<s>
A	O
social	B-Application
VPN	I-Application
is	O
a	O
virtual	B-Application
private	I-Application
network	I-Application
that	O
is	O
created	O
among	O
individual	O
peers	O
,	O
automatically	O
,	O
based	O
on	O
relationships	O
established	O
by	O
them	O
through	O
a	O
social	O
networking	O
service	O
.	O
</s>
<s>
A	O
social	B-Application
VPN	I-Application
aims	O
at	O
providing	O
peer-to-peer	O
(	O
P2P	O
)	O
network	O
connectivity	O
between	O
a	O
user	O
and	O
his	O
or	O
her	O
friends	O
,	O
in	O
an	O
easy	O
to	O
set	O
up	O
manner	O
that	O
hides	O
from	O
the	O
users	O
the	O
complexity	O
in	O
setting	O
up	O
and	O
maintaining	O
authenticated/encrypted	O
end-to-end	O
VPN	B-Application
tunnels	O
.	O
</s>
<s>
An	O
architecture	O
of	O
a	O
social	B-Application
VPN	I-Application
is	O
based	O
on	O
a	O
centralized	O
infrastructure	O
where	O
users	O
authenticate	O
,	O
discover	O
their	O
friends	O
and	O
exchange	O
cryptographic	O
public	B-Application
keys	I-Application
,	O
and	O
a	O
P2P	B-Architecture
overlay	I-Architecture
which	O
is	O
used	O
to	O
route	O
messages	O
between	O
VPN	B-Application
endpoints	O
.	O
</s>
<s>
A	O
routed	O
VPN	B-Application
connection	O
across	O
the	O
Internet	O
logically	O
operates	O
as	O
a	O
dedicated	O
Wide	O
Area	O
Network	O
(	O
WAN	O
)	O
link	O
.	O
</s>
<s>
A	O
social	B-Application
VPN	I-Application
uses	O
a	O
virtual	B-General_Concept
network	I-General_Concept
interface	I-General_Concept
(	O
such	O
as	O
TUN/TAP	B-Protocol
devices	O
in	O
Windows	O
and	O
Unix	O
systems	O
)	O
to	O
capture	O
and	O
inject	O
IP	O
packets	O
from	O
a	O
host	O
.	O
</s>
<s>
Once	O
captured	O
,	O
packets	O
are	O
encrypted	O
,	O
encapsulated	O
,	O
and	O
routed	O
over	O
an	O
overlay	B-Architecture
network	I-Architecture
.	O
</s>
<s>
A	O
social	B-Application
VPN	I-Application
uses	O
online	O
social	O
networks	O
to	O
distribute	O
public	B-Application
keys	I-Application
and	O
advertise	O
node	O
address	O
to	O
friends	O
.	O
</s>
<s>
The	O
acquired	O
public	B-Application
keys	I-Application
are	O
used	O
to	O
establish	O
encrypted	O
communication	O
between	O
two	O
endpoints	O
.	O
</s>
<s>
Symmetric	O
keys	O
are	O
exchanged	O
during	O
the	O
process	O
of	O
establishing	O
an	O
end-to-end	O
link	O
by	O
two	O
social	B-Application
VPN	I-Application
peers	O
.	O
</s>
<s>
Routing	O
in	O
the	O
social	B-Application
VPN	I-Application
is	O
peer-to-peer	O
.	O
</s>
<s>
A	O
social	B-Application
VPN	I-Application
uses	O
dynamic	O
IP	O
address	O
assignment	O
and	O
translation	O
to	O
avoid	O
collision	O
with	O
existing	O
(	O
private	O
)	O
address	O
spaces	O
of	O
end	O
hosts	O
,	O
and	O
to	O
allow	O
the	O
system	O
to	O
scale	O
to	O
the	O
number	O
of	O
users	O
that	O
today	O
's	O
successful	O
online	O
social	O
network	O
services	O
serve	O
(	O
tens	O
of	O
millions	O
)	O
.	O
</s>
<s>
A	O
social	B-Application
VPN	I-Application
uses	O
names	O
derived	O
from	O
the	O
social	O
network	O
service	O
to	O
automatically	O
assign	O
host	O
names	O
to	O
endpoints	O
.	O
</s>
<s>
Hamachi	O
is	O
a	O
zero-configuration	O
VPN	B-Application
which	O
uses	O
a	O
security	O
architecture	O
different	O
from	O
that	O
of	O
social	B-Application
VPN	I-Application
.	O
</s>
<s>
The	O
leafnetworks	O
VPN	B-Application
also	O
supports	O
the	O
creation	O
of	O
networks	O
using	O
the	B-Application
Facebook	I-Application
API	O
.	O
</s>
<s>
An	O
open-source	O
social	B-Application
VPN	I-Application
implementation	O
based	O
on	O
the	B-Application
Facebook	I-Application
social	O
network	O
service	O
and	O
the	O
Brunet	O
P2P	B-Architecture
overlay	I-Architecture
is	O
available	O
for	O
Windows	O
and	O
Linux	O
systems	O
under	O
MIT	O
license	O
.	O
</s>
<s>
It	O
uses	O
the	O
P2P	B-Architecture
overlay	I-Architecture
to	O
create	O
direct	O
VPN	B-Application
connections	O
between	O
pairs	O
of	O
computers	O
(	O
nodes	O
)	O
.	O
</s>
<s>
To	O
establish	O
a	O
connection	O
,	O
two	O
nodes	O
advertise	O
their	O
P2P	O
node	O
address	O
(	O
as	O
well	O
as	O
public	B-Application
keys	I-Application
for	O
secure	O
communication	O
)	O
to	O
each	O
other	O
through	O
an	O
online	O
social	O
network	O
.	O
</s>
<s>
Once	O
each	O
node	O
acquires	O
the	O
node	O
address	O
(	O
and	O
public	B-Application
keys	I-Application
)	O
of	O
the	O
other	O
node	O
,	O
an	O
IP-to-nodeAddress	O
mapping	O
is	O
created	O
and	O
IP	O
packets	O
can	O
be	O
routed	O
through	O
the	O
VPN	B-Application
tunnel	O
.	O
</s>
