<s>
OutGuess	B-Application
is	O
a	O
steganographic	O
software	O
for	O
hiding	O
data	O
in	O
the	O
most	O
redundant	O
content	O
data	O
bits	O
of	O
existing	O
(	O
media	O
)	O
files	O
.	O
</s>
<s>
It	O
is	O
written	O
in	O
C	B-Language
and	O
published	O
as	O
Free	B-Application
Software	I-Application
under	O
the	O
terms	O
of	O
the	O
old	O
BSD	B-Operating_System
license	I-Operating_System
.	O
</s>
<s>
It	O
has	O
been	O
tested	O
on	O
a	O
variety	O
of	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
and	O
is	O
included	O
in	O
the	O
standard	O
software	B-Application
repositories	I-Application
of	O
the	O
popular	O
Linux	O
distributions	O
Debian	O
and	O
Arch	O
Linux	O
(	O
via	O
user	O
repository	O
)	O
and	O
their	O
derivatives	O
.	O
</s>
<s>
OutGuess	B-Application
determines	O
bits	O
in	O
the	O
decoy	O
data	O
that	O
it	O
considers	O
most	O
expendable	O
and	O
then	O
distributes	O
secret	O
bits	O
based	O
on	O
a	O
shared	O
secret	O
in	O
a	O
pseudorandom	O
pattern	O
across	O
these	O
redundant	O
bits	O
,	O
flipping	O
some	O
of	O
them	O
according	O
to	O
the	O
secret	O
data	O
.	O
</s>
<s>
For	O
JPEG	O
images	O
,	O
OutGuess	B-Application
recompresses	O
the	O
image	O
to	O
a	O
user-selected	O
quality	O
level	O
and	O
then	O
embeds	O
secret	O
bits	O
into	O
the	O
least	O
significant	O
bits	O
(	O
LSB	O
)	O
of	O
the	O
quantized	O
coefficients	O
while	O
skipping	O
zeros	O
and	O
ones	O
.	O
</s>
<s>
Subsequently	O
,	O
corrections	O
are	O
made	O
to	O
the	O
coefficients	O
to	O
make	O
the	O
global	O
histogram	B-Algorithm
of	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
DCT	B-General_Concept
)	O
coefficients	O
match	O
that	O
of	O
the	O
decoy	O
image	O
,	O
counteracting	O
detection	O
by	O
the	O
chi-square	O
attack	O
that	O
is	O
based	O
on	O
the	O
analysis	O
of	O
first-order	O
statistics	O
.	O
</s>
<s>
OutGuess	B-Application
was	O
originally	O
developed	O
in	O
Germany	O
in	O
1999	O
by	O
Niels	O
Provos	O
.	O
</s>
<s>
In	O
response	O
,	O
Provos	O
implemented	O
a	O
method	O
that	O
exactly	O
preserves	O
the	O
DCT	B-General_Concept
histogram	B-Algorithm
on	O
which	O
this	O
attack	O
is	O
based	O
.	O
</s>
<s>
He	O
released	O
it	O
in	O
February	O
2001	O
in	O
OutGuess	B-Application
version	O
0.2	O
,	O
which	O
is	O
not	O
backward	O
compatible	O
to	O
older	O
versions	O
.	O
</s>
<s>
It	O
was	O
broken	O
by	O
an	O
attack	O
published	O
in	O
2002	O
that	O
uses	O
statistics	O
based	O
on	O
discontinuities	O
across	O
the	O
JPEG	O
block	O
boundaries	O
(	O
blockiness	O
)	O
of	O
the	O
decoded	O
image	O
and	O
can	O
estimate	O
the	O
lengths	O
of	O
messages	O
embedded	O
by	O
OutGuess	B-Application
.	O
</s>
<s>
OutGuess	B-Application
was	O
abandoned	O
and	O
the	O
official	O
website	O
was	O
shut	O
down	O
in	O
September	O
2015	O
.	O
</s>
<s>
A	O
fork	O
called	O
OutGuess	B-Application
Rebirth	O
(	O
OGR	O
)	O
was	O
released	O
in	O
2013	O
by	O
Laurent	O
Perch	O
,	O
with	O
some	O
bug	O
fixes	O
and	O
a	O
graphical	O
user	O
interface	O
for	O
Windows	B-Application
.	O
</s>
<s>
In	O
November	O
2018	O
,	O
Debian	O
developer	O
Joao	O
Eriberto	O
Mota	O
Filho	O
imported	O
the	O
source	O
code	O
into	O
a	O
new	O
repository	O
on	O
GitHub	B-Application
to	O
continue	O
development	O
,	O
and	O
since	O
then	O
released	O
some	O
new	O
minor	O
versions	O
that	O
include	O
bug	O
fixes	O
from	O
several	O
people	O
.	O
</s>
