[tor-bugs] #19998 [Core Tor/Tor]: Stop allowing 3DES in TLS ciphersuites

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#19998: Stop allowing 3DES in TLS ciphersuites
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     Reporter:  nickm         |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.2.9.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:  .2            |   Reviewer:
      Sponsor:                |
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 Thanks to the SWEET32 attack, 3des is getting lots of attention.

 Right now, Tor is willing in principle to negotiate a 3DES TLS connection.

 But the good news is (I think) that two non-obsolete Tor instances will
 never actually do so. Here is my reasoning:
    * Our source code has always preferred AES to 3DES. So the only way to
 get 3DES would be if one party didn't support AES.
    * OpenSSL began supporting AES in version 0.9.7.
    * Tor has required OpenSSL 0.9.7 or later since 7da93b80ca7a6ba , which
 was in 0.2.0.10-alpha.

 So this cipher shouldn't get negotiated, unless you're doing something
 very very weird.

 I suggest that the best fix is to stop servers from ever choosing it.

 I suggest that as an additional fix, clients should reject a connection to
 any server that  _does_ choose it.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/19998>
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