<s>
In	O
cryptography	O
,	O
a	O
known-key	B-General_Concept
distinguishing	I-General_Concept
attack	I-General_Concept
is	O
an	O
attack	O
model	O
against	O
symmetric	B-Algorithm
ciphers	I-Algorithm
,	O
whereby	O
an	O
attacker	O
who	O
knows	O
the	O
key	O
can	O
find	O
a	O
structural	O
property	O
in	O
cipher	O
,	O
where	O
the	O
transformation	O
from	O
plaintext	O
to	O
ciphertext	O
is	O
not	O
random	O
.	O
</s>
<s>
The	O
chosen-key	B-General_Concept
distinguishing	I-General_Concept
attack	I-General_Concept
is	O
strongly	O
related	O
,	O
where	O
the	O
attacker	O
can	O
choose	O
a	O
key	O
to	O
introduce	O
such	O
transformations	O
.	O
</s>
<s>
Known-/chosen	O
-key	O
distinguishing	O
attacks	O
apply	O
in	O
the	O
"	O
open	B-General_Concept
key	I-General_Concept
model	I-General_Concept
"	O
instead	O
.	O
</s>
<s>
They	O
are	O
known	O
to	O
be	O
applicable	O
in	O
some	O
situations	O
where	O
block	O
ciphers	O
are	O
converted	O
to	O
hash	B-Error_Name
functions	I-Error_Name
,	O
leading	O
to	O
practical	O
collision	B-Algorithm
attacks	I-Algorithm
against	O
the	O
hash	B-Error_Name
.	O
</s>
<s>
Known-key	B-General_Concept
distinguishing	I-General_Concept
attacks	I-General_Concept
were	O
first	O
introduced	O
in	O
2007	O
by	O
Lars	O
Knudsen	O
and	O
Vincent	O
Rijmen	O
in	O
a	O
paper	O
that	O
proposed	O
such	O
an	O
attack	O
against	O
7	O
out	O
of	O
10	O
rounds	O
of	O
the	O
AES	B-Algorithm
cipher	I-Algorithm
and	O
another	O
attack	O
against	O
a	O
generalized	O
Feistel	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
Their	O
attack	O
finds	O
plaintext/ciphertext	O
pairs	O
for	O
a	O
cipher	O
with	O
a	O
known	B-General_Concept
key	I-General_Concept
,	O
where	O
the	O
input	O
and	O
output	O
have	O
s	O
least	O
significant	O
bits	O
set	O
to	O
zero	O
,	O
in	O
less	O
than	O
2s	O
time	O
(	O
where	O
s	O
is	O
fewer	O
than	O
half	O
the	O
block	O
size	O
)	O
.	O
</s>
<s>
These	O
attacks	O
have	O
also	O
been	O
applied	O
to	O
reduced-round	O
Threefish	B-Algorithm
(	O
Skein	B-Algorithm
)	O
and	O
Phelix	B-Algorithm
.	O
</s>
