<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
tcpcrypt	B-Protocol
is	O
a	O
transport	B-Architecture
layer	I-Architecture
communication	O
encryption	O
protocol	O
.	O
</s>
<s>
Unlike	O
prior	O
protocols	O
like	O
TLS	B-Protocol
(	O
SSL	O
)	O
,	O
tcpcrypt	B-Protocol
is	O
implemented	O
as	O
a	O
TCP	B-Protocol
extension	O
.	O
</s>
<s>
Tcpcrypt	B-Protocol
has	O
been	O
published	O
as	O
an	O
Internet	O
Draft	O
.	O
</s>
<s>
Experimental	O
user-space	B-Operating_System
implementations	O
are	O
available	O
for	O
Linux	B-Operating_System
,	O
Mac	O
OS	O
X	O
,	O
FreeBSD	O
and	O
Windows	O
.	O
</s>
<s>
There	O
is	O
also	O
a	O
Linux	B-Operating_System
kernel	I-Operating_System
implementation	O
.	O
</s>
<s>
The	O
TCPINC	B-Protocol
(	O
TCP	B-Protocol
Increased	I-Protocol
Security	I-Protocol
)	O
working	O
group	O
was	O
formed	O
in	O
June	O
2014	O
by	O
IETF	O
to	O
work	O
on	O
standardizing	O
security	O
extensions	O
in	O
the	O
TCP	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
In	O
May	O
2019	O
the	O
working	O
group	O
released	O
and	O
as	O
an	O
experimental	O
standard	O
for	O
Tcpcrypt	B-Protocol
.	O
</s>
<s>
Tcpcrypt	B-Protocol
provides	O
opportunistic	B-Protocol
encryption	I-Protocol
—	O
if	O
either	O
side	O
does	O
not	O
support	O
this	O
extension	O
,	O
then	O
the	O
protocol	O
falls	O
back	O
to	O
regular	O
unencrypted	O
TCP	B-Protocol
.	O
</s>
<s>
Tcpcrypt	B-Protocol
also	O
provides	O
encryption	O
to	O
any	O
application	O
using	O
TCP	B-Protocol
,	O
even	O
ones	O
that	O
do	O
not	O
know	O
about	O
encryption	O
.	O
</s>
<s>
Unlike	O
TLS	B-Protocol
,	O
tcpcrypt	B-Protocol
itself	O
does	O
not	O
do	O
any	O
authentication	O
,	O
but	O
passes	O
a	O
unique	O
"	O
session	O
ID	O
"	O
down	O
to	O
the	O
application	O
;	O
the	O
application	O
can	O
then	O
use	O
this	O
token	O
for	O
further	O
authentication	O
.	O
</s>
<s>
This	O
aligns	O
with	O
tcpcrypt	B-Protocol
's	O
goals	O
of	O
ubiquitous	O
transparent	O
encryption	O
,	O
which	O
revived	O
interest	O
in	O
standardization	O
of	O
the	O
protocol	O
.	O
</s>
<s>
An	O
official	O
IETF	O
mailing	O
list	O
was	O
created	O
for	O
tcpcrypt	B-Protocol
in	O
March	O
2014	O
,	O
followed	O
by	O
the	O
formation	O
of	O
the	O
TCPINC	B-Protocol
(	O
TCP	B-Protocol
Increased	I-Protocol
Security	I-Protocol
)	O
working	O
group	O
in	O
June	O
and	O
a	O
new	O
version	O
of	O
the	O
draft	O
specification	O
.	O
</s>
<s>
Tcpcrypt	B-Protocol
enforces	O
TCP	B-Protocol
timestamps	O
and	O
adds	O
its	O
own	O
TCP	B-Protocol
options	O
to	O
each	O
data	O
packet	O
,	O
amounting	O
to	O
36	O
bytes	O
per	O
packet	O
compared	O
to	O
plain	O
TCP	B-Protocol
.	O
</s>
<s>
With	O
a	O
mean	O
observed	O
packet	O
size	O
for	O
TCP	B-Protocol
packets	O
of	O
471	O
bytes	O
,	O
this	O
can	O
lead	O
to	O
an	O
overhead	O
of	O
8%	O
of	O
useful	O
bandwidth	O
.	O
</s>
<s>
Compared	O
to	O
TLS/SSL	B-Protocol
,	O
tcpcrypt	B-Protocol
is	O
designed	O
to	O
have	O
a	O
lower	O
performance	O
impact	O
.	O
</s>
<s>
In	O
part	O
this	O
is	O
because	O
tcpcrypt	B-Protocol
does	O
not	O
have	O
built-in	O
authentication	O
,	O
which	O
can	O
be	O
implemented	O
by	O
the	O
application	O
itself	O
.	O
</s>
<s>
Cryptography	O
primitives	O
are	O
used	O
in	O
such	O
a	O
way	O
to	O
reduce	O
load	O
on	O
the	O
server	B-Application
side	O
,	O
because	O
a	O
single	O
server	B-Application
usually	O
has	O
to	O
provide	O
services	O
for	O
far	O
more	O
clients	O
than	O
reverse	O
.	O
</s>
<s>
The	O
current	O
user	B-Operating_System
space	I-Operating_System
implementations	O
are	O
considered	O
experimental	O
and	O
are	O
reportedly	O
unstable	O
on	O
some	O
systems	O
.	O
</s>
<s>
It	O
also	O
does	O
not	O
support	O
IPv6	B-Protocol
yet	O
,	O
which	O
is	O
currently	O
only	O
supported	O
by	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
version	O
.	O
</s>
<s>
It	O
is	O
expected	O
that	O
once	O
tcpcrypt	B-Protocol
becomes	O
a	O
standard	O
,	O
operating	O
systems	O
will	O
come	O
with	O
tcpcrypt	B-Protocol
support	O
built-in	O
,	O
making	O
the	O
user	B-Operating_System
space	I-Operating_System
solution	O
unnecessary	O
.	O
</s>
