Hi everyone,
I’ve been doing research to see how some of the pluggable transports are
getting blocked with DPI. I used a Cyberoam filter under my control for
testing, and an iBoss filter at a different location.
OBFS4 is blocked behind both filters. Cyberoam is doing some sort of timing
attack, but I’m not sure what. When a bridge is used by lots of people, then it
doesn’t work. Even enabling Iat mode=1 or 2 doesn’t fix the issue. When I tried
a bridge with not many users, it worked no matter what Iat mode was set at.
Behind iBoss, they are fingerprinting Packet Interarrival times. Iat mode 1 and
2 worked no matter how much load the bridges had on them.
Hopefully this information can help people understand a little more about how
these transports are filtered.
Thanks,
Justin.
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