[tor-dev] Proposal 222: Stop sending client timestamps
desnacked at riseup.net
Thu Aug 22 16:33:02 UTC 2013
Nick Mathewson <nickm at 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
> 0. Summary
> There are a few places in Tor where clients and servers send
> timestamps. I list them and discuss how to eliminate them.
> 1. Introduction
> Despite this late date, many hosts aren't running NTP and
> 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.
how does the client verify the contents of the AUTHENTICATE cell
(including the timestamp), if the timestamp is encrypted with a random
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