<s>
A	O
reflector	B-General_Concept
,	O
in	O
cryptology	O
,	O
is	O
a	O
component	O
of	O
some	O
rotor	O
cipher	O
machines	O
,	O
such	O
as	O
the	O
Enigma	O
machine	O
,	O
that	O
sends	O
electrical	O
impulses	O
that	O
have	O
reached	O
it	O
from	O
the	O
machine	O
's	O
rotors	O
,	O
back	O
in	O
reverse	O
order	O
through	O
those	O
rotors	O
.	O
</s>
<s>
The	O
reflector	B-General_Concept
simplified	O
using	O
the	O
same	O
machine	O
setup	O
for	O
encryption	O
and	O
decryption	O
,	O
but	O
it	O
creates	O
a	O
weakness	O
in	O
the	O
encryption	O
:	O
with	O
a	O
reflector	B-General_Concept
the	O
encrypted	O
version	O
of	O
a	O
given	O
letter	O
can	O
never	O
be	O
that	O
letter	O
itself	O
.	O
</s>
<s>
The	O
comparable	O
WW	O
II	O
U.S.	O
cipher	O
machine	O
,	O
SIGABA	O
,	O
did	O
not	O
include	O
a	O
reflector	B-General_Concept
.	O
</s>
<s>
The	O
reflector	B-General_Concept
is	O
also	O
known	O
as	O
the	O
reversing	O
drum	O
or	O
,	O
from	O
the	O
German	O
,	O
the	O
Umkehrwalze	O
or	O
UKW	O
.	O
</s>
