<s>
Obfuscated	B-Protocol
TCP	I-Protocol
(	O
ObsTCP	B-Protocol
)	O
was	O
a	O
proposal	O
for	O
a	O
transport	B-Architecture
layer	I-Architecture
protocol	O
which	O
implements	O
opportunistic	B-Protocol
encryption	I-Protocol
over	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
.	O
</s>
<s>
It	O
was	O
designed	O
to	O
prevent	O
mass	O
wiretapping	O
and	O
malicious	O
corruption	O
of	O
TCP	O
traffic	O
on	O
the	O
Internet	O
,	O
with	O
lower	O
implementation	O
cost	O
and	O
complexity	O
than	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
.	O
</s>
<s>
In	O
2010	O
June	O
,	O
a	O
separate	O
proposal	O
called	O
tcpcrypt	B-Protocol
has	O
been	O
submitted	O
,	O
which	O
shares	O
many	O
of	O
the	O
goals	O
of	O
ObsTCP	B-Protocol
:	O
being	O
transparent	O
to	O
applications	O
,	O
opportunistic	O
and	O
low	O
overhead	O
.	O
</s>
<s>
It	O
requires	O
even	O
less	O
configuration	O
(	O
no	O
DNS	B-Protocol
entries	O
or	O
HTTP	O
headers	O
)	O
.	O
</s>
<s>
Unlike	O
ObsTCP	B-Protocol
,	O
tcpcrypt	B-Protocol
also	O
provides	O
primitives	O
down	O
to	O
the	O
application	O
to	O
implement	O
authentication	O
and	O
prevent	O
man-in-the-middle	O
attacks	O
(	O
MITM	O
)	O
.	O
</s>
<s>
ObsTCP	B-Protocol
was	O
created	O
by	O
Adam	O
Langley	O
.	O
</s>
<s>
The	O
concept	O
of	O
obfuscating	O
TCP	O
communications	O
using	O
opportunistic	B-Protocol
encryption	I-Protocol
evolved	O
through	O
several	O
iterations	O
.	O
</s>
<s>
The	O
experimental	O
iterations	O
of	O
ObsTCP	B-Protocol
used	O
TCP	O
options	O
in	O
'	O
SYN	O
 '	O
packets	O
to	O
advertise	O
support	O
for	O
ObsTCP	B-Protocol
,	O
the	O
server	O
responding	O
with	O
a	O
public	O
key	O
in	O
the	O
'	O
SYNACK	O
 '	O
.	O
</s>
<s>
The	O
present	O
(	O
third	O
)	O
iteration	O
uses	O
special	O
DNS	B-Protocol
records	O
(	O
or	O
out	O
of	O
band	O
methods	O
)	O
to	O
advertise	O
support	O
and	O
keys	O
,	O
without	O
modifying	O
the	O
operation	O
of	O
the	O
underlying	O
TCP	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
ObsTCP	B-Protocol
is	O
a	O
low	O
cost	O
protocol	O
intended	O
to	O
protect	O
TCP	O
traffic	O
,	O
without	O
requiring	O
public	O
key	O
certificates	O
,	O
the	O
services	O
of	O
Certificate	B-Architecture
Authorities	I-Architecture
,	O
or	O
a	O
complex	O
Public	B-Architecture
Key	I-Architecture
Infrastructure	I-Architecture
.	O
</s>
<s>
A	O
server	O
using	O
ObsTCP	B-Protocol
advertises	O
a	O
public	O
key	O
and	O
a	O
port	O
number	O
.	O
</s>
<s>
A	O
DNS	B-Protocol
'	I-Protocol
A	I-Protocol
record	I-Protocol
 '	I-Protocol
may	O
be	O
used	O
to	O
advertise	O
server	O
support	O
for	O
ObsTCP	B-Protocol
(	O
with	O
a	O
DNS	B-Protocol
'	I-Protocol
CNAME	I-Protocol
record	I-Protocol
 '	I-Protocol
providing	O
a	O
'	O
friendly	O
 '	O
name	O
)	O
.	O
</s>
<s>
A	O
client	O
connecting	O
to	O
an	O
ObsTCP	B-Protocol
server	O
parses	O
the	O
DNS	B-Protocol
entries	O
,	O
uses	O
HTTP	O
header	O
records	O
,	O
or	O
uses	O
cached/out	O
of	O
band	O
data	O
to	O
obtain	O
the	O
public	O
key	O
and	O
port	O
number	O
,	O
before	O
connecting	O
to	O
the	O
server	O
and	O
encrypting	O
traffic	O
.	O
</s>
