[tor-bugs] #17242 [Tor]: Implement client and service support for proposal 224

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#17242: Implement client and service support for proposal 224
-------------------------+------------------------------
 Reporter:  dgoulet      |          Owner:
     Type:  enhancement  |         Status:  new
 Priority:  Medium       |      Milestone:  Tor: 0.2.???
Component:  Tor          |        Version:
 Severity:  Normal       |     Resolution:
 Keywords:  tor-hs       |  Actual Points:
Parent ID:  #12424       |         Points:  large
  Sponsor:               |
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Comment (by asn):

 Some notes from the vault:

 - What happens when prop250 gets deployed, but maybe enough dirauths are
 down so that the consensus does not have a shared random value? You can
 find
 [https://gitweb.torproject.org/user/asn/torspec.git/commit/?h=prop250_final_v1&id=0e3af7a31a073f69a9bd537eebc1cc64216d2ca0
 here] a small patch for prop224 that defines how clients should do
 disaster recovery when there is no shared random value in the consensus.

 - Also, in the case the Shared Random Value system screws up and causes
 reachability issues for clients and HSes, we should maybe introduce a
 consensus parameter `ProbabilisticHSDirSelection` that dirauths can set to
 off and then clients will fallback to the current HSDir selection
 procedure which does not require any SRVs. We could do this for a day or
 three, till we fix the SRV bug.

 - Finally we still have not decided on the encoding of prop224 hidden
 service addresses. There have been many suggestions like using the base58
 encoding or the zkey encoding from GNS. Also, about chunking up the
 address to 5-char blocks. Also, about using some bytes of the address for
 metadata like Bitcoin is doing (for example, checksum, or to denote the
 security level of hidden services). Currently we have 3 free bits on the
 hidden service address, but we could also just expand the address by a
 byte or two to add more information if we feel it's helpful.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17242#comment:10>
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