<s>
Protocol	B-Protocol
encryption	I-Protocol
(	O
PE	O
)	O
,	O
message	B-Protocol
stream	I-Protocol
encryption	I-Protocol
(	O
MSE	O
)	O
or	O
protocol	B-Protocol
header	I-Protocol
encrypt	I-Protocol
(	O
PHE	O
)	O
are	O
related	O
features	O
of	O
some	O
peer-to-peer	O
file-sharing	O
clients	B-Protocol
,	O
including	O
BitTorrent	B-Protocol
clients	B-Protocol
.	O
</s>
<s>
MSE/PE	B-Protocol
is	O
implemented	O
in	O
BitComet	B-Protocol
,	O
BitTornado	O
,	O
Deluge	B-Language
,	O
Flashget	B-Protocol
,	O
KTorrent	B-Language
,	O
libtorrent	B-Language
(	O
used	O
by	O
various	O
BitTorrent	B-Protocol
clients	B-Protocol
,	O
including	O
qBittorrent	B-Application
)	O
,	O
Mainline	O
,	O
μTorrent	B-Application
,	O
qBittorrent	B-Application
,	O
rTorrent	B-Language
,	O
Transmission	B-Language
,	O
Tixati	B-Protocol
and	O
Vuze	B-Application
.	O
</s>
<s>
PHE	O
was	O
implemented	O
in	O
old	O
versions	O
of	O
BitComet	B-Protocol
.	O
</s>
<s>
Similar	O
protocol	B-Protocol
obfuscation	I-Protocol
is	O
supported	O
in	O
up-to-date	O
versions	O
of	O
some	O
other	O
(	O
non-BitTorrent	O
)	O
systems	O
including	O
eMule	B-Protocol
.	O
</s>
<s>
As	O
of	O
January	O
2005	O
,	O
BitTorrent	B-Protocol
traffic	O
made	O
up	O
more	O
than	O
a	O
third	O
of	O
total	O
residential	O
internet	O
traffic	O
,	O
although	O
this	O
dropped	O
to	O
less	O
than	O
20%	O
as	O
of	O
2009	O
.	O
</s>
<s>
These	O
systems	O
were	O
designed	O
initially	O
to	O
provide	O
anonymity	O
or	O
confidentiality	O
,	O
but	O
became	O
required	O
in	O
countries	O
where	O
Internet	O
Service	O
Providers	O
were	O
granted	O
the	O
power	O
to	O
throttle	O
BitTorrent	B-Protocol
users	O
and	O
even	O
ban	O
those	O
they	O
believed	O
were	O
guilty	O
of	O
illegal	O
file	O
sharing	O
.	O
</s>
<s>
Protocol	B-Protocol
header	I-Protocol
encryption	I-Protocol
(	O
PHE	O
)	O
was	O
conceived	O
by	O
RnySmile	O
and	O
first	O
implemented	O
in	O
BitComet	B-Protocol
version	O
0.60	O
on	O
8	O
September	O
2005	O
.	O
</s>
<s>
Some	O
software	O
like	O
IPP2P	O
claims	O
BitComet	B-Protocol
traffic	O
is	O
detectable	O
even	O
with	O
PHE	O
.	O
</s>
<s>
Since	O
there	O
are	O
no	O
open	O
specifications	O
to	O
this	O
protocol	O
implementation	O
the	O
only	O
possibility	O
to	O
support	O
it	O
in	O
other	O
clients	B-Protocol
would	O
have	O
been	O
via	O
reverse	O
engineering	O
.	O
</s>
<s>
In	O
late	O
January	O
2006	O
the	O
developers	O
of	O
Vuze	B-Application
(	O
then	O
known	O
as	O
Azureus	B-Application
)	O
decided	O
to	O
design	O
and	O
simultaneously	O
implement	O
a	O
new	O
,	O
open	O
protocol	B-Protocol
obfuscation	I-Protocol
method	O
,	O
called	O
message	B-Protocol
stream	I-Protocol
encryption	I-Protocol
(	O
MSE	O
)	O
.	O
</s>
<s>
It	O
was	O
included	O
in	O
Azureus	B-Application
CVS	O
snapshot	O
2307-B29	O
on	O
19	O
January	O
2006	O
.	O
</s>
<s>
After	O
negotiations	O
between	O
different	O
BitTorrent	B-Protocol
developers	O
a	O
new	O
proposal	O
was	O
written	O
and	O
then	O
implemented	O
into	O
the	O
Azureus	B-Application
and	O
μTorrent	B-Application
betas	O
within	O
days	O
.	O
</s>
<s>
In	O
μTorrent	B-Application
,	O
the	O
new	O
protocol	O
was	O
called	O
protocol	B-Protocol
encryption	I-Protocol
(	O
PE	O
)	O
.	O
</s>
<s>
supports	O
MSE/PE	B-Protocol
as	O
of	O
build	O
v1.34	O
but	O
is	O
not	O
enforced	O
by	O
default	O
.	O
</s>
<s>
BitComet	B-Protocol
version	O
0.63	O
was	O
released	O
7	O
March	O
2006	O
.	O
</s>
<s>
It	O
removed	O
the	O
old	O
protocol	B-Protocol
header	I-Protocol
encryption	I-Protocol
and	O
implemented	O
the	O
new	O
MSE/PE	B-Protocol
to	O
be	O
compatible	O
with	O
Azureus	B-Application
and	O
μTorrent	B-Application
.	O
</s>
<s>
BitTornado	O
supports	O
MSE/PE	B-Protocol
as	O
of	O
build	O
T-0.3.18	O
.	O
</s>
<s>
BitTorrent	B-Protocol
(	O
Mainline	O
)	O
supports	O
MSE/PE	B-Protocol
since	O
version	O
4.9.2-beta	O
on	O
May	O
2	O
,	O
2006	O
.	O
</s>
<s>
Deluge	B-Language
supports	O
MSE/PE	B-Protocol
as	O
of	O
Deluge-0.5.1	O
.	O
</s>
<s>
KTorrent	B-Language
implemented	O
MSE/PE	B-Protocol
in	O
SVN	B-Application
version	O
535386	O
on	O
April	O
29	O
,	O
2006	O
.	O
</s>
<s>
libtorrent	B-Language
implemented	O
protocol	B-Protocol
encryption	I-Protocol
in	O
v0.13	O
released	O
on	O
10	O
December	O
2011	O
.	O
</s>
<s>
rTorrent	B-Language
supports	O
MSE/PE	B-Protocol
as	O
of	O
rTorrent-0.7.0	O
.	O
</s>
<s>
Transmission	B-Language
supports	O
MSE/PE	B-Protocol
as	O
of	O
Transmission-0.90	O
.	O
</s>
<s>
Vuze	B-Application
(	O
formerly	O
Azureus	B-Application
)	O
supports	O
the	O
final	O
spec	O
since	O
25	O
January	O
2006	O
(	O
CVS	O
snapshot	O
2307-B33	O
)	O
.	O
</s>
<s>
Azureus	B-Application
version	O
2.4.0.0	O
was	O
released	O
10	O
February	O
2006	O
,	O
and	O
was	O
the	O
first	O
stable	O
version	O
of	O
a	O
client	O
to	O
support	O
MSE/PE	B-Protocol
.	O
</s>
<s>
However	O
,	O
glitches	O
in	O
Azureus	B-Application
 '	O
implementation	O
resulted	O
in	O
improperly	O
encrypted	O
pieces	O
that	O
failed	O
hash	O
checking	O
.	O
</s>
<s>
μTorrent	B-Application
premiered	O
MSE/PE	B-Protocol
4	O
days	O
after	O
Azureus	B-Application
with	O
beta	O
1.4.1	O
build	O
407	O
.	O
μTorrent	B-Application
version	O
1.5	O
(	O
build	O
436	O
)	O
was	O
released	O
on	O
7	O
March	O
2006	O
;	O
it	O
was	O
the	O
first	O
stable	O
version	O
of	O
μTorrent	B-Application
with	O
PE	O
.	O
</s>
<s>
The	O
BitComet	B-Protocol
PHE	O
method	O
used	O
in	O
versions	O
0.60	O
to	O
0.62	O
is	O
neither	O
published	O
,	O
nor	O
is	O
it	O
compatible	O
with	O
MSE/PE	B-Protocol
.	O
</s>
<s>
MSE/PE	B-Protocol
uses	O
key	B-Protocol
exchange	I-Protocol
combined	O
with	O
the	O
infohash	O
of	O
the	O
torrent	B-Protocol
to	O
establish	O
an	O
RC4	B-Algorithm
encryption	O
key	O
.	O
</s>
<s>
The	O
key	B-Protocol
exchange	I-Protocol
helps	O
to	O
minimize	O
the	O
risk	O
of	O
passive	O
listeners	O
,	O
and	O
the	O
infohash	O
helps	O
avoid	O
man-in-the-middle	O
attacks	O
.	O
</s>
<s>
RC4	B-Algorithm
is	O
chosen	O
for	O
its	O
speed	O
.	O
</s>
<s>
To	O
ensure	O
compatibility	O
with	O
other	O
clients	B-Protocol
that	O
do	O
n't	O
support	O
this	O
specification	O
,	O
users	O
may	O
also	O
choose	O
whether	O
unencrypted	O
incoming	O
or	O
outgoing	O
connections	O
are	O
still	O
allowed	O
.	O
</s>
<s>
Supported	O
clients	B-Protocol
propagate	O
the	O
fact	O
that	O
they	O
have	O
MSE/PE	B-Protocol
enabled	O
through	O
PEX	O
and	O
DHT	B-Operating_System
.	O
</s>
<s>
AES	B-Algorithm
was	O
proposed	O
as	O
the	O
encryption	O
method	O
,	O
but	O
not	O
adopted	O
because	O
it	O
consumed	O
too	O
much	O
CPU	O
time	O
.	O
</s>
<s>
The	O
required	O
Diffie	B-Protocol
–	I-Protocol
Hellman	I-Protocol
keys	O
to	O
achieve	O
a	O
security	O
equal	O
to	O
AES	B-Algorithm
would	O
have	O
been	O
much	O
bigger	O
or	O
require	O
elliptic	O
curve	O
cryptography	O
,	O
making	O
the	O
handshake	O
more	O
expensive	O
in	O
terms	O
of	O
used	O
CPU	O
time	O
.	O
</s>
<s>
Analysis	O
of	O
the	O
BitTorrent	B-Protocol
protocol	I-Protocol
encryption	I-Protocol
(	O
a.k.a.	O
</s>
<s>
Bram	O
Cohen	O
,	O
the	O
inventor	O
of	O
BitTorrent	B-Protocol
,	O
opposed	O
adding	O
encryption	O
to	O
the	O
BitTorrent	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
Cohen	O
stated	O
he	O
was	O
worried	O
that	O
encryption	O
could	O
create	O
incompatibility	O
between	O
clients	B-Protocol
.	O
</s>
<s>
He	O
also	O
stressed	O
the	O
point	O
that	O
the	O
majority	O
of	O
ISPs	O
do	O
n't	O
block	O
the	O
torrent	B-Protocol
protocol	O
.	O
</s>
<s>
Many	O
BitTorrent	B-Protocol
community	O
users	O
responded	O
strongly	O
against	O
Cohen	O
's	O
accusations	O
.	O
</s>
<s>
Cohen	O
later	O
added	O
encrypted	O
connections	O
to	O
his	O
Mainline	B-Protocol
client	I-Protocol
with	O
the	O
ability	O
to	O
receive	O
but	O
not	O
originate	O
them	O
.	O
</s>
<s>
Notably	O
,	O
when	O
μTorrent	B-Application
was	O
purchased	O
by	O
BitTorrent	B-Protocol
,	O
Inc	O
.	O
and	O
then	O
became	O
the	O
next	O
mainline	O
release	O
,	O
the	O
ability	O
to	O
originate	O
encrypted	O
connections	O
was	O
retained	O
,	O
but	O
it	O
became	O
turned	O
off	O
by	O
default	O
.	O
</s>
<s>
In	O
an	O
interview	O
in	O
2007	O
,	O
Cohen	O
stated	O
"	O
The	O
so-called	O
'	O
encryption	O
 '	O
of	O
BitTorrent	B-Protocol
traffic	O
is	O
n't	O
really	O
encryption	O
,	O
it	O
's	O
obfuscation	O
.	O
</s>
