<s>
The	O
Playfair	B-Algorithm
cipher	I-Algorithm
or	O
Playfair	B-Algorithm
square	I-Algorithm
or	O
Wheatstone	O
–	O
Playfair	B-Algorithm
cipher	I-Algorithm
is	O
a	O
manual	O
symmetric	B-Algorithm
encryption	I-Algorithm
technique	O
and	O
was	O
the	O
first	O
literal	O
digram	O
substitution	O
cipher	O
.	O
</s>
<s>
The	O
technique	O
encrypts	O
pairs	O
of	O
letters	O
(	O
bigrams	O
or	O
digrams	O
)	O
,	O
instead	O
of	O
single	O
letters	O
as	O
in	O
the	O
simple	O
substitution	O
cipher	O
and	O
rather	O
more	O
complex	O
Vigenère	B-Algorithm
cipher	I-Algorithm
systems	O
then	O
in	O
use	O
.	O
</s>
<s>
The	O
Playfair	B-Algorithm
cipher	I-Algorithm
was	O
the	O
first	O
cipher	O
to	O
encrypt	O
pairs	O
of	O
letters	O
in	O
cryptologic	O
history	O
.	O
</s>
<s>
The	O
first	O
recorded	O
description	O
of	O
the	O
Playfair	B-Algorithm
cipher	I-Algorithm
was	O
in	O
a	O
document	O
signed	O
by	O
Wheatstone	O
on	O
26	O
March	O
1854	O
.	O
</s>
<s>
The	O
first	O
published	O
solution	O
of	O
the	O
Playfair	B-Algorithm
cipher	I-Algorithm
was	O
described	O
in	O
a	O
19-page	O
pamphlet	O
by	O
Lieutenant	O
Joseph	O
O	O
.	O
Mauborgne	O
,	O
published	O
in	O
1914	O
.	O
</s>
<s>
The	O
Playfair	B-Algorithm
cipher	I-Algorithm
uses	O
a	O
5	O
by	O
5	O
table	O
containing	O
a	O
key	O
word	O
or	O
phrase	O
.	O
</s>
<s>
There	O
are	O
several	O
minor	O
variations	O
of	O
the	O
original	O
Playfair	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
Like	O
most	O
classical	O
ciphers	O
,	O
the	O
Playfair	B-Algorithm
cipher	I-Algorithm
can	O
be	O
easily	O
cracked	O
if	O
there	O
is	O
enough	O
text	O
.	O
</s>
<s>
Cryptanalysis	O
of	O
Playfair	O
is	O
similar	O
to	O
that	O
of	O
four-square	B-Algorithm
and	O
two-square	B-Algorithm
ciphers	I-Algorithm
,	O
though	O
the	O
relative	O
simplicity	O
of	O
the	O
Playfair	O
system	O
makes	O
identifying	O
candidate	O
plaintext	O
strings	O
easier	O
.	O
</s>
<s>
A	O
different	O
approach	O
to	O
tackling	O
a	O
Playfair	B-Algorithm
cipher	I-Algorithm
is	O
the	O
shotgun	B-Algorithm
hill	I-Algorithm
climbing	I-Algorithm
method	O
.	O
</s>
<s>
This	O
is	O
obviously	O
beyond	O
the	O
range	O
of	O
typical	O
human	O
patience	O
,	O
but	O
computers	O
can	O
adopt	O
this	O
algorithm	O
to	O
crack	O
Playfair	B-Algorithm
ciphers	I-Algorithm
with	O
a	O
relatively	O
small	O
amount	O
of	O
text	O
.	O
</s>
<s>
Another	O
aspect	O
of	O
Playfair	O
that	O
separates	O
it	O
from	O
four-square	B-Algorithm
and	O
two-square	B-Algorithm
ciphers	I-Algorithm
is	O
the	O
fact	O
that	O
it	O
will	O
never	O
contain	O
a	O
double-letter	O
digram	O
,	O
e.g.	O
</s>
<s>
A	O
good	O
tutorial	O
on	O
reconstructing	O
the	O
key	O
for	O
a	O
Playfair	B-Algorithm
cipher	I-Algorithm
can	O
be	O
found	O
in	O
chapter	O
7	O
,	O
"	O
Solution	O
to	O
Polygraphic	O
Substitution	O
Systems	O
,	O
"	O
of	O
,	O
produced	O
by	O
the	O
United	O
States	O
Army	O
.	O
</s>
<s>
Another	O
cryptanalysis	O
of	O
a	O
Playfair	B-Algorithm
cipher	I-Algorithm
can	O
be	O
found	O
in	O
Chapter	O
XXI	O
of	O
Helen	O
Fouché	O
Gaines	O
,	O
Cryptanalysis	O
/	O
a	O
study	O
of	O
ciphers	O
and	O
their	O
solutions	O
.	O
</s>
<s>
The	O
German	O
Army	O
,	O
Air	O
Force	O
and	O
Police	O
used	O
the	O
Double	B-Algorithm
Playfair	B-Algorithm
cipher	I-Algorithm
as	O
a	O
medium-grade	O
cipher	O
in	O
WWII	O
,	O
based	O
on	O
the	O
British	O
Playfair	B-Algorithm
cipher	I-Algorithm
they	O
had	O
broken	O
early	O
in	O
WWI	O
.	O
</s>
<s>
Advanced	O
thematic	O
cryptic	O
crosswords	O
like	O
The	O
Listener	O
Crossword	O
(	O
published	O
in	O
the	O
Saturday	O
edition	O
of	O
the	O
British	O
newspaper	O
The	O
Times	O
)	O
occasionally	O
incorporate	O
Playfair	B-Algorithm
ciphers	I-Algorithm
.	O
</s>
<s>
Use	O
of	O
the	O
Playfair	B-Algorithm
cipher	I-Algorithm
is	O
generally	O
explained	O
as	O
part	O
of	O
the	O
preamble	O
to	O
the	O
crossword	O
.	O
</s>
<s>
The	O
novel	O
Have	O
His	O
Carcase	O
by	O
Dorothy	O
L	O
.	O
Sayers	O
gives	O
a	O
blow-by-blow	O
account	O
of	O
the	O
cracking	O
of	O
a	O
Playfair	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
The	O
World	O
War	O
2	O
thriller	O
The	O
Trojan	O
Horse	O
by	O
Hammond	O
Innes	O
conceals	O
the	O
formula	O
for	O
a	O
new	O
high-strength	O
metal	O
alloy	O
using	O
the	O
Playfair	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
In	O
the	O
film	O
National	O
Treasure	O
:	O
Book	O
of	O
Secrets	O
,	O
a	O
treasure	O
hunt	O
clue	O
is	O
encoded	O
as	O
a	O
Playfair	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
In	O
the	O
audio	O
book	O
Rogue	O
Angel	O
:	O
God	O
of	O
Thunder	O
,	O
a	O
Playfair	B-Algorithm
cipher	I-Algorithm
clue	O
is	O
used	O
to	O
send	O
Anja	O
Creed	O
to	O
Venice	O
.	O
</s>
<s>
In	O
the	O
novel	O
York	O
:	O
The	O
Map	O
of	O
Stars	O
(	O
part	O
three	O
of	O
a	O
trilogy	O
for	O
children	O
)	O
by	O
Laura	O
Ruby	O
,	O
a	O
clue	O
to	O
solving	O
the	O
Morningstarr	O
cipher	O
is	O
encrypted	O
using	O
the	O
Playfair	B-Algorithm
cipher	I-Algorithm
.	O
</s>
<s>
The	O
Playfair	B-Algorithm
cipher	I-Algorithm
serves	O
as	O
a	O
plot	O
device	O
in	O
a	O
season	O
2	O
episode	O
of	O
the	O
2019	O
Batwoman	O
(	O
TV	O
series	O
)	O
.	O
</s>
