<s>
In	O
the	O
history	O
of	O
cryptography	O
,	O
a	O
grille	B-Algorithm
cipher	O
was	O
a	O
technique	O
for	O
encrypting	O
a	O
plaintext	O
by	O
writing	O
it	O
onto	O
a	O
sheet	O
of	O
paper	O
through	O
a	O
pierced	O
sheet	O
(	O
of	O
paper	O
or	O
cardboard	O
or	O
similar	O
)	O
.	O
</s>
<s>
His	O
proposal	O
was	O
for	O
a	O
rectangular	O
stencil	B-Algorithm
allowing	O
single	O
letters	O
,	O
syllables	O
,	O
or	O
words	O
to	O
be	O
written	O
,	O
then	O
later	O
read	O
,	O
through	O
its	O
various	O
apertures	O
.	O
</s>
<s>
This	O
variant	O
is	O
also	O
an	O
example	O
of	O
steganography	O
,	O
as	O
are	O
many	O
of	O
the	O
grille	B-Algorithm
ciphers	O
.	O
</s>
<s>
The	O
Cardan	O
grille	B-Algorithm
was	O
invented	O
as	O
a	O
method	O
of	O
secret	O
writing	O
.	O
</s>
<s>
The	O
original	O
Cardan	O
Grille	B-Algorithm
met	O
that	O
aim	O
.	O
</s>
<s>
But	O
,	O
few	O
if	O
any	O
ciphers	O
have	O
ever	O
achieved	O
this	O
second	O
condition	O
,	O
so	O
the	O
point	O
is	O
generally	O
a	O
cryptanalyst	O
's	O
delight	O
whenever	O
the	O
grille	B-Algorithm
ciphers	O
are	O
used	O
.	O
</s>
<s>
The	O
attraction	O
of	O
a	O
grille	B-Algorithm
cipher	O
for	O
users	O
lies	O
in	O
its	O
ease	O
of	O
use	O
(	O
condition	O
1	O
)	O
.	O
</s>
<s>
A	O
grille	B-Algorithm
is	O
easily	O
usable	O
for	O
protection	O
of	O
brief	O
information	O
such	O
as	O
a	O
key	O
word	O
or	O
a	O
key	O
number	O
in	O
such	O
a	O
use	O
.	O
</s>
<s>
In	O
the	O
example	O
,	O
a	O
grille	B-Algorithm
has	O
eight	O
irregularly	O
placed	O
(	O
ideally	O
randomly	O
)	O
holes	O
–	O
equal	O
to	O
the	O
length	O
of	O
a	O
key	O
word	O
TANGIERS	O
.	O
</s>
<s>
The	O
grille	B-Algorithm
is	O
placed	O
on	O
a	O
gridded	O
sheet	O
(	O
not	O
required	O
in	O
actual	O
practice	O
)	O
and	O
the	O
letters	O
written	O
in	O
from	O
top	O
to	O
bottom	O
.	O
</s>
<s>
Removing	O
the	O
grille	B-Algorithm
,	O
the	O
grid	O
is	O
filled	O
with	O
random	O
letters	O
and	O
numbers	O
.	O
</s>
<s>
Then	O
,	O
one	O
hopes	O
,	O
only	O
the	O
possessor	O
of	O
the	O
grille	B-Algorithm
or	O
a	O
copy	O
can	O
read	O
out	O
the	O
hidden	O
letters	O
or	O
numbers	O
–	O
which	O
could	O
,	O
for	O
example	O
,	O
be	O
the	O
key	O
to	O
a	O
polyalphabetic	O
cipher	O
such	O
as	O
that	O
proposed	O
around	O
the	O
same	O
time	O
by	O
Giambattista	O
della	O
Porta	O
.	O
</s>
<s>
The	O
grille	B-Algorithm
and	O
the	O
grid	O
are	O
kept	O
separately	O
.	O
</s>
<s>
If	O
there	O
is	O
only	O
one	O
copy	O
of	O
the	O
grille	B-Algorithm
and	O
one	O
of	O
the	O
grid	O
,	O
the	O
loss	O
of	O
either	O
results	O
is	O
the	O
loss	O
of	O
both	O
.	O
</s>
<s>
Clearly	O
,	O
in	O
the	O
case	O
of	O
communication	O
by	O
grille	B-Algorithm
cipher	O
,	O
both	O
sender	O
and	O
recipient	O
must	O
possess	O
an	O
identical	O
copy	O
of	O
the	O
grille	B-Algorithm
.	O
</s>
<s>
The	O
loss	O
of	O
a	O
grille	B-Algorithm
leads	O
to	O
the	O
probable	O
loss	O
of	O
all	O
secret	O
correspondence	O
encrypted	O
with	O
that	O
grille	B-Algorithm
.	O
</s>
<s>
Either	O
the	O
messages	O
cannot	O
be	O
read	O
(	O
i.e.	O
,	O
decrypted	O
)	O
or	O
someone	O
else	O
(	O
with	O
the	O
lost	O
grille	B-Algorithm
)	O
may	O
be	O
reading	O
them	O
.	O
</s>
<s>
A	O
further	O
use	O
for	O
such	O
a	O
grille	B-Algorithm
has	O
been	O
suggested	O
:	O
it	O
is	O
a	O
method	O
of	O
generating	O
pseudo-random	B-Error_Name
sequences	I-Error_Name
from	O
a	O
pre-existing	O
text	O
.	O
</s>
<s>
This	O
view	O
has	O
been	O
proposed	O
in	O
connection	O
with	O
the	B-Library
Voynich	I-Library
manuscript	I-Library
.	O
</s>
<s>
It	O
appears	O
to	O
have	O
been	O
a	O
transposition	O
tool	O
that	O
produced	O
something	O
much	O
like	O
the	O
Rail	B-Algorithm
fence	I-Algorithm
cipher	I-Algorithm
and	O
resembled	O
a	O
chess	O
board	O
.	O
</s>
<s>
Whereas	O
the	O
ordinary	O
Cardan	O
grille	B-Algorithm
has	O
arbitrary	O
perforations	O
,	O
if	O
his	O
method	O
of	O
cutting	O
holes	O
is	O
applied	O
to	O
the	O
white	O
squares	O
of	O
a	O
chess	O
board	O
a	O
regular	O
pattern	O
results	O
.	O
</s>
<s>
Shorter	O
messages	O
are	O
filled	O
with	O
null	O
letters	O
(	O
i.e.	O
,	O
padding	B-Algorithm
)	O
.	O
</s>
<s>
Rectangular	O
Cardan	O
grilles	B-Algorithm
can	O
be	O
placed	O
in	O
four	O
positions	O
.	O
</s>
<s>
The	O
trellis	O
or	O
chessboard	O
has	O
only	O
two	O
positions	O
,	O
but	O
it	O
gave	O
rise	O
to	O
a	O
more	O
sophisticated	O
turning	O
grille	B-Algorithm
with	O
four	O
positions	O
that	O
can	O
be	O
rotated	O
in	O
two	O
directions	O
.	O
</s>
<s>
Baron	O
Edouard	O
Fleissner	O
von	O
Wostrowitz	O
,	O
a	O
retired	O
Austrian	O
cavalry	O
colonel	O
,	O
described	O
a	O
variation	O
on	O
the	O
chess	O
board	O
cipher	O
in	O
1880	O
and	O
his	O
grilles	B-Algorithm
were	O
adopted	O
by	O
the	O
German	O
army	O
during	O
World	O
War	O
I	O
.	O
</s>
<s>
These	O
grilles	B-Algorithm
are	O
often	O
named	O
after	O
Fleissner	O
,	O
although	O
he	O
took	O
his	O
material	O
largely	O
from	O
a	O
German	O
work	O
,	O
published	O
in	O
Tübingen	O
in	O
1809	O
,	O
written	O
by	O
Klüber	O
who	O
attributed	O
this	O
form	O
of	O
the	O
grille	B-Algorithm
to	O
Cardano	O
,	O
as	O
did	O
Helen	O
Fouché	O
Gaines	O
.	O
</s>
<s>
Bauer	O
notes	O
that	O
grilles	B-Algorithm
were	O
used	O
in	O
the	O
18th	O
century	O
,	O
for	O
example	O
in	O
1745	O
in	O
the	O
administration	O
of	O
the	O
Dutch	O
Stadthouder	O
William	O
IV	O
.	O
</s>
<s>
Later	O
,	O
the	O
mathematician	O
C	O
.	O
F	O
.	O
Hindenburg	O
studied	O
turning	O
grilles	B-Algorithm
more	O
systematically	O
in	O
1796	O
.	O
</s>
<s>
'[they]are	O
often	O
called	O
Fleissner	O
grilles	B-Algorithm
in	O
ignorance	O
of	O
their	O
historical	O
origin.	O
'	O
</s>
<s>
One	O
form	O
of	O
the	O
Fleissner	O
(	O
or	O
Fleißner	O
)	O
grille	B-Algorithm
makes	O
16	O
perforations	O
in	O
an	O
8x8	O
grid	O
–	O
4	O
holes	O
in	O
each	O
quadrant	O
.	O
</s>
<s>
The	O
grille	B-Algorithm
has	O
four	O
positions	O
–	O
North	O
,	O
East	O
,	O
South	O
,	O
West	O
.	O
</s>
<s>
The	O
encipherer	O
places	O
the	O
grille	B-Algorithm
on	O
a	O
sheet	O
and	O
writes	O
the	O
first	O
16	O
letters	O
of	O
the	O
message	O
.	O
</s>
<s>
Then	O
,	O
turning	O
the	O
grille	B-Algorithm
through	O
90	O
degrees	O
,	O
the	O
second	O
16	O
are	O
written	O
,	O
and	O
so	O
on	O
until	O
the	O
grid	O
is	O
filled	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
construct	O
grilles	B-Algorithm
of	O
different	O
dimensions	O
;	O
however	O
,	O
if	O
the	O
number	O
of	O
squares	O
in	O
one	O
quadrant	O
is	O
odd	O
,	O
even	O
if	O
the	O
total	O
is	O
an	O
even	O
number	O
,	O
one	O
quadrant	O
or	O
section	O
must	O
contain	O
an	O
extra	O
perforation	O
.	O
</s>
<s>
Illustrations	O
of	O
the	O
Fleissner	O
grille	B-Algorithm
often	O
take	O
a	O
6x6	O
example	O
for	O
ease	O
of	O
space	O
;	O
the	O
number	O
of	O
apertures	O
in	O
one	O
quadrant	O
is	O
9	O
,	O
so	O
three	O
quadrants	O
contain	O
2	O
apertures	O
and	O
one	O
quadrant	O
must	O
have	O
3	O
.	O
</s>
<s>
The	O
method	O
gained	O
wide	O
recognition	O
when	O
Jules	O
Verne	O
used	O
a	O
turning	O
grille	B-Algorithm
as	O
a	O
plot	O
device	O
in	O
his	O
novel	O
Mathias	O
Sandorf	O
,	O
published	O
in	O
1885	O
.	O
</s>
<s>
Fleissner	O
Grilles	B-Algorithm
were	O
constructed	O
in	O
various	O
sizes	O
during	O
World	O
War	O
I	O
and	O
were	O
used	O
by	O
the	O
German	O
Army	O
at	O
the	O
end	O
of	O
1916	O
.	O
</s>
<s>
Each	O
grille	B-Algorithm
had	O
a	O
different	O
code	O
name	O
:	O
-	O
5x5	O
ANNA	O
;	O
6X6	O
BERTA	O
;	O
7X7	O
CLARA	O
;	O
8X8	O
DORA	O
;	O
9X9	O
EMIL	O
;	O
10X10	O
FRANZ	O
.	O
</s>
<s>
Another	O
method	O
of	O
indicating	O
the	O
size	O
of	O
the	O
grille	B-Algorithm
in	O
use	O
was	O
to	O
insert	O
a	O
key	O
code	O
at	O
the	O
start	O
of	O
the	O
cipher	O
text	O
:	O
E	O
=	O
5	O
;	O
F	O
=	O
6	O
and	O
so	O
on	O
.	O
</s>
<s>
The	O
grille	B-Algorithm
can	O
also	O
be	O
rotated	O
in	O
either	O
direction	O
and	O
the	O
starting	O
position	O
does	O
not	O
need	O
to	O
be	O
NORTH	O
.	O
</s>
<s>
They	O
are	O
constructed	O
from	O
the	O
example	O
grille	B-Algorithm
,	O
beginning	O
in	O
the	O
NORTH	O
position	O
,	O
but	O
one	O
is	O
formed	O
by	O
rotating	O
the	O
grille	B-Algorithm
clockwise	O
and	O
the	O
other	O
anticlockwise	O
.	O
</s>
<s>
He	O
observed	O
that	O
Fleissner	O
's	O
method	O
could	O
be	O
applied	O
to	O
a	O
fractionating	O
cipher	O
,	O
such	O
as	O
a	O
Delastelle	O
Bifid	B-Algorithm
or	O
Four-Square	B-Algorithm
,	O
with	O
considerable	O
increase	O
in	O
security	O
.	O
</s>
<s>
Grille	B-Algorithm
ciphers	O
are	O
also	O
useful	O
device	O
for	O
transposing	O
Chinese	O
characters	O
;	O
they	O
avoid	O
the	O
transcription	O
of	O
words	O
into	O
alphabetic	O
or	O
syllabic	O
characters	O
to	O
which	O
other	O
ciphers	O
(	O
for	O
example	O
,	O
substitution	O
ciphers	O
)	O
can	O
be	O
applied	O
.	O
</s>
<s>
After	O
World	O
War	O
I	O
,	O
machine	O
encryption	O
made	O
simple	O
cipher	O
devices	O
obsolete	O
,	O
and	O
grille	B-Algorithm
ciphers	O
fell	O
into	O
disuse	O
except	O
for	O
amateur	O
purposes	O
.	O
</s>
<s>
Yet	O
,	O
grilles	B-Algorithm
provided	O
seed	O
ideas	O
for	O
transposition	O
ciphers	O
that	O
are	O
reflected	O
in	O
modern	O
cryptography	O
.	O
</s>
<s>
The	O
unsolved	O
D'Agapeyeff	B-Algorithm
cipher	I-Algorithm
,	O
which	O
was	O
set	O
as	O
a	O
challenge	O
in	O
1939	O
,	O
contains	O
14x14	O
dinomes	O
and	O
might	O
be	O
based	O
on	O
Sacco	O
's	O
idea	O
of	O
transposing	O
a	O
fractionated	O
cipher	O
text	O
by	O
means	O
of	O
a	O
grille	B-Algorithm
.	O
</s>
<s>
The	O
distribution	O
of	O
grilles	B-Algorithm
,	O
an	O
example	O
of	O
the	O
difficult	O
problem	O
of	O
key	O
exchange	O
,	O
can	O
be	O
eased	O
by	O
taking	O
a	O
readily-available	O
third-party	O
grid	O
in	O
the	O
form	O
of	O
a	O
newspaper	O
crossword	O
puzzle	O
.	O
</s>
<s>
Although	O
this	O
is	O
not	O
strictly	O
a	O
grille	B-Algorithm
cipher	O
,	O
it	O
resembles	O
the	O
chessboard	O
with	O
the	O
black	O
squares	O
shifted	O
and	O
it	O
can	O
be	O
used	O
in	O
the	O
Cardan	O
manner	O
.	O
</s>
<s>
The	O
original	O
Cardano	O
Grille	B-Algorithm
was	O
a	O
literary	O
device	O
for	O
gentlemen	O
's	O
private	O
correspondence	O
.	O
</s>
<s>
Obtaining	O
the	O
grille	B-Algorithm
itself	O
is	O
a	O
chief	O
goal	O
of	O
the	O
attacker	O
.	O
</s>
<s>
But	O
all	O
is	O
not	O
lost	O
if	O
a	O
grille	B-Algorithm
copy	O
ca	O
n't	O
be	O
obtained	O
.	O
</s>
<s>
The	O
later	O
variants	O
of	O
the	O
Cardano	O
grille	B-Algorithm
present	O
problems	O
which	O
are	O
common	O
to	O
all	O
transposition	O
ciphers	O
.	O
</s>
<s>
Possession	O
of	O
several	O
messages	O
written	O
using	O
the	O
same	O
grille	B-Algorithm
is	O
a	O
considerable	O
aid	O
.	O
</s>
<s>
Gaines	O
,	O
in	O
her	O
standard	O
work	O
on	O
hand	O
ciphers	O
and	O
their	O
cryptanalysis	O
,	O
gave	O
a	O
lengthy	O
account	O
of	O
transposition	O
ciphers	O
,	O
and	O
devoted	O
a	O
chapter	O
to	O
the	O
turning	O
grille	B-Algorithm
.	O
</s>
