Defend against entry node path bias attacks

The defense counts the circuit failure rate for each guard for the past N
circuits. Failure is defined as the ability to complete a first hop, but not
finish completing the circuit all the way to the exit.

If the failure rate exceeds a certain amount, a notice is emitted.

If it exceeds a greater amount, a warn is emitted and the guard is disabled.

These values are governed by consensus parameters which we intend to tune as
we perform experiments and statistical simulations.

1 files changed, 11 insertions, 0 deletions

diff --git a/src/or/or.h b/src/or/or.h
index 7ff628411a..3a53e5ed86 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -3550,6 +3550,17 @@ typedef struct {
    * control ports. */
   int DisableNetwork;
 
+  /**
+   * Parameters for path-bias detection.
+   * @{
+   */
+  int PathBiasCircThreshold;
+  double PathBiasNoticeRate;
+  double PathBiasDisableRate;
+  int PathBiasScaleThreshold;
+  int PathBiasScaleFactor;
+  /** @} */
+
 } or_options_t;
 
 /** Persistent state for an onion router, as saved to disk. */