[tor-bugs] #19317 [Metrics/CollecTor]: Sanitize TCP ports in bridge descriptors

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#19317: Sanitize TCP ports in bridge descriptors
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 Reporter:  karsten            |          Owner:
     Type:  enhancement        |         Status:  new
 Priority:  Medium             |      Milestone:
Component:  Metrics/CollecTor  |        Version:
 Severity:  Normal             |     Resolution:
 Keywords:                     |  Actual Points:
Parent ID:                     |         Points:
 Reviewer:                     |        Sponsor:
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Comment (by karsten):

 Huh, good point, didn't think of that.  How about we make the following
 two changes, one related to your suggestion and one unrelated?

  - Take out the `% 65535 + 1` part to make this calculation a little less
 complicated, at the risk of accidentally changing 1 in 2^16^ ports to 0.
  - Add clarifying sentence: "All calculations assume that inputs and
 outputs are in network byte order."  Does that make sense, or is there a
 better sentence to add here?  (We'll want to add a similar sentence to the
 IP address sanitizing part.)

 New paragraph would be:

  - Each non-zero TCP port is replaced with `H(port | bridge identity |
 secret)[:2]` written as decimal number.  The input `port` is the 2-byte
 long binary representation of the TCP port.  The `bridge identity` is the
 20-byte long binary representation of the bridge's long-term identity
 fingerprint.  The `secret` is a 33-byte long secure random string that
 changes once per month for all descriptors and statuses published in that
 month.  `H()` is SHA-256.  The `[:2]` operator means that we pick the 2
 most significant bytes of the result.  All operations assume network byte
 order for their inputs and outputs.  TCP ports that are 0 in the original
 descriptor are left unchanged.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/19317#comment:2>
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