<s>
VTun	B-Application
is	O
a	O
networking	O
application	O
which	O
can	O
set	O
up	O
Virtual	O
Tunnels	O
over	O
TCP/IP	B-Protocol
networks	I-Protocol
.	O
</s>
<s>
It	O
supports	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
,	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
(	O
PPP	O
)	O
and	O
Serial	B-Protocol
Line	I-Protocol
Internet	I-Protocol
Protocol	I-Protocol
(	O
SLIP	O
)	O
protocols	O
.	O
</s>
<s>
It	O
exists	O
as	O
the	O
reference	O
implementation	O
of	O
the	O
Tun/Tap	B-Protocol
user-space	O
tunnel	O
driver	O
which	O
was	O
included	O
in	O
the	O
Linux	B-Application
kernel	B-Operating_System
as	O
of	O
version	O
2.4	O
,	O
also	O
originally	O
developed	O
by	O
Maxim	O
Krasnyansky	O
.	O
</s>
<s>
Like	O
most	O
other	O
applications	O
of	O
its	O
nature	O
,	O
VTun	B-Application
creates	O
a	O
single	O
connection	O
between	O
two	O
machines	O
,	O
over	O
which	O
it	O
multiplexes	O
all	O
traffic	O
.	O
</s>
<s>
VTun	B-Application
connections	O
are	O
initiated	O
via	O
a	O
TCP	O
connection	O
from	O
the	O
client	O
to	O
the	O
server	O
.	O
</s>
<s>
VTun	B-Application
uses	O
a	O
Private	O
Shared	O
Key	O
to	O
negotiate	O
a	O
handshake	O
via	O
a	O
challenge	O
and	O
response	O
.	O
</s>
<s>
A	O
continual	O
source	O
of	O
concern	O
,	O
and	O
the	O
target	O
of	O
more	O
than	O
one	O
strongly	O
worded	O
security	O
assessment	O
,	O
is	O
that	O
the	O
VTun	B-Application
server	O
and	O
client	O
binary	O
applications	O
can	O
be	O
completely	O
built	O
without	O
encryption	O
support	O
.	O
</s>
<s>
When	O
such	O
binaries	O
are	O
used	O
,	O
the	O
encryption	O
between	O
both	O
endpoints	O
is	O
only	O
a	O
simple	B-Algorithm
XOR	I-Algorithm
cipher	I-Algorithm
,	O
which	O
is	O
completely	O
trivial	O
to	O
decode	O
.	O
</s>
