[tor-bugs] #26083 [Obfuscation/Obfsproxy]: Bridge detector. Fake?

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#26083: Bridge detector. Fake?
-----------------------------------+---------------------
 Reporter:  cypherpunks            |          Owner:  asn
     Type:  defect                 |         Status:  new
 Priority:  Medium                 |      Milestone:
Component:  Obfuscation/Obfsproxy  |        Version:
 Severity:  Normal                 |     Resolution:
 Keywords:                         |  Actual Points:
Parent ID:                         |         Points:
 Reviewer:                         |        Sponsor:
-----------------------------------+---------------------

Comment (by cypherpunks):

 Here's the code in case Pastebin or someone else deletes it with a DMCA,

 {{{
 #!text/x-python
 import os
 import socks
 import socket
 import sys
 import time

 obfs4_detected = 0

 host =  sys.argv[1]
 port = int(sys.argv[2])
 print "Wait for 100 sec. Verify target: " +host, port
 s = socks.socksocket()
 s.set_proxy(socks.SOCKS5, "127.0.0.1", 9150)
 s.connect((host, port))
 rand_string = os.urandom(16384)
 s.send(rand_string)
 s.settimeout(15)
 try:
  data = s.recv(16384)
  if data == "":
   obfs4_detected = 1

 except socket.timeout:
  obfs4_detected = 0

 s.close()

 if obfs4_detected == 1:
  s = socks.socksocket()
  s.set_proxy(socks.SOCKS5, "127.0.0.1", 9150)
  s.connect((host, port))

  rand_string = os.urandom(8191)
  s.send(rand_string)
  start = time.time()
  s.settimeout(95)
  try:
   data = s.recv(16384)
   if data == "":
    end = time.time()
    delta = end - start
    if delta >= 29:
     obfs4_detected = 1

  except socket.timeout:
   obfs4_detected = 0

  s.close()

 if obfs4_detected:
  print "DETECTED!!!!!111"
 else:
  print "NOT OBFS4?"
 }}}

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26083#comment:2>
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