<s>
Crypto1	B-Algorithm
is	O
a	O
proprietary	O
encryption	O
algorithm	O
(	O
stream	B-Algorithm
cipher	I-Algorithm
)	O
and	O
authentication	O
protocol	O
created	O
by	O
NXP	O
Semiconductors	O
for	O
its	O
MIFARE	O
Classic	O
RFID	B-Application
contactless	O
smart	O
cards	O
launched	O
in	O
1994	O
.	O
</s>
<s>
Crypto1	B-Algorithm
is	O
a	O
stream	B-Algorithm
cipher	I-Algorithm
very	O
similar	O
in	O
its	O
structure	O
to	O
its	O
successor	O
,	O
Hitag2	O
.	O
</s>
<s>
a	O
48-bit	O
linear	B-Architecture
feedback	I-Architecture
shift	I-Architecture
register	I-Architecture
for	O
the	O
state	O
of	O
the	O
cipher	O
,	O
</s>
<s>
The	O
usual	O
operation	O
of	O
Crypto1	B-Algorithm
and	O
Hitag2	O
ciphers	O
uses	O
nonlinear	O
feedback	O
only	O
during	O
the	O
initialization/authentication	O
stage	O
,	O
switching	O
to	O
operation	O
as	O
a	O
LFSR	B-Architecture
with	O
a	O
nonlinear	O
output	O
filter	O
(	O
filter	O
generator	O
)	O
for	O
the	O
rest	O
of	O
the	O
communications	O
.	O
</s>
