<s>
In	O
cryptography	O
,	O
the	O
International	B-Algorithm
Data	I-Algorithm
Encryption	I-Algorithm
Algorithm	I-Algorithm
(	O
IDEA	O
)	O
,	O
originally	O
called	O
Improved	B-Algorithm
Proposed	I-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
(	O
IPES	O
)	O
,	O
is	O
a	O
symmetric-key	B-Algorithm
block	O
cipher	B-Application
designed	O
by	O
James	O
Massey	O
of	O
ETH	O
Zurich	O
and	O
Xuejia	O
Lai	O
and	O
was	O
first	O
described	O
in	O
1991	O
.	O
</s>
<s>
The	O
algorithm	O
was	O
intended	O
as	O
a	O
replacement	O
for	O
the	O
Data	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
(	O
DES	B-Algorithm
)	O
.	O
</s>
<s>
IDEA	O
is	O
a	O
minor	O
revision	O
of	O
an	O
earlier	O
cipher	B-Application
Proposed	B-Algorithm
Encryption	I-Algorithm
Standard	I-Algorithm
(	O
PES	B-Algorithm
)	O
.	O
</s>
<s>
The	O
cipher	B-Application
was	O
designed	O
under	O
a	O
research	O
contract	O
with	O
the	O
Hasler	O
Foundation	O
,	O
which	O
became	O
part	O
of	O
Ascom-Tech	O
AG	O
.	O
</s>
<s>
The	O
cipher	B-Application
was	O
patented	O
in	O
a	O
number	O
of	O
countries	O
but	O
was	O
freely	O
available	O
for	O
non-commercial	O
use	O
.	O
</s>
<s>
IDEA	O
was	O
used	O
in	O
Pretty	B-Application
Good	I-Application
Privacy	I-Application
(	O
PGP	O
)	O
v2.0	O
and	O
was	O
incorporated	O
after	O
the	O
original	O
cipher	B-Application
used	O
in	O
v1.0	O
,	O
BassOmatic	B-Algorithm
,	O
was	O
found	O
to	O
be	O
insecure	O
.	O
</s>
<s>
IDEA	O
derives	O
much	O
of	O
its	O
security	O
by	O
interleaving	O
operations	O
from	O
different	O
groups	O
modular	O
addition	O
and	O
multiplication	O
,	O
and	O
bitwise	O
eXclusive	O
OR	O
(	O
XOR	B-Application
)	O
which	O
are	O
algebraically	O
"	O
incompatible	O
"	O
in	O
some	O
sense	O
.	O
</s>
<s>
Bitwise	O
XOR	B-Application
(	O
exclusive	O
OR	O
)	O
(	O
denoted	O
with	O
a	O
blue	O
circled	O
plus	O
)	O
.	O
</s>
<s>
The	O
overall	O
structure	O
of	O
IDEA	O
follows	O
the	O
Lai	B-Algorithm
–	I-Algorithm
Massey	I-Algorithm
scheme	I-Algorithm
.	O
</s>
<s>
XOR	B-Application
is	O
used	O
for	O
both	O
subtraction	O
and	O
addition	O
.	O
</s>
<s>
To	O
work	O
with	O
16-bit	O
words	O
(	O
meaning	O
4	O
inputs	O
instead	O
of	O
2	O
for	O
the	O
64-bit	O
block	O
size	O
)	O
,	O
IDEA	O
uses	O
the	O
Lai	B-Algorithm
–	I-Algorithm
Massey	I-Algorithm
scheme	I-Algorithm
twice	O
in	O
parallel	O
,	O
with	O
the	O
two	O
parallel	O
round	O
functions	O
being	O
interwoven	O
with	O
each	O
other	O
.	O
</s>
<s>
,	O
the	O
best	O
attack	O
applied	O
to	O
all	O
keys	O
could	O
break	O
IDEA	O
reduced	O
to	O
6	O
rounds	O
(	O
the	O
full	O
IDEA	B-Algorithm
cipher	I-Algorithm
uses	O
8.5	O
rounds	O
)	O
.	O
</s>
<s>
Independently	O
in	O
2012	O
,	O
full	O
8.5-round	O
IDEA	O
was	O
broken	O
using	O
a	O
narrow-bicliques	O
attack	O
,	O
with	O
a	O
reduction	O
of	O
cryptographic	O
strength	O
of	O
about	O
2bits	O
,	O
similar	O
to	O
the	O
effect	O
of	O
the	O
previous	O
bicliques	O
attack	O
on	O
AES	B-Algorithm
;	O
however	O
,	O
this	O
attack	O
does	O
not	O
threaten	O
the	O
security	O
of	O
IDEA	O
in	O
practice	O
.	O
</s>
<s>
This	O
is	O
still	O
of	O
negligible	O
probability	O
to	O
be	O
a	O
concern	O
to	O
a	O
randomly	O
chosen	O
key	O
,	O
and	O
some	O
of	O
the	O
problems	O
are	O
fixed	O
by	O
the	O
constant	O
XOR	B-Application
proposed	O
earlier	O
,	O
but	O
the	O
paper	O
is	O
not	O
certain	O
if	O
all	O
of	O
them	O
are	O
.	O
</s>
<s>
A	O
patent	O
application	O
for	O
IDEA	O
was	O
first	O
filed	O
in	O
Switzerland	B-Protocol
(	O
CH	O
A	O
1690/90	O
)	O
on	O
May	O
18	O
,	O
1990	O
,	O
then	O
an	O
international	O
patent	O
application	O
was	O
filed	O
under	O
the	O
Patent	O
Cooperation	O
Treaty	O
on	O
May	O
16	O
,	O
1991	O
.	O
</s>
<s>
Patents	O
were	O
eventually	O
granted	O
in	O
Austria	O
,	O
France	O
,	O
Germany	O
,	O
Italy	O
,	O
the	O
Netherlands	O
,	O
Spain	O
,	O
Sweden	O
,	O
Switzerland	B-Protocol
,	O
the	O
United	O
Kingdom	O
,	O
(	O
,	O
filed	O
May	O
16	O
,	O
1991	O
,	O
issued	O
June	O
22	O
,	O
1994	O
and	O
expired	O
May	O
16	O
,	O
2011	O
)	O
,	O
the	O
United	O
States	O
(	O
,	O
issued	O
May	O
25	O
,	O
1993	O
and	O
expired	O
January	O
7	O
,	O
2012	O
)	O
and	O
Japan	O
(	O
JP	O
3225440	O
,	O
expired	O
May	O
16	O
,	O
2011	O
)	O
.	O
</s>
<s>
MediaCrypt	O
AG	O
is	O
now	O
offering	O
a	O
successor	O
to	O
IDEA	O
and	O
focuses	O
on	O
its	O
new	O
cipher	B-Application
(	O
official	O
release	O
in	O
May	O
2005	O
)	O
IDEA	B-Algorithm
NXT	I-Algorithm
,	O
which	O
was	O
previously	O
called	O
FOX	O
.	O
</s>
<s>
Hüseyin	O
Demirci	O
,	O
Erkan	O
Türe	O
,	O
Ali	O
Aydin	O
Selçuk	O
,	O
A	O
New	O
Meet	O
in	O
the	O
Middle	O
Attack	O
on	O
The	O
IDEA	O
Block	O
Cipher	B-Application
,	O
10th	O
Annual	O
Workshop	O
on	O
Selected	B-Application
Areas	I-Application
in	I-Application
Cryptography	I-Application
,	O
2004	O
.	O
</s>
<s>
Xuejia	O
Lai	O
and	O
James	O
L	O
.	O
Massey	O
and	O
S	O
.	O
Murphy	O
,	O
Markov	O
ciphers	B-Application
and	O
differential	O
cryptanalysis	O
,	O
Advances	O
in	O
Cryptology	O
—	O
Eurocrypt	B-Device
'	O
91	O
,	O
Springer-Verlag	O
(	O
1992	O
)	O
,	O
pp.1738	O
.	O
</s>
