[Bug 39544] New: Prefer stream ciphers over blocks ones

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=39544

           Summary: Prefer stream ciphers over blocks ones
           Product: Wocky
           Version: git master
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: General
        AssignedTo: telepathy-bugs at lists.freedesktop.org
        ReportedBy: marco.barisione at collabora.co.uk
         QAContact: telepathy-bugs at lists.freedesktop.org


On cellular networks there is a big difference in power consumption if packets
(including the TCP and IP overhead) are smaller than about 125 bytes. See
http://xmpp.org/extensions/xep-0286.html#sect-id152122 for details.
Making sure that the activity due to keepalives only uses the low power FACH
channel means we can visibly increase the battery life of phones.

Usually I would say it's ridiculous to do anything to save just a few bytes,
but, considering how cellular networks work, switching to a stream ciphers
could help with smaller packets.
I took some measurements:
- AES-128-CBC: the packet is always bigger than 125 bytes.
- ARCFOUR-128 with XMPP pings: the packet is 92 bytes. To big when we also
  consider TCP and IP overhead.
- ARCFOUR-128 with whitespace pings: 26 bytes.

So using RC4 + whitespace pings (see bug #39543) would make us use the FACH
channel for keepalive pings.

We could always prefer RC4 over AES-128-CBC, but RC4 is less secure (it's easy
to crack if you get a lot of data).
>From a performance point of view (both CPU and memory), I'm not sure if there
is any significant difference.

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