[tor-bugs] #12930 [Obfuscation/Pluggable transport]: Someone, somewhere needs to unescape pluggable transport "SMETHOD ARGS" arguments.

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#12930: Someone, somewhere needs to unescape pluggable transport "SMETHOD ARGS"
arguments.
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 Reporter:  yawning                          |          Owner:  asn
     Type:  defect                           |         Status:  new
 Priority:  Medium                           |      Milestone:
Component:  Obfuscation/Pluggable transport  |        Version:
 Severity:  Normal                           |     Resolution:
 Keywords:  goptlib                          |  Actual Points:
Parent ID:                                   |         Points:
 Reviewer:                                   |        Sponsor:
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Comment (by catalyst):

 If there are to be any code changes, they should probably be in the
 BridgeDB implementation and maybe the pluggable transport client of `tor`.
 I like the idea of using something like Bourne shell variable syntax,
 e.g., `a=b=c` sets `$a` to the string  `b=c`. Variable (key) names may not
 contain `=` but values may, without needing quoting or escaping.  I know
 obfs4 worked around the `=` escaping problem by using unpadded base64, but
 could other transports need `=` in argument values in the future? (maybe
 as query parameters to URLs?)

 Here's how I understand the existing data flow:
 1.  `SMETHOD ARGS`
  - comma-separated key=value pairs
  - `,` and `=` (but not `\` -- at least not consistently, e.g. goptlib)
 escaped by `\` ([https://gitweb.torproject.org/torspec.git/tree/pt-
 spec.txt#n566 pt-spec.txt#n566])
  - no provision for escaping whitespace
 2. `transport` lines in `extra-info`
  - comma-separated key=value pairs
 ([https://gitweb.torproject.org/torspec.git/tree/bridgedb-spec.txt#n113
 bridgedb-spec.txt#n113])
  - no specification for escaping any characters
  - apparently copied unchanged from `SMETHOD ARGS`
 ([https://gitweb.torproject.org/tor.git/tree/src/or/transports.c#n1624
 transports.c#n1624]) apart from deleting the `ARGS:` prefix.
 3. BridgeDB (as output to users)
  - space-separated key=value pairs
 ([https://gitweb.torproject.org/torspec.git/tree/bridgedb-spec.txt#n350
 bridgedb-spec.txt#n350])
  - no specification for escaping any characters
 4. `Bridge` line in `torrc` or Tor Browser config dialog
  - space-separated key=value pairs
  - no specification for escaping any characters
 5. encoded in SOCKS username/password
  - semicolon-separated key=value pairs
  - `;`, `=`, and `\` escaped by `\`
 ([https://gitweb.torproject.org/torspec.git/tree/pt-spec.txt#n638 pt-
 spec.txt#n638])
  - currently, `transports.c` doesn't escape `=`, contrary to spec
 ([https://gitweb.torproject.org/tor.git/tree/src/or/transports.c#n1668
 transports.c#n1668])
  - on the other hand,
 [https://gitweb.torproject.org/torspec.git/tree/proposals/180-pluggable-
 transport.txt#n157 180-pluggable-transport.txt#n157] doesn't specify
 escaping of `=` when sending to the transport's SOCKS proxy, so maybe this
 can remain unchanged

 Proposed spec changes will go in a separate ticket.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/12930#comment:10>
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