesing karsten.loesing@gmx.net Date: Sun Feb 13 21:24:40 2011 +0100

Add first version of bridge-db-spec.txt. --- bridge-db-spec.txt | 106 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 106 insertions(+), 0 deletions(-)

diff --git a/bridge-db-spec.txt b/bridge-db-spec.txt new file mode 100644 index 0000000..a9e2c8f --- /dev/null +++ b/bridge-db-spec.txt @@ -0,0 +1,106 @@ + + BridgeDB specification + +0. Preliminaries + + This document specifies how BridgeDB processes bridge descriptor files + to learn about new bridges, maintains persistent assignments of bridges + to distributors, and decides which descriptors to give out upon user + requests. + +1. Importing bridge network statuses and bridge descriptors + + BridgeDB learns about bridges from parsing bridge network statuses and + bridge descriptors as specified in Tor's directory protocol. BridgeDB + SHOULD parse one bridge network status file and at least one bridge + descriptor file. + +1.1. Parsing bridge network statuses + + Bridge network status documents contain the information which bridges + are known to the bridge authority at a certain time. We expect bridge + network statuses to contain at least the following two lines for every + bridge in the given order: + + "r" SP nickname SP identity SP digest SP publication SP IP SP ORPort SP + DirPort NL + "s" SP Flags NL + + BridgeDB parses the identity from the "r" line and scans the "s" line + for flags Stable and Running. BridgeDB MUST discard all bridges that + do not have the Running flag. BridgeDB MAY only consider bridges as + running that have the Running flag in the most recently parsed bridge + network status. BridgeDB MUST also discard all bridges for which it + does not find a bridge descriptor. BridgeDB memorizes all remaining + bridges as the set of running bridges that can be given out to bridge + users. +# I'm not 100% sure if BridgeDB discards (or rather doesn't use) bridges +# for which it doesn't have a bridge descriptor. But as far as I can see, +# it wouldn't learn the bridge's IP and OR port in that case, so we +# shouldn't use it. Is this a bug? -KL +# What's the reason for parsing bridge descriptors anyway? Can't we learn +# a bridge's IP address and OR port from the "r" line, too? -KL + +1.2. Parsing bridge descriptors + + BridgeDB learns about a bridge's most recent IP address and OR port + from parsing bridge descriptors. Bridge descriptor files MAY contain + one or more bridge descriptors. We expect bridge descriptor to contain + at least the following lines in the stated order: + + "@purpose" SP purpose NL + "router" SP nickname SP IP SP ORPort SP SOCKSPort SP DirPort NL + ["opt "] "fingerprint" SP fingerprint NL + + BridgeDB parses the purpose, IP, ORPort, and fingerprint. BridgeDB + MUST discard bridge descriptors if the fingerprint is not contained in + the bridge network status(es) parsed in the same execution or if the + bridge does not have the Running flag. BridgeDB MAY discard bridge + descriptors which have a different purpose than "bridge". BridgeDB + memorizes the IP addresses and OR ports of the remaining bridges. If + there is more than one bridge descriptor with the same fingerprint, + BridgeDB memorizes the IP address and OR port of the most recently + parsed bridge descriptor. +# I think that BridgeDB simply assumes that descriptors in the bridge +# descriptor files are in chronological order. If not, it would overwrite +# a bridge's IP address and OR port with an older descriptor, which would +# be bad. The current cached-descriptors* files should write descriptors +# in chronological order. But we might change that, e.g., when trying to +# limit the number of descriptors in Tor. Should we make the assumption +# that descriptors are ordered chronologically, or should we specify that +# we have to check that explicitly? -KL + +2. Assigning bridges to distributors + +# In this section I'm planning to write how BridgeDB should decide to +# which distributor (https, email, unallocated/file bucket) it assigns a +# new bridge. I should also write down whether BridgeDB changes +# assignments of already known bridges (I think it doesn't). The latter +# includes cases when we increase/reduce the probability of bridges being +# assigned to a distributor or even turn off a distributor completely. +# -KL + +3. Selecting bridges to be given out via https + +# This section is about the specifics of the https distributor, like which +# IP addresses get bridges from the same ring, how often the results +# change, etc. -KL + +4. Selecting bridges to be given out via email + +# This section is about the specifics of the email distributor, like which +# characters do we recognize in email addresses, how long we don't give +# out new bridges to the same email address, etc. -KL + +5. Selecting unallocated bridges to be stored in file buckets + +# This section is about kaner's bucket mechanism. I want to cover how +# BridgeDB decides which of the unallocated bridges to add to a file +# bucket. -KL +# I'm not sure if there's a design bug in file buckets. What happens if +# we add a bridge X to file bucket A, and X goes offline? We would add +# another bridge Y to file bucket A. OK, but what if A comes back? We +# cannot put it back in file bucket A, because it's full. Are we going to +# add it to a different file bucket? Doesn't that mean that most bridges +# will be contained in most file buckets over time? -KL +