Checking all of these parameter lists for every single connection every second
seems like it could be an expensive waste.
Updating globally cached versions when there is a new consensus will still
allow us to apply consensus parameter updates to all existing connections
immediately.
This unifies CircuitIdleTimeout and PredictedCircsRelevanceTime into a single
option, and randomizes it.
It also gives us control over the default value as well as relay-to-relay
connection lifespan through the consensus.
Conflicts:
src/or/circuituse.c
src/or/config.c
src/or/main.c
src/test/testing_common.c
This defense will cause Cisco, Juniper, Fortinet, and other routers operating
in the default configuration to collapse netflow records that would normally
be split due to the 15 second flow idle timeout.
Collapsing these records should greatly reduce the utility of default netflow
data for correlation attacks, since all client-side records should become 30
minute chunks of total bytes sent/received, rather than creating multiple
separate records for every webpage load/ssh command interaction/XMPP chat/whatever
else happens to be inactive for more than 15 seconds.
The defense adds consensus parameters to govern the range of timeout values
for sending padding packets, as well as for keeping connections open.
The defense only sends padding when connections are otherwise inactive, and it
does not pad connections used solely for directory traffic at all. By default
it also doesn't pad inter-relay connections.
Statistics on the total padding in the last 24 hours are exported to the
extra-info descriptors.
