Filename: 098-todo.txt
Title: Proposals that should be written
Version: $Revision$
Last-Modified: $Date$
Author: Nick Mathewson, Roger Dingledine
Created: 26-Jan-2007
Status: Meta

Overview:

   This document lists ideas that various people have had for improving the
   Tor protocol.  These should be implemented and specified if they're
   trivial, or written up as proposals if they're not.

   This is an active document, to be edited as proposals are written and as
   we come up with new ideas for proposals.  We should take stuff out as it
   seems irrelevant.


For protocol version 2:

  - Fix onionskin handshake scheme to be more mainstream, less nutty.
    Can we just do
        E(HMAC(g^x), g^x) rather than just E(g^x) ?
    No, that has the same flaws as before. We should send
        E(g^x, C) with random C and expect g^y, HMAC_C(K=g^xy).
    Better ask Ian; probably Stephen too.
  - Versioned CREATE and friends
  - Length on CREATE and friends
  - Versioning on circuits
  - Versioning on create cells
  - SHA1 is showing its age
  - Not being able to upgrade ciphersuites or increase key lengths is
    lame.
  - Paul has some ideas about circuit creation; read his PET paper once it's
    out.
  - Allow more TLS ciphersuites.

Any time:

  - Some ideas for revising the directory protocol:
    - Should we also look into a "delta since last network-status
      checkpoint" scheme, to reduce overhead further?
    - Extend the "r" line in network-status to give a set of buckets (say,
      comma-separated) for that router.
      - Buckets are deterministic based on IP address.
      - Then clients can choose a bucket (or set of buckets) to
        download and use.
    - We need a way for the authorities to declare that nodes are in a
      family.  Also, it kinda sucks that family declarations use O(N^2) space
      in the descriptors.
  - REASON_CONNECTFAILED should include an IP.
  - Spec should incorporate some prose from tor-design to be more readable.
  - Spec when we should rotate which keys
  - Spec how to publish descriptors less often
  - Describe pros and cons of non-deterministic path lengths
  - get rid of the Named flag, or automate it at the dir auth end,
    or automate it at the client end, or something.

  - We should use a variable-length path length by default -- 3 +/- some
    distribution. Need to think harder about allowing values less than 3,
    and there's a tradeoff between having a wide variance and performance.

Things that should change...

B.1. ... but which will require backward-incompatible change

  - Circuit IDs should be longer.
  - IPv6 everywhere.
  - Maybe, keys should be longer.
    - Maybe, key-length should be adjustable.  How to do this without
      making anonymity suck?
  - Drop backward compatibility.
  - We should use a 128-bit subgroup of our DH prime.
  - Handshake should use HMAC.
  - Multiple cell lengths.
  - Ability to split circuits across paths (If this is useful.)
  - SENDME windows should be dynamic.

  - Directory
     - Stop ever mentioning socks ports

B.1. ... and that will require no changes

   - Mention multiple addr/port combos
   - Advertised outbound IP?
   - Migrate streams across circuits.

B.2. ... and that we have no idea how to do.

   - UDP (as transport)
   - UDP (as content)
   - Use a better AES mode that has built-in integrity checking,
     doesn't grow with the number of hops, is not patented, and
     is implemented and maintained by smart people.

Let onion keys be not just RSA but maybe DH too, for Paul's reply onion
design.

