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Comment by detaro

13 hours ago

What privacy concern do you have that does not apply to TCP 80/443?

Tracking sessions across different physical connections has some non-trivial privacy implications:

https://http3-explained.haxx.se/en/quic/quic-connections#con...

  • How do you imagine other protocols handle switching physical connections? With HTTP 1, you send your session ID as a cookie after wasting time creating a new TCP connection

    • Yes, obviously, but we already know how that is used. This is a more complex protocol that might enable attack vectors that were not possible before and we do not think about when accessing websites:

      But see the notes taken from the HTTP/3 RFC itself, written by the authors:

      10.11. Privacy Considerations

         Several characteristics of HTTP/3 provide an observer an opportunity
         to correlate actions of a single client or server over time.  These
         include the value of settings, the timing of reactions to stimulus,
         and the handling of any features that are controlled by settings.
      
         As far as these create observable differences in behavior, they could
         be used as a basis for fingerprinting a specific client.
      
         HTTP/3's preference for using a single QUIC connection allows
         correlation of a user's activity on a site.  Reusing connections for
         different origins allows for correlation of activity across those
         origins.
      
         Several features of QUIC solicit immediate responses and can be used
         by an endpoint to measure latency to their peer; this might have
         privacy implications in certain scenarios.