149-using-netinfo-data.txt 1.5 KB

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  1. Filename: 149-using-netinfo-data.txt
  2. Title: Using data from NETINFO cells
  3. Author: Nick Mathewson
  4. Created: 2-Jul-2008
  5. Status: Open
  6. Target: 0.2.1.x
  7. Overview
  8. Current Tor versions send signed IP and timestamp information in
  9. NETINFO cells, but don't use them to their fullest. This proposal
  10. describes how they should start using this info in 0.2.1.x.
  11. Motivation
  12. Our directory system relies on clients and routers having
  13. reasonably accurate clocks to detect replayed directory info, and
  14. to set accurate timestamps on directory info they publish
  15. themselves. NETINFO cells contain timestamps.
  16. Also, the directory system relies on routers having a reasonable
  17. idea of their own IP addresses, so they can publish correct
  18. descriptors. This is also in NETINFO cells.
  19. Learning the time and IP address
  20. We need to think about attackers here. Just because a router tells
  21. us that we have a given IP or a given clock skew doesn't mean that
  22. it's true. We believe this information only if we've heard it from
  23. a majority of the routers we've connected to recently, including at
  24. least 3 routers. Routers only believe this information if the
  25. majority includes at least one authority.
  26. Avoiding MITM attacks
  27. Current Tors use the IP addresses published in the other router's
  28. NETINFO cells to see whether the connection is "canonical". Right
  29. now, we prefer to extend circuits over "canonical" connections. In
  30. 0.2.1.x, we should refuse to extend circuits over non-canonical
  31. connections without first trying to build a canonical one.