tor/changes/feature4900

  o Minor features:

    - Avoid hash-flooding denial-of-service attacks by using the secure
      SipHash-2-4 hash function for our hashtables.  Without this
      feature, an attacker could degrade performance of a targeted
      client or server by flooding their data structures with a large
      number of data entries all calculated to be stored at the same
      hash table position, thereby degrading hash table
      performance. With this feature, hash table positions are derived
      from a randomized cryptographic key using SipHash-2-4, and an
      attacker cannot predict which entries will collide.
      Closes ticket 4900.