<s>
The	O
summation	B-Algorithm
generator	I-Algorithm
,	O
created	O
in	O
1985	O
,	O
by	O
Rainer	O
Rueppel	O
,	O
was	O
a	O
cryptography	O
and	O
security	O
front-runner	O
in	O
the	O
late	O
1980s	O
.	O
</s>
<s>
It	O
operates	O
by	O
taking	O
the	O
output	O
of	O
two	O
LFSRs	B-Architecture
through	O
an	O
adder	O
with	O
carry	O
.	O
</s>
<s>
However	O
,	O
through	O
the	O
early	O
1990s	O
various	O
attacks	O
against	O
the	O
summation	B-Algorithm
generator	I-Algorithm
eventually	O
led	O
to	O
its	O
fall	O
to	O
a	O
correlation	O
attack	O
.	O
</s>
<s>
In	O
1995	O
Klapper	O
and	O
Goresky	O
were	O
able	O
to	O
determine	O
the	O
summation	B-Algorithm
generator	I-Algorithm
's	O
sequence	O
in	O
only	O
219	O
bits	O
.	O
</s>
<s>
An	O
improved	O
summation	B-Algorithm
generator	I-Algorithm
with	O
2-bit	O
memory	O
was	O
then	O
proposed	O
by	O
cryptographers	O
Lee	O
and	O
Moon	O
.	O
</s>
<s>
The	O
objective	O
in	O
the	O
modification	O
was	O
to	O
make	O
the	O
summation	B-Algorithm
generator	I-Algorithm
immune	O
to	O
correlation	O
attack	O
.	O
</s>
<s>
An	O
attack	O
against	O
the	O
improved	O
summation	B-Algorithm
generator	I-Algorithm
was	O
reported	O
by	O
Mex-Perera	O
and	O
Shepherd	O
in	O
2002	O
by	O
exploiting	O
linear	O
relations	O
.	O
</s>
<s>
Using	O
this	O
attack	O
a	O
PC	O
can	O
calculate	O
the	O
initial	O
state	O
of	O
the	O
summation	B-Algorithm
generator	I-Algorithm
within	O
3	O
minutes	O
even	O
with	O
256	O
bit	O
LFSRs	B-Architecture
.	O
</s>
