<s>
Cryptoloop	B-Application
is	O
a	O
Linux	B-Operating_System
kernel	I-Operating_System
's	O
disk	O
encryption	O
module	B-Application
that	O
relies	O
on	O
the	O
Crypto	B-Application
API	I-Application
,	O
which	O
is	O
a	O
cryptography	O
framework	O
introduced	O
in	O
version	O
2.5.45	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
mainline	O
.	O
</s>
<s>
Cryptoloop	B-Application
was	O
first	O
introduced	O
in	O
the	O
2.5.x	O
kernel	B-Operating_System
series	O
;	O
its	O
functionality	O
was	O
later	O
incorporated	O
into	O
the	O
device	B-Application
mapper	I-Application
,	O
a	O
generic	O
framework	O
used	O
to	O
map	O
one	O
block	O
device	O
onto	O
another	O
.	O
</s>
<s>
Cryptoloop	B-Application
can	O
create	O
an	O
encrypted	O
file	B-Application
system	I-Application
within	O
a	O
partition	B-Application
or	O
from	O
within	O
a	O
regular	O
file	O
in	O
the	O
regular	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Once	O
a	O
file	O
is	O
encrypted	O
,	O
it	O
can	O
be	O
moved	O
to	O
another	O
storage	B-Application
device	I-Application
.	O
</s>
<s>
This	O
is	O
accomplished	O
by	O
making	O
use	O
of	O
a	O
loop	B-Application
device	I-Application
,	O
a	O
pseudo	O
device	O
that	O
enables	O
a	O
normal	O
file	O
to	O
be	O
mounted	B-Application
as	O
if	O
it	O
were	O
a	O
physical	O
device	O
.	O
</s>
<s>
By	O
encrypting	O
I/O	B-General_Concept
to	O
the	O
loop	B-Application
device	I-Application
,	O
any	O
data	O
being	O
accessed	O
must	O
first	O
be	O
decrypted	O
before	O
passing	O
through	O
the	O
regular	O
file	B-Application
system	I-Application
;	O
conversely	O
,	O
any	O
data	O
being	O
stored	O
will	O
be	O
encrypted	O
.	O
</s>
<s>
Cryptoloop	B-Application
is	O
vulnerable	O
to	O
watermarking	O
attacks	O
,	O
making	O
it	O
possible	O
to	O
determine	O
presence	O
of	O
watermarked	O
data	O
on	O
the	O
encrypted	O
filesystem	B-Application
:	O
</s>
<s>
This	O
attack	O
exploits	O
weakness	O
in	O
IV	O
computation	O
and	O
knowledge	O
of	O
how	O
file	B-Application
systems	I-Application
place	O
files	O
on	O
disk	O
.	O
</s>
<s>
This	O
attack	O
works	O
with	O
file	B-Application
systems	I-Application
that	O
have	O
soft	O
block	O
size	O
of	O
1024	O
or	O
greater	O
.	O
</s>
<s>
At	O
least	O
ext2	B-Application
,	O
ext3	B-Application
,	O
reiserfs	B-Application
and	O
minix	B-Operating_System
have	O
such	O
property	O
.	O
</s>
<s>
Newer	O
versions	O
of	O
cryptoloop	B-Application
's	O
successor	O
,	O
dm-crypt	O
,	O
are	O
less	O
vulnerable	O
to	O
this	O
type	O
of	O
attack	O
if	O
used	O
correctly	O
.	O
</s>
