<s>
In	O
cryptography	O
,	O
the	O
Cellular	B-Algorithm
Message	I-Algorithm
Encryption	I-Algorithm
Algorithm	I-Algorithm
(	O
CMEA	B-Algorithm
)	O
is	O
a	O
block	O
cipher	B-Application
which	O
was	O
used	O
for	O
securing	O
mobile	O
phones	O
in	O
the	O
United	O
States	O
.	O
</s>
<s>
CMEA	B-Algorithm
is	O
one	O
of	O
four	O
cryptographic	O
primitives	O
specified	O
in	O
a	O
Telecommunications	O
Industry	O
Association	O
(	O
TIA	O
)	O
standard	O
,	O
and	O
is	O
designed	O
to	O
encrypt	O
the	O
control	O
channel	O
,	O
rather	O
than	O
the	O
voice	O
data	O
.	O
</s>
<s>
In	O
1997	O
,	O
a	O
group	O
of	O
cryptographers	O
published	O
attacks	O
on	O
the	O
cipher	B-Application
showing	O
it	O
had	O
several	O
weaknesses	O
which	O
give	O
it	O
a	O
trivial	O
effective	O
strength	O
of	O
a	O
24-bit	O
to	O
32-bit	O
cipher	B-Application
.	O
</s>
<s>
Some	O
accusations	O
were	O
made	O
that	O
the	O
NSA	O
had	O
pressured	O
the	O
original	O
designers	O
into	O
crippling	O
CMEA	B-Algorithm
,	O
but	O
the	O
NSA	O
has	O
denied	O
any	O
role	O
in	O
the	O
design	O
or	O
selection	O
of	O
the	O
algorithm	O
.	O
</s>
<s>
The	O
ECMEA	O
and	O
SCEMA	O
ciphers	B-Application
are	O
derived	O
from	O
CMEA	B-Algorithm
.	O
</s>
<s>
CMEA	B-Algorithm
is	O
described	O
in	O
.	O
</s>
<s>
Both	O
of	O
these	O
are	O
unusually	O
small	O
for	O
a	O
modern	O
cipher	B-Application
.	O
</s>
<s>
The	O
non-linear	O
operations	O
use	O
a	O
keyed	O
lookup	B-Data_Structure
table	I-Data_Structure
called	O
the	O
T-box	O
,	O
which	O
uses	O
an	O
unkeyed	O
lookup	B-Data_Structure
table	I-Data_Structure
called	O
the	O
CaveTable	O
.	O
</s>
<s>
The	O
algorithm	O
is	O
self-inverse	B-Algorithm
;	O
re-encrypting	O
the	O
ciphertext	O
with	O
the	O
same	O
key	O
is	O
equivalent	O
to	O
decrypting	O
it	O
.	O
</s>
<s>
CMEA	B-Algorithm
is	O
severely	O
insecure	O
.	O
</s>
<s>
The	O
"	O
improved	O
"	O
CMEA	B-Algorithm
,	O
CMEA-I	O
,	O
is	O
not	O
much	O
better	O
:	O
chosen-plaintext	O
attack	O
of	O
it	O
requires	O
less	O
than	O
850	O
plaintexts	O
in	O
its	O
adaptive	O
version	O
.	O
</s>
