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Re: [tor-bugs] #26122 [Obfuscation/Obfsproxy]: obfs4: remove byte threshold for disconnection (was: obfs4proxy: closeAfterDelay() should to conform to obfs4 spec)



#26122: obfs4: remove byte threshold for disconnection
-----------------------------------+-------------------------
 Reporter:  cypherpunks            |          Owner:  dcf
     Type:  enhancement            |         Status:  closed
 Priority:  Medium                 |      Milestone:
Component:  Obfuscation/Obfsproxy  |        Version:
 Severity:  Normal                 |     Resolution:  wontfix
 Keywords:                         |  Actual Points:
Parent ID:                         |         Points:
 Reviewer:                         |        Sponsor:
-----------------------------------+-------------------------
Changes (by dcf):

 * component:  Obfuscation/Censorship analysis => Obfuscation/Obfsproxy
 * type:  defect => enhancement


Old description:

> obfs4-spec.txt:
> > On the event of a failure at this point implementations SHOULD delay
> dropping the TCP connection from the client by a random interval to make
> active probing more difficult.
>
> closeAfterDelay() can to violate spec by closing connection immediately.

New description:

 As currently implemented, an obfs4 server disconnects an unauthenticated
 client after 8192–16383 received bytes or 30–90 seconds. (The exact values
 are chosen randomly from these ranges for each server.) The patch in
 comment:1 proposes to remove the byte threshold and keep the time
 threshold, as a mitigation against active-probing distinguishers such as
 the one in #26083.

 Original description:
 > obfs4-spec.txt:
 > > On the event of a failure at this point implementations SHOULD delay
 dropping the TCP connection from the client by a random interval to make
 active probing more difficult.
 >
 > closeAfterDelay() can to violate spec by closing connection immediately.

--

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26122#comment:5>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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