<s>
In	O
the	O
field	O
of	O
security	O
engineering	O
,	O
an	O
oracle	B-General_Concept
attack	I-General_Concept
is	O
an	O
attack	O
that	O
exploits	O
the	O
availability	O
of	O
a	O
weakness	O
in	O
a	O
system	O
that	O
can	O
be	O
used	O
as	O
an	O
"	O
oracle	B-Application
"	O
to	O
give	O
a	O
simple	O
go/no	O
go	O
indication	O
to	O
inform	O
attackers	O
how	O
close	O
they	O
are	O
to	O
their	O
goals	O
.	O
</s>
<s>
The	O
attacker	O
can	O
then	O
combine	O
the	O
oracle	B-Application
with	O
a	O
systematic	O
search	O
of	O
the	O
problem	O
space	O
to	O
complete	O
their	O
attack	O
.	O
</s>
<s>
The	O
padding	B-Application
oracle	I-Application
attack	I-Application
,	O
and	O
compression	B-General_Concept
oracle	I-General_Concept
attacks	I-General_Concept
such	O
as	O
BREACH	B-Protocol
,	O
are	O
examples	O
of	O
oracle	B-General_Concept
attacks	I-General_Concept
,	O
as	O
was	O
the	O
practice	O
of	O
"	O
crib-dragging	O
"	O
in	O
the	O
cryptanalysis	O
of	O
the	O
Enigma	O
machine	O
.	O
</s>
<s>
An	O
oracle	B-Application
need	O
not	O
be	O
100%	O
accurate	O
:	O
even	O
a	O
small	O
statistical	O
correlation	O
with	O
the	O
correct	O
go/no	O
go	O
result	O
can	O
frequently	O
be	O
enough	O
for	O
a	O
systematic	O
automated	O
attack	O
.	O
</s>
<s>
In	O
a	O
compression	B-General_Concept
oracle	I-General_Concept
attack	I-General_Concept
the	O
use	O
of	O
adaptive	O
data	B-General_Concept
compression	I-General_Concept
on	O
a	O
mixture	O
of	O
chosen	O
plaintext	O
and	O
unknown	O
plaintext	O
can	O
result	O
in	O
content-sensitive	O
changes	O
in	O
the	O
length	O
of	O
the	O
compressed	O
text	O
that	O
can	O
be	O
detected	O
even	O
though	O
the	O
content	O
of	O
the	O
compressed	O
text	O
itself	O
is	O
then	O
encrypted	O
.	O
</s>
<s>
The	O
CRIME	O
and	O
BREACH	B-Protocol
attacks	O
are	O
examples	O
of	O
protocol	O
attacks	O
using	O
this	O
phenomenon	O
.	O
</s>
