(Forwarding this mail to tor-dev, since I accidentally sent it to tor-assistants)
Hey Philipp,
another thing we should think about is what should happen when ScrambleSuit is run in bridges that don't support server-side PT parameters.
In the past this was not a problem, because ScrambleSuit would not run at all in those older versions of Tor. However, after we introduced the automatic generation of scramblesuit fallback passwords, scramblesuit will happily startup, generate a fallback password, and pass it to Tor. The problem is that Tor will simply ignore the fallback password (see parse_smethod_line() in tor-0.2.4.x), but still pass the scramblesuit bridge to BridgeDB.
So if I'm not mistaken, BridgeDB might see some scramblesuit bridges without a password. Such bridges are pretty much useless, since clients can't connect to them.
What should we do about this?
One solution might involve scramblesuit somehow recognizing the version of Tor, and refusing to start if Tor doesn't support server-side bridge parameters.