<s>
is	O
a	O
peer-to-peer	O
file-sharing	O
(	O
P2P	O
)	O
application	O
from	O
Japan	O
designed	O
for	O
use	O
with	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
Its	O
author	B-Application
is	O
known	O
by	O
the	O
pseudonym	O
.	O
</s>
<s>
Perfect	B-Application
Dark	I-Application
was	O
developed	O
with	O
the	O
intention	O
for	O
it	O
to	O
be	O
the	O
successor	O
to	O
both	O
Winny	B-Protocol
and	O
Share	B-Application
software	O
.	O
</s>
<s>
While	O
Japan	O
's	O
Association	O
for	O
Copyright	O
of	O
Computer	O
Software	O
reported	O
that	O
in	O
January	O
2014	O
,	O
the	O
number	O
of	O
nodes	O
connected	O
on	O
Perfect	B-Application
Dark	I-Application
(	O
)	O
was	O
less	O
than	O
on	O
Share	B-Application
(	O
)	O
,	O
but	O
more	O
than	O
on	O
Winny	B-Protocol
(	O
)	O
,	O
Netagent	O
in	O
2018	O
reported	O
Winny	B-Protocol
being	O
the	O
largest	O
with	O
50	O
000	O
nodes	O
followed	O
by	O
Perfect	B-Application
Dark	I-Application
with	O
30	O
000	O
nodes	O
followed	O
by	O
Share	B-Application
with	O
10	O
000	O
.	O
</s>
<s>
Netagent	O
asserts	O
that	O
the	O
number	O
of	O
nodes	O
on	O
Perfect	B-Application
Dark	I-Application
have	O
fallen	O
since	O
2015	O
while	O
the	O
numbers	O
of	O
Winny	B-Protocol
hold	O
steady	O
.	O
</s>
<s>
Netagent	O
reports	O
that	O
users	O
of	O
Perfect	B-Application
Dark	I-Application
are	O
most	O
likely	O
to	O
share	B-Application
books/manga	O
.	O
</s>
<s>
Perfect	B-Application
Dark	I-Application
is	O
still	O
being	O
actively	O
developed	O
.	O
</s>
<s>
The	O
author	B-Application
does	O
not	O
ask	O
that	O
the	O
program	O
's	O
users	O
at	O
this	O
point	O
become	O
dedicated	O
"	O
users	O
"	O
of	O
the	O
software	O
.	O
</s>
<s>
Instead	O
,	O
the	O
author	B-Application
asks	O
them	O
to	O
participate	O
in	O
the	O
test	O
phase	O
.	O
</s>
<s>
Through	O
this	O
test	O
phase	O
,	O
the	O
author	B-Application
hopes	O
for	O
bug	B-Error_Name
reports	O
and	O
discussion	O
that	O
will	O
help	O
shape	O
Perfect	B-Application
Dark	I-Application
into	O
a	O
better	O
program	O
.	O
</s>
<s>
The	O
author	B-Application
implements	O
an	O
architecture	O
called	O
DKT+DHT+DU	O
in	O
the	O
design	O
of	O
the	O
network	O
.	O
</s>
<s>
"	O
DHT	O
"	O
for	O
Distributed	B-Operating_System
Hash	I-Operating_System
Table	I-Operating_System
.	O
</s>
<s>
Perfect	B-Application
Dark	I-Application
has	O
higher	O
bandwidth	O
and	O
hard	B-Device
drive	I-Device
space	O
requirements	O
than	O
its	O
predecessors	O
Winny	B-Protocol
and	O
Share	B-Application
.	O
</s>
<s>
The	O
minimum	O
upload	B-Application
speed	O
is	O
100	O
kbit/s	O
.	O
</s>
<s>
Perfect	B-Application
Dark	I-Application
requires	O
more	O
network	O
bandwidth	O
and	O
hard	B-Device
disk	I-Device
space	O
than	O
Winny	B-Protocol
or	O
Share	B-Application
,	O
forcing	O
a	O
fairer	O
load	O
on	O
all	O
users	O
.	O
</s>
<s>
If	O
a	O
user	O
does	O
not	O
have	O
Perfect	B-Application
Dark	I-Application
configured	O
with	O
the	O
proper	O
settings	O
or	O
if	O
the	O
user	O
is	O
unable	O
to	O
support	O
the	O
settings	O
,	O
download	O
rates	O
will	O
be	O
restricted	O
and	O
priority	O
will	O
be	O
given	O
to	O
other	O
users	O
.	O
</s>
<s>
This	O
is	O
intended	O
to	O
increase	O
the	O
retention	O
rate	O
of	O
the	O
Perfect	B-Application
Dark	I-Application
network	O
.	O
</s>
<s>
It	O
requires	O
to	O
share	B-Application
at	O
minimum	O
40	O
GB	O
of	O
hard	B-Device
drive	I-Device
space	O
,	O
for	O
its	O
"	O
Unity	O
"	O
folder	O
(	O
a	O
huge	O
distributed	B-Operating_System
hash	I-Operating_System
table	I-Operating_System
used	O
as	O
a	O
distributed	O
data	O
store	O
)	O
.	O
</s>
<s>
Perfect	B-Application
Dark	I-Application
requires	O
NTFS	B-Application
file	I-Application
system	I-Application
instead	O
of	O
FAT32	B-Application
,	O
because	O
FAT32	B-Application
is	O
limited	O
to	O
a	O
file	O
size	O
of	O
4	O
GB	O
,	O
while	O
Perfect	B-Application
Dark	I-Application
can	O
download	O
files	O
up	O
to	O
the	O
size	O
of	O
32	O
GB	O
.	O
</s>
<s>
Like	O
other	O
Japanese	O
sharing	O
software	O
,	O
Perfect	B-Application
Dark	I-Application
has	O
its	O
own	O
proprietary	B-Application
P2P	O
network	O
called	O
"	O
Unity	O
"	O
.	O
</s>
<s>
One	O
of	O
the	O
biggest	O
characteristics	O
of	O
Perfect	B-Application
Dark	I-Application
is	O
its	O
powerful	O
search	O
capability	O
.	O
</s>
<s>
By	O
using	O
distributed	B-Operating_System
hash	I-Operating_System
tables	I-Operating_System
,	O
search	O
performance	O
is	O
greatly	O
improved	O
compared	O
to	O
Winny	B-Protocol
or	O
Share	B-Application
,	O
making	O
it	O
unnecessary	O
to	O
rely	O
on	O
the	O
construction	O
of	O
node	B-Protocol
clusters	O
.	O
</s>
<s>
This	O
is	O
in	O
contrast	O
to	O
Winny	B-Protocol
and	O
Share	B-Application
,	O
where	O
cluster	O
keywords	O
,	O
such	O
as	O
"	O
DVDISO	O
"	O
or	O
"	O
アニメ	O
"	O
/	O
"	O
anime	O
"	O
are	O
used	O
to	O
specify	O
what	O
types	O
of	O
files	O
the	O
user	O
is	O
searching	O
for	O
.	O
</s>
<s>
The	O
concept	O
of	O
"	O
tree	B-Algorithm
search	I-Algorithm
"	O
brings	O
about	O
strong	O
search	O
ability	O
.	O
</s>
<s>
Perfect	B-Application
Dark	I-Application
includes	O
an	O
original	O
feature	O
named	O
"	O
flow	O
"	O
:	O
a	O
window	O
where	O
text	O
lines	O
written	O
by	O
users	O
scroll	O
vertically	O
.	O
</s>
<s>
Since	O
version	O
1.02	O
Perfect	B-Application
Dark	I-Application
has	O
an	O
option	O
to	O
automatically	O
update	O
itself	O
through	O
its	O
own	O
(	O
Unity	O
)	O
network	O
.	O
</s>
<s>
Perfect	B-Application
dark	I-Application
has	O
a	O
simple	O
message	B-Application
board	I-Application
feature	O
.	O
</s>
<s>
The	O
overall	O
structure	O
of	O
the	O
Perfect	B-Application
Dark	I-Application
network	O
broadly	O
resembles	O
recent	O
versions	O
of	O
Freenet	B-Protocol
,	O
only	O
with	O
a	O
heavier	O
use	O
of	O
distributed	B-Operating_System
hash	I-Operating_System
tables	I-Operating_System
.	O
</s>
<s>
The	O
anonymity	O
relies	O
on	O
a	O
mixnet	B-Protocol
where	O
traffic	O
is	O
forwarded	O
according	O
to	O
certain	O
probability	O
,	O
as	O
well	O
as	O
the	O
deniability	O
of	O
the	O
distributed	O
data	O
storage	O
(	O
"	O
Unity	O
"	O
)	O
which	O
is	O
stored	O
and	O
transferred	O
in	O
encrypted	O
blocks	O
while	O
the	O
keys	O
are	O
distributed	O
separately	O
.	O
</s>
<s>
Perfect	B-Application
Dark	I-Application
uses	O
RSA	B-Architecture
(	O
1024-bit	O
)	O
and	O
AES	B-Algorithm
(	O
128-bit	O
)	O
to	O
encrypt	O
data	O
transmitted	O
between	O
peers	O
.	O
</s>
<s>
Published	O
files	O
and	O
boards	O
(	O
including	O
automatic	O
updates	O
from	O
the	O
author	B-Application
,	O
where	O
enabled	O
)	O
are	O
usually	O
signed	O
with	O
160-bit	O
ECDSA	O
signatures	O
.	O
</s>
<s>
Automatic	O
updates	O
of	O
the	O
software	O
are	O
additionally	O
protected	O
with	O
a	O
2048-bit	O
RSA	B-Architecture
signature	O
.	O
</s>
<s>
The	O
author	B-Application
believes	O
that	O
initially	O
,	O
a	O
layer	O
of	O
obscurity	O
due	O
to	O
the	O
closed-source	B-Application
nature	O
of	O
the	O
program	O
will	O
frustrate	O
attempted	O
attacks	O
on	O
its	O
anonymity	O
,	O
as	O
well	O
as	O
deter	O
"	O
free	O
riders	O
"	O
and	O
junk	O
files	O
degrading	O
the	O
network	O
.	O
</s>
<s>
However	O
,	O
the	O
author	B-Application
has	O
stated	O
that	O
it	O
may	O
become	O
open-source	O
in	O
the	O
future	O
should	O
an	O
acceptable	O
solution	O
to	O
these	O
problems	O
be	O
found	O
.	O
</s>
<s>
The	O
Japanese	O
security	O
firm	O
NetAgent	O
is	O
claiming	O
(	O
2010	O
)	O
that	O
they	O
have	O
created	O
software	O
capable	O
of	O
deciphering	O
encrypted	O
information	O
such	O
as	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
original	O
computer	O
uploading	B-Application
a	O
file	O
as	O
well	O
as	O
the	O
file	O
name	O
and	O
other	O
details	O
of	O
Perfect	B-Application
Dark	I-Application
.	O
</s>
<s>
A	O
Perfect	B-Application
Dark	I-Application
user	O
was	O
arrested	O
for	O
the	O
first	O
time	O
on	O
27	O
January	O
2010	O
.	O
</s>
<s>
The	O
user	O
had	O
been	O
uploading	B-Application
and	O
sharing	O
an	O
episode	O
of	O
the	O
Japanese	O
animation	O
TV	O
series	O
Fullmetal	O
Alchemist	O
:	O
Brotherhood	O
with	O
Perfect	B-Application
Dark	I-Application
and	O
was	O
charged	O
with	O
breach	O
of	O
copyright	O
law	O
.	O
</s>
<s>
On	O
10	O
June	O
2010	O
,	O
a	O
second	O
user	O
,	O
a	O
43-year-old	O
man	O
,	O
was	O
arrested	O
on	O
the	O
suspicion	O
of	O
uploading	B-Application
roughly	O
one	O
thousand	O
copyrighted	O
files	O
including	O
the	O
Big	O
Windup	O
!	O
</s>
<s>
On	O
8	O
October	O
2010	O
,	O
a	O
42-year-old	O
woman	O
was	O
arrested	O
for	O
uploading	B-Application
the	O
Mitsudomoe	O
anime	O
television	O
series	O
.	O
</s>
