Netflow record collapsing defense.

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.

1 files changed, 25 insertions, 0 deletions

diff --git a/src/or/rephist.h b/src/or/rephist.h
index ff4810a56d..4d95bff0d0 100644
--- a/src/or/rephist.h
+++ b/src/or/rephist.h
@@ -119,5 +119,30 @@ extern int onion_handshakes_requested[MAX_ONION_HANDSHAKE_TYPE+1];
 extern int onion_handshakes_assigned[MAX_ONION_HANDSHAKE_TYPE+1];
 #endif
 
+/**
+ * Represents the type of a cell for padding accounting
+ */
+typedef enum padding_type_t {
+    /** A RELAY_DROP cell */
+    PADDING_TYPE_DROP,
+    /** A CELL_PADDING cell */
+    PADDING_TYPE_CELL,
+    /** Total counts of padding and non-padding together */
+    PADDING_TYPE_TOTAL,
+    /** Total cell counts for all padding-enabled channels */
+    PADDING_TYPE_ENABLED_TOTAL,
+    /** CELL_PADDING counts for all padding-enabled channels */
+    PADDING_TYPE_ENABLED_CELL
+} padding_type_t;
+
+/** The amount of time over which the padding cell counts were counted */
+#define REPHIST_CELL_PADDING_COUNTS_INTERVAL (24*60*60)
+void rep_hist_padding_count_read(padding_type_t type);
+void rep_hist_padding_count_write(padding_type_t type);
+char *rep_hist_get_padding_count_lines(void);
+void rep_hist_reset_padding_counts(void);
+void rep_hist_prep_published_padding_counts(time_t now);
+void rep_hist_padding_count_timers(uint64_t num_timers);
+
 #endif