Nick Mathewson nickm@torproject.org writes:
Filename: 222-remove-client-timestamps.txt Title: Stop sending client timestamps Authors: Nick Mathewson Created: 22 August 2013 Target: 0.2.5.x Status: Open
Summary
There are a few places in Tor where clients and servers send timestamps. I list them and discuss how to eliminate them.
Introduction
Despite this late date, many hosts aren't running NTP and
<snipage>
field, so this change should be safe.
2.2. AUTHENTICATE (server)
The AUTHENTICATE cell is not ordinarily sent by clients. It contains an 8-byte timestamp and a 16-byte random value. Instead, let's replace both with a 24-byte (truncated) HMAC of the current time, using a random key.
This will achieve the goal of including a timestamp in the cell (preventing replays even in the presence of bad entropy), while at the same time not including the time here.
Hey Nick,
how does the client verify the contents of the AUTHENTICATE cell (including the timestamp), if the timestamp is encrypted with a random key?