<s>
A5/2	B-Algorithm
is	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
used	O
to	O
provide	O
voice	O
privacy	O
in	O
the	O
GSM	O
cellular	O
telephone	O
protocol	O
.	O
</s>
<s>
It	O
was	O
designed	O
in	O
1992-1993	O
(	O
finished	O
March	O
1993	O
)	O
as	O
a	O
replacement	O
for	O
the	O
relatively	O
stronger	O
(	O
but	O
still	O
weak	O
)	O
A5/1	B-Algorithm
,	O
to	O
allow	O
the	O
GSM	O
standard	O
to	O
be	O
exported	O
to	O
countries	O
"	O
with	O
restrictions	O
on	O
the	O
import	O
of	O
products	O
with	O
cryptographic	O
security	O
features	O
"	O
.	O
</s>
<s>
The	O
cipher	O
is	O
based	O
on	O
a	O
combination	O
of	O
four	O
linear-feedback	B-Architecture
shift	I-Architecture
registers	I-Architecture
with	O
irregular	O
clocking	O
and	O
a	O
non-linear	O
combiner	O
.	O
</s>
<s>
In	O
1999	O
,	O
Ian	O
Goldberg	O
and	O
David	O
A	O
.	O
Wagner	O
cryptanalyzed	O
A5/2	B-Algorithm
in	O
the	O
same	O
month	O
it	O
was	O
reverse	O
engineered	O
,	O
and	O
showed	O
that	O
it	O
was	O
extremely	O
weak	O
–	O
so	O
much	O
so	O
that	O
low	O
end	O
equipment	O
can	O
probably	O
break	O
it	O
in	O
real	O
time	O
.	O
</s>
<s>
In	O
2003	O
,	O
Elad	O
Barkan	O
,	O
Eli	O
Biham	O
and	O
Nathan	O
Keller	O
presented	O
a	O
ciphertext-only	O
attack	O
based	O
on	O
the	O
error	B-Error_Name
correcting	I-Error_Name
codes	I-Error_Name
used	O
in	O
GSM	O
communication	O
.	O
</s>
<s>
They	O
also	O
demonstrated	O
a	O
vulnerability	O
in	O
the	O
GSM	O
protocols	O
that	O
allows	O
a	O
man-in-the-middle	O
attack	O
to	O
work	O
whenever	O
the	O
mobile	O
phone	O
supports	O
A5/2	B-Algorithm
,	O
regardless	O
of	O
whether	O
it	O
was	O
actually	O
being	O
used	O
.	O
</s>
<s>
Since	O
July	O
1	O
,	O
2006	O
,	O
the	O
GSMA	O
(	O
GSM	O
Association	O
)	O
mandated	O
that	O
GSM	O
Mobile	O
Phones	O
will	O
not	O
support	O
the	O
A5/2	B-Algorithm
Cipher	O
any	O
longer	O
,	O
due	O
to	O
its	O
weakness	O
,	O
and	O
the	O
fact	O
that	O
A5/1	B-Algorithm
is	O
deemed	O
mandatory	O
by	O
the	O
3GPP	O
association	O
.	O
</s>
<s>
In	O
July	O
2007	O
,	O
the	O
3GPP	O
has	O
approved	O
a	O
change	O
request	O
to	O
prohibit	O
the	O
implementation	O
of	O
A5/2	B-Algorithm
in	O
any	O
new	O
mobile	O
phones	O
,	O
stating	O
:	O
"	O
It	O
is	O
mandatory	O
for	O
A5/1	B-Algorithm
and	O
non	O
encrypted	O
mode	O
to	O
be	O
implemented	O
in	O
mobile	O
stations	O
.	O
</s>
<s>
It	O
is	O
prohibited	O
to	O
implement	O
A5/2	B-Algorithm
in	O
mobile	O
stations.	O
"	O
</s>
<s>
If	O
the	O
network	O
does	O
not	O
support	O
A5/1	B-Algorithm
then	O
an	O
unencrypted	O
connection	O
can	O
be	O
used	O
.	O
</s>
