<s>
A	O
nonlinear-feedback	B-Algorithm
shift	I-Algorithm
register	I-Algorithm
(	O
NLFSR	B-Algorithm
)	O
is	O
a	O
shift	B-General_Concept
register	I-General_Concept
whose	O
input	O
bit	O
is	O
a	O
non-linear	O
function	O
of	O
its	O
previous	O
state	O
.	O
</s>
<s>
For	O
an	O
n-bit	O
shift	B-General_Concept
register	I-General_Concept
r	O
its	O
next	O
state	O
is	O
defined	O
as	O
:	O
</s>
<s>
Nonlinear-feedback	B-Algorithm
shift	I-Algorithm
registers	I-Algorithm
are	O
components	O
in	O
modern	O
stream	B-Algorithm
ciphers	I-Algorithm
,	O
especially	O
in	O
RFID	B-Application
and	O
smartcard	O
applications	O
.	O
</s>
<s>
NLFSRs	B-Algorithm
are	O
known	O
to	O
be	O
more	O
resistant	O
to	O
cryptanalytic	O
attacks	O
than	O
Linear	B-Architecture
Feedback	I-Architecture
Shift	I-Architecture
Registers	I-Architecture
(	O
LFSRs	B-Architecture
)	O
.	O
</s>
<s>
It	O
is	O
known	O
how	O
to	O
generate	O
an	O
n-bit	O
NLFSR	B-Algorithm
of	O
maximal	O
length	O
2n	O
,	O
generating	O
a	O
De	B-Language
Bruijn	I-Language
sequence	I-Language
,	O
by	O
extending	O
a	O
maximal-length	O
LFSR	B-Architecture
with	O
n	O
stages	O
;	O
but	O
the	O
construction	O
of	O
other	O
large	O
NLFSRs	B-Algorithm
with	O
guaranteed	O
long	O
periods	O
remains	O
an	O
open	O
problem	O
.	O
</s>
<s>
Using	O
bruteforce	O
methods	O
,	O
a	O
list	O
of	O
maximum-period	O
n-bit	O
NLFSRs	B-Algorithm
for	O
n	O
≤	O
25	O
has	O
been	O
made	O
as	O
well	O
as	O
for	O
n	O
=	O
27	O
.	O
</s>
<s>
New	O
methods	O
suggest	O
usage	O
of	O
evolutionary	B-Algorithm
algorithms	I-Algorithm
in	O
order	O
to	O
introduce	O
non-linearity	O
.	O
</s>
<s>
In	O
these	O
works	O
,	O
an	O
evolutionary	B-Algorithm
algorithm	I-Algorithm
learns	O
how	O
to	O
apply	O
different	O
operations	O
on	O
strings	O
from	O
LFSR	B-Architecture
to	O
enhance	O
their	O
quality	O
to	O
meet	O
the	O
criteria	O
of	O
a	O
fitness	O
function	O
,	O
here	O
the	O
NIST	O
protocol	O
,	O
effectively	O
.	O
</s>
